CHASE, Justice.

You may explain, but you cannot alter, a written contract, by parol testimony. A case of explanation, implies uncertainty, ambiguity, and doubt, upon the face of the writing. But the proposition now, is a plain case of alteration: that is, an offer to prove by witnesses, that the assignor promised something, beyond the plain words and meaning of his written contract. Such evidence is inadmissible; and has been so adjudged by the Supreme Court, in Clarke v. Russel, 3 Dall. Rep. 415. As to the authority of Moscs v. M`Farlan, it has always been suspected, and has lately been over-ruled, on the principle, *341 that the previous decision, ther brought into question, was pronounced by a competent Court.

I grant, that chancery will not confine itself to the strict rule, in cases of fraud, and of trust. But we are sitting as Judges at common-law; and I can perceive no reason to depart from it.

PETERS, Justice.

If we were sitting as Judges in a state Court, I should be inclined to admit the testimony, in order to attain the real justice of the cause; as there is no Court of equity in Pennsylvania. But there is no such defect in the federal jurisdiction; and, therefore, when the party comes to the common law side of the Court, he must be content with the strict common law rule of evidence.