Commentary for Kiddushin 126:2

This is the problem with the mishnah—what does it mean when he says “on condition that my father consents.” The first clause seems to mean that the father says yes. If he is silent, she is not betrothed.
The second clause implies that “consent” means the father did not protest. Silence is acquiescence.
The last clause implies that to undo the kiddushin, the father must actively protest. His earlier silence is not sufficient. Thus the three clauses of the mishnah do not all seem to agree one with the other.

R. Yannai indeed agrees, the mishnah refers to two different contexts. In the first clause, the meaning of the statement is that the father must say yes, whereas in the last two clauses, the meaning of the statement is that my father not object. To Resh Lakish, it is preferable to say the mishnah refers to two different circumstances, i.e. the betrother said two different things, rather than attribute the mishnah to two different tannaim.