Years ago, when Iwas an undergraduate math major at the University of Wyoming, I came across an interesting book in our library. It was a book oi counterexamples to propositions in real analysis (the mathematics of the real numbers). l/Iathematicians work more or less like the rest of us. They consider propositions. It one seems to them to be plausibly true, then they set about to prove it, to establish the proposition as atheorem. Instead of setting out to prove propositions, the psychologists, neuroscientists, and other empirical types among us, set out to show that a proposition is supported by the data, and that it is the best such proposition so supported. The philosophers among us, when they are not causing trouble by arguing that AI is a dead end or that cognitive science can get along without representations, work pretty much like the mathematicians: we set out to prove certain propositions true on the basis oi logic, first principles, plausible assumptions, and others' data. But, back to the book of real analysis counterexamples. If some mathematician happened to think that some proposition about continuity, say, was plausibly true, he or she would then set out to prove it. If the proposition was in fact not a theorem, then alot oi precious time would be wasted trying to prove it. WouIdn't it be great to have a book that listed plausibly true propositions that were in fact not true, and listed with each such proposition a counterexample to it'? Of course it would.