CORRESPONDENCE WITH ELIZABETH
[664] I can truly say that the question your Highness asks me, seems to be the one which I can most reasonably be asked, in the light of my published writings. There are two things in the human soul which all the knowledge we can have of its nature depends on. The one is that it thinks; the other is that, since it is united to the body, it can act and be acted upon along with it. I have said hardly anything about the second, and I have devoted all my efforts [665] to making the first properly understood, since my main purpose was to prove the distinction which there is between the soul and the body. Only the former could be useful for this purpose, and the second would detract from it. But since your Highness is so perceptive that I cannot hide anything from you, I shall now try to explain how I conceive the union of the soul with the body, and how it has the power to move it.
First, I note that there are in us certain primitive notions, which are like archetypes which we use as patterns for constructing all the rest of our knowledge. There are only a very few such notions. The most general ones apply to everything we can conceive — being, number, duration, etc. Apart from these, in the case of body taken by itself, we have only the notion of extension, from which there follow those of shape and motion; in the case of the soul taken by itself, only that of thought (which includes the perceptions of the understanding and the inclinations of the will); and finally, as for the soul and the body taken together, we have only the notion of their union, on which depends that of the power which the soul has to move the body, and of the power which the body has to act on the soul, and to cause its sensations and passions.
I also note that all human scientific knowledge consists only in keeping these notions properly distinct, and not attributing any of them to things they do not belong to. If we want to explain [666] something problematic by means of a notion which does not belong to it, we cannot fail to go wrong. It is the same if we want to explain one of these notions by means of another. The reason is because they are primitive notions, and each of them can be understood only through itself. In so far as our reliance on the senses has made the notions of extension, shapes, and motions much more familiar to us than the others, the main cause of our errors lies in the fact that we usually want to use these notions to explain things they do not apply to — for example, when the imagination is used for conceiving the nature of the soul, and also when the way in which the soul moves the body is conceived in terms of the way in which one body moves another.
This is why, in the Meditations, which your Highness was so kind as to read, I tried to get the reader to conceive the notions which belong to the soul alone, by distinguishing them from those which belong to the body alone. So the next thing I have to explain is how to conceive the notions which belong to the union of the soul with the body, without using notions which belong to the body alone or the soul alone. Here I think it will be useful to consider what I wrote at the end of my response to the sixth set of objections. I said that the only place where we can find these simple notions is in our soul, which has all of them within itself by its very nature. However, the soul does not [667] always keep them sufficiently distinct from each other, and sometimes even attributes them to the wrong objects.
So I believe that up till now we have confused the notion of the power by which the soul acts on the body with the notion of the power by which one body acts on another. We have also attributed both of them, not to the soul (since we do not yet know its nature), but to various qualities of bodies, such as weight, heat, and others, which we have imagined to be a kind of thing — that is to say, we have imagined them to have an existence distinct from that of bodies, and consequently to be substances, even though we have called them ‘qualities’. In order to conceive them, we have sometimes used notions which are within us for knowing body, and sometimes those which are there for knowing the soul, depending on whether we have attributed to them something material or something immaterial. For example, we have supposed that weight is a thing-like quality, and that all we know about it is that it has the power to move the body it is in towards the centre of the earth. However, we have no difficulty in conceiving how it moves this body, or how it is united with it. We certainly do not think that it happens through a thing-like contact between two surfaces, since we observe within ourselves that we have a special notion for conceiving it. I believe that we are misusing this notion in applying it [668] to weight, which is not a real thing distinct from body (as I hope to show in my Physics), but I believe that it has been given to us as a means for conceiving how the soul moves the body. . . . .
Descartes to Elizabeth, 28th June, 1643
[680] On the question you were good enough to pose me, you have put to the test the bad explanation I gave you in my last letter. I am therefore deeply obliged to your Highness for patiently condescending [681] to listen to me once again on the same subject, and for giving me the opportunity to take into account the things I left out. It seems to me that my main omission was as follows. I distinguished between three kinds of primitive ideas or notions, each of which is known in its own special way, and not by comparison with one another — namely the notions we have of the soul, of the body, and of the union between the soul and the body. What I should then have done was to explain the difference between these three sorts of notions, and between the operations of the soul by which we have them; and to describe the means by which we can make each of them familiar and natural to us. After that, I should have said why I used the analogy with weight, and explained that, although one might wish to conceive the soul as material (which is strictly what it is to conceive its union with the body), this does not stop one from subsequently knowing that it is separable from it. I believe this covers everything which you Highness has required of me.
First, then, there is a great difference which I observe between these three sorts of notions. The soul conceives itself only through pure understanding. Body (that is, extension, shapes, and motions) can also been known through the understanding alone, but much better through the understanding helped by the imagination. Finally, things which belong to the union of the soul and the body are known [692] only obscurely through the understanding alone, and even through the understanding helped by the imagination; but they are known very clearly through the senses. This is why people who never philosophise, and use only their senses, have no doubt that the soul moves the body, and that the body acts on the soul. They consider both of them as a single thing — that is to say, they conceive their union, since to conceive the union of two things is to conceive them as a single thing. It is metaphysical thinking (which exercises the pure understanding) that has the function of making us familiar with the notion of the soul. It is the study of mathematics (which mainly exercises the imagination in the consideration of shapes and motions) that gets us into the habit of forming thoroughly distinct notions of body. Finally, it is through immersing ourselves in real life and everyday social contacts, and abstaining from meditation or studying things which exercise the imagination, that we learn to conceive the union of the soul and the body.
I am half afraid that your Highness might think that I can’t be serious about what I have just said; but this would conflict with the respect I owe you, and which I never fail to observe. I can truly say that there is one main rule which I have always followed in my studies, and which I believe has been the most useful to me for acquiring such knowledge as I have. This is never to spend more than a very few hours a day on thoughts which occupy the imagination; never to spend more than a very few hours a year on thoughts which occupy the understanding [693] alone; and to devote the remainder of my time to indulging in sensory experience, and giving my spirit a rest. Among exercises of the imagination I include even serious conversation, and anything which requires concentration. This is why I have retired to the country. Even in the busiest city in the world, I could have as much time to myself as I now spend studying; but I would not be able to use it as effectively, because my spirit would be exhausted by the concentration which the hustle and bustle of city life demands. I take the liberty of saying this to your Highness as evidence of my genuine admiration of your ability, despite all the business and cares to which people who combine high intelligence with high birth are permanently subject, to find the time for the meditations necessary to acquire a good knowledge of the distinction between the soul and the body.
In my judgment, it is these meditations, rather than thoughts which require less concentration, which have enabled you to discover a certain obscurity in our notion of the union between the soul and the body. In my view, the human spirit is incapable of having, at one and the same time, a sufficiently distinct conception, both of the distinction between the soul and the body, and of their union. The reason for this is that it means simultaneously conceiving them as one thing and as two — which is a contradiction. I had assumed that your Highness’s spirit was still preoccupied with the reasons which prove the distinction between the soul and the body. I did not want to ask you to delete them, in order to make room for displaying the [694] notion of their union, which everybody always experiences for themselves without doing any philosophising — that is to say, that they are a single person, which is a combination of body and of thinking, of such a nature that this thinking can move the body, and sense the accidents to which it is subject. This is why, in my previous letter, I used the analogy of weight, and of other qualities which we usually imagine to be united with some body or other in the same way as our thinking is united with our bodies. I know that the analogy is imperfect, since these qualities are not things, as we imagine them to be. I did not worry about this, because I believed that your Highness was already entirely persuaded that the soul is a substance distinct from the body.
Your Highness remarks that it is easier to attribute matter and extension to the soul, than it is to attribute to it the capacity to move a body and to be moved by it without having any matter. But please feel free to attribute such matter and extension to the soul, since this is nothing other than to conceive it as united to the body. Once you have formed a good conception of this, and tested it in your own inner experience, it will be easy for you to consider that the matter which you will have attributed to this thinking is not the thinking itself, and that the extension of this matter is of a different nature from the extension of this thinking, in that the first is determined to a particular place from which it excludes all other bodily extension, whereas this is not true of the second. Thus [695] your Highness will have no difficulty in returning to the knowledge of the distinction between the soul and the body, despite the fact that you have had a conception of their union.
Finally, I believe that it is absolutely necessary, just once in a lifetime, to acquire a thorough comprehension of the fundamentals of metaphysics, since it is these which give us knowledge of God and of our soul. However, I also believe that it would be very harmful to overload the understanding with meditation on such things, since it would crowd out the functions of the imagination and the senses. So the best policy is to rest content with your memory of, and belief in, the conclusions which you have drawn on one single occasion, and to spend the rest of the time you have available for study on thoughts where the understanding acts in co-operation with the imagination and the senses. . . .
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