Sam Kosofsky asked:
The Gemara goes through a lot of proofs that kiddushin isn't tofes in the case where a mamzer would result. Didn't we learn recently that anyone that you're not allowed to have biah with you can't marry. Was that just logistics or was that the rule? If so why didn't the Gemara just repeat that rule?
The Kollel replies:
I think the quote you are referring to is Rav Yeshavav on 64a: "Kol she'Ein Lo Bi'ah b'Yisrael ha'Vlad Mamzer." This is Rav Yeshavav's interpretation of Rebbi Akiva's view. However, the other Tana'im hold that there are many cases (for example, marriages involving an Isur Lav) in which there is an Isur, but no Mamzerus results. The rule is then when there is no Tefisas Kidushin, only then is there Mamzerus.
D. Zupnik