of inference, therefore, rather than deduction, are those that must be examined if we are to accept the world of science or any world outside of our own dreams. Let us take a simple example of an induction which we have all performed in practice. If we are hungry, we eat certain things we see and not others--it may be said that we infer edibility inductively from a certain visual and olfactory appearance. The history of this process is that children a few months old put everything into their mouths unless they are stopped; sometimes the result is pleasant, sometimes unpleasant; they repeat the former rather than the latter. That is to say: given that an object having a certain visual and olfactory appearance has been found pleasant to eat, an object having a very similar appearance will be eaten; but when a certain appearance has been found connected with unpleasant consequences when eaten, a similar appearance does not lead to eating next time. The question is: what logical justification is there for our behaviour? Given all our past experience, are we more likely to be nourished by bread than by a stone? It is easy to see why we think so, but can we, as philosophers justify this way of thinking? It is, of course, obvious that unless one thing can be a sign of another both science and daily life would be impossible. More particularly, reading involves this principle. One accepts printed words as signs, but this is only justifiable by means of induction. I do not mean that induction is necessary to establish the existence of other people, though that also, as we have seen, is true. I mean something simpler. Suppose you want your hair cut, and as you walk along the street you see a notice “hair-cutting, first floor”. It is only by means of induction that you can _establish_ that this _notice_ makes it in some degree probable that there is a hair-cutter’s establishment on the first floor. I do not mean that you employ the principle of induction; I mean that you act in accordance with it, and that you would have to appeal to it if you were accompanied by a long-haired sceptical philosopher who refused to go upstairs till he was persuaded there was some point in doing so.