O'Hara v. Hall

— 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. Russell, 3 Dall. 415. As to the authority of Moses v. Macferlan, it has always been suspected, and has lately been overruled, on the principle, *that the previous decision, there 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.

— 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.