our assent to communicated opinions until we have examined them carefully, and found them true. We must then methodically and carefully examine our opinions, and accept only those as true which we clearly and distinctly apprehend. In this investigation we shall first know that we are thinking beings, that there is a God upon whom we depend, and that from him follows the possibility of a true knowledge of all things since he is their cause. We shall find likewise that we bear in us eternal truths, like the law of causality; that we conceive likewise a bodily or extended divisible and movable nature as an actual object; that we have certain affections and sensations, the causes of which are yet unknown to us. In these few propositions are contained, as it seems to me, the most important principles of human knowledge." "The philosopher ought to accept nothing as true that he does not perceive to be such; and if he trusts the senses without examination, he reposes more confidence in the inconsiderate judgments of childhood than in the decisions of mature reason." CHAPTER VII. THE PHILOSOPHY OF NATURE. (a) THE MATHEMATICAL IN I. EXTENSION AS THE ATTRIBUTE OF BODY. 1. Body as an Object of Thought. N the progress of methodical inquiry, the reality of our mind, of God, and of bodies, has been put beyond doubt. We know clearly and distinctly that there are things without us which exist independently of our thought, and are, therefore, substances; that they are finite like ourselves in distinction from God, bodily in distinction from us who are spiritual. This perception of the opposition between mind and body forms the concluding point of the metaphysics and the starting point of the philosophy of nature: it is the transition from the doctrine of knowledge to the doctrine of body. The fundamental question of physics is, What are bodies in themselves? In what does their attribute consist? From the opposition of the two substances, it follows that no property of spiritual beings can be mingled with the conception of body; that all mere subjective modes of conception, particularly our modes of sensation, must be subtracted from it. Bodies are what they are after the subtraction of all their sensible qualities. They are, even when we do not perceive them: their perceivable or sensible qualities do not, therefore, belong to their nature as such. A stone seems hard when we touch it: if it changes into dust, it does not cease to be stone, though it is indeed no longer hard. What is true of hardness, is true also of warmth and cold, color, weight, etc. Color does not belong to the nature of stone, since there are transparent stones: weight does not belong to the nature of bodies, since there are some, as fire, which are not heavy. In the sifting and criticism of the concept of body, Descartes follows exactly the same course as in the examination of mind. In the knowledge of self, the point was to ascertain the pure concept of our nature; in the knowledge of the world without us, the puré concept of body. In the former case, it was necessary to separate from our nature every thing that does not necessarily belong to it, every thing the reality of which can be doubted; and nothing remained except the activity of thought itself, and that constituted the attribute of mind. And in like manner every thing must now be separated from the nature of body that does not necessarily belong to it, every thing which can be separated from it without annihilating the independent existence or substance of bodies. Nothing thus remains except pure materiality or extension, and this is the attribute of body. If the two attributes, opposed in their natures, are mingled with each other, as in considering our modes of thought and sensation as properties of bodies, there arises a twofold confusion, and we deceive ourselves, both concerning the nature of bodies and ourselves. To conceive bodies as the substance in which universal concepts and sensible properties inhere, is to transform them into thinking natures, or to anthropomorphize them. The fundamental aim of the Cartesian philosophy of nature is just the opposite. It aims to free physics from all anthropomorphism, and to apprehend the nature of objects after the subtraction of the mental nature of man. Involuntarily we attribute our properties to body, and our mode of considering them is likewise the veil which hides them from our eyes. To remove this veil is therefore the first condition of knowing them. When the veil, which is woven, as it were, out of our mental nature, falls off, nothing else can be revealed than body in its naked ness, in its nature opposed to, and deprived of, mind; and this is merely extension. Mind is as the self-conscious, likewise the self-active, inner nature: all self-action is of a spiritual nature. Completely opposed to this is the inert state of the being which is acted upon merely from without; i.e., of extended being, or matter. Extension is, therefore, the attribute of body: the opposition between mind and body is equivalent to the opposition between thinking and extended substance. Since all further inferences and problems of Descartes' philosophy depend upon this concept of extension, the grounding of it should be explained yet more searchingly. We must make clear to ourselves the fact, that, from the point of view of the Cartesian doctrine of mind, no other conception of body is possible, and that this, as an object of thought and the opposite of mind, contains no other attribute than extension. Body is to be considered purely physically, i.e., as a mere object of knowledge; and this can be done only when our consideration fulfils the conditions under which objects are first of all possible. The common opinion is, that they are given without any thing further, and we have only to open our senses to receive them, and await their impressions: they are the models; we, the table of wax. But the matter is not so simple. There is no object without a placing of myself over against it, without distinguishing myself from the thing, and the thing from myself; i.e., without separating my nature from the nature of the thing, and without stepping opposite to the external world as a self-conscious or thinking being. There is no object without subject, no "thou" without "I." There is no subject without the certainty of self, no self-conscious discrimination without thought. Thought only has objects, since it causes them to arise. They are as little given as thought itself, which is no existing, ready-made thing, but an activity which only reaches as far as we are certain of it, as it illuminates consciousness. Without the thinking certainty of self, the 66 cogito ergo sum," there are no objects, also no bodies as objects. In our sensations, things do not stand opposite to us: they touch us and grasp us. They are not our objects, but our states and affections: we are not free from them, but under their impression; and, therefore, we do not know what they are, but only how we are sensible of them. To consider body as an object, according to the requirements of knowl edge, is, therefore, exactly the same as taking an attitude, not of sensation, but of pure thought, towards body; to place it over against the mind, and to separate it from every thing of a mental nature, i.e., to place it opposite to the mind, to consider it as the opposite of mind, as an inert, merely extended being, destitute of a self. If the mind is only a thinking being, body is only extended: if that according to its nature is bodiless, this is mindless. These two concepts mutually demand and support each other.1 2. Body as Quantity of Space. - Body is an extended substance: it is nothing more. As the mind is nothing without thought, so the body is nothing without extension. Between substance and attribute, there is no real difference. Body and extension are, therefore, identical. A body without extension is either a word without meaning, or a confused concept. Extension is distinguished in length, breadth, and thickness; it has no other distinctions than those of spatial dimensions; it is merely spatial. Extension and space are, therefore, identical. Body distinctly conceived is, therefore, nothing except quantity of space. The physical concept of it is, therefore, identical with the mathematical. Space is related to Body as universal extension to a limited portion of it. Every body is a limited quantity of space: without it are others, some of which immediately surround it. The space which the body occupies is its place, and, in reference to its surroundings, its position. The external place is the space (superficies) in which the surrounding and surrounded bodies touch each other. The inner place is the space which 1 Princ., ii. secs. 4, 9, 11. Œuvres, iii. |