There is a machloket whether a chazaka occurs after 2 incidents or 3 incidents. Rashi always says not to do a brit milah if previous 2 boys died after a brit. But Abaye married Chomah even though 2 of her previous husbands had died. Why is this even an argument? There is proof from our Parsha this week that Rashi is correct. After 2 of her husbands died, Tamar would not marry Shelah!! What's the kashia?
Daniel Ettedgui, Boca Raton, USA
Interestingly enough, the Rishon - R' Chaim Paltiel (Bereishis 38:11), first asks your question, but then asks that the question is in fact the other way around. The Pasuk explicitly says that Yehudah wanted to wait for Shelah to marry Tamar "until he gets older." Why would this help the problem of Katlanis if we rule that 2 husbands dying is enough to stop a third from marrying her? He answers that she was only a Katlanis for marrying minors, as both of Shelah's brothers were minors when they married her. He therefore wanted to wait until Shelah was a Gadol, at which time he held there was no proof that this would be detrimental to him. (Many other Meforshim Al ha'Torah deal with this question as well, see for example the Chizkuni on the Passuk ibid.).
All the best,
Yaakov Montrose