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, since they no longer act on the person in whose mind they are pictured and the latter has no longer any chance of experiencing their force by actually feeling them. Now, this indication itself will necessarily assume a quantitative character: it will be pointed out, for example, that a certain feeling has more strength than another feeling, that it is necessary to take more account of it, that it has played a greater part; and how could this be known unless the later history of the person were known in advance, with the precise actions in which this multiplicity of states or inclinations has issued? Therefore, if Paul is to have an adequate idea of Peter's state at any moment of his history, there are only two courses open; either, like a novelist who knows whither he is conducting his characters, Paul must already know Peter's final act, and must thus be able to supplement his mental image of the successive states through which Peter is going to pass by some indication of their value in relation to the whole of Peter's history; or he must make up his mind to pass through these different states, not in imagination, but in reality. The former hypothesis must be put on one side since the very point at issue is whether, the antecedents alone being given, Paul will be able to foresee the final act. We find ourselves compelled, therefore, to alter radically the idea which we had formed of Paul: he is not, as we had thought at first, a spectator whose eyes pierce the future, but an actor who plays Peter's part in advance. And notice that you cannot exempt him from any detail of this part, for the most common-place events have their importance in a life-story; and even supposing that they have not, you cannot decide that they are insignificant except in relation to the final act, which, by hypothesis, is not given. Neither have you the right to cut short—were it only by a second—the different states of consciousness through which Paul is going to pass before Peter; for the effects of the same feeling, for example, go on accumulating at every moment of duration, and the sum total of these effects could not be realized all at once unless one knew the importance of the feeling, taken in its totality, in relation to the final act, which is the very thing that is supposed to remain unknown. But if Peter and Paul have experienced the same feelings in the same order, if their minds have the same history, how will you distinguish one from the other? Will it be by the body in which they dwell? They would then always differ in some respect, viz., that at no moment of their history would they have a mental picture of the same body. Will it be by the place which they occupy in time? In that case they would no longer be present at the same events: now, by hypothesis, they have the same past and the same present, having the same experience. You must now make up your mind about it: Peter and Paul are one and the same person, whom you call Peter when he acts and Paul when you recapitulate his history. The more complete you made the sum of the conditions which, when known, would have enabled you to predict Peter's future action, the closer became your grasp of his existence and the nearer you came to living his life over again down to its smallest details: you thus reached the very moment when, the action taking place, there was no longer anything to be foreseen, but only something to be done. Here again any attempt to reconstruct ideally an act really willed ends in the mere witnessing of the act whilst it is being performed or when it is already done.
Hence meaningless to ask whether an act can be foreseen when all its antecedents are given.
Hence it is a question devoid of meaning to ask: Could or could not the act be foreseen, given the sum total of its antecedents? For there are two ways of assimilating these antecedents, the one dynamic the other static. In the first case we shall be led by imperceptible steps to identify ourselves with the person we are dealing with, to pass through the same series of states, and thus to get back to the very moment at which the act is performed; hence there can no longer be any question of foreseeing it. In the second case, we presuppose the final act by the mere fact of annexing to the qualitative description of the previous states the quantitative appreciation of their importance. Here again the one party is led merely to realize that the act is not yet performed when it is to be performed, and the other, that when performed it is performed. This, like the previous discussion, leaves the question of freedom exactly where it was to begin with.
The two fallacies involved: (1) regarding intensity as a magnitude, not a quality; (2) substituting material symbol for dynamic process.
By going deeper into this twofold argument, we shall find, at its very root, the two fundamental illusions of the reflective consciousness. The first consists in regarding: intensity as a mathematical property of psychic states and not, as we said at the beginning of this essay, as a special quality, as a particular shade of these various states. The second consists in substituting for the concrete reality or dynamic progress, which consciousness perceives, the material symbol of this progress when it has already reached its end, that is to say, of the act already accomplished together with the series of its antecedents. Certainly, once the final act is completed, I can ascribe to all the antecedents their proper value, and picture the interplay of these various elements as a conflict or a composition of forces. But to ask whether, the antecedents being known as well as their value, one could foretell the final act, is to beg the question; it is to forget that we cannot know the value of the antecedents without knowing the final act, which is the very thing that is not yet known; it is to suppose wrongly that the symbolical diagram which we draw in our own way for representing the action when completed has been drawn by the action itself whilst progressing, and drawn by it in an automatic manner.
Claiming to foresee an action always comes back to confusing time with space.
Now, in these two illusions themselves a third one is involved, and you will see that the question whether the act could or could not be foreseen always comes back to this: Is time space? You begin by setting side by side in some ideal space the conscious states which succeed one another in Peter's mind, and you perceive his life as a kind of path Μ Ο X Y traced out by a moving body M in space. You then blot out in thought the part Ο X Y of this curve, and you inquire whether, knowing Μ Ο, you would have been able to determine the portion Ο X of the curve which the moving body describes beyond O.
Such is, in the main, the question which you put when you bring in a philosopher Paul, who lives before Peter and has to picture to himself the conditions under which Peter will act. You thus materialize these conditions; you make the time to come into a road already marked out across the plain, which we can contemplate from the top of the mountain, even if we have not traversed it and are never to do so. But, now, you soon notice that the knowledge of the part Μ Ο of the curve would not be enough, unless you were shown the position of the points of this line, not only in relation to one another, but also in relation to the points of the whole line Μ O X Y; which would amount to being given in advance the very elements which have to be determined. So you then alter your hypothesis; you realize that time does not require to be seen, but to be lived; and hence you conclude that, if your knowledge of the line Μ Ο was not a sufficient datum, the reason must have been that you looked at it from the outside instead of identifying yourself with the point M, which describes not only Μ Ο but also the whole curve, and thus making its movement your own. Therefore, you persuade Paul to come and coincide with Peter; and naturally, then, it is the line Μ Ο X Y which Paul traces out in space, since, by hypothesis, Peter describes this line. But in no wise do you prove thus that Paul foresaw Peter's action; you only show that Peter acted in the way he did, since Paul became Peter. It is true that you then come back, unwittingly, to your former hypothesis, because you continually confuse the line Μ Ο X Y in its tracing with the line Μ Ο X Y already traced, that is to say, time with space. After causing Paul to come down and identify himself with Peter as long as was required, you let him go up again and resume his former post of observation. No wonder if he then perceives the line Μ Ο X Y complete: he himself has just been completing it.