Thus, not only do I exist, but other entities exist also, that is to say, the objects of my sensations; and even if these objects are merely ideas, still these ideas are not me.
But everything outside myself, everything which acts upon my senses, I call matter, and all the particles of matter which I suppose to be united into separate entities I call bodies. Thus all the disputes of the idealists and the realists have no meaning for me; their distinctions between the appearance and the reality of bodies are wholly fanciful.
I am now as convinced of the existence of the universe as of my own. I next consider the objects of my sensations, and I find that I have the power of comparing them, so I perceive that I am endowed with an active force of which I was not previously aware.
To perceive is to feel; to compare is to judge; to judge and to feel are not the same. Through sensation objects present themselves to me separately and singly as they are in nature; by comparing them I rearrange them, I shift them so to speak, I place one upon another to decide whether they are alike or different, or more generally to find out their relations. To my mind, the distinctive faculty of an active or intelligent being is the power of understanding this word "is." I seek in vain in the merely sensitive entity that intelligent force which compares and judges; I can find no trace of it in its nature. This passive entity will be aware of each object separately, it will even be aware of the whole formed by the two together, but having no power to place them side by side it can never compare them, it can never form a judgment with regard to them.
To see two things at once is not to see their relations nor to judge of their differences; to perceive several objects, one beyond the other, is not to relate them. I may have at the same moment an idea of a big stick and a little stick without comparing them, without judging that one is less than the other, just as I can see my whole hand without counting my fingers.63 These comparative ideas, 'greater', 'smaller', together with number ideas of 'one', 'two', etc. are certainly not sensations, although my mind only produces them when my sensations occur.
We are told that a sensitive being distinguishes sensations from each other by the inherent differences in the sensations; this requires explanation. When the sensations are different, the sensitive being distinguishes them by their differences; when they are alike, he distinguishes them because he is aware of them one beyond the other. Otherwise, how could he distinguish between two equal objects simultaneously experienced? He would necessarily confound the two objects and take them for one object, especially under a system which professed that the representative sensations of space have no extension.
When we become aware of the two sensations to be compared, their impression is made, each object is perceived, both are perceived, but for all that their relation is not perceived. If the judgment of this relation were merely a sensation, and came to me solely from the object itself, my judgments would never be mistaken, for it is never untrue that I feel what I feel.
Why then am I mistaken as to the relation between these two sticks, especially when they are not parallel? Why, for example, do I say the small stick is a third of the large, when it is only a quarter? Why is the picture, which is the sensation, unlike its model which is the object? It is because I am active when I judge, because the operation of comparison is at fault; because my understanding, which judges of relations, mingles its errors with the truth of sensations, which only reveal to me things.
Add to this a consideration which will, I feel sure, appeal to you when you have thought about it: it is this—If we were purely passive in the use of our senses, there would be no communication between them; it would be impossible to know that the body we are touching and the thing we are looking at is the same. Either we should never perceive anything outside ourselves, or there would be for us five substances perceptible by the senses, whose identity we should have no means of perceiving.
This power of my mind which brings my sensations together and compares them may be called by any name; let it be called attention, meditation, reflection, or what you will; it is still true that it is in me and not in things, that it is I alone who produce it, though I only produce it when I receive an impression from things. Though I am compelled to feel or not to feel, I am free to examine more or less what I feel.
Being now, so to speak, sure of myself, I begin to look at things outside myself, and I behold myself with a sort of shudder flung at random into this vast universe, plunged as it were into the vast number of entities, knowing nothing of what they are in themselves or in relation to me. I study them, I observe them; and the first object which suggests itself for comparison with them is myself.
All that I perceive through the senses is matter, and I deduce all the essential properties of matter from the sensible qualities which make me perceive it, qualities which are inseparable from it. I see it sometimes in motion, sometimes at rest,64 hence I infer that neither motion nor rest is essential to it, but motion, being an action, is the result of a cause of which rest is only the absence. When, therefore, there is nothing acting upon matter it does not move, and for the very reason that rest and motion are indifferent to it, its natural state is a state of rest.
I perceive two sorts of motions of bodies, acquired motion and spontaneous or voluntary motion. In the first the cause is external to the body moved, in the second it is within. I shall not conclude from that that the motion, say of a watch, is spontaneous, for if no external cause operated upon the spring it would run down and the watch would cease to go. For the same reason I should not admit that the movements of fluids are spontaneous, neither should I attribute spontaneous motion to fire which causes their fluidity.65
You ask me if the movements of animals are spontaneous; my answer is, "I cannot tell," but analogy points that way. You ask me again, how do I know that there are spontaneous movements? I tell you, "I know it because I feel them." I want to move my arm and I move it without any other immediate cause of the movement but my own will. In vain would any one try to argue me out of this feeling, it is stronger than any proofs; you might as well try to convince me that I do not exist.
If there were no spontaneity in men's actions, nor in anything that happens on this earth, it would be all the more difficult to imagine a first cause for all motion. For my own part, I feel myself so thoroughly convinced that the natural state of matter is a state of rest, and that it has no power of action in itself, that when I see a body in motion I at once assume that it is either a living body or that this motion has been imparted to it. My mind declines to accept in any way the idea of inorganic matter moving of its own accord, or giving rise to any action.
Yet this visible universe consists of matter, matter diffused and dead,66 matter which has none of the cohesion, the organisation, the common feeling of the parts of a living body, for it is certain that we who are parts have no consciousness of the whole. This same universe is in motion, and in its movements, ordered, uniform, and subject to fixed laws, it has none of that freedom which appears in the spontaneous movements of men and animals. So the world is not some huge animal which moves of its own accord; its movements are therefore due to some external cause, a cause which I cannot perceive, but the inner voice makes this cause so apparent to me that I cannot watch the course of the sun without imagining a force which drives it, and when the earth revolves I think I see the hand that sets it in motion.
If I must accept general laws whose essential relation to matter is unperceived by me, how much further have I got? These laws, not being real things, not being substances, have therefore some other basis unknown to me. Experiment and observation have acquainted us with the laws of motion; these laws determine the results without showing their causes; they are quite inadequate to explain the system of the world and the course of the universe. With the help of dice Descartes made heaven and earth; but he could not set his dice in motion,