In December, 1973, Carolyn C. Clevenger (plaintiff), the mother of two daughters, consulted the defendant, an obstetrician and gynecologist, for a physical examination and “to discuss having [her] tubes tied.” The defendant performed a tubal ligation on the plaintiff on January 10, 1974. The plaintiff s third daughter was born March 17, 1975.

The plaintiffs commenced this action, alleging negligence and breach of contract. The judge directed a verdict for the defendant on the negligence count, and the plaintiffs do not challenge that ruling in this appeal. The judge submitted the contract count to the jury, reserving leave to enter a verdict for the defendant notwithstanding a verdict in favor of the plaintiffs, and he also submitted interrogatories to the jury concerning the contract claim. The jury returned a verdict for the defendant, and the plaintiffs have appealed from a judgment for the defendant on that verdict. We conclude that the evidence did not warrant submitting the case to the jury on the contract count, even considering certain evidence which the judge excluded.2 Consequently, we need not pass on various issues that the plaintiffs have argued in this appeal, which we transferred here on our own motion.3

*156The evidence in this case, taken in its form most favorable to the plaintiffs, does not disclose an enforceable promise by the defendant that the plaintiff would not have another child. The only evidence on which a promise, guaranty, or warranty of a specific result could have been based is the testimony of the plaintiff as to what the defendant told her in the course of her initial visit to the defendant in December, 1973.4 Because the plaintiffs testimony concerning that conversation is crucial to the disposition of this appeal, we set it forth fully, omitting only one interruption when the witness started to recite what another physician had told her. The plaintiff testified: “Well, after the initial visit, I mean the initial examination, we went in and he said that I was in good health. And I said that I was interested in having my tubes tied. And he said, well, you know, that is not an operation that you go into lightly. And I said, I know. I said, I have had a lot of problems with my back. When I had my second child I had a back operation, as after I had my first baby and then I had problems delivering my second baby, and I was really frightened to have any more, and I — we couldn’t afford any more. And I said, I know that this is what I would like to do. He said, well, you know, this is a permanent thing. You are not going to have any more children after this operation. It is not something — have you discussed this with your husband? And I said, yes, we have had two years to think about it. I said, I wanted the operation done after [my second child], and I was too young at that time. The physician that I had at that time was Doctor Dorman, and he told me that — [interruption], ... So I waited two years, and was going to *157go back to the other doctor. I was afraid he wouldn’t do it, so I consulted [the defendant]. So he said we will do it. You are in good health, in reason, why not. As long as you know it’s a permanent thing. This is it. There is no reversal. You are not going to have any more children. I said, I know. That is what I want. I don’t want any more. He said he would make an appointment for the hospital and take care of things from there.”

The only other evidence that might bear on the question whether the defendant promised a specific result was certain postoperative conversations. These conversations could not have created an enforceable contractual obligation, but the evidence was arguably relevant as to the defendant’s state of mind at the time of the pre-operative conversation, as tending to show that the defendant had believed that after the operation the plaintiff would not be able to have a child. One postoperative conversation occurred in July, 1974, when the plaintiff telephoned the defendant.5 The judge ultimately struck this testimony on his own motion. Testimony of two conversations, also occurring in the summer of 1974, between the plaintiff’s mother and the defendant was also excluded.6 Even if all the excluded testimony had been admitted, the evidence would not have warranted a finding of a promise of a specific result.

In a recent discussion of a case involving a claim that a physician had contracted to achieve a particular medical result, we noted that actions based on such alleged contracts *158are allowed but that there must be “clear proof.” Sullivan v. O’Connor, 363 Mass. 579, 582-583 (1973).7 In Salem Orthopedic Surgeons, Inc. v. Quinn, 377 Mass. 514, 517 (1979), we characterized the Sullivan case as adopting the view that recovery may be had against a physician “who expressly agrees to produce a certain medical result and then, without fault, fails to do so” (emphasis supplied). Some courts have taken the position that there must be separate consideration for the physician’s promise,8 and at least one has adopted the view that a higher burden of proof (“clear and convincing evidence”) is required than in the normal civil action (Sard v. Hardy, 281 Md. 432, 453 [1977]). Some States require enforceable medical contracts to be in writing. See Note, Physicians and Surgeons — Sullivan v. O’Connor: A Liberal View of the Contractual Liability of Physicians and Surgeons, 54 N.C.L. Rev. 885, 902 n.102 (1976), citing statutes in Michigan, Ohio, and Pennsylvania.

“Clear proof” does not require proof of special consideration for the promise nor does it heighten the burden of proof. What it does require is that the trier of fact give *159attention to particular factors in deciding whether the physician made a statement which, in the context of the relationship, could have been reasonably interpreted by the patient as a promise that a given result or cure would be achieved. 9 The factors relevant in such an appraisal and their respective values or weights will vary with the circumstances of given cases. Some of the possible factors are noted in the Sullivan case. It should be regarded as a negative factor, although one not in itself determinative, that the physician and patient did not focus on the question whether the physician was undertaking to achieve a given result. The trier of fact should not adopt a relaxed attitude that might subject a physician to liability for making statements reasonably calculated only to reassure a patient or, as in this case, for stating the significant consequences that could be expected to follow upon a successful surgical procedure.

Here the defendant rightly emphasized the significance of a tubal ligation which, according to the testimony, is effective in the overwhelming percentage of the cases where the surgical procedure is carried out with due care.10 The defendant’s words were designed to make sure that the plaintiff knew the operation was non-reversible in character. See Rogala v. Silva, 16 Ill. App. 3d 63, 66-67 (1973). The parties did not focus on the question of a promise, nor were the words used promissory in nature. Doubt could be lessened or removed in such a case if the physician were to *160call attention to the possibility that the operation might not succeed despite all standard surgical precautions. But we are persuaded on the whole that the case for liability was not sufficiently demonstrated to warrant submission to the jury.

Judgment affirmed.

(dissenting, with whom Liacos and Abrams, JJ., join). For various reasons discussed below, I respectfully dissent. I write on the assumption that Sullivan v. O’Connor, 363 Mass. 579 (1973), remains the law and that, in consequence, there is no obstacle to the plaintiffs seeking damages for the defendant’s alleged breach of a contract to produce a medical result. I believe that errors in the exclusion of evidence so prejudiced the plaintiff that she is entitled to a new trial. Moreover, I cannot agree with the holding of the court that the evidence, either with or without those statements which I believe were erroneously excluded, was insufficient to prove the existence of an express contract to produce a specific medical result. I would therefore reverse the judgment entered below and remand the case for a new trial.

1. Errors in excluding evidence. The plaintiff sought to introduce in evidence three statements made by the defendant in the summer of 1974. These statements, and the circumstances in which they were made, are set forth in the court’s opinion, supra at notes 5-6. In substance, all the statements asserted that it was impossible for the plaintiff to be pregnant. The judge initially allowed the plaintiff to testify as to one of these statements made to her. He later reversed himself, however, and he ordered the testimony struck and instructed the jury to disregard it. Although the precise reason for striking the testimony is unclear, the judge apparently relied on a supposed rule of law to the effect that “[a]ny statement after the contract has been performed, in this case after the operation took place, concern*161ing that contract, what might have been a promise, is inadmissible to establish that the contract was made under certain terms and conditions.” The judge later excluded evidence of other similar statements to the plaintiffs mother on the ground of the hearsay rule, holding, in effect, that the plaintiff had the burden of demonstrating the admissibility of the statements under some exception to that rule.

It is clear that no unilateral statement or conduct by a party to a contract occurring after the performance of the contract can change the obligations of the parties thereunder. 1 But statements made at any time after the making of the contract may shed light on the meaning ascribed by the parties to the language they used. See, e.g., Gishen v. Dura Corp., 362 Mass. 177, 182 (1972); Jennings v. Whitehead & Atherton Mach. Co., 138 Mass. 594, 596 (1885). “This evidence is not received for the purpose of constructing a new contract or varying the old one, . . . but is to enable the judge to understand the subject matter of the agreement as it lay in the minds of the parties and the meaning that they themselves put upon any doubtful or ambiguous terms they may have used, and so to apply their language correctly to the subject matter which was in their contemplation.” Rizzo v. Cunningham, 303 Mass. 16, 21 (1939).

In this case, the various statements made by the defendant, when considered with the other evidence in the case, might lead a jury to infer not only that the defendant believed the plaintiff to be incapable of becoming pregnant in the summer of 1974, but also that he had previously prom*162ised to make her so. Thus, testimony concerning the postoperative statements was relevant to aid the jury in determining what the parties meant by their pre-operative conversation, and it was therefore presumptively admissible.

Reliance on the hearsay rule as a ground for excluding the evidence is unpersuasive. In classical terms, hearsay is an out-of-court statement offered to prove the truth of the matter asserted. W.B. Leach & P.J. Liacos, Massachusetts Evidence 183 (4th ed. 1967). McCormick, Evidence § 246, at 584 (2d ed. 1972). Fed. R. Evid. 801(c). In this case, the jury was not asked to believe that the plaintiff could never become pregnant after the surgery by the defendant. Indeed, the contrary was the foundation of the lawsuit — the plaintiff did again become pregnant notwithstanding the surgery. Rather, the jury was asked by the plaintiff to believe that the defendant had promised and intended that the plaintiff would be rendered incapable of becoming pregnant. Offered for such a purpose, the defendant’s statements were simply not hearsay. See Productora e Im-portadora de Papel, S.A. de C.V. v. Fleming, 376 Mass. 826, 842 (1978); Commonwealth v. Leaster, 362 Mass. 407, 412 (1972).

Even if the proffered statements were technically hearsay, they were so obviously admissions by the defendant as to be admissible as a matter of course. There was no necessity for the plaintiff to pursue the empty formalism of citing the “admission exception” to the hearsay rule (if, indeed, the statements could be admitted only under such an “exception” to the rule).2 Accordingly, I would hold that testimony concerning the statements was improperly excluded.

*163I believe further that the error in excluding the statements caused substantial prejudice to the plaintiff. In response to special interrogatories, the jury answered inconsistently that (1) the defendant promised the plaintiff she would not have children, but that (2) the defendant did not breach the contract of which such promise was a part. In my view, this inconsistency stemmed in part from the erroneous evidentiary rulings and reflected confusion over the import of the evidence.3 The plaintiff was entitled to place before the jury evidence susceptible of being interpreted as an admission by the defendant that, if he had performed what he had promised to do, the plaintiff could not be pregnant in the summer of 1974. Having been prevented from doing so, the plaintiff is now entitled to a new trial.

2. Sufficiency of the evidence. I also disagree with the conclusion of the court that there was insufficient evidence of an express contract for the case to go to the jury. In arriving at its conclusion that the evidence was insufficient, the court cites our decision in Sullivan v. O’Connor, 363 Mass. 579 (1973), for the proposition that there must be “clear proof” that the defendant contracted to achieve a particular medical result.4 The court then notes that “[i]t should be regarded as a negative factor, although one not itself determinative, that the physician and patient did not focus on the question whether the physician was undertaking to achieve a given result.”

*164I believe that in this case there was in fact evidence of a promissory “focus” on an agreed result, and that, the jury could have found a reasonable expectation by the plaintiff of a particular result.

It could be found from the plaintiff s testimony that the sole result which she desired to obtain from the tubal ligation was that she would become incapable of having children thereafter. The court apparently views the defendant’s statements as “reasonably calculated only to reassure a patient or, as in this case, for stating the significant consequences that could be expected to follow upon a successful surgical procedure.” It relies on this view of the evidence to decide that, in the context of this particular professional relationship, the physician was not promising a specific result. Plainly, however, the defendant’s secret intentions have nothing to do with the objective meaning of his words. The jury could reasonably have inferred, based on the plaintiff’s testimony alone and without reference to the defendant’s statements that were excluded, that the plaintiff desired not to have to endure further pregnancies. Furthermore, the defendant had reason to know that such was the plaintiff’s intention and should bear any risk that his own language would be misunderstood. See, e.g., Restatement (Second) of Contracts § 227 (2) (b) (Tent. Drafts Nos. 1-7, 1973). It was, therefore, open to the jury to find, as they did, that a contract to produce a particular medical result arose and that the plaintiff reasonably understood the defendant to warrant her future sterility. The fact that we, as judges, might not draw the same inference is beside the point. Similarly, it is unimportant that the parties omitted to use words like “warranty,” “guaranty,” or the like and that the plaintiff, rather than the defendant, proposed the procedure.5 It is enough that the evidence, reasonably *165viewed, permitted the inferences necessary for the jury to conclude that the parties made an express contract looking toward achievement of a particular medical result.

The law generally permits the formation of a binding contractual obligation whether or not the parties are specifically aware of the legal consequences of their acts. Restatement (Second) of Contracts § 21B (Tent. Drafts Nos. 1-7, 1973). If the court harbors hostility for the holding of Sullivan, I believe it would be better to deal directly with the continued wisdom of allowing contractual remedies for medical procedures which fail to produce a promised result rather than to impose artificial obstacles to pursuing the disfavored remedy. Cf. Salem Orthopedic Surgeons, Inc. v. Quinn, 377 Mass. 514, 520-521 (1979).

3. The plaintiff seasonably raised and argued some questions of law relating to the measure of her damages. Because the court has decided to affirm the judgment for the defendant and has not discussed these questions, it would be inappropriate for me to do so.

4. I would hold (a) that there was sufficient evidence to go to the jury on the contract issue and (b) that the judge erred in excluding evidence of the defendant’s admissions. I would therefore reverse the judgment and remand the case to the Superior Court for a new trial.