Let us again remind ourselves that there is an element of artificiality in isolating elements within the one process leading from stimulus to reaction. Whenever a stimulus produces a reaction, we may consider the reaction as the effect of the stimulus, or as the cause of further effects. The former is the natural way of viewing the reaction when we are concerned with knowledge; the latter is the natural way when we are concerned with desire and will. In desire, we wish to change something in ourselves or in our environment or both. The question is: What can we discover introspectively about desire? I think that here, as in the case of knowledge, the purely behaviouristic account is more important causally than the introspective account, and applies over a much wider range. Desire as a characteristic of behaviour, as considered in Chapter III, begins very low in the scale of evolution, and remains, even in human beings, the whole of what can be discovered in a large number of instances. The Freudian “unconscious” desires give a formula which is useful as explaining causally a number of acts, but these desires do not exist as anything except ways of behaving. Some desires, on the other hand, are conscious and explicit. What, exactly, is added in these last that is not present in the others? Let us take some stock instance, say, Demosthenes desiring to become a great orator. This was a desire of which he was conscious, and in accordance with which he deliberately moulded his actions. One may suppose, to begin with, a merely behaviouristic tendency to do such things as seemed likely to impress his companions. This is a practically universal characteristic of human nature, which is displayed naively by children. Then come attempts, just like those of rats in mazes, to reach the goal; wrong turnings, leading to derision; right turnings, leading to a brief nibble at the cheese of admiration. Self-observation, still of a behaviourist kind, may lead to the formula: I want to be admired. At this point the desire has become “conscious”. When this point has been reached, knowledge can be brought to bear on the problem of achieving the desired end. By association, the means come to be desired also. And so Demosthenes arrives at the decision to subject himself to a difficult training as an orator, since this seems the best way of achieving his end. The whole development is closely analogous to that of explicit knowledge out of mere sensitivity; it is, indeed, part of the very same evolution. We cannot, in our integral reaction to a situation, separate out one event as knowledge and another as desire; both knowledge and desire are features which characterise the reaction, but do not exist in isolation.