Kiddushin, Chapter 2, Mishnah 3. This mishnah is a direct continuation of the previous one, which dealt with a case where a mistake was made in identifying the item with which the kiddushin were performed - for example, she thought it was wine and it turned out to be honey, or the reverse. Our mishnah brings additional examples, in which a man betroths a woman on a particular condition, and it turns out that the condition is not fulfilled.
The cases of mistake in the mishnah:
"Al menas she'ani kohen" venimtza Levi - he told her that he is betrothing her on condition that he is a kohen, and it turned out that he is a Levi. And likewise the reverse: he said that he is a Levi, and it turned out that he is a kohen.
"Al menas she'ani nasin" venimtza mamzer - a nasin is one of those whom a Jew may not marry. Both the nasin and the mamzer are forbidden to marry an ordinary Jew, and both are problematic statuses, except that he mistakenly identified his own status. And likewise the reverse: he said that he is a mamzer, and it turned out that he is a nasin.
"Al menas she'ani ben ir" venimtza ben kerach - a ben ir is a resident of a small town, and a ben kerach is a resident of a large city. He said that he is from the small town, and it turned out that he is from the large city. And likewise the reverse: he said that he is a ben kerach, and it turned out that he is a ben ir.
"Al menas shebeisi karov lamerchatz" venimtza rachok - and likewise the reverse: he stipulated that his house is far from the bathhouse, and it turned out that it is close.
"Al menas sheyesh li bas o shifchah gadeles" ve'ein lo - a "gadeles" is a woman who braids women's hair, a professional like a hairdresser. Some explain that the reading should be "megadeles," meaning a grown daughter or a grown maidservant who is capable of doing the household work. Either way, he stipulated that he has such a daughter or maidservant, and he does not. And likewise the reverse: he stipulated that he does not have one, and it turned out that he does.
"Al menas she'ein li banim" veyesh lo - and likewise the reverse: he stipulated that he has children, and it turned out that he does not.
The ruling of the mishnah:
In all of these cases "einah mekudeshes" - she is not betrothed. And this is so even "af al pi she'amrah: belibi hayah li zos hakavanah af al pi chen" - even though she said: in my heart this was my intention nonetheless. That is, even if the woman claims that in her thoughts and inwardly she made up her mind to be betrothed to him even if that condition would not be fulfilled, the kiddushin do not take effect.
The reason for this: what was in her heart is not relevant, since unspoken thoughts have no legal force. An intention that was not expressed with the mouth is as though it was never expressed at all. What determines the matter is that he betrothed her on one particular condition, and it turned out that the condition was not true, and therefore she is not betrothed.
And so too when the condition comes from her mouth:
The mishnah concludes that the same ruling applies not only when he sets the conditions, but even when she sets them. If she said that she agrees to be betrothed on condition that she is such and such, and it turned out that this is not so, that condition too is not valid and the kiddushin do not take effect.
In summary: in this mishnah we learned a series of cases in which the kiddushin were performed on a condition relating to the status of the one betrothing, to his place of residence, to the closeness of his house to the bathhouse, or to the members of his household, and it turned out that the condition was not fulfilled. In all of these the woman is not betrothed, and even her claim that in her heart she agreed to be betrothed in any case is of no help, because unspoken thoughts have no legal force. And this ruling is the same whether the condition came from his side or from hers.