1) The Gemara does not have a Havah Amina that the Eid after Tashmish does not work at all. Rather, the Gemara had a Havah Amina that the examination has only limited reliability. The check is relied upon only to prevent a significant loss of Taharos. Therefore, the Havah Amina is that if the last time she checked (before the examination after Tashmish) was a full 24 hours ago, then we do rely on the examination after Tashmish because otherwise she will lose a full 24 hours of Taharos. However, if the last examination was less than 24 hours before the examination after Tashmish, we do not have to be so lenient because not so many Taharos will be lost. It is only in the second case that the Gemara had a Havah Amina that the Eid would not work to limit the time for Taharos.

2) There is a good reason for why there is a Havah Amina that the examination after Tashmish is not so reliable. This is stated in the Gemara earlier (5a, and also later on 16b) that she might experience a flow of a very small amount of blood, which will become covered by the Shichvas Zera of Tashmish, and as a result the examination after Tashmish will not reveal this small drop of blood. This concern about the blood becoming hidden is sufficiently strong, in the Havah Amina, to cause the loss of a small amount of Taharos but Chazal were not prepared to lose 24 hours worth of Taharos because of this concern.

3) The Chidushei ha'Ramban (5a, DH Hashta) remarks that there is a certain paradox in this logic. It is more likely that there was bleeding in the last 24-hour period than in a period of less than 24 hours, so we should really be more Machmir concerning a full 24 hours than concerning a period of less than 24 hours. However, the Ramban writes that the possibility of losing Taharos unnecessarily is a more siginificant concern. We are prepared to lose a small amount of Taharos for this concern, but we are lenient so that we should not lose a larger amount.

4) The Chochmas Betzalel here points out that the Havah Amina that the Eid after Tashmish might not work is actually reflected in the Talmud Yerushalmi as a dispute between Amora'im concerning which examination is effective: the one before Tashmish or the one afterwards. Levi maintains there that the examination before Tashmish is not reliable because she is in too much of a hurry to do a sufficiently-thorough examination. This is equivalent to the opinion of Shmuel here (5a) that the check before Tashmish is not reliable. Rebbi Zeira in the Talmud Yerushalmi disagrees with Levi and maintains that it is the examination after Tashmish which is not reliable because the color of the blood becomes faded by the Shichvas Zera.

It transpires that the Havah Amina (beginning of 5b) is actually the conclusion according to Zeira, and is opposed to the opinion of Shmuel on 5a, whose conclusion is that the examination before Tashmish is unacceptable.

5) Concerning checking after Tashmish for non-Taharos reasons; the Gemara later (12a) does ask whether she should check immediately after Tashmish to make her husband liable for a Chatas if she finds herself to be Tamei. However, it does not seem that the Gemara there (12a) is connected to the Havah Amina on 5b.

Kol Tuv,

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