QUESTION: The Gemara discusses a case in which a person claims, "This is my
son, and he is a Kohen." Rebbi says that he is believed inasmuch as we may
give the son Terumah to eat, but we may not permit him to marry the daughter
of a Kohen Meyuchas. Rebbi Chiya says that if we accept his testimony with
regard to Terumah, we must also accept his testimony with regard to Yichus,
while if we do not accept his testimony with regard to Yichus, we should not
accept it at all (the Gemara understands that Rebbi Chiya maintains that the
testimony is not accepted at all).
Why is a father not believed to testify that his son is a Kohen? The issue
of Kehunah is a matter of Isur, for which a single witness is believed ("Ed
Echad Ne'eman b'Isurim").
ANSWER: The ROSH (Gitin Perek 5) writes that a person is not believed to
testify about himself that he is a Kohen in order to be permitted to eat
Terumah, because by claiming to be a Kohen he and his descendants would
receive a great benefit, and therefore we must suspect such a person to be
lying. The Rosh seems to be of the opinion that the only reason that one is
not believed to testify that he is a Kohen is because we are concerned that
he is lying for personal gain. This might also explain why a father is not
believed to say that his son is a Kohen.
TOSFOS in our Sugya points out that the statement, "This is my son, and he
is a Kohen," implies that there are two details that we do not know which
the father is informing us of - first, that the child is his son, and
second, that the child is a valid Kohen. Tosfos asks that if we do not know
that the child is his son, then why is the father not believed that his son
is a valid Kohen with a "Migu" that he could have said that the child is
*not* his son and is a Kohen? Had he made that claim, he would have been
believed because he would not be claiming to be the child's father, and thus
he would be testifying about an unrelated person, about whom he is believed
to testify!
Tosfos answers that he is not believed even though he has a "Migu," because
according to his present statement he is a relative and one is not believed
to say that his relative is a Kohen.
There seems to be a flaw in this logic, since, according to the Rosh, the
only reason why a relative is not believed for Kehunah is because he might
be lying, but if there is a "Migu," we have reason to say that he is *not*
lying, so why is he not believed even though he is a relative? It appears
that Tosfos learns that there is some other reason why a relative is not
believed. (The TOSFOS HA'ROSH rejects Tosfos' logic and suggests another
answer to Tosfos' question. See KOVETZ HE'OROS Yevamos 65, who suggests a
Chidush regarding the Pesul of a Karov (relative) testifying, which may be
applied here.)
Perhaps we can answer that although, with regard to Kehunah, a relative is
not accepted as a witness because we suspect that he might be lying,
nevertheless, since when *two* witnesses are necessary a relative is not
valid as a witness even if we *do not* suspect him of lying, the Chachamim
made a general rule that a relative is not accepted as a witness for Kehunah
just as he is not accepted for normal, two-witness testimony. Therefore,
even in a case where there is a "Migu" (and thus there is reason to believe
that he is not lying), the testimony of a relative is not believed. (E.
Kornfeld)