soul and body 
xb. descartes to princess elizabeth1
Egmond, 28 June 1643.
I am most deeply obliged to your Highness for condescending, after experience of my previous ill success in explaining the problem you were pleased to propound to me, to be patient enough to listen to me once more on the same subject, and to give me an opportunity of making remarks on matters I had passed over. My chief omissions seem to be the following. I began by distinguishing three kinds of primitive ideas or notions, each of which is known in a specific way and not by comparison to another kind; viz. the notion of soul, the notion of body, and the notion of the union between soul and body. I still had to explain the difference between these three kinds of notions, and again between the operations of the soul by means of which we get them, and to show the means of becoming readily familiar with each kind. Further, I had to explain why I used the comparison of gravity. Next, I had to show that even if we try to conceive of the soul as material (which means, properly speaking, to conceive of its union with the body), we cannot help going on to recognise that it is separable from the body. This, I think, is the sum of the task your Highness has set me.
In the first place, then, I discern this great difference between the three kinds of notions: the soul is conceived only by pure intellect; body (i.e. extension, shape, and movement) can likewise be known by pure intellect, but is known much better when intellect is aided by imagination; finally, what belongs to the union of soul and body can be understood only in an obscure way either by pure intellect or even when the intellect is aided by imagination, but is understood very clearly by means of the senses. Consequently, those who never do philosophise and make use
1 [Corresp., No. 310;   Oeuvres, A.-T., vol. in, p. 690.—ed.]

LETTERS
only of their senses have no doubt that the soul moves the body and the body acts on the soul; indeed, they consider the two as a single thing, i.e. they conceive of their union; for to conceive of the union between two things is to conceive of them as a single thing. Metaphysical reflections, which exercise the pure intellect, are what make us familiar with the notion of soul; the study of mathematics, which chiefly exercises the imagination in considering figures and movements, accustoms us to form very distinct notions of body; finally, it is just by means of ordinary life and conversation, by abstaining from meditating and from studying things that exercise the imagination, that one learns to conceive the union of soul and body.
I am half afraid that your Highness may think I am not speaking seriously here; but that would be contrary to the respect that I owe to your Highness and will never fail to pay. I can truly say that the chief rule I have always observed in my studies, and the one I think has been most serviceable to me in acquiring some measure of knowledge, has been never to spend more than a few hours a day in thoughts that demand imagination, or more than a few hours a year in thoughts that demand pure intellect; I have given all the rest of my time to the relaxation of my senses and the repose of my mind. I here count among exercises of imagination all serious conversations, and everything that demands attention. This is what made me retire to the country; it is true that in the busiest city in the world I might have as many hours to myself as I now spend in study, but I could not employ them so usefully when my mind was wearied by the attention that the troubles of life demand.
I take the liberty of writing thus to your Highness, to express my sincere admiration of your Highness's ability, among all the business and cares that are never lacking to persons who combine high intelligence and high birth, to
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find leisure for the meditations that are necessary for proper understanding of the distinction between soul and body. I formed the opinion that it was these meditations, rather than thoughts demanding less attention, that made your Highness find some obscurity in our notion of their union. It seems to me that the human mind is incapable of distinctly conceiving both the distinction between body and soul and their union, at one and the same time; for that requires our conceiving them as a single thing and simultaneously conceiving them as two things, which is self-contradictory. I supposed that your Highness still had very much in mind the arguments proving the distinction of soul and body; and I did not wish to ask you to lay them aside, in order to represent to yourself that notion of their union which everybody always has in himself without doing philosophy—viz. that there is one single person who has at once body and consciousness, so that this consciousness can move the body and be aware of the events that happen to it. Accordingly, I used in my previous letter the simile of gravity and other qualities, which we imagine to be united to bodies as consciousness is united to ours. I did not worry over the fact that this simile is lame, because these qualities are not, as one imagines, realities; for I thought your Highness was already fully convinced that the soul is a substance distinct from the body.
Your Highness, however, makes the remark that it is easier to ascribe matter and extension to the soul than to ascribe to it the power of moving a body and being moved by it without having any matter. Now I would ask your Highness to hold yourself free to ascribe ' matter and extension ' to the soul; for this is nothing else than to conceive the soul as united to the body. After forming a proper conception of this, and experiencing it in your own case, your Highness will find it easy to reflect that the matter you thus ascribe to your consciousness (pensde) is not the
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consciousness itself; again, the extension of the matter is essentially different from the extension of the consciousness, for the first extension is determined to a certain place, and excludes any other corporeal extension from that place, whereas the second does not. In this way your Highness will assuredly find it easy to come back to a realisation of the distinction between soul and body, in spite of having conceived of them as united.
Finally, I think it is very necessary to have got a good understanding, for once in one's life, of the principles of metaphysics, because it is from these that we have knowledge of God and of our soul. But I also think it would be very harmful to occupy one's intellect often with meditating on them, for it would be the less able to find leisure for the functioning of the imagination and the senses; the best thing is to be content with retaining in memory and in belief the conclusions one has drawn once for all, and to spend the rest of one's time for study in reflections in which the intellect co-operates with the imagination and the senses. . . .