I discuss the structure of genealogical debunking arguments. I argue that they undermine our
mathematical beliefs if they undermine our moral beliefs. The contrary appearance stems from a
confusion of arithmetic truths with (first-order) logical truths, or from a confusion of reliability
with justification. I conclude with a discussion of the cogency of debunking arguments, in light
of the above. Their cogency depends on whether information can undermine all of our beliefs of
a kind, F, without giving us direct reason to doubt that our F-beliefs are modally secure.