'A paper read at the International Congress of Philosophy at Geneva in 1904, and published in the "Revue de métaphysique et de morale" under the title "Le Paralogisme Psycho-physiologique."' (231)

Notes:

'When we speak of external objects, we have to choose... between two notation-systems. We can treat external objects, and the changes they exhibit, as a system of things or as a system of ideas. And either of these two systems will work, provided we keep strictly to the one we have chosen.

Let us, first of all, try to distinguish the two systems with precision. When realism speaks of things and idealism of ideas, it is not merely a dispute about words; realism and idealism are two different notation-systems, that is to say, two different ways of setting about the analysis of reality. For the idealist, there is nothing in reality over and above what appears to his consciousness or to consciousness in general. It would be absurd to speak of a property of matter which could not be represented in idea. There is no virtuality, or, at least, nothing definitely virtual; whatever exists is actual or could become so. Idealism is, then, a notation-system which implies that everything essential in matter is displayed or displayable in the idea which we have of it, and that the real world is articulated in the very same way as it is presented in idea. The hypothesis of realism is the exact reverse. When realism affirms that matter exists independently of the idea, the meaning is that beneath our idea of matter there is an inaccessible cause of that idea, that behind perception, which is actual, there are hidden powers and virtualitres ; in short, realism assumes that the divisions and articulations visible in our perception are purely relative to our manner of perceiving...

That these two postulates are mutually exclusive, that consequently it is illegitimate to apply the two notation-systems at the same time to the same object, every one will agree. Now, I require nothing more for my present purpose...

The thesis of parallelism appears consistent only when wc employ at the same time, in the same proposition, both notation-systems together.' (234-237)

'First of all, then, we will place ourselves at the idealist standpoint, and consider, as an example, the perception of the objects which at any given moment occupy the visual field. These objects act on the visual centres in the brain through the retina and the optic nerve. There they bring about a modification of atomic and molecular dispositions. What is the rela- tion of this cerebral modification to the external objects?

The thesis of parallelism is that the cerebral state caused by the objects, and not the objects themselves, determines conscious perception, and therefore, so long as the cerebral state exists, all the objects perceived might, by a touch as it were of a magic wand, cease to exist, it would in no way alter what is going on in consciousness. But it is obvious that on the idealist hypothesis such a proposition is absurd. External objects are for the idealist images, and the brain is one of them. There is nothing in things themselves over and above what is displayed or displayable in the images. There is nothing, then, in the dancing about of cerebral atoms over and above a dance of atoms. Since this is all we have supposed to be in the brain, it is all that will be found there or that can be got out of it.' (237-238)

'Now, — should I say to the realist, — you began by giving yourself a brain, and saying that objects external to it modify it in such a way as to raise up ideas of themselves. Then you did away with these objects external to the brain, and ascribed to the cerebral modification the power of providing by its own resources the idea of the objects. But, in withdrawing the objects which encase it, you are withdrawing also, whether you will or no, the cerebral state, for it owes to them all its properties and its reality. You only preserve this cerebral state because you pass surreptitiously to the idealist notation-system, where you can posit as isolable by right what is isolated in idea.' (245)

'as our knowledge of matter can never get clean away from space, and as the reciprocal implication with which realism deals, however deep it be, can never become extraneous to space without becoming extraneous to science, realism in its explanations can never get beyond idealism.' (248)

On the 'flicker' of realism and idealism:

'You began by speaking — should I say again to the philosopher — of the brain such as we see it, such as it stands out in the midst of the presentation: so you assumed it to be a part of presentation, an idea, and you were in idealism. There, I repeat, the relation of the brain to the rest of presentation can only be the relation of part to whole. Thence, all of a sudden, you have fled to a reality supposed to tie beneath the presentation. Very good : but such reality is subspatial, which amounts to saying that the brain is no more an independent entity. What you have to do with now is the totality of the real, in itself unknowable, over which is spread the totality of the presentation. You are now, indeed, In realism; and no more in this realism than in the idealism of a moment ago are the cerebral states the equivalent of the whole of presentation: it is — I must repeat it — the whole world of things which is again implied (but, this time, concealed and unknowable) in the whole of perception. But Io! taking the brain apart and dealing with things separately, you are actually continuing to decompose and rccompose reality along the same lines and according to the same laws as presentation, which means that you no longer distinguish the one from the other. Back you are, then, in idealism; there you ought to remain. But not at all! You do indeed preserve the brain as it is even in presentation, therefore as an idea, but you forget that if the real is thus spread out in the presentation, if it is extension and not tension, it can no longer compress within itself the powers and virtualities postulated by realism; unheedingly you erect the cerebral movements into the equivalent of the whole of presentation. You are therefore oscillating from idealism to realism and from realism to idealism, but so quickly that you do not perceive the see-saw motion and you think yourself all the time astride the two systems joined into one. This apparent reconciliation of two irreconcilable affirmations is the very essence of the thesis of parallelism.' (249-250)

'In this study I have only tried to bring to light the contradiction inherent in the thesis itself. Just because the consequences to which it leads, and the postulates which it contains, cover, so to say, the whole domain of philosophy, it has seemed to me that this critical examination is incumbent on, and may serve as the starting-point of, a theory of the mind considered in its relation to the determinism of nature.' (254-255)