Hume Studies

64. ON HUME'S IS-OUGHT THESIS The famous thesis of Hume about "is" and "ought" I take to be, as I believe it has generally been taken to be: (1) For any factual statement e and any ethical statement h, h is not deducible from e. My object in these brief notes is neither to defend nor to attack (1) , but just to point out certain mistakes which have been made, or are apt to be made, about (1), or about what Hume's thesis is. A. Max Black has taken Hume's thesis to be that "only statements of fact can follow- from statements of facti* ¡ a thesis, Black thinks, which Popper and "many other philos c be ; osophers" believe. That is. Black took Hume's thesis to (2)For any factual e and any non-factual h, h is not deducible . from e. It is certain, however, that Popper does not believe (2), and I hope it is untrue that many other philosophers believe it. For (2) is obviously false, and on the contrary, every factual statement has at least one nonfactual consequence; since from any factual statement 'f, the statement *f or not-f , which is not factual, is deducible . But this leaves Hume's thesis (1) untouched, since there is no excuse for confusing it with the foolish thesis (2) . B. If a statement h is not deducible from a statement e, then given e, the falsity of h is possible; or in other words, h has less than maximum probability in relation to e. So part at least of the content of Hume's thesis (1) is: (3)For any factual e and ethical h, P(h/e)