OPINION

This is a direct appeal by the Commonwealth in a ease involving Appellee’s alleged possession and delivery of a chemical compound claimed to be either a controlled substance or a designer drug. A central issue is whether the portions of the Controlled Substance, Drug, Device and Cos-' metic Act under which Appellee was charged—relating to “analogues” of scheduled controlled substances, as well as “substantially similar” designer drugs—are unconstitutionally vague.

I. Background

At all relevant times, Appellee owned and operated a smoke shop in York County. On April 17, May 30, and July 11, 2013, undercover police officers entered the shop and purchased small packets of substances having brand names such as “Winter Haze” and “V-8 Air Freshener.” Laborato*198ry testing performed for the Commonwealth by Michael Coyer, PhD—a forensic toxicologist and the Commonwealth’s eventual expert witness—revealed that these products contained the chemical PB-22, which the prosecution alleged to be either a controlled substance as an “analogue” of the known synthetic cannabinoid JWH-018,1 or a designer drug. On July 15, 2013, the police executed search warrants at Ap-pellee’s residence and business. At each location they seized additional packets of substances containing PB-22. Appellee was charged, under the Controlled Substance, Drug, Device and Cosmetic Act (the “Act”),2 with three counts of delivery of a controlled substance, one count of possession with intent to deliver a controlled substance, and one count of possession, or possession with intent to distribute, a designer drug. See 35 P.S. § 780-113(a)(30), (36).3

Before describing the procedural history, it is helpful to review the legislation, including a material revision made in early July 2013, between the second and third undercover purchases. See Act of July 2, 2013, P.L. 242, No. 40 (“Act 40”). In relevant part, the Act defines a controlled substance as a substance listed in Schedules I through V of the Act. See 35 P.S. § 780-102.4 These are known as “scheduled” drugs. See, e.g., 40 P.S. § 908-1. It defines designer drug as “a substance other than a controlled substance that is intended for human consumption and that either has a chemical structure substantially similar to that of a controlled substance in Schedules I, II or III ... or that produces an effect substantially similar to that of a controlled substance in Schedules I, II or III.” 35 P.S. § 780-102.5 The schedules are set forth in the Act, see 35 P.S. § 780-104, although only Schedule I is relevant to this dispute.6

*199Act 40 amended the description of Schedule I. In both the .pre- and post-amendment timeframes, Schedule I included JWH-018 by name as a synthetic can-nabinoid. See 35 P.S. § 780-104(l)(vii)(4) (2011); id. § 780-104(l)(vii)(2)(B) (2013). In the pre-amendment version, Schedule I encompassed all “analogues” of the named synthetic cannabinoids. See 35 P.S. § 780-104(l)(vii) (2011) (subsuming within Schedule I “[sjynthetic cannabinoids or any material, compound, mixture or preparation which contains ... the following substances, including their analogues ..,: ... (4) JWH-018”). With the Act 40 revisions, Schedule I now encompasses compounds which are synthetic cannabinoids falling into thirteen specified “chemical designations,” as well as analogues of those compounds. Thus, Schedule I now includes:

Synthetic cannabinoids, including any material, compound, mixture or preparation that is not listed as a controlled substance in Schedules I, II, III, IV and V, ... which contains any quantity of the following substances [or] their ... analogues, ... ivhenevef the existence of these ... analogues ... i[s] possible within the specific chemical designation

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35 P.S. § 780-104(l)(vii) (2013) (emphasis added).7 Only the second specified chemical designation is potentially relevant to this matter:

2. Naphthoylindoles or any compound containing a 3-(-l-naphthoyl) indole structure with substitution at the nitrogen atom of the indole ring whether or not further substituted in the indole ring to any extent and whether or not substituted in the naphthyl ring to any extent. This shall include the following: ... (B) jwh-018....

Id. § 780-104(l)(vii)(2)(B) (2013).8 Notably, the Act has never provided a definition of “analogue” or, for the designer-drug provision, “substantially similar.”

Appellee filed an omnibus pre-trial motion which included a request for habeas corpus relief. See Commonwealth v. Hock, 556 Pa. 409, 414-15 & n.2, 728 A.2d 943, 945 & n.2 (1999) (noting that a pre-trial habeas petition tests whether the Commonwealth’s evidence is sufficient to make out a prima facie case of guilt). Appellee *200made several discreet assertions in support of his habeas request.

First, he argued that both controlled-substance charges relating to dates after July 2, 2013—ie,, the third delivery count and the possession count—should be dismissed because PB-22 is not a controlled substance under the revised Schedule I. Appellee reasoned that JWH-018 is a na-phthoylindole, whereas PB-22 is an ester.9 As the two compounds fall into different structural classes, Appellee maintained, PB-22 could not be an analogue of JWH-018 for purposes of the amended Section 780-104(l)(vii), given that that version expressly classifies prohibited synthetic can-nabinoids by “specific chemical designation.” 35 P.S. § 780-104(l)(vii) (2013). In this regard, Appellee proffered that the statutory phrase, “within the specific chemical designation,” id., should be understood to mean that the purported analogue must fall into the same structural classification. See Omnibus Pretrial Motion at 2-3. Notably, Appellee did not challenge the constitutional validity of the analogue provision in the revised statute.

Appellee also advanced that the sole designer-drug charge should be dismissed for two reasons. First, he argued that the Commonwealth failed to offer any evidence that PB-22 has a chemical structure which is substantially similar to that of JWH-018, and that the Commonwealth’s own evidence, including Dr. Coyer’s lab reports, indicated that the physiological and toxicological properties of PB-22 are unknown—thus negating any claim that its effects are substantially similar to those of JWH-018. See Omnibus Pretrial Motion at 5. Alternatively, Appellee argued that the term “substantially similar” was void for vagueness as applied to the two compounds in question. See id.

Finally, Appellee argued that, in the relevant scientific field, there is no consensus as to the definition of an “analogue” of a chemical compound, nor is there a generally-accepted methodology for determining whether one molecule is an analogue of another. As applied to this case, Appellee reasoned that, if scientists cannot agree on whether PB-22 is an analogue of JWH-018, the average citizen could not be on notice of such a relationship between the two chemicals and, therefore, that PB-22 is an illegal drug. That being the case, Appellee continued, it would offend due process, under the void-for-vagueness doctrine, for the Commonwealth to prosecute him under subsection 780-113(a)(30) for delivering PB-22 as an alleged controlled substance in the pre-July 2, 2013, timeframe. See id. at 3-4.10

*201To summarize, then, Appellee made three essential contentions: (1) that Section 780-104(l)(vii) was vague as applied to PB-22 before July 2, 2013; (2) that PB-22 was not a prohibited substance under Section 780-104(l)(vii) after July 2, 2013; and (3) that the designer-drug provision, Section 780-113(a)(36), could not validly be applied to PB-22. Because subsection (a)(36) predicates culpability in the disjunctive on a substantially similar effect or chemical structure, this latter argument had two subparts: (a) since PB-22’s effects were unknown, they could not possibly be proved to be substantially similar to those of JWH-018; and (b) either the Commonwealth did not satisfy its burden to demonstrate that PB-22 and JWH-018 shared a substantially similar chemical structure, or the term “substantially similar” was vague as applied to the structures of those two chemicals.

The common pleas court held a hearing on the habeas motion at which Dr. Coyer testified as an expert for the Commonwealth and two expert witnesses testified on behalf of Appellee. Dr. Coyer opined, to a reasonable degree of scientific certainty, that PB-22 is an analogue of JWH-018. See N.T., Nov. 7, 2014, at 35. He conceded, however, that there was no definition of “analogue” in the relevant scientific field, but that he considered the term to mean a compound which “has a similar structure but may possess different properties.” Id. at 36. In terms of methodology, Dr. Coyer indicated that he used a four-part process to arrive at this type of expert opinion: he visually compared two-dimensional diagrams of the molecules in question; he compared their potency or function; he reviewed his colleagues’ unpublished reports, anecdotal evidence, and peer-reviewed articles, if any; and he drew upon his experience conducting chemical analy-ses in his capacity as a forensic toxicologist. See id. at 40-42. However, Dr. Coyer was unable to identify any peer-reviewed articles suggesting that his methodology was a generally-accepted means for determining whether one compound is an analogue of another. Finally, he clarified that his method did not employ a comparison of three-dimensional molecular illustrations. See id. at 51.

Appellee’s first expert witness was John W. Huffman, PhD, an organic chemist and professor emeritus at Clemson University who had been active in .the cannabinoid field for decades. Dr. Huffman, for whom JWH-018 is named, created the compound when conducting federally-funded research into how such chemicals interact with the body’s cannabinoid receptors. He agreed with Dr. Coyer that there was no scientific definition of “analogue” and that PB-22 and JWH-018 were in different structural classes. See id. at 61, 81-82. Therefore, Dr. Huffman opined that the two compounds were not analogues and did not have similar structures. See id. at 90-91. Referring to a peer-reviewed scientific paper, Dr. *202Huffman also noted, consistent with Dr. Coyer’s lab reports, that scientists had no knowledge of PB-22’s pharmacological or toxicological effects, or of whether the two chemicals have similar effects. That being the case, he continued, there was no agreement in the scientific community on whether PB-22 could properly-be classified as a synthetic cannabinoid, see id, at 83-84, notwithstanding that one team of chemists had labeled it- as such “a few years ago.” Id. at 84. Dr. Huffman stated that he had never heard of anyone else using Dr. Coyer’s four-part technique for discerning whether one molecule is an analogue of another. He testified that such methodology was not generally accepted in the scientific field, particularly as three-dimensional modeling, not two-dimensional diagraming, was the accepted standard for comparative analysis of molecular structures. See id, at 76-77, 81-82,

' Appellee also presented the expert testimony of Heather Harris, PhD, a forensic analytical chemist and chair of the Structure Subcommittee of the Advisory Committee for the Evaluation of Controlled Substance Analogues (“ACECSA”), a national scientific body. Dr. Harris explained that 'the mission of ACECSA—which also includes members of law enforcement agencies—is to develop methods for forensic chemists to use in discerning whether one chemical is an analogue of another. She testified that ACECSA had not yet developed such a methodology. See id. at 96, Dr. Harris also discussed an entity funded by the federal Drug Enforcement Agency called the Scientific Working Group • for the Analysis of Seized Drugs (“SWGDRUG”), which publishes recommendations fór chemists involved in testing controlled substances. She noted SWGDRUG includes an analogue subcommittee which had as yet been unable to devise a methodology for determining whether a particular chemical is an analogue of a controlled substance. See id. at 97-98. Dr. Harris additionally related that she had recently reviewed the scientific literature. Based on that, review, she opined that Dr. Coyer’s comparison methodology was not generally accepted in the scientific field. She added that she had been unable to locate any generally-accepted methodology. As well, Dr. Harris testified that there is also no commonly-accepted scientific definition of the phrase “substantially similar,” which she viewed to be a subjective term. Ultimately, she rendered her own professional opinion, to a reasonable degree of scientific certainty, that PB-22 and JWH-018 áre not substantially similar. See id. at 102.

The common pleas court granted Appel-lee’s habeas motion and dismissed all charges against him.11 In its Rule 1925(a) opinion, the court relied largely on the testimony of Drs. Hoffman and Harris. Based on such proofs, as well as portions of Dr. Coyer’s testimony, the court determined that the public at large could not have been on notice that PB-22 was prohibited as either an analogue of JWH-018 or a compound with a chemical structure or effect substantially similar to that of JWH-018. The court thus found the relevant portions of the Act unconstitutionally vague as applied to PB-22. As such, it concluded that the Commonwealth had failed to make out a prima facie case because it could not show that the products in question were prohibited substances under the Act. See Commonwealth v. Herman, No. CP-67-CR-2400-2014, slip op. at 8-9 (C.P. York May 28, 2015). *203See generally Commonwealth v. McBride, 528 Pa. 153, 157-58, 595 A.2d 589, 591 (1991) (observing that, to make out a pri-ma facie case, the government must demonstrate a crime was committed, probably by the accused).12

The county court’s decision is now on direct appeal to this Court. See 42 Pa.C.S. § 722(7) (giving this Court exclusive appellate jurisdiction of common pleas court decisions ruling a statute unconstitutional).13 At the heart of that decision is the court’s holding that the Act is unconstitutionally vague as applied to PB-22.

Presently, the Commonwealth argues that the common pleas court erred in granting relief based on a judicial finding that the terms “analogue” and “substantially similar” were unconstitutionally vague as applied. The Commonwealth maintains that the expert witnesses all confirmed that the two compounds, JWH-018 and PB-22, had structurally similar molecular components, albeit they differed regarding whether the two chemicals were sufficiently similar to meet statutory requirements. In the Commonwealth’s view, whether they are sufficiently alike to be considered “substantially similar” or “analogues” is a question of fact for the jury to determine upon hearing expert testimony from both sides.14 In this regard the Commonwealth urges that statutory words should be understood according to their common usage, see Brief for Appellant at 16 (quoting 1 Pa.C.S. § 1903(a)), and that, here, the dictionary defines “analogue” as “[o]ne of a group of chemical compounds similar in structure but different in composition,” id. (quoting Random House Webster’s College Dictionary 47 (2d ed. 2001))—a definition that juries can comprehend and apply.

Finally, the Commonwealth points to three unpublished United States District Court decisions rejecting a void-for-vagueness claim in situations where the defendants were charged under the federal Analogue Act, and the chemicals at issue were PB-22 and JWH-018, or some variant of them. See United States v. Hoyt, 2014 WL 5023093 (W.D. Va. Oct. 8, 2014), reprinted in Brief for Appellant at app. 27a; United States v. Bays, 2014 WL 3764876 (N.D. Tex. July 31, 2014), reprinted in Brief for Appellant at app. 34a; United States v. Johnson, 2014 WL 7330936 (D. Nev. Dec. 19, 2014), reprinted in Brief for Appellant at app. 47a.15 It adds that a number of other jurisdictions have concluded that the *204terms “analogue” and “substantially similar” are not void for vagueness when applied to other controlled substances. See Brief for Appellant at 20-23 (citing cases). The Commonwealth maintains that these other decisions provide guidance and additionally militate in favor of reaching the same conclusion to maintain uniformity across jurisdictions. See id. at 18 (quoting 1 Pa.C.S. § 1927 (“Statutes uniform with those of other states shall be interpreted and construed to effect their general purpose to make uniform the laws of those states which enact them.”)).

II. Analysis

A. The void-for-vagueness doctrine

The concept of unconstitutional vagueness arises from due process norms. See U.S. CONST, amends. V, XIV; Welch v. United States, — U.S. -, -, 136 S.Ct. 1257, 1261-62, 194 L.Ed.2d 387 (2016) (observing that the void-for-vagueness doctrine is grounded in the Fifth Amendment with regard to the federal government, and the Fourteenth Amendment with regard to the States). It prevents the government from imposing sanctions under a criminal law that fails to give fair notice of the proscribed conduct. See Johnson v. United States, — U.S. -, -, 135 S.Ct. 2551, 2556, 192 L.Ed.2d 569 (2015) (citing Kolender v. Lawson, 461 U.S. 352, 357-58, 103 S.Ct. 1855, 1858, 75 L.Ed.2d 903 (1983)); see also Papachristou v. City of Jacksonville, 405 U.S. 156,

162, 92 S.Ct. 839, 843, 31 L.Ed.2d 110 (1972) (“Living under [the] rule of law entails various suppositions, one of which is that ‘[all persons] are entitled to be informed as to what the State commands or forbids.’ ” (quoting Lanzetta v. New Jersey, 306 U.S. 451, 453, 59 S.Ct. 618, 619, 83 L.Ed. 888 (1939) (second alteration in original))). Relatedly, the doctrine safeguards against arbitrary or discriminatory enforcement by the government, see FCC v. Fox Television Stations, Inc., 567 U.S. 239, 252-54, 132 S.Ct. 2307, 2317, 183 L.Ed.2d 234 (2012), as well as jury verdicts “unfettered by any legally fixed standards as to what is prohibited by the statute.” State v. Golston, 67 So.3d 452, 463 (La. 2011). Still, due process recognizes that because we are “[c]ondemned to the use of words, we can never expect mathematical certainty” in legislative draftsmanship. Grayned v. City of Rockford, 408 U.S. 104, 110, 92 S.Ct. 2294, 2300, 33 L.Ed.2d 222 (1972). Ultimately, the inquiry is whether the law “forbids or requires the doing of an act in terms so vague that [persons] of common intelligence must necessarily guess at its meaning and differ as to its application^]” Connolly v. Gen. Constr. Co., 269 U.S. 385, 391, 46 S.Ct. 126, 127, 70 L.Ed. 322 (1926).

Where, as here, a vagueness challenge does not involve First Amendment freedoms, it is “examined in the light of the facts of the case at hand,” United *205States v. Powell, 423 U.S. 87, 92, 96 S.Ct. 316, 319, 46 L.Ed.2d 228 (1975) (internal quotation marks and citation omitted), and “the statute is judged on an as-applied basis.” Maynard v. Cartwright, 486 U.S. 356, 361, 108 S.Ct. 1853, 1858, 100 L.Ed.2d 372 (1988); Commonwealth v. Heinbaugh, 467 Pa. 1, 5, 354 A.2d 244, 245 (1976). Thus, we consider the record developed in the common pleas court and evaluate whether Appellee met his burden to demonstrate that the statutory terms in question are unconstitutionally vague as applied to the chemicals JWH-018 and PB-22. In doing so, we bear in mind that statutes enjoys a strong presumption of validity and will only be declared void if they clearly and plainly violate the Constitution, with all doubts resolved in favor of a finding of constitutionality. See Commonwealth v. Bullock, 590 Pa. 480, 487, 913 A.2d 207, 211-12 (2006). See generally In re Adoption of E.M.A., 487 Pa. 152, 155, 409 A.2d 10, 11-12 (1979) (noting that this presumption pertains in an as-applied vagueness challenge), superseded by statute on other grounds, 23 Pa.C.S. § 2701(7); In re Adoption of R.B.F., 569 Pa. 269, 281, 803 A.2d 1195, 1202 (2002). We defer to the common pleas court’s findings of fact that are supported by the record, but we review questions of law—including the Act’s constitutionality—de novo. See Commonwealth v. Davidson, 595 Pa. 1, 11, 938 A.2d 198, 203 (2007).

B. The controlled-substance analogue counts prior to Act 40

As most of the charges against Appellee involve the claim that PB-22 is a chemical analogue of JWH-018, and the bulk of the pre-trial hearing testimony related to the term “analogue,” we first question whether the Act’s use of the term prior to the Act 40 amendments was unconstitutionally vague as applied to those two chemicals.16 As an initial matter, although the federal Analogue Act defines “analogue” in terms of a substantially similar chemical structure, see 21 U.S.C. § 802(32)(A)(i), and a number of our sister States have legislation containing a similar definition of a controlled substance analogue, see, e.g., Cal. Health & Safety Code § 11401(b); Colo. Rev. Stat. § 18-18-102(6); 720 III. Comp. Stat. 570/401; Kan. Stat. §§ 65-4101(g), 21-5701(b); La. Rev. Stat. § 40:961(8); Ohio Rev. Code § 3719.01(HH); Tex. Health & Safety Code §§ 481.002(6), 481.102, the Pennsylvania enactment provides no such definition or any other express guidance. Additionally, the Act defines designer drugs in such terms and clarifies that designer drugs are not within the set of chemicals which constitute controlled substances. See 35 P.S. § 780-102. Thus, although many jurisdictions appear to equate controlled substance analogues with a certain group of compounds whose chemical structure is substantially similar to that of the controlled substance in question, this type of equivalence is not reasonably supported by the express terms of the Act.

Such a lack of guidance would not be especially problematic if an accepted meaning of the word “analogue” existed within the relevant scientific community, *206or if there was general acceptance that PB-22 is, in fact, an analogue of JWH-018. However, the expert testimony for both parties at the habeas hearing confirmed that there is no widely accepted definition of the term “analogue” as applied to these types of organic molecules. See N.T., Nov. 7, 2014, at 34-35 (testimony of Dr. Coyer); id. at 82 (testimony of Dr. Huffman). The testimony also established that JWH-018 and PB-22 are in different structural classes, see supra note 9, and Dr. Huffman testified that chemicals in different structural classes are not analogues of one another—and that, specifically, PB-22 is not an analogue of JWH-018. See id. at 90-91. Dr. Huffman did clarify on cross-examination that the more particularized term “structural analogue” is sometimes used to refer to compounds that can be synthesized from a common parent molecule, and that the phrase can also refer to chemicals with the same basic molecular structure. See id. at 88. And Dr. Coyer opined that PB-22 is an analogue of JWH-018 insofar as its structure is concerned. See id. at 35-37. As to whether PB-22 is a synthetic cannabinoid in terms of mimicking the effects of known cannabinoids, however, Dr. Coyer was only able to state that some “initial testing may have been done” to ascertain its effects as such, id. at 37, and that in informal conversations some chemists group PB-22 together with JWH-018. See also id. at 38 (explaining that there was “a talk” focusing on whether a group of new compounds, including PB-22, were synthetic cannabinoids, but he did not wish to speak about that talk because it was only “a meeting”).

Particularly in light of the admitted lack of scientific studies as to PB-22’s effects within the body, we find this type of evidence to be insufficient to establish that there is any agreement in the scientific community that PB-22 is a known synthetic cannabinoid. Moreover—and more to the point—it appears there is no scientifically accepted method for ascertaining whether PB-22 is an analogue of JWH-018. In this respect, Appellee’s second expert, Dr. Harris, was in a unique position to know whether, from a legal perspective, scientists are aware of any methodology to determine whether a compound under investigation can be considered an analogue of a controlled substance. She belonged to ACECSA, a national scientific committee specially dedicated to discovering or fashioning such methods for law enforcement agencies to use. Dr. Harris testified that, as of the date of the hearing, ACECSA had not yet devised such a method. See id. at 96. She added that SWGDRUG’s analogue subcommittee had been similarly unable to formulate any such methodology, ultimately concluding that “it comes down to a subjective determination dependent not only upon what you are evaluating, but also the experience within [sic] the molecule itself.” Id. at 97.

Under these circumstances, we find resonance in the argument Appellee made in his habeas motion suggesting that scientists in the relevant field have not been able to agree on a method to determine analogue status and cannot agree on whether PB-22 is an analogue of JWH-018—and if that is true of scientists, it is difficult to see how the average citizen can be on notice of such status. The court in United States v. Forbes, 806 F.Supp. 232 (D. Colo. 1992), faced a similar situation with regard to alphaethyltryptamine (“AET”), which the government claimed was a controlled-substance analogue of the scheduled drugs dimethyltryptamine (“DMT”) and diethyltryptamine (“DET”). After hearing pre-trial expert testimony from both sides not unlike that adduced in the present case, the court stated that “[t]he scientific community cannot even agree on a methodology to use” to deter*207mine analogue status under the federal statute. Id. at 237 (emphasis added). Thus, the court concluded, “a defendant cannot determine [such status] in advance of his contemplated conduct[.]” Id.

The same observations apply to the question of whether PB-22 is an analogue of JWH-018 under the Act (at least prior to its Act 40 revisions). The average citizen would necessarily have to “guess at” PB-22’s status and “differ as to [the] application” of the analogue prohibition contained in Section 780-104(l)(vii). Connally, 269 U.S. at 391, 46 S.Ct. at 127. Consequently, we agree with Appellee and the common pleas court that the pre-Act 40 statute was unconstitutionally vague as applied to PB-22 and JWH-018.17

Nor are we persuaded by the Commonwealth’s assertion that the vagueness question can be dispensed with by .characterizing as a jury question whether PB-22 is an analogue of JWH-018. We need not address whether PB-22’s analogue status could theoretically be a question for the fact-finder if the Act were constitutional. The point here is that the Commonwealth’s argument starts from the assumption that the act is not vague as applied to PB-22, which is the very issue before this Court.

We also differ with the government’s suggestion that because the Act is part of a uniform law, Section 1927 of the Statutory Construction Act directs that it be construed uniformly with similar laws of other jurisdictions. Although the Act is based on the Uniform Controlled Substances Act of 1970, see 35 P.S. Ch. 6, Table, Section 1927 does not necessarily apply. For one thing, neither the Act’s title nor its provisions suggest an intention to conform Pennsylvania’s drug regular tions to those of other jurisdictions. See Allegheny Cnty. v. Rendell, 580 Pa. 149, 166 n.6, 860 A.2d 10, 21 n.6 (2004) (explaining that Section 1927 only pertains where the substantive language of the enactment indicates that it is “part', óf a uniform enactment among several states”). Just-as important, many states have now adopted a later version of the -uniform act which was revised to include a definition of “controlled substance analog” which is exr pressed in terms of substantial .similarity to a controlled substance,- see Unif, .Con-tbolled Substances Act § 101(3).(1990)— in other words, which tracks the Act’s definition of a designer drug. See supra note 17. Other state .decisions, such..as those highlighted by the Commonwealth, are based on the Í990 definition and, as such, do not support the Commonwealth’s uniformity argument relative to the Act’s “analogue” provision. -See, e.g., People v. Lucero, 381 P.3d 436, 440 (Colo. App. 2016); State v. Barnes, 275 Kan. 364, 64 P.3d 405, 408 (2003); State v. Smith, 189 Wis.2d 496, 525 N.W.2d 264, 267 (1995). See generally Richard L. Braun, Uniform Controlled Substances Act of 1990,; 13 CAMPBELL L. REV. 365, 367 (1991) (confirming that the ,19,90 uniform act’s controlled-substance analogue provision was drafted to encompass -designer drugs).

Finally, and as noted, the Commonwealth highlights several federal decisions-, including three United States District Court opinions, which hold' that, under- the federal Analogue Act, PB-22 is an ána-*208logue of JWH-018. However, those disputes do not purport to address the salient issue before this Court because, as with the 1990 version of the uniform act, they relate to the federal Analogue Act’s definition of a “controlled substance analogue” as a chemical having a substantially similar chemical structure to a scheduled drug. See 21 U.S.C. § 802(32)(A)(i). Their present relevance, if any, is thus limited to the designer-drug charge (discussed below) as the Act defines designer drug in similar terms, but it provides no definition of “analogue.”

Accordingly, we hold that in the pre-Act 40 timeframe the analogue provision was unconstitutionally vague as applied to PB-22 as an alleged analogue of JWH-018. That being the case, the common pleas court acted properly in dismissing the charges lodged against Appellee based on the April and May 2013 undercover purchases.

C. The controlled-substance analogue counts after Act 40

Appellee was also charged with delivery of a controlled substance (PB-22) based on the July 11, 2013, undercover purchase, and with a possession with intent to deliver a controlled substance based on the July 15, 2013, packet seizures. Both of those charges were lodged pursuant to the Act as amended by Act 40. As explained, Appellee never claimed in his habeas motion that the amended statute’s use of the term “analogue” was unconstitutionally vague as applied. Rather, he maintained that PB-22 was not a prohibited substance inasmuch as it was excluded from Schedule I due to the statute’s use of specific chemical designations. He asserted, in this respect, that PB-22 is not in any of the listed designations, and specifically, is not the same chemical designation as JWH-018. See N.T., Nov. 7, 2014, at 32-33, 108-10 (reflecting defense counsel’s repetition at the habeas hearing of this non-constitutional, interpretive basis for challenging the post-July 2 controlled-substance charges). On appeal, Appellee continues to forward this same argument as his only contention with regard to these charges. See Brief for Appellee at 4-8.18

As described above, the statutory description of Schedule I cannabinoids as stated in the revised Act only prohibited certain chemicals and their analogues within thirteen enumerated chemical designations—the relevant one being na-phthoylindoles inasmuch as it includes JWH-018, see 35 P.S. § 780-104(l)(vii)(2)(B) (2013)—and a “catchall” category of CB1 agonists, which is not presently relevant. See supra note 8. The prosecution’s expert confirmed that PB-22 is in a different chemical classification than JWH-018, and that it falls within a class of compounds known as indole carboxylic acids rather than naphthoylindoles. See N.T., Nov. 7, 2014, at 47. This has now been confirmed by the General Assembly in its most recent revision to the Act, see Act of June 8, 2016, P.L. 258, No. 37 (“Act 37”), in which the legislative body named PB-22 as a scheduled controlled substance under that very chemical designation. See 35 P.S. § 780-104(l)(vii)(2.2) (2016) (listing PB-22 as one of a group of Schedule I controlled substances within the chemical designation “[ijndole carboxylic acids”).

*209Accordingly, the Commonwealth failed to identify a valid statutory basis on which Appellee could be charged with delivery of a controlled substance, or possession with intent to deliver a controlled substance, based his conduct after July 2, 2013. We therefore affirm the common pleas court’s dismissal of the relevant counts against Appellee, although we disagree with its analysis insofar as it suggested that the post-amendment Act’s use of “analogue” is unconstitutionally vague.19 See Commonwealth v. Flanagan, 578 Pa. 587, 611, 854 A.2d 489, 503 (2004) (explaining that “this Court has the ability to affirm a valid judgment or order for any reason appearing as of record”). By reaching our holding on these grounds, we not only resolve Appellee’s claim on the terms in which he has framed it, we also “adhere to the sound tenet of jurisprudence that courts should avoid constitutional issues when the issue at hand may be decided upon other grounds.” In re Fiori, 543 Pa. 592, 600, 673 A.2d 905, 909 (1996) (citing Rescue Army v. Mun. Court, 331 U.S. 549, 568-69, 67 S.Ct. 1409, 1419-20, 91 L.Ed. 1666 (1947)); accord Threlkeld v. State, 558 S.W.2d 472, 474 (Tex. Crim. App. 1977) (“This Court will not pass on the [constitutional] validity of any part of the Controlled Substances Act which is not shown to have been violated[.]” (citation omitted)).

D. The designer-drug count and the “substantially similar” descriptor

Finally, Appellee was' charged with a single count of possession with intent to distribute, or possession, of a de-. signer drug. To review, the Act prohibits the “knowing or intentional ... possession with intent to distribute, or possession^] of a designer drug,” 35 P.S. § 780-113(a)(36); see supra note 3, which is defined in relevant part as “a substance other than a controlled substance that, is intended for human consumption and that ... has a chemical structure substantially similar to that of a controlled substance in Schedules I, II or III ... or that produces an effect substantially similar to that of a controlled substance in Schedules I, II or III.” Id. § 780-102.20

Before the common pleas court, Appel-lee claimed an entitlement to habeas relief on this charge solely on the basis that the “substantially similar” descriptor was vague. The common pleas court agreed with Appellee and expressed its rationale in succinct terms. The court found that “experts have been unable to reach an agreement on a method for analyzing and determining the similarities between the chemical structures ... of PB-22 and JWH-018.” Herman, No. CP-67-CR-2400-2014, slip op. at 9. It concluded that “[t]his disagreement renders the designer drug statute unconstitutionally vague.” Id. In his appellate brief, Appellee only argues that .that the effects of PB-22 are unknown, see Brief for Appellee at 8-9, which is not in dispute. Appellee appears to overlook that, unlike the federal CSA, the Act’s definition of designer drug is phrased in the disjunctive. Thus, he may still be liable under Section 780-113(a)(36) if PB-22’s chemical structure is substantially similar to that of JWH-018. The salient issue is whether that term—“substantially simi*210lar”—is vague as applied 'to the chemical structures of PB-22 and JWH-018.

Although the bulk of the testimony at the habeas hearing focused on the term “analogue,” the county court’s finding that experts disagree on a method for determining substantial similarity as between chemical structures is supported by the record.21 Initially, the experts agreed that, although ¡the overall molecular structures of the two chemicals were different, they had similar components. See N.T., Nov. 7, 2014, at 25, 38-39 (testimony of Dr. Coyer), 85-86 (testimony of Dr. Huffman). Dr. Coyer went further and opined that their components were “very similar,” id. at 25, and his testimony as a whole was acknowledged by Appellee as subsuming an expression that the overall molecular structures were substantially similar. See id. at 99. The defense experts disagreed. Dr. Huffman opined that the two molecules did hot have “similar structures,” id. at 91; see dlso id. at 86 (“[T]he total structures are different.”),'and Dr. Harris indicated that they were not “structurally similar as a whole.” Id. at 99. Just as important, both defense experts highlighted the importance o’f three-dimensional comparisons in reaching-a conclusion on structural similarity. See 'id. at 77 (Dr. Huffman), 100 (Dr. Harris). Dr. "Harris continued by expressing that “substantially similar” is not a ■scientific term and “substantial” means different things to different people. Id. at 101.

We have difficulty, however, with the common pleas court’s ultimate holding. While the term “analogue” may be somewhat nebulous (particularly in á scientific setting), the concept of similarity is well known to persons of ordinary intelligence, and we see no reason why such individuals would have difficulty applying it to evidence of the molecular structures of PB-22 and JWH-018. Accord United States v. McKinney, 79 F.3d 105, 108 (8th Cir. 1996) (rejecting a claim that the federal Analogue Act’s use of “substantially similar” was vague, and explaining that “a reasonable layperson could ... have'examined a chemical chart and intelligently decided for himself or herself, by comparing their chemical diagrams, whether the chemical structures of the two substances were substantially similar”), judgment vacated on other grounds, 520 U.S. 1226, 117 S.Ct. 1816, 137 L.Ed.2d 1025 (1997). The fact that the parties’ experts disagreed on the ultimate issue of substantial similarity in this case is not dispositive, particularly given the obvious visual similarities in the two-dimensional diagrams of the molecules.22 Accord United States v. *211Klecker, 348 F.3d 69, 72 (4th Cir. 2003) (where diagrams of the two molecules at issue revealed “considerable similarities,” holding that the “substantially similar” standard was not vague as applied notwithstanding that the parties’ experts disagreed on the question of whether they were substantially similar). The “substantial” qualifier speaks to the degree of similarity needed to bring a substance within the designer drug prohibition. Still, “substantial similarity” is not a scientific concept, accord . Controlled Substance Analogues 4, and although that adjective may be qualitative, the Supreme Court has stressed that it does not “doubt the constitutionality of laws that call for the application of a qualitative standard such as ‘substantial risk’ to real-world conduct”— noting, further, that “ ‘the law is full of instances where a man’-s fate depends on his estimating rightly ,.. some matter of degree.’” Johnson, — U.S. at -, 135 S.Ct. at 2561 (quoting Nash v. United States, 229 U.S. 373, 377, 33 S.Ct. 780, 781, 57 L.Ed. 1232 (1913)); see 21 AM. JUR. 2D § 17 (2017).

We also observe that the vast weight of authority from other jurisdictions supports the conclusion that “substantially similar” is not a vague term per se when used in comparing two chemical compounds. The federal circuit courts which have examined this question have generally found that use of the “substantially similar” phraseology in the controlled , substance arena does not suffer from unconstitutional vagueness.23 This view is also held by most appellate courts in other states.24 As applied specifically to PB-22 and JWH-018, moreover, Appellee has not drawn our attention to any court in any jurisdiction which has held that the sub'stantially-similar descriptor is unconstitutionally vague; as noted above, the Commonwealth has included in its appendix three United States District Court decisions which have held that the federal Analogue Act—which, in relevant part, uses the same substantial-similarity standard as the designer drug provision presently under challenge—is not unconstitutionally vague as applied to these chemicals.

Additionally, unlike the controlled-substance analogue offense, the designer drug provision has an express culpability prerequisite whereby a defendant can only be convicted if the government proves he acted knowingly or intentionally. See 35 P.S. § 780-113(a)(36). Scienter requirements of this nature help alleviate vagueness concerns, both- with regard to the adequacy of notice of the proscribed conduct, see Village of Hoffman Estates v. Flipside, Hoffman Estates, Inc., 455 U.S. 489, 499, 102 S.Ct. 1186, 1193, 71 L.Ed.2d 362 (1982), and as a means of limiting *212prosecutorial discretion, see McFadden v. United States, — U.S. -, -, 135 S.Ct. 2298, 2307, 192 L.Ed.2d 260 (2015). The McFadden Court, which dealt with the federal Analogue Act, interpreted the scienter mandate as to controlled-substance analogues as meaning that the government must show that the defendant either knew that the substance was a controlled-substance analogue regardless of his .knowledge of its identity, or knew that it satisfied the specific statutory prerequisites making it a controlled substance analogue. Those prerequisites include a substantially similar chemical structure to that of a scheduled controlled substance. See id. at -, 135 S.Ct. at 2305 (quoting 21 U.S.C. § 802(32)(A)). The Court concluded: “A defendant who possesses a substance with knowledge of those features knows all of the facts that make his conduct illegal!;.]” Id.; see also Hoffman Estates, 455 U.S. at 499 & n.14, 102 S.Ct. at 1193 & n.14 (reciting that the Supreme Court “has recognized that a scienter requirement may mitigate a law’s vagueness, especially with respect to the adequacy of notice to the complainant that- his conduct is proscribed,” and citing cases); Boyce Motor Lines, Inc. v. United States, 342 U.S. 337, 342, 72 S.Ct. 329, 331-32, 96 L.Ed. 367 (1952) (indicating that a “knowingly” mens rea requirement “does much to destroy any force in the argument” that enforcement of the regulation in question would violate due process on vagueness grounds); United States v. Novak, 841 F.3d 721, 728-29 (7th Cir. 2016) (summarizing the McFadden scienter analysis, including the mandate that the government prove the accused knew the chemical structure was substantially similar to that of a scheduled controlled substance); cf. Tiplick v. State, 43 N.E.3d 1259, 1265 (Ind. 2015) (relying on an express scienter requirement in rejecting a vagueness challenge to a counterfeit-controlled-substance statute).

There is no issue of statutory construction presently before this Court relating to the scope of the scienter requirement contained in Section 780-113(a)(36). Nevertheless, the Supreme Court’s analysis in McFadden bears upon the vagueness issue in the following way. Under the canon of constitutional avoidance, if a statute is susceptible of two reasonable constructions, one of which would raise constitutional difficulties and the other of which would not, we adopt the latter construction. See MCI WorldCom, Inc. v. PUC, 577 Pa. 294, 311, 844 A.2d 1239, 1249 (2004). Although the designer drag provision does not expressly state that, to be culpable, the defendant must know that the chemical he possesses has a molecular structure substantially similar to that of a scheduled drug, a narrow construction along those lines would be reasonable. See 18 Pa.C.S. § 302(d) (providing generally that where the law prescribes a particular level of scienter, it applies to all elements of the offense in question); see also id. § 107(a) (specifying that Title 18’s preliminary provisions—including Section 302—apply to offenses defined in any statute). If a broader interpretation of the statute would render it vague as applied, the court would be obligated to adopt the narrower construction delineated above because, under McFadden, such a construction would alleviate vagueness concerns.

Dissenting from the above, Justice Wecht initially suggests that an offense based on a substantial similarity of chemical structures fails to give adequate notice of the prohibited conduct as required by due process, because most citizens are not organic chemists and the substances they purchase ordinarily are not accompanied by chemistry books or comparative chemical-structure diagrams. See Concurring and Dissenting Opinion at 219-22.

*213While we certainly understand the concern, we are not convinced that an ordinary citizen’s lack of expertise in organic chemistry constitutes a viable basis to conclude that the statute is unconstitutionally vague. If it were, much of the Act would be invalid because many drugs appearing in the schedules are listed by their chemical formulae or technical designations. See 35 P.S. § 780-104 (listing such scheduled drugs as “N-ethyl-3-piperidyl benzilate,” “Delta-6 cis or trans tetrahydrocannabinol and their optical isomers,” and “2-(4-Chlo-ro-2,5-dimethoxyphenyl)ethanamine (2C-C)”). A large part of the federal Controlled Substances Act would likewise fall. See 21 U.S.C. § 812 (enumerating many controlled substances by chemical formulae). See generally United States v. Niemoeller, 2003 WL 1563863, at *4 (S.D. Ind. Jan. 24, 2003) (observing that “it takes a chemist to understand many of the compounds on schedule I under the Controlled Substances Act”). More generally, any offense which is predicated on an act or circumstance, the understanding of which involves specialized knowledge, would be at risk of invalidation under the vagueness doctrine.

That doctrine has not developed so strictly as to impose a blanket prohibition along these lines, and we believe it would be misguided to invalidate substantial portions of our controlled-substance legislation on the basis that compounds subject to regulation or criminalization are described by reference to technical formulae unintelligible to the general public. Accord, e.g., State v. Heinrichs, 845 N.W.2d 450, 455 (Iowa Ct. App. 2013) (“[W]e decline to find the schedule of controlled substances is constitutionally defective because it uses scientific terms that are obscure to persons of ordinary intelligence lacking in specialized knowledge. ‘The use of scientific or technical terminology or terms of art common in a regulated field does not automatically render a statute unconstitutionally vague.’ ” (quoting United States v. Caseer, 399 F.3d 828, 836-37 (6th Cir. 2005))). As one federal court noted more generally:

When dealing with legislation on complex or technical matters—whether it concerns intricate corporate tax issues, the details of electronic securities transactions, or international trade in “dual use” technologies—Congress can expect a person who wishes to engage in the activity to acquire the necessary specialized knowledge to conform the person’s conduct to law. Similarly, when dealing with the distribution of organic chemical compounds for human consumption and with intended or hoped-for central nervous system effects, Congress could reasonably expect and require persons engaged in that activity to possess or obtain the specialized knowledge needed to conform their conduct to law.

Niemoeller, 2003 WL 1563863, at *4; accord State v. Shalash, 13 N.E.3d 1202, 1210 (Ohio Ct. App. 2014). In our view the above proceeds from a reasonable conception of the scope of discretion the legislative branch retains when it seeks to regulate activity that is potentially harmful to the public, and such activity can only be described using technical terminology understandable to individuals with specialized training.

As discussed, moreover, an available interpretation of the designer drug statute incorporates a mens rea whereby defendants are only criminally liable if they act knowingly or intentionally with regard to all elements—including, for purposes of the present as-applied challenge, the alleged circumstance that PB-22’s chemical structure is substantially similar to that of JWH-018. This limitation helps ensure the statute does not become a trap for unwitting members of the public who have no expertise in organic chemistry. Instead, *214the statute is quite reasonably aimed at those who traffic in novel compounds which are essentially the same as scheduled controlled substances but contain minor differences designed to evade the statutory schedules. The General Assembly can “reasonably expect and require persons engaged in that activity to possess or obtain the specialized knowledge needed to conform their conduct to law.” Niemoeller, 2003 WL 1563863, at *4.

In a separate line of attack, Justice Wecht acknowledges the Supreme Court’s recent guidance in McFadden, as well as Colautti v. Franklin, 439 U.S. 379, 99 S.Ct. 675, 58 L.Ed.2d 596 (1979), where a statute’s lack of a scienter requirement contributed to the Supreme Court’s finding that it was vague. See id. at 401, 99 S.Ct. at 688. Further, he recognizes that the Supreme Court has issued other decisions containing language similar to McFadden’s, indicating that scienter requirements mitigate, alleviate, or ameliorate vagueness concerns. See Concurring and Dissenting Opinion at 224-25 (citing cases). He also highlights a decision of this Court stating that “vagueness challenges fail when a statute has a specific intent requirement because a defendant cannot complain he did not understand the crime .... ” Id. at 225 n.5 (quoting Commonwealth v. Hendrickson, 555 Pa. 277, 284, 724 A.2d 315, 319 (1999)). Nevertheless, Justice Wecht offers that the concept that a scienter prerequisite can help alleviate vagueness difficulties has been criticized by commentators, and that it is in tension with the maxim that ignorance of the law is not an excuse. See id. at 224-25.

Because the void-for-vagueness doctrine is grounded on federal due process norms, we believe the Supreme Court’s pronouncements are particularly germane to the resolution of the matter before us, notwithstanding the thoughtful contributions of learned commentators. As far back as 1979, the Supreme Court stated it “ha[d] long recognized that the constitutionality of a vague statutory standard is closely related to whether that standard incorporates a requirement of mens rea.” Colautti, 439 U.S. at 395, 99 S.Ct. at 685. McFadden, in particular, is highly relevant since it dealt with a federal statute prohibiting knowing or intentional conduct—including possession with intent to distribute—relative to a controlled-substance analogue which, under the federal system, is defined using the same substantially-similar-chemical-structure phraseology as Pennsylvania’s designer drug statute. See 21 U.S.C. §§ 802(32)(A) (defining “controlled substance analogue” in terms of a chemical structure “which is substantially similar to the chemical structure of a controlled substance in schedule I or schedule II”), 841(a) (reflecting an express “knowingly or intentionally” mens rea); accord McFadden, — U.S. at - n.2, 135 S.Ct. at 2305 n.2 (reflecting that the government had to prove, inter alia, that the substance in question was “substantially similar in chemical structure to a controlled substance”).25

Further, if the law being enforced only prohibits knowing or intentional conduct, any ignorance by a defendant which could defeat culpability would not be offered as an excuse. See generally 18 Pa.C.S. § 302(h). It would be advanced as a basis to conclude that the Commonwealth failed to prove an element of the offense. Thus, any perceived tension with the legal maxim involving ignorance of the law is illusory. See, e.g., United States v. Int’l Miner*215als & Chem. Corp., 402 U.S. 558, 561-62, 91 S.Ct. 1697, 1700, 29 L.Ed.2d 178 (1971); Staples v. United States, 511 U.S. 600, 622 n.3, 114 S.Ct. 1793, 1805 n.3, 128 L.Ed.2d 608 (1994) (Ginsburg, J., concurring) (“The mens rea presumption requires knowledge only of the facts that make the defendant’s conduct illegal, lest it conflict with the related presumption ,.. that ... ignorance of the law ... is no defense ....” (emphasis added)); United States v. Elias, 1999 WL 1204529, at *1 (D. Idaho Apr. 20, 1999) (explaining that Staples and two other Supreme Court decisions “have not altered the traditional rule that ignorance of the law is no excuse, but have only stated that knowledge is required where the statute specifically imposes that type of requirement”); cf. Winget v. Rockwood, 69 F.2d 326, 332 (8th Cir. 1934) (in a civil setting, distinguishing ignorance of the law from ignorance of certain facts); Ciesielski v. Prudential Ins. Co. of Am., 416 Pa. 146, 148, 205 A.2d 42, 43 (1964) (same).26

Finally, we differ with any suggestion that we are treating the analogue provision and the designer drug statute in a logically inconsistent fashion. See Concurring and Dissenting Opinion at 226-27 (Wecht, J.). Although a chemical analogue of a controlled substance would most naturally be understood as a molecule with a substantially similar chemical structure, as noted above the General Assembly has precluded that meaning by specifying that analogues and designer drugs are mutually exclusive categories—and has done so without providing any substitute standard for understanding what it intended to signify by the word “analogue.” See supra note 17.

In summary, then, the common pleas court did not account for the difference between the concepts of analogue and substantial similarity, the latter of which is more readily apprehensible' to the lay citizen in the context of comparing chemical structures; nor did it recognize that, unlike the controlled-substance provision, the designer drug provision includes a narrowing scienter specification. Moreover, like the federal appellate court in Meeker, we find in this case that there are “considerable similarities” as between the two molecules based on their two-dimensional diagrams. Klecker, 348 F.3d at 72; see Johnson, 2014 WL 7330936, at *5 (concluding that “the readily apparent similarities between the chemical structures t of 5F-PB-22 [a variant of PB-22], and the scheduled substances JWH-018 and AM-2201 [as reflected in two-dimensional diagrams], are enough to put a reasonable person on notice that 5F-PB-22 and JWH-018 are substantially similar”).

In light of the foregoing, we conclude that predicating criminal liability on a jury determination—perhaps'assisted by expert evidence—as to whether JWH-018 and PB-22 have substantially sinjilar' chemical structures does not give rise to a circumstance in which the average citizen- ’must necessarily guess at the types of .behavior that are proscribed by Section 780-113(a)(36). For the samé reasons—particularly-those relating to the scienter provision—the discretion of government agents is adequately circumscribed to guard against arbitrary or discriminatory prosecutions. That being the case, this provision withstands the-present void-for-vagueness challenge.27

*216Accordingly, we reverse the holding of the court of common pleas as respects the designer-drug charge.

III. Conclusion

For reasons given above, we affirm in part, reverse in part, and remand for further proceedings consistent with this opinion.

Justices Baer, Dougherty and Mundy join the opinion.

Justice Donohue files a concurring and dissenting opinion in which Justices Todd and Wecht join.

Justice Wecht files a concurring and dissenting opinion in which Justices Todd and Donohue join.

CONCURRING AND DISSENTING OPINION

I concur with the learned Majority’s reasoning and disposition of the first two issues presented, namely its affirmance of the trial court’s dismissal of the counts for possession and distribution of controlled substance analogues, both prior to and after the Act 40 amendments to the Controlled Substance, Drug, Device and Cosmetic Act, 35 P.S. §§ 780-101-144 (the “Act”). With respect to the pre-Act 40 amendment counts, I particularly agree with the Majority’s rationale that the expert testimony did not demonstrate any agreement in the scientific community that there is a scientifically accepted methodology for determining whether PB-22 is an analogue of JWH-018, or indeed if the two compounds are in fact analogues. As the Majority properly concludes, if scientists are unable to agree on these fundamental points, then the term “analogue” in the Act is unconstitutionally vague because it is unreasonable to expect the average citizen to be on notice of such status. Majority Op. at 206-07.

Applying precisely the same reasoning, however, I must conclude that the definition of “designer drug” in the Act, specifically, a substance, inter alia, with “a chemical structure substantially similar to that *217of a controlled substance in Schedule I, II or III in the Act,” 35 P.S. § 780-102 (emphasis added), as applied to PB-22,1 is also unconstitutionally vague. As with “analogues,” the expert witnesses could not agree that any scientifically accepted methodology existed for determining whether the molecular components of PB-22 are “substantially similar” to JWH-018. The trial court found that the experts “have been unable to reach an agreement on a method for analyzing and determining the similarities between the chemical structures ... of PB-22 and JWH-018.” Trial Court Opinion, 5/28/2015, at 9. Moreover, the three experts called by the parties to testify could not agree on whether the chemical structure of PB-22 is in fact “substantially similar” to that of JWH-018. Dr. Michael Coyer, Ph.D, a forensic toxicologist, testifying as an expert for the Commonwealth, opined, using his methodology of, inter alia, visually comparing two-dimensional diagrams of the molecules, that the components of PB-22 and JWH-018 are “very similar.” N.T., 11/7/2014, at 25, 36. John Hoffman, Ph.D, testifying for Herman, opined that PB-22 and JWH-018 are not even in the same structural class, do not have “similar structures,” and that three-dimensional modeling, rather than two-dimensional modeling, is the appropriate standard for comparing molecular structures. Id. at 81-82, 91. Heather Harris, Ph.D, a forensic analytical chemist, also testifying on behalf of Herman, agreed with Hoffman that the chemical structures PB-22 and JWH-018 are “not structurally similar as a whole,” and that three-dimensional modeling, rather than the two-dimensional modeling used by Coyer, is a better indicator of similarity. Id. at 99,100.

As shown, the experts could not agree on whether the chemical structure of PB-22 is “substantially similar” to that of JWH-018. More fundamentally, they could not even agree on a methodology accepted in the relevant scientific community for analyzing chemical compounds to determine whether they are substantially similar to each other. Accordingly, based on the same reasoning relied upon by the Majority with respect to whether these compounds are analogues—that if scientists cannot agree on what constitutes substantial similarity, then the average citizen cannot be on notice that PB-22 is an illegal drug—we must likewise find that the definition of “designer drug” is constitutionally vague.

The Majority contends that “analogue” and “designer drug” present different issues for a jury because while the term “analogue” is not expressly defined in the Act (and is thus “somewhat nebulous”), the concept of “substantial similarity” is well-known to persons of ordinary intelligence. Majority Op. at 210. I must disagree. The lack of a statutory definition is not an impediment to providing a jury with a clear understanding of an undefined statutory term. The rules of statutory construction provide that an undefined statutory term must be construed according to its common and approved usage. 1 Pa.C.S. § 1903(a). This Court has repeatedly indicated that dictionaries should be used as source material to identify this “common and approved usage.” See, e.g., Philadelphia Eagles Football Club, Inc. v. City of Philadelphia, 573 Pa. 189, 823 A.2d 108, 127 n.31 (2003); Fogle v. Malvern Courts, Inc., 554 Pa. 633, 722 A.2d 680, 682 (1999); Love v. City of Philadelphia, 518 Pa. 370, 543 A.2d 531, 532 (1988). Dictionaries de*218fine “analogue” as “[o]ne of a group of chemical compounds similar in structure but different in composition,“Random House Webster’s College Dictionary 47 (2d ed. 2001), or as “[a] compound with a molecular structure closely similar to that of another.” Oxford English Dictionary 431 (2d. 1989)..

With respect to whether chemical compounds are'“analogues” or have “substantially similar” chemical structures, both require the jury to consider the same fundamental-concept—that of the degree of the, similarity of chemical structures in question. Because experts cannot even agree on a scientifically acceptable methodology. for analyzing this concept, much less demonstrate any likelihood of agreement among themselves on the outcome of such an analysis, the average citizen cannot be expected to be on adequate notice of'whether the possession or sale of the compounds at issue here violated the provisions of the Act.

Therefore, I dissent from the Majority’s disposition of the trial court’s determination with respect to the count for possession, or possession with intent to distribute, a designer drug. 35 P.S. § 780-113(a)(30), (36). I would affirm the trial court’s order in its entirety.

■ Justices Tódd and Wecht join this concurring and dissenting opinion.

CONCURRING AND DISSENTING OPINION

I agree with the points adeptly articulated in Justice Donohue’s concurring and dissenting opinion. Like Justice Donohue, I concur in the learned Majority’s disposition of the issues regarding the classification of PB-22 as an “analogue!’ of JWH-018, both before and after the Act 40 amendments to the Controlled Substance, Drug, Device and Cosmetic Act, 35 P.S. §§ 780-101, et seq. I depart from the Majority at the same juncture as Justice Do-nohue, in that I conclude that the definition of a “designer drug”1 suffers from the same constitutional infirmity as the “anar-logue” provision, 35 P.S. § 780—104(l)(vii), as applied to PB-22. Accordingly, I respectfully dissent.

As Justice Donohue highlights, the expert testimony presented in this case revealed a significant problem: the scientific community recognizes no accepted standard or methodology for determining whether two substances are “analogues” or whether their chemical structures are “substantially similar” to each other. The inability to discern an intelligible or predictable standard for applying these concepts strikes the same constitutional blow to the definition of a designer drug that the Majority deems fatal to the analogue provision. I join Justice Donohue’s-opinion, and add the following,

“[T]he void-for-vagueness doctrine requires that a penal statute define the criminal offense with sufficient definiteness that ordinary people can understand what conduct is prohibited and in a manner that does not encourage arbitrary and discriminatory enforcement.” Commonwealth v. Mikulan, 504 Pa. 244, 470 A.2d 1339, 1342 *219(1983) (quoting Kolender v. Lawson, 461 U.S. 352, 357, 103 S.Ct. 1855, 75 L.Ed.2d 903 (1983)). Even more succinctly, due process requires that a criminal statute must provide “reasonable standards by which a person may gauge his future conduct.” Commonwealth v. Mayfield, 574 Pa. 460, 832 A.2d 418, 422 (2003). A statute is unconstitutionally vague if it fails to satisfy either the “fair warning” prong or the “arbitrary or discriminatory enforcement” prong. See Hill v. Colorado, 530 U.S. 703, 732, 120 S.Ct. 2480, 147 L.Ed.2d 597 (2000). In my view, as applied to PB-22 during the relevant timeframe,2 the definition of a designer drug is deficient in both respects.

The Majority concludes that, unlike the statutorily undefined and “somewhat nebulous” concept of a controlled substance analogue, Maj. Op. at 210, the definition of a designer drug is not unconstitutionally vague because, inter alia, its operative language—substantially similar—is not specialized or technical, and “the concept of similarity is well known to persons of ordinary intelligence.” Id. With that much I certainly agree. However, it is not the statute’s call for comparison that places it outside the bounds of ordinary comprehension. It is the object of that comparison— chemical structure—that is problematic. We can expect the average citizen to understand common words like “substantial” and “similar.” But the law cannot fairly impart upon the general populace a working knowledge of organic chemistry. As the United States Court of Appeals for the Sixth Circuit has noted, “we do not impute specialized knowledge to the ‘person of ordinary intelligence’ by whom we judge the statute’s vagueness.” United States v. Caseer, 399 F.3d 828, 837 (6th Cir. 2005). To predicate criminal punishment upon the application of such knowledge raises serious due process concerns. Criminal laws apply to everyone. One must not be required to hold a doctorate in chemistry in order to recognize the conduct that is forbidden by those laws.3

In support of the contention that an ordinary citizen fairly may be asked to compare the chemical structures of different molecules, on pain of committing a criminal offense, the Majority relies upon United States v. McKinney, 79 F.3d 105 (8th Cir. 1996). See Maj. Op. at 210-11. In McKinney, the United States Court of Appeals for the Eighth Circuit rejected an argument that the term “substantially similar” in the federal definition of a “controlled substance analogue,” 21 U.S.C. § 802(32)(A), is unconstitutionally vague. In doing so, the McKinney court set forth the dubious proposition that “a reasonable layperson could ... have examined a chemical chart and intelligently decided for himself or herself, by comparing their *220chemical- diagrams, • whether the chemical structure of two substances were substantially similar.” McKinney, 79 F.3d at 108. A reproduction of the diagrams of the chemical structures at issue in the instant case demonstrates the troublesome nature of this proposition:

[[Image here]]

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Brief for Commonwealth at 14 (reproduced from Report of Dr. Coyer at 6).

[[Image here]]

[[Image here]]

Brief for Commonwealth at 15 (reproduced from Report of Dr. Huffman at 2).

Several difficulties with this approach plainly are apparent. First, to conclude that such diagrams fairly apprise an ordinary citizen of the prohibited status of a chemical, one must assume that an ordinary citizen is able to locate, interpret, and understand these diagrams. Surely, the typical packet of “Winter Haze” or “V-8 Air Freshener” is not labeled with an illustration of the chemical structure of PB-22 alongside potentially “similar” controlled substances. Nor are such products sold with a chemistry textbook that may aid a consumer in recognizing the nature of the various atoms, bonds, or functional groups that, together, give the substance its identity. Second, even if the ordinary citizen is presented with these diagrams, and can understand what they represent, there remains no principled standard by which to compare them and to ascertain their substantial similarity. Anyone can observe superficial similarities between two chemical diagrams. Indeed, the above diagrams of PB-22 and JWH-018 contain comparable lines, symbols, and polygonal shapes that *221make them appear similar at first glance. But does the additional “0” in the diagram of PB-22 make a difference? Does the extra “N” substantially change its structure? Is it significant that the two hexagonal shapes at the end seem to attach to the remainder of the structure in a different place? Absent any accepted metric for comparison, we cannot assume that a citizen’s determination that these substances are “substantially similar” is based upon a reasoned analysis of “chemical structure,” rather than any number of inapt considerations, such as the total number of atoms in the structure, the prevalence of straight lines compared to angled lines, or each diagram’s degree of resemblance to some other object.

From these two-dimensional diagrams of their chemical structures, today’s Majority finds “considerable similarities” between PB-22 and JWH-018. Maj. Op. at 212 (quoting United States v. Klecker, 348 F.3d 69, 72 (4th Cir. 2003). Respectfully, I cannot agree that these diagrams provide sufficient information to an ordinary citizen so as to establish “fair warning” that PB-22 is a designer drug, unlawful to possess, manufacture, or distribute. See Grayned v. City of Rockford, 408 U.S. 104, 108, 92 S.Ct. 2294, 33 L.Ed.2d 222 (1972) (“Vague laws may trap the innocent by not providing fair warning.”); F.C.C. v. Fox Television Stations, Inc., 567 U.S. 239, 132 S.Ct. 2307, 2317, 183 L.Ed.2d 234 (2012) (“A fundamental principle in our legal system is that laws which regulate persons or entities must give fair notice of conduct that is forbidden or required.”).

Because the chemical structure of PB-22 is the dispositive feature with regard to the classification of that substance as a “designer drug” within the relevant time frame, and because that feature patently is beyond the scope of knowledge attributable to a citizen of ordinary intelligence, neither the commonly-understood concept of “similarity” nor the fact that the chemical structures of PB-22 and JWH-018 can be rendered as two-dimensional diagrams adequately cures the definition’s indeterminacy. What remains is an overly broad description that lacks clear parameters by which an individual may gauge whether conduct is lawful, and whereby an individual may bé guilty of a crime based upon a subjective determination for which there is no ascertainably right or wrong answer. Consequently, the definition of a designer drug is written in “terms so vague that men of common intelligence must necessarily guess at its meaning and differ as to its application,” which “violates the first essential of due process of law.” Lanzetta v. New Jersey, 306 U.S. 451, 453, 59 S.Ct. 618, 83 L.Ed. 888 (1939) (quoting Connolly v. General Const. Co., 269 U.S. 385, 391, 46 S.Ct. 126, 70 L.Ed. 322 (1926)).

Not only does the definition of a designer drug fail to provide the general populace with fair warning that PB-22 is a prohibited substance, but its imprecision also runs afoul of another requirement of due process under the void-for-vagueness doctrine. The definition allows for “arbitrary and discriminatory enforcement.” Kolender, 461 U.S. at 357, 103 S.Ct. 1855. The same absence of recognizable standards that leaves an ordinary citizen to guess whether PB-22 falls within the ambit of the definition also transforms the duties of the police officer, the prosecutor, and the judiciary into guesswork. “A vague law impermissibly delegates basic policy matters to policemen, judges, and juries for resolution on an ad hoc and subjective basis, with the attendant dangers of arbitrary and discriminatory application.” Grayned, 408 U.S. at 108-09, 92 S.Ct. 2294. The Supreme Court of the United States further has recognized that, although the void-for-vagueness principle focuses upon both fair notice and the poten*222tial for arbitrary enforcement, “the more important aspect of vagueness doctrine ‘is not actual notice, but the other principal element of the doctrine—the requirement that a legislature establish minimal guidelines to govern law enforcement.’ ” Kolender, 461 U.S. at 358, 103 S.Ct. 1855 (quoting Smith v. Goguen, 415 U.S. 566, 574, 94 S.Ct. 1242, 39 L.Ed.2d 605 (1974)). Rather than specifically delineating the necessary features of a substance in a manner that provides guidelines to law enforcement and allows for predictable application, the definition of a designer drug leaves the determination of the substance’s prohibited status to the untrained discretion of the participants in the criminal justice system.

Like the ordinary citizen, police officers, prosecutors, and judges are not chemists. A prosecuting authority may deem a substance to be “close enough” to a controlled substance in one circumstance, but, because there is no standard for assessing whether that determination is accurate, the identical comparison in another circumstance may result in a conclusion that the substances do not share a “substantially similar” chemical structure. Both conclusions are as reasonable as they are inconsistent. When determining whether a given substance is an actually-scheduled controlled substance, law enforcement or prosecuting authorities may submit that substance to a laboratory, which can return a “yes” or “no” answer as to whether that substance is prohibited.4 By contrast, whether a given substance is a “designer drug” is to be determined by an unprincipled judgment call, which allows for enforcement that is, at best, exceptionally discretionary, and, at worst, arbitrary or discriminatory.

The Majority relies upon the abundance of decisions from other jurisdictions that have held that the term “substantially similar” is not unconstitutionally vague as applied to various substances. See Maj. Op. at 211. Many of these decisions are lacking in persuasive value. The Majority cites *223United States v. Granberry, 916 F.2d 1008 (6th Cir. 1990), upon which many federal and state courts rely in rejecting vagueness challenges to the “substantially similar” language, including in a number of the other decisions that the Majority cites. See, e.g., United States v. Turcotte, 405 F.3d 515, 531-32 (7th Cir. 2005); United States v. Fisher, 289 F.3d 1329, 1333-34 (11th Cir. 2002); State v. Srack, 49 Kan.App.2d 761, 314 P.3d 890, 896 (2013); State v. Shalash, 13 N.E.3d 1202, 1209 (Ohio Ct. App. 2014). However, Granberry, itself, applied the following reasoning to the federal definition of a controlled substance analogue:

Despite Cranberry's contention to the contrary, the term “controlled substance analogue” in § 813 is clearly and specifically defined, in terms readily comprehensible to the ordinary reader. It provides adequate notice of what conduct is prohibited. The statute makes plain that drugs which have been chemically designed to be similar to controlled substances, but which are not themselves listed on the controlled substance schedules, will nonetheless be considered as schedule I substances if 1) they are substantially similar chemically to drugs that are on those schedules, 2) if they produce similar effects on the central nervous system as drugs that are on those schedules, or 3) are intended or represented to produce effects similar to those produced by drugs that are on those schedules. There is nothing vague about the statute.

Granberry, 916 F.2d at 1010. The entirety of the Granberry court’s analysis entailed a summary of the statutory definition, and a conclusory assertion that “[t]here is nothing vague” about that definition. Id. Other courts may deem this discussion to be sufficient. I am not so persuaded.

In other cases that the Majority cites, the courts relied heavily upon the federal circuit courts’ consistent rejection of similar challenges. See, e.g., Turcotte, 405 F.3d at 531 (“The circuit courts considering this issue have unanimously held that the -... Analogue Provision is not unconstitutionally vague.”); State v. Alley, 155 Idaho 972, 318 P.3d 962, 973 (App. 2014) (“There is broad agreement in the federal circuit courts that the statute is not unconstitutionally vague.”); Srack, 314 P.3d at 896 (“Other federal Circuit Courts of Appeals have reached a similar conclusion.”); Shalash, 13 N.E.3d at 1209. (citing Turcotte and noting that “every federal circuit court that has addressed this issue has ‘held that the ,.. Analogue Provision is not unconstitutionally vague.’”). Although uniformity in the federal "circuit courts certainly is worthy of note, I find significant that much of - this consensus can .be traced to thinly reasoned cases like Granberry and McKinney. Where, as here, faithful application of due process .-principles pursuant to the void-for-vagueness doctrine reveals clear deficiencies in a statute, I would not yield to the contrary case law of other jurisdictions, absent persuasive analysis.

The Majority notes that “Appellee has not drawn our attention to any court in any jurisdiction which has held that the substantially-similar descriptor is unconstitutionally vague[.]” Maj. Op. at 211; However, in its discussion of the analogue provision, the Majority -relies upon a decision which held precisely that; See Maj. Op. at 206-07 (applying United States v. Forbes, 806 F.Supp. 232 (D. Colo. 1992)). The Majority implicitly confines its -application-of Forbes to the term “analogue” only, but the court in Forbes held that, “[ajlthough the ‘substantially similar’ language -may be generally susceptible to -adequate definition, it runs afoul of the vagueness doctrine when it is applied to .... -the circum*224stances of this case.” Forbes, 806 F. Supp. at 237. Of particular salience to the instant case, the Forbes court noted that “[t]he scientific community cannot even agree on a methodology to use to determine structural similarity.” Id. (emphasis added). The Majority quotes a portion of this statement to suggest that the absence of recognized standards precluded a determination of “analogue status.” Maj. Op. at 206. However, the Majority overlooks the fact that it was the “substantially similar” descriptor that the Forbes court found problematic. That descriptor was held to be unconstitutionally vague in Forbes based upon precisely the same circumstance that was revealed in the instant case—the scientific community cannot even agree on a methodology for determining whether a substance “has a chemical structure substantially similar to that of a controlled substance” so as to qualify as a designer drug. 35 P.S. § 780-102(b). Forbes certainly supports the Majority’s conclusion that the analogue provision is unconstitutionally vague, but it equally supports the same conclusion with regard to the definition of a designer drug.

The Majority’s final reason for rejecting the vagueness challenge to the designer drug definition is that “the designer drug provision has an express culpability prerequisite whereby a defendant can only be convicted if the government proves he acted knowingly or intentionally.” Maj. Op. at 211. To be sure, the Supreme Court of the United States long has held that “the constitutionality of a vague statutory standard is closely related to whether that standard incorporates a requirement of mens rea.” Colautti v. Franklin, 439 U.S. 379, 395, 99 S.Ct. 675, 58 L.Ed.2d 596 (1979).

[T]he requirement of a specific intent to do a prohibited act may avoid those consequences to the accused which may otherwise render a vague or indefinite statute invalid. ... The requirement that the act must be willful or purposeful may not render certain, for all purposes, a statutory definition of the crime which is in some respects uncertain. But it does relieve the statute of the objection that it punishes without warning an offense of which the accused was unaware. ■

Id. at 395 n.13, 99 S.Ct. 675 (quoting Screws v. United States, 325 U.S. 91, 101-102, 65 S.Ct. 1031, 89 L.Ed. 1495 (1945) (plurality)). Today’s Majority draws support from the Supreme Court’s decision in McFadden v. United States, — U.S. -, 135 S.Ct. 2298, 192 L.Ed.2d 260 (2015), wherein the Court determined that the scienter element of the statute at issue, which prohibits an individual from knowingly manufacturing, distributing, or possessing with intent to distribute a controlled substance analogue, does not require knowledge of the identity of the substance, but does require either (1) knowledge that the substance is controlled, or (2) knowledge of the features of the substance that make it a controlled substance analogue. Id. at 2302. The McFadden Court also noted that the scienter requirement “‘alleviate[s] vagueness concerns,’ ‘narrow[s] the scope of the [its] prohibition[,] and limit[s] prosecutorial discretion.’ ” Id. at 2307 (quoting Gonzales v. Carhart, 550 U.S. 124, 149-50, 127 S.Ct. 1610, 167 L.Ed.2d 480 (2007) (bracketed material in original)).

Although the relevance of a scienter requirement to the vagueness inquiry is well-settled under the precedents of the Supreme Court of the United States, the Court has been careful not to suggest that the presence of a mens rea element is dispositive. Rather, the Supreme Court has stated that a scienter requirement may “mitigate,” City of Chicago v. Morales, 527 U.S. 41, 110, 119 S.Ct. 1849, 144 L.Ed.2d *22567 (1999), “alleviate,” Gonzales, 550 U.S. at 149, 127 S.Ct. 1610, or “ameliorate,” Hill, 530 U.S. at 732, 120 S.Ct. 2480, constitutional vagueness concerns.5 Even framed as merely a factor to consider when confronting a vagueness challenge, the proposition has not gone uncriticized, because it appears to create tension with the familiar maxim: ignorantia juris non excusat (“ignorance of the law excuses not”). Professor Wayne R. LaFave has noted:

One “knowingly” commits an offense when he knows that his acts will bring about certain results (those defined in the statute in question), and whether he knows that deliberately causing such results is proscribed by statute is immaterial. Because it is knowledge of the consequences of one’s actions and not knowledge of the existence or meaning of the criminal law which is relevant, it seems clear that uncertain language in a statute is not clarified by the addition of a scienter element.

1 Wayne R. Lafave, Substantive Criminal Law § 2.3 (2d ed. 2003) (footnotes omitted). Another commentator has opined:

“Scienter” has frequently been found a component of the offense created by the statute charged with indefiniteness, and on each occasion the statute has been sustained, in part on the notion that the requirement of guilty knowledge clarified it. Yet it is evident that, unless the Court has been fooling itself in these cases, the “scienter” meant must be some other kind of scienter than that traditionally known to the common law—the knowing performance of an act with intent to bring about that thing, whatever it is, which the statute proscribes, knowledge of the fact that it is so proscribed being immaterial. Such scienter would clarify nothing; a clarifi-catory “scienter” must envisage not only a knowing what is done but a knowing that what is done is unlawful or, at least, so “wrong” that it is probably unlawful. One difficulty here is that it is uncertain whether the courts which subsequently enforce the statutes which the Court sustains will employ the same brand of “scienter” as the Court; if not, and if “scienter” was essential to the Court’s holding, then of course the statute which is constitutional is not being administered and the statute which is being administered is not constitutional. In any event, “scienter” has become a recognized element of the lore of vagueness, and represents at its best, a tool to be designedly used in the service of other ends; at its worst, a port of entry for the ethical predilections of the then sitting Court.

Anthony G. Amsterdam, Note, The Void-for-Vagueness Doctrine in the Supreme Court, 109 U. Pa. L. Rev. 67, 87 n.98 (1960) (citations omitted) (cited in Vill. of Hoffman Estates v. Flipside, Hoffman Estates, Inc., 455 U.S. 489, 499 n.14, 102 S.Ct. 1186, 71 L.Ed.2d 362 (1982)).

The Supreme Court, at least on one occasion, has invoked the proposition that a scienter requirement reduces the threat of vagueness particularly as compared to the dangers posed by strict liability offenses, which require no proof of mens rea to establish guilt. See Colautti, 439 U.S. at 395-97, 99 S.Ct. 675. In Colautti, the Court expressed the concept not only through the positive statement that the presence of a scienter requirement mitigates constitu*226tional vagueness concerns, but through the inverse, that “[t]he lack of- any scienter requirement exacerbates the uncertainty of-the-statute.” Id. at 401, 99 S.Ct. 675. The Court cautioned that, “[bjecause of the absence of a scienter requirement in the provision ... the statute is little more than-, ‘a trap for those who act in good faith.’ ” Id. at 395, 99 S.Ct. 675 (quoting United States v. Ragen, 314 U.S. 513, 524, 62 S.Ct 374, 86 L.Ed. 383 (1942)).

Turning to "the instant case, the Majority notes that the designer drug provision prohibits the “knowing or intentional manufacture, distribution, possession with intent to distribute, or possession of a designer drug"” 35 P.S. § 780-113(a)(36) (emphasis added). The Majority explains that “[sjciénter' requirements of this nature help alleviate vagueness concerns, both with regard to the adequacy of notice of the proscribed conduct and, as a means of limiting prosecutorial discretion.” Maj. Op. at 211-12 (citations omitted). As discussed above,- there is certainly precedential support for this proposition. However, if the scienter "provision of 35 P.S. § 780-113(a)(36) helps to rescue the definition of a designer drug from a finding of vagueness, the same logic should apply to 35 P.S. § 780-113(a)(30) as it relates to the term “analogue,” which the Majority concludes is unconstitutionally vague.

Admittedly, 35 P.S. § 780-113(a)(30) does not use the same scienter language as its designér drug counterpart,6 but we never have held that the manufacture, delivery, or possession with intent to deliver a controlled substance is a strict liability offense. Indeed, construing the statute in Commonwealth v. Rambo, 488 Pa. 334, 412 A.2d 535, 537 (1980), we relied upon the definition of “possession” provided by Subsection 301(c) of the Crimes Code, which defines the term as “an act, within the meaning of this section, if the possessor knowingly procured or received the thing possessed or was aware of his control thereof for a sufficient period to have been able to terminate his possession.” 18 Pa. C.S. § 301(c). We held that “[sjuch knowledge is required by statute and our case law in order to prove possession of a controlled substance.” Rambo, 412 A.2d at 537; accord Commonwealth v. Valette, 531 Pa. 384, 613 A.2d 548, 549-50 (1992) (“In drug possession cases, the Commonwealth must prove that a defendant had knowing or intentional possession of a controlled substance .... ”). Furthermore, Subsection 302(c) of the Crimes Code provides a default scienter requirement where such a term is not otherwise specified by a criminal statute. 18 Pa.C.S. § 302(c) (“When the culpability sufficient to establish a material element of an offense is not prescribed by law, such element is established if a person acts intentionally, knowingly or recklessly with respect thereto.”). Accordingly, 35 P.S. § 780-113(a)(30) does not define the manufacture, delivery, or possession with intent to deliver a controlled substance analogue as a strict liability offense—the statute requires proof of scienter. If the scienter requirement of 35 P.S. § 780-*227113(a)(36) helps to “alleviate vagueness concerns” with regard to the definition of a designer drug, Maj. Op. at 211, the fact that 35 P.S. § 780-113(a)(30) also requires proof of scienter should mitigate the vagueness of the term “analogue” in the same manner.

Ultimately, even if the scienter requirement in the charging statute helps to alleviate concerns about the vagueness of the definition of a designer drug, it does not help enough. At most, the scienter requirement may constitute a “means of limiting prosecutorial discretion,” Maj. Op. at 211-12, in that it makes the elements of the crime more difficult to prove, particularly if it necessitates that a “defendant must know that the chemical he possesses has a molecular structure substantially similar to that of a scheduled drug.” Maj. Op. at 212. Nevertheless, the scienter requirement does not aid in the provision of “fair warning” to the ordinary citizen that a given substance falls within the definition. The statute must allow an individual to gauge the legality of conduct in the first place, and the words “knowing” and “intentional” do not provide the standards that are necessary for the definition to be made amenable to intelligible or consistent application, by either those who are subject to it or those who seek to enforce it. A mens rea term is not a Rosetta Stone that enables one to decipher a statute that is inherently indeterminate. The problem remains that “chemical structure substantially similar to that of a controlled substance,” 35 P.S. § 780-102(b), is an amorphous and unduly subjective standard, which lies beyond the scope of knowledge attributable to an ordinary citizen, and which cannot be ascertained reliably, even by the most qualified of experts. Terms like “knowing” and “intentional” shed no additional light upon the meaning of that definition. In the words of Justice Anthony Kennedy: “Scienter cannot save so vague a statute as this.” Hill, 530 U.S. at 774, 120 S.Ct. 2480 (Kennedy, J., dissenting).

I recognize that the designer drug statute is a product of the General Assembly’s ongoing struggle to prohibit newly-developed and potentially dangerous intoxicants. To be sure, this-area of criminal law is in constant flux. I have little doubt that, in some secluded laboratory somewhere, almost immediately after a substance is criminalized, fiendish chemists set to work developing a substance similar in effect, but distinct in identity. Undoubtedly, the designer drug statute targets such substances, even those yet to be invented. I understand that the General Assembly sought to get ahead of these manufacturers, rather than always playing catch-up to ever-changing technology. Still, it is the General Assembly’s duty to define the law. Although “we can never expect mathematical certainty from our language,” Grayned, 408 U.S. at 110, 92 S.Ct. 2294, due process requires clarity and specificity in the exercise of the legislative function, particularly in regard to laws with penal effect. This Court may well be able to discern the purpose underlying an enactment. But it is not our prerogative to fill in the gaps, to improve creatively upon an unduly vague statutory standard, in order to “get us there.”

I appreciate the import of the legislative purpose that animates the designer drug statute. I recognize as well the difficulty of drafting language sufficiently tailored to achieve that worthwhile purpose. But importance of purpose and difficulty of drafting do not relieve the General Assembly of its obligation to define criminal offenses in a manner that enables ordinary people to gauge whether their conduct is lawful, and in a fashion that does not encourage arbitrary or discriminatory enforcement. A statute cannot leave the definition of erimi-*228nality itself to the subjective determination of a police officer, a prosecutor, a judge, or a jury.

Many years ago, Chief Justice Morrison Waite cautioned against the pernicious effect of such a broad grant of legislative authority:

It would certainly be dangerous if the legislature could set a net large enough to catch all possible offenders, and leave it to the courts to step inside and say who could be rightfully detained, and who should be set at large. This would, to some extent, substitute the judicial for the legislative department of the government.

United States v. Reese, 92 U.S. 214, 221, 23 L.Ed. 563 (1875). Because 35 P.S. § 780-102(b) defines a designer drug in an imper-missibly vague manner, it casts such an overbroad net. Therefore, I agree with the trial court’s determination that 35 P.S. § 780-102(b) was unconstitutional as applied to PB-22, and I would affirm the trial court’s order in its entirety. I respectfully dissent.

Justices Todd and Donohue join this concurring and dissenting opinion.