Page:Russell - The Problems of Philosophy, 1912.djvu/128

124 never told us there were such people as Brown and Jones and Robinson and Smith, and the particular premisses did not tell us that there were four of them, whereas the particular proposition deduced does tell us both these things.

But the newness of the knowledge is much less certain if we take the stock instance of deduction that is always given in books on logic, namely, "All men are mortal; Socrates is a man, therefore Socrates is mortal." In this case, what we really know beyond reasonable doubt is that certain men, A, B, C, were mortal, since, in fact, they have died. If Socrates is one of these men, it is foolish to go the roundabout way through "all men are mortal" to arrive at the conclusion that probably Socrates is mortal. If Socrates is not one of the men on whom our induction is based, we shall still do better to argue straight from our A, B, C, to Socrates, than to go round by the general proposition, "all men are mortal." For the probability that Socrates is mortal is greater, on our data, than the probability that all men are mortal.