For the sake of greater definiteness, let us imagine a person called upon to make a seemingly free decision under serious circumstances: we shall call him Peter. The question is whether a philosopher Paul, living at the same period as Peter, or, if you prefer, a few centuries before, would have been able, knowing _all_ the conditions under which Peter acts, to foretell with certainty the choice which Peter made. There are several ways of picturing the mental condition of a person at a given moment. We try to do it when e.g. we read a novel; but whatever care the author may have taken in depicting the feelings of his hero, and even in tracing back his history, the end, foreseen or unforeseen, will add something to the idea which we had formed of the character: the character, therefore, was only imperfectly known to us. In truth, the deeper psychic states, those which are translated by free acts, express and sum up the whole of our past history: if Paul knows all the conditions under which Peter acts, we must suppose that no detail of Peter's life escapes him, and that his imagination reconstructs and even lives over again Peter's history. But we must here make a vital distinction. When I myself pass through a certain psychic state, I know exactly the intensity of this state and its importance in relation to the others, not by measurement or comparison, but because the intensity of e.g. a deep-seated feeling is nothing else than the feeling itself. On the other hand, if I try to give you an account of this psychic state, I shall be unable to make you realize its intensity except by some definite sign of a mathematical kind: I shall have to measure its importance, compare it with what goes before and what follows, in short determine the part which it plays in the final act. And I shall say that it is more or less intense, more or less important, according as the final act is explained by it or apart from it. On the other hand, for my own consciousness, which perceived this inner state, there was no need of a comparison of this kind: the intensity was given to it as an inexpressible quality of the state itself. In other words, the intensity of a psychic state is not given to consciousness as a special sign accompanying this state and denoting its power, like an exponent in algebra; we have shown above that it expresses rather its shade, its characteristic colouring, and that, if it is a question of a feeling, for example, its intensity consists in being felt. Hence we have to distinguish two ways of assimilating the conscious states of other people: the one dynamic, which consists in experiencing them oneself; the other static, which consists in substituting for the consciousness of these states their image or rather their intellectual symbol, their idea. In this case the conscious states are _imagined_ instead of being _reproduced_; but, then, to the image of the psychic states themselves some indication of their _intensity_ should be added,