Scientific induction is an attempt to regularise the above process, which we may call “physiological induction”. It is obvious that, as practised by animals, infants, and savages, physiological induction is a frequent source of error. There is Dr. Watson’s infant who induced, from two examples, that whenever he saw a certain rat there would be a loud noise. There is Edmund Burke, who induced from one example (Cromwell) that revolutions lead to military tyrannies. There are savages who argue, from one bad season, that the arrival of a white man causes bad crops. The inhabitants of Siena, in 1348, thought that the Black Death was a punishment for their pride in starting to build too large a cathedral. Of such examples there is no end. It is very necessary, therefore, if possible, to find some method by which induction can be practised so as to lead, in general, to correct results. But this is a problem of scientific method, with which we will not yet concern ourselves. What does concern us at present is the fact that all inference, of the sort that really occurs, is a development of this one principle of conditioning. In practice, inference is of two kinds, one typified by induction, the other by mathematical reasoning. The former is by far the more important, since, as we have seen, it covers all use of signs and all empirical generalisations as well as the habits of which they are the verbal expression. I know that, from the traditional standpoint, it seems absurd to talk of inference in most cases of this sort. For example, you find it stated in the paper that such and such a horse has won the Derby. According to my own use of words, you practise an induction when you arrive thence at the belief that that horse has won. The stimulus consists of certain black marks on white paper--or perhaps on pink paper. This stimulus is only connected with horses and the Derby by association, yet your reaction is one appropriate to the Derby. Traditionally, there was only inference where there was a “mental process”, which, after dwelling upon the “premisses”, was led to assert the “conclusion” by means of insight into their logical connection. I am not saying that the process which such words as the above are intended to describe never takes place; it certainly does. What I am saying is that, genetically and causally, there is no important difference between the most elaborate induction and the most elementary “learned reaction”. The one is merely a developed form of the other, not something radically different. And our determination to believe in the results of inductions, even if, as logicians, we see no reason to do so, is really due to the potency of the principle of association; it is an example--perhaps the most important example--of what Dr. Santayana calls “animal faith”.