פירוש על קידושין 128:13

In our mishnah R. Meir seems to say that people will make statements that cause doubts to arise. Such is the man who says “I have given in betrothal my eldest daughter, but I do not know whether the eldest of the seniors or the eldest of the juniors, or the youngest of the seniors who is older than the eldest of the juniors.” R. Yose says that there is no doubt that this statement refers to the oldest daughter. A person does not make a statement that cause a doubt to arise. Therefore we interpret his statement in accordance.
But in another mishnah from Nedarim the two tannaim disagree over the meaning of “Until pene’ Pesah.” R. Meir seems to be certain of this statement’s meaning—it means before Pesah begins. But R. Yose seems to think it is doubtful—maybe it means until Pesah is over in which case his vow is effective until Pesah is over.