DESCARTES

THE PRINCIPLES OF PHILOSOPHY

Translation © George MacDonald Ross, 1998–1999

Part I. The Principles of Human Knowledge

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51. What substance is, and that this term is applied to God and created beings in different senses.

As for what we view as things or modes of things, it is worthwhile considering each one separately. The only meaning we can give to ‘substance’ is that it is a thing which exists in such a way that it does not need anything else in order for it to exist. There is only one substance we can make sense of as existing independently of absolutely everything else, namely God. By contrast, we perceive that all other substances can exist only through the co-operation of God. Consequently, the term ‘substance’ cannot be applied to God and other things univocally (in the usual scholastic terminology) — in other words, it is impossible to have a distinct understanding of any sense of the term which is common both to God and to created beings.

52. That the term ‘substance’ applies to mind and body in the same sense, and how substance is known.

However, we can use a unitary concept of substance for understanding created bodily substance and created mind (or thinking substance), in that they are things which need nothing other than God in order to exist. However, we cannot initially recognise that something is a substance simply from the fact that it is an existing thing, because this in itself alone does not affect us. However, we can easily recognise it from any of its attributes, by virtue of the common notion that absence of attributes (or properties or qualities) is equivalent to absence of being. So from the fact that we perceive the presence of an attribute, we conclude that there must necessarily also be present some existing thing, or substance, to which it can be attributed.

53. That each substance has one distinctive attribute — that of mind is thought, and that of body is extension.

Although the presence of substance can be recognised through any attribute, each substance has just one distinctive property, [n.7] which constitutes its nature and essence, and which is the foundation of all its other properties. So, extension in length, breadth, and depth, constitutes the nature of bodily substance; and thought constitutes the nature of thinking substance. And everything else which can be attributed to body presupposes extension, and is only a mode of that which is extended; [n.8] similarly, all the contents of our minds are merely different modes of thinking. Thus, for example, we can only make sense of shape in that which is extended, or of motion in extended space; and we can only make sense of imagination, or sensation, or willing in a thinking thing. Whereas we can make sense of extension without shape or motion, and of thought without imagination or sensation, and so on. This should be obvious to anyone who considers it carefully.

54. How we can have clear and distinct notions of thinking and bodily substance, and of God.

So we can certainly have two clear and distinct notions or ideas: one of created thinking substance, and one of bodily substance. The way to achieve this is by carefully separating all the attributes of thought from the attributes of extension. In the same way, we can also have a clear and distinct idea of uncreated and independent thinking substance, namely of God. However we must not suppose that it adequately reveals to us everything that there is in God; nor should we pretend that it contains anything which we are not aware of as actually being included in it, and which we do not vividly perceive as belonging to the nature of a totally perfect being. Nobody can deny that we have such an idea of God within ourselves, unless they judge that there is no notion whatever of God in human minds.

55. How duration, order, and number are also understood distinctly.

We shall also have a perfectly distinct understanding of duration, order, and number, as long as we refrain from attaching the concept of substance to them. For example, we should think of the duration of each thing as nothing other than the mode through which our conception of that thing is limited to its continuing existence. Similarly, order and number are not separate from ordered and numbered things, but are merely modes through which we consider those things.

56. What modes, qualities, and attributes are.

Here, by ‘modes’, I obviously mean the same as what I have elsewhere called ‘attributes’, or ‘qualities’. However, they should be called ‘modes’ when we consider a substance to be affected or variegated [n.9] by them; they should be called ‘qualities’ when this variegation is the basis for giving them a name; and they should be called ‘attributes’ when we view them more generally, and only in so far as they exist in the substance. So, strictly speaking, we say that there are no modes or qualities in God, but only attributes, because it is incomprehensible how he could be subject to any variegation. And even among created things, we should use the term ‘attribute’ rather than ‘quality’ or ‘mode’ for anything which is in things only in one and the same way [n.10] — for example, existence and duration in that which exists and continues to exist.

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60. On distinctions; and firstly, real distinction.

Now number, as applied to things themselves, arises from their being distinguished from one another; and there are three sorts of distinction, namely ‘real’, ‘modal’, and ‘of reason’. Strictly speaking, a ‘real’ distinction is only one between two or more substances. And we perceive that they are really distinct from each other only by virtue of the fact that we can understand the one clearly and distinctly without the other. Acknowledging God, we are certain that he can bring about whatever we understand distinctly. So much so, that, for example, we are certain that it is possible for extended or bodily substance to exist, even though we do not yet know for certain that any such thing actually exists, simply from the fact that we already have an idea of it. Furthermore, if it exists, each and every part of it as defined by our thought is really distinct from the other parts of the same substance. Likewise, it is certain that each one of us is really distinct from every other thinking substance, and from every bodily substance, simply by virtue of the fact that each one of us understands that we are a thinking thing, and can in thought shut out from ourselves every other substance, whether thinking or extended. And even if we suppose that God has joined a bodily substance to such a thinking substance so closely that they could not be joined more closely, and thus welded together something unitary out of these two, nevertheless, they remain really distinct, because, however closely he might have united them, he could not have divested himself of the power he previously had of separating them, or of keeping one of them in existence without the other. And things which God can separate, or preserve separately, are really distinct.

61. On modal distinction.

There are two sorts of modal distinction. One is the distinction between a mode in the strict sense, and the substance of which it is a mode; and the other is the distinction between two modes of the same substance. The first can be recognised from the fact that we can have a clear perception of the substance independently of the mode we say differs from it, but we cannot, conversely, understand the mode independently of the substance. For example, shape and motion are modally distinct from the bodily substance they exist in; and affirmation and memory are modally distinct from the mind. The other sort can be recognised from the fact that one mode can be known independently of the other, and vice versa; but neither can be known independently of the substance which they both exist in. For example, if a stone moves and is square, I can understand its square shape independently of its motion; and, conversely, its motion independently of its square shape; but I cannot understand the motion or the shape independently of the substance of the stone. However, when a mode of one substance differs from another substance, or from a mode of another substance (as the motion of one body differs from another body, or from mind; and as motion differs from duration [n.13]), it seems more appropriate to call the distinction real rather than modal. This is because these modes are not clearly understood independently of the really distinct substances of which they are modes.

62. On distinction of reason.

Finally, a distinction of reason is that between a substance and one of its attributes, without which the substance cannot be understood; or between two such attributes of one and the same substance. It is recognised from the fact that we cannot form a clear and distinct idea of the substance if we exclude the attribute from it; or, in the second case, that we cannot perceive clearly the idea of the one attribute if we separate it from the other. For example, there is only a distinction of reason between any substance whatever and its duration, since it ceases to exist at all if it ceases to have duration. Again, all the modes of thinking which we consider as existing in objects differ only in reason, both from the objects they are thought of as being in, and from each other in one and the same object. I remember that I once conflated this sort of distinction with the modal sort, at the end of my reply to the first set of objections to my Meditations on First Philosophy. But in that passage there was no need to distinguish them precisely, and it was enough for my purpose to distinguish both of them from a real distinction.

63. How thought and extension can be distinctly known as constituting the nature of mind and body.

Thought and extension can be considered as constituting the natures of intelligent and bodily substance respectively. Given this, they should not be conceived as anything other than thinking substance and extended substance themselves, that is, as mind and body. Not only is this the clearest and most distinct way of conceiving them, but it is also easier to form a conception of extended substance or of thinking substance than of substance alone, leaving out the fact that it thinks or that it is extended. For there is no little difficulty in abstracting the notion of substance from the notions of thought or extension, since they differ from it only through a distinction of reason. A concept does not become more distinct by virtue of our including less in it, but only in so far as we carefully distinguish whatever we include in it from everything else.

64. How they can also be known as modes of substance.

Thought and extension can also be taken as modes of substance, that is in so far as one and the same mind can have many different thoughts; and one and the same body, while retaining its same quantity, can be extended in many different ways — now longer, but less wide or deep, and now wider, but shorter. In that case, they are modally different from substance. They can be understood just as clearly and distinctly as substance, provided they are considered not as substances (i.e. things separate from other things), but only as modes of things. For by the very fact that we consider them as in the substances of which they are modes, we distinguish them from those substances, and recognise them for what they really are. But if, on the other hand, we wanted to consider them independently of the substances they exist in, we would thereby be considering them as subsistent things, and thus we would be confusing the ideas of mode and substance.

65. How their modes are also to be known.

Thought and extension themselves have various modes in their turn; and these are best perceived if we consider them only as modes of the things they are in. Examples of modes of thought are understanding, imagination, memory, volition, etc.; and examples of modes of extension (or modes spread over extension) are all shapes, and the position and motion of parts. In the case of motion, it is best perceived if we think only of motion from one place to another, and ignore the force which initiates it (however, I shall try and explain it in the appropriate place).