Yevamot

Pentateuchal, it being written in the Scriptures, Thou shalt not uncover the nakedness of thy daughter-in-law?  — Read, 'the daughter-in-law of his son'. But is there any limitation  for the daughter-in-law of one's son? Surely it was taught: His daughter-in-law is a forbidden relative, and the daughter-in-law of his son is a forbidden relative of the second degree; and the same principle is to be applied to one's son and son's son to the end of all generations!  — But read, 'the daughter-in-law of his daughter' for R. Hisda said: I heard from a great man-And who is he? R Ammi- [the following statement]: 'The daughter-in.law was forbidden only on account of the daughter-in-law'; and when the soothsayers  told me, 'You will be a teacher', I thought, 'If I would be a great man  I would explain it  on my own; and should I be a Scripture teacher of little children I would ask the Rabbis who come to the school house.  Now I am in a position to explain it on my own: The daughter-in-law of one's daughter was forbidden only on account of the daughter-in-law of one's son. Said Abaye to Raba: I can explain it to you: Take as an example a daughter-in-law of the house of Bar Zithai.  R. Papa said: As for example a daughter-in-law in the house of R. Papa b. Abba.  R. Ashi said: As for example a daughter-in-law of the house of Mari b.Isak. An inquiry was made: What [is the law in respect of] the wife of a mother's maternal brother? Did the Rabbis forbid as a preventive measure only the wife. of a father's maternal brother and the wife of a mother's paternal brother because in these cases there is a paternal strain,  but where there is no paternal strain  the Rabbis did not pass any preventive measure, or is there no difference? R. Safra replied: She herself  is forbidden as a preventive measure; shall we come and superimpose a preventive measure upon a preventive measure! Said Raba: Are not others  forbidden as a preventive measure to a preventive measure? His mother, e.g., Is a forbidden relative, his mother's mother is a forbidden relative of the second degree, and yet was his father's mother forbidden as a preventive measure against his mother's mother  And what is the reason? Because they are both called 'grandmother'  His father's wife is a forbidden relative, his father's father's wife is a forbidden relative of the second degree, and yet was his mother's father's wife forbidden as a preventive measure against his father's father's wife! And what is the reason? Because they are both called 'grandfather'.  The wife of his father's paternal brother is a forbidden relative, the wife of his father's maternal brother is a forbidden relative of the second degree, and yet was the wife of his mother's paternal brother forbidden as a preventive against the wife of his father's maternal brother! And what is the reason? Because they are both called uncle!  What, then, is the law?  Come and hear: When R. Judah b. Shila came  he stated that In the West  the rule was laid down  that whenever a female  is a forbidden relative the wife of the male  is forbidden in the second degree as a preventive measure; and Raba remarked: 'Is this a general rule? Surely one's mother-in-law is a forbidden relative and yet is one's father-in-law's wife permitted, the daughter of his mother-in-law is a forbidden relative and yet is the wife of the son of his mother-in-law permitted, his step-daughter is a forbidden relative and yet is the wife of his step-son permitted, the daughter of his step-daughter is a forbidden relative and yet is the wife of the son of his step-son permitted'; what, then, does R. Judah b. Shila's [reported rule] include? Does it not then include the case of the wife of a mother's maternal brother, since 'wherever a female  as a forbidden relative  the wife of the male  is forbidden in the second degree as a preventive measure'! What is the difference between those  and this?  — In this case  she becomes related to him by one act of betrothal;  in those cases  they do not become related to him until two acts of betrothal have taken place. R. Mesharsheya of Tusaneya  sent to R. Papi: Will our Master instruct us as to what is the law concerning the wife of the father's father's [paternal]  brother, and a father's father's sister?  Seeing that the degree below is incest,  has a preventive measure been issued in respect also of the degree above,  or perhaps [not]. since the relationship has branched off?  Come and hear: Who are the forbidden relatives of the second degree [etc.];  and these  were not enumerated among them!  — Some might have been mentioned and others omitted.  What other omissions were made such as to justify this omission also? — The forbidden relatives of the second degree, of the School of R. Hiyya,  were also omitted. Amemar permitted the wife of one's father's father's brother and one's father's father's sister. Said R. Hillel to R. Ashi:  'I saw the [list of] forbidden relatives of the second degree of Mar the son of Rabana  and sixteen were written down as forbidden cases. Would they not be the eight of the Baraitha,  the six of the School of R. Hiyya,  and these two,  in all sixteen? — But according to your view there should be seventeen, since there is also the case of the wife of a mother's maternal brother, who in accordance with our decision is forbidden!' — 'This is no difficulty.