 One classic challenge for Nicod’s criterion is the notorious raven paradox. Suppose we want to test the hypothesis that all ravens are black, which we formalize \(\forall x(Rx \supset Bx)\). That’s logically equivalent to \(\forall x(\neg Bx \supset \neg Rx)\), by contraposition. And Nicod’s Criterion says this latter hypothesis is confirmed by the discovery of any object that is not black and not a raven—a red shirt, for example, or a pair of blue underpants (Hempel 1937, 1945). But walking the halls of my department noting non-black non-ravens hardly seems a reasonable way to verify that all ravens are black. How can “indoor ornithology” (Goodman 1954) be good science?!