Yevamos 47

R' Yehuda told a Ger that claimed he didn't have a proper Geirus, that he's only believed about himself but is not believed about his children Tosfos explains that he's not actually believed on himself either, because if it's true he's a gentile who is Pasul to be a witness, Therefore, he's only prohibited to marry a Jewess, not because we assume he's a gentile, but because we prohibit anything that a person believes he's prohibited in. However, regarding other people we don't believe him to be a gentile. Therefore if he has relations with a Jewess, we don't prohibit her to a Kohain the same way we would prohibit someone who had relations with a gentile. Tosfos asks: what difference does it make to the child if the father was a Goy, since the mother was a Jewess, so the child is a regular Jew. Tosfos answers : R' Yehuda must hold like the Shita that if a Jewess has relations with a gentile, this would render the child to be a Mamzer. Therefore the father is not believed to make the child a Mamzer. Rabbi Chaim Smulowitz. Have you been disappointed in your level of learning? Do you think your intellectually qualified to learn Tosfos but you don't have the time or skills to learn them properly? So try my English E-Sefer " Gemara in Tosfos" Sukka series. Only 2.49 a piece. Who says quality Torah publications cannot be affordable? Available at tosfos.ecwid.com