Domestic animals which are habitually fed by a certain person will run towards that person as soon as they see him. We say that they expect food, and in fact their behaviour is very like what it would be if they saw food. But really we have only an example of “conditioning”: they have often seen first the farmer and then the food, so that in time they react to the farmer as they originally reacted to the food. Infants soon learn to react to the sight of the bottle, although at first they only react to the touch of it. When they can speak, the same law makes them say “dinner” when they hear the dinner-bell. It is quite unnecessary to suppose that they first think “that bell means dinner”, and then say “dinner”. The sight of dinner (by previous “learned reaction”) causes the word “dinner”: the bell frequently precedes the sight of dinner; therefore in time the bell produces the word “dinner”. It is only subsequent reflection, probably at a much later age, that makes the child say “I knew dinner was ready because I heard the bell”. Long before he can say this, he is acting as if he knew it. And there is no good reason for denying that he knows it, when he acts as if he did. If knowledge is to be displayed by behaviour, there is no reason to confine ourselves to _verbal_ behaviour as the sole kind by which knowledge can manifest itself. The situation, stated abstractly, is as follows. Originally, stimulus A produced reaction C; now stimulus B produces it, as a result of association. Thus B has become a “sign” of A, in the sense that it causes the behaviour appropriate to A. All sorts of things may be signs of other things, but with human beings words are the supreme example of signs. All signs depend upon some practical induction. Whenever we read or hear a statement, its effect upon us depends upon induction in this sense, since the words are signs of what they mean, in the sense that we react to them, in certain respects, as we should to what they stand for. If some one says to you “your house is on fire”, the effect upon you is practically the same as if you saw the conflagration. You may, of course, be the victim of a hoax, and in that case your behaviour will not be such as achieves any purpose you have in view. This risk of error exists always, since the fact that two things have occurred together in the past cannot prove conclusively that they will occur together in the future.