Delphi Collected Works of René Descartes

by René Descartes

  Epistemon. Since Polyander is satisfied I likewise give my assent, and I shall not push the dispute further. However I do not see that during the two hours that we have been here and that we have been arguing, he has advanced much. All that Polyander has learnt by the help of this wonderful method of which you so boast, consists solely of the fact that he doubts that he thinks and that he is a thinking thing. A wonderful knowledge in truth! Many words for small results! as much could be said in four words and we should have all given our assent. As for me if I had to employ as many words and as much time in learning something of so small an importance, I confess I should not resign myself to it without regret. Those who are our instructors tell us much more about the matter; they are much more confident; nothing stops them; they take everything upon them and decide about all. Nothing turns them aside from their plan, nothing astonishes them, whatever happens; when they feel themselves pressed too hard, an equivocation or the distinguo saves them from all embarrassment. And more, be certain that their method will always be preferred to that of one like you who doubts all and who fears so much to trip that he keeps treading the same spot and thus makes no advance.

  Eudoxus. I never intended to prescribe to anyone the method he ought to follow in the search after truth, but merely to expound that of which I have availed myself, so that if it were found bad it would be set aside; if it were found good and useful others would avail themselves of it in turn; and I always left full liberty to all to set it aside or to admit it. If it is now said that it has advanced me little, it is for experience to decide as to that: and I am certain, provided that you continue to lend me your attention, you will yourself confess that we cannot take too many precautions in the establishment of our bases, and that once they are well established we shall push the consequences further and with much more facility than we had dared to promise ourselves; so that I believe that all the errors which are found in the sciences come from the fact that we have in the beginning formed our judgments too precipitately by admitting as principles obscure things of which we had no clear and distinct notion. The truth of this is shown by the modicum of progress that we have made in the sciences whose principles are certain and known by all; for, on the other hand, in the others, whose principles are obscure or uncertain, those who desire sincerely to express their thought will be forced to confess that after having employed much time, and having read many great volumes, they have to recognise that they know nothing and have learnt nothing.

  It must not then appear astonishing to you, my dear Epistemon, if, desiring to lead Polyander in the way that is surer than that in which I was trained to walk, I am so careful and exact that I hold that only to be true of which I have a certainty equal to that with which I am aware that I am, I think, I am a thinking thing.

  Epistemon. You seem to me to resemble these tumblers who always fall back on their feet, so ceaselessly do you return to your principle. Yet if you proceed by this path you will go neither far nor quickly. How, as a matter of fact, shall you always find truths of which you are as certain as of your existence?

  Eudoxus. That is not as difficult as you think; for all the truths succeed one another and are united by a common bond; the whole secret consists simply in beginning with the first and most simple, and in rising little by little, and so to speak by gradations, to those more remote and complicated. Who now will doubt that what I have set forth as first principle is the first of the things which we might come to know with the help of a method? It is certain that we cannot doubt it, even were we to doubt of all things in the world. As then we are certain of having begun well, we must take pains not to deceive ourselves in what follows, we must apply our whole care not to admit that to be true which is liable to the smallest doubt. Pursuing this plan we must in my opinion allow Polyander to speak; for as he follows no guidance but that of his common sense, and as his reason is corrupted by no prejudices, it is difficult for him to be deceived, or at any rate he would easily perceive that this was so, and he would without any trouble return to the right road. Let him then speak, and set forth what he himself alleges he has seen in your principle.

  Polyander. So many things are contained in the idea of a thinking thing that whole days would be required to develope them. We shall only treat of the principal ones and those that can make the notion clearer and hinder our confounding it with what bears no relationship to it. I mean by a thinking being....

  THE WORLD

  OR; TREATISE ON THE LIGHT

  Translated by Michael S. Mahoney

  Written between 1629 and 1633, this treatise contains a nearly complete version of Descartes’ philosophy, covering method, metaphysics, physics and biology. The World is founded upon the heliocentric view, first explicated in Western Europe by Copernicus. Descartes delayed the book’s release upon news of the Roman Inquisition’s conviction of Galileo for “suspicion of heresy” and sentencing to house arrest. Some material from the treatise was revised for publication as Principles of Philosophy (1644), Descartes’ Latin textbook originally intended to replace the Aristotelian textbooks used in universities. In the Principles the heliocentric tone was relaxed with a relativist frame of reference. The World was not published in its entirety until 1677.

  Before Descartes begins to describe his theories in physics, he introduces the concept that there is no relationship between our sensations and what creates these sensations, casting doubt on the Aristotelian belief that such a relationship existed. From here, he describes how fire is capable of breaking wood apart into its minuscule parts through the rapid motion of the particles of fire within the flames. Descartes explains that this rapid motion of particles is what gives fire its heat, since heat is nothing more than the motion of particles and what causes it to produce light.

  According to Descartes, the motion, or agitation, of these particles is what gives substances their properties (i.e. their fluidity and hardness). Fire is the most fluid and has enough energy to render most other bodies fluid, while the particles of air lack the force necessary to do the same. Hard bodies have particles that are all equally hard to separate from the whole. Based on his observations of how resistant nature is to a vacuum, Descartes deduces that all particles in nature are packed together so that there is no void or empty space in nature. He describes substances as consisting only of three elementary elements: fire, air and earth, from which the properties of any substance can be characterised by its composition of these elements, the size and arrangement of the particles in the substance, and the motion of its particles.

  In the treatise, Descartes also elaborates on how the universe may have started from utter chaos and with these basic laws could have had its particles arranged so as to resemble the universe that we can observe today. Once the particles in the chaotic universe began to move, the overall motion would have been circular, as there is no void in nature, so whenever a single particle moves, another particle must also move to occupy the space where the previous particle once was. This type of circular motion would have created what Descartes observed to be the orbits of the planets about the sun, with the heavier objects spinning out towards the outside of the vortex and the lighter objects remaining closer to the centre. To explain this, Descartes employs the analogy of a river that carried both floating debris and heavy boats. If the river abruptly arrived at a sharp bend, the boats would follow Descartes third law of motion and hit the shore of the river since the flow of the particles in the river would not have enough force to change the direction of the boat. However, the much lighter floating debris would follow the river since the particles in the river would have sufficient force to change the direction of the debris. In the heavens, the circular flow of celestial particles, or aether, causes the motion of the planets to be circular.

  The first edition’s title page

  CONTENTS

  CHAPTER ONE On the Difference Between Our Sensations and the Things That Produce Them

  CHAPTER TWO In What the Heat and Light of Fire Consistsr />
  CHAPTER THREE On Hardness and Liquidity

  CHAPTER FOUR On the Void, and How it Happens that Our Senses Are Not Aware of Certain Bodies

  CHAPTER FIVE On the Number of Elements and on Their Qualities

  CHAPTER SIX Description of a New World, and on the Qualities of the Matter of Which it is Composed

  CHAPTER SEVEN On the Laws of Nature of this New World

  CHAPTER EIGHT On the Formation of the Sun and the Stars of the New World

  CHAPTER NINE On the Origin and the Course of the Planets and Comets in General; and of Comets in Particular

  CHAPTER TEN On the Planets in General, and in Particular on the Earth and Moon

  CHAPTER ELEVEN On Weight

  CHAPTER TWELVE On the Ebb and Flow of the Sea

  CHAPTER THIRTEEN On Light

  CHAPTER FOURTEEN On the Properties of Light

  CHAPTER FIFTEEN That the Face of the Heaven of that New World Must Appear to Its Inhabitants Completely Like That of Our World

  ENDNOTES

  Andreas Cellarius’ illustration of the Copernican system, from the Harmonia Macrocosmica (1708)— ‘The World’ rests on the heliocentric view, first explicated in Western Europe by Copernicus.

  CHAPTER ONE On the Difference Between Our Sensations and the Things That Produce Them

  In proposing to treat here of light, the first thing I want to make clear to you is that there can be a difference between our sensation1 of light (i.e. the idea that is formed in our imagination through the intermediary of our eyes) and what is in the objects that produces that sensation in us (i.e. what is in the flame or in the sun that is called by the name of “light”). For, even though everyone is commonly persuaded that the ideas that are the objects of our thought are wholly like the objects from which they proceed, nevertheless I can see no reasoning that assures us that this is the case. On the contrary, I note many experiences that should cause us to doubt it.

  You well know that words bear no resemblance to the things they signify, and yet they do not cease for that reason to cause us to conceive of those things, indeed often without our paying attention to the sound of the words or to their syllables. Thus it can happen that, after having heard a discourse, the sense of which we have very well understood, we might not be able to say in what language it was uttered.2 Now, if words, which signify nothing except by human convention, suffice to cause us to conceive of things to which they bear no resemblance, why could not nature also have established a certain sign that would cause us to have the sensation of light, even though that sign in itself bore no similarity to that sensation? Is it not thus that she has established laughter and tears, to cause us to read joy and sorrow on the faces of men?

  But perhaps you will say that our ears in fact cause us to hear only the sound of the words, or our eyes to see only the countenance of him who laughs or cries, and that it is our mind that, having remembered what those sounds and that countenance signify, represents their meaning to us at the same time.3 To that I could respond that it is nonetheless our mind that represents to us the idea of light each time the action that signifies it touches our eye. But, rather than lose time in disputation, I would do better to adduce another example.

  Do you think that, even when we do not pay attention to the meaning of words and hear only their sound, the idea of that sound, which forms in our thought, is anything like the object that is the cause of it? A man opens his mouth, moves his tongue, forces out his breath: in all these actions I see nothing that is not very different from the idea of the sound that they cause us to imagine. Also, most philosophers assure us that sound is nothing other than a certain vibration of air that strikes against our ears. Thus, if our sense of hearing were to report to our mind the true image of its object, then, instead of causing us to conceive of sound, it would have to cause us to conceive of the motion of the parts of air that then vibrate against our ears. But, because not everyone will perhaps want to believe what the philosophers say, I will adduce another example.

  Of all our senses, touch is the one thought least misleading and most certain, so that, if I show you that even touch causes us to conceive many ideas that in no way resemble the objects that produce them, I do not think you will find it strange if I say that sight can do the same. Now, there is no one who does not know that the ideas of tickling and of pain, which are formed in our thought when bodies from without touch us, bear no resemblance whatever to those bodies. One passes a feather lightly over the lips of a child who is falling asleep, and he perceives that someone is tickling him.4 Do you think the idea of tickling that he conceives resembles anything in this feather? A soldier returns from battle; during the heat of combat he could have been wounded without being aware of it. But now that he begins to cool off, he feels pain and believes he has been wounded. A surgeon is called, the soldier’s armor is removed, and he is examined. In the end, one finds that what he felt was nothing but a buckler or a strap, which was caught under his armor and was pressing on him and making him uncomfortable. If, in causing him to feel this strap, his sense of touch had impressed its image on his thought, there would have been no need of a surgeon to show him what he was feeling.

  Now, I see no reason that forces us to believe that what is in the objects from which the sensation of light comes to us is any more like that sensation than the actions of a feather and of a strap are like tickling and pain. Nevertheless, I have not adduced these examples to make you believe absolutely that this light is something different in the objects from what it is in our eyes, but only so that you will doubt it and so that, forbearing from being preoccupied by the contrary, you can now better examine with me what light is.

  CHAPTER TWO In What the Heat and Light of Fire Consists

  I know of only two sorts of bodies in the world in which light is found, to wit, the stars and flame, or fire.5 And, because the stars are without a doubt farther from human knowledge than is fire or flame, I shall try first to explicate what I observe regarding flame.

  When flame burns wood or some other similar material, we can see with our eyes that it moves the small parts of the wood and separates them from one another, thus transforming the subtler parts into fire, air, and smoke, and leaving the grosser parts as ashes. Hence, someone else may, if he wishes, imagine the form of “fire,” the quality of “heat,” and the action that “burns” it to be completely different things in this wood.6 For my part, afraid of misleading myself if I suppose anything more than what I see must of necessity be there, I am content to conceive there the motion of its parts. For, posit “fire” in the wood, posit “heat” in the wood, and make the wood “burn” as much as you please. If you do not suppose in addition that some of its parts are moved or detached from their neighbors, I cannot imagine that it would undergo any alteration or change. By contrast, remove the “fire,” remove the “heat,” prevent the wood from “burning:” provided only that you grant me that there is some power that violently moves the subtler of its parts and separates them from the grosser, I find that that alone will be able to cause in the wood all the same changes that one experiences when it burns.

  Now, insofar as it does not seem to me possible to conceive that one body could move another unless it itself were also moving,7 I conclude from this that the body of the flame that acts against the wood is composed of small parts, which move independently of one another with a very fast and very violent motion. Moving in this way, they push and move with them the parts of the body that they touch and that do not offer them too much resistance. I say that its parts move independently of one another because, even though several of them often act in accord and conspire together to bring about a single effect, we gee nonetheless that each of them acts on its own against the bodies they touch. I say also that their motion is very fast and very violent because, being so small that we cannot distinguish them by sight, they would not have the force they have to act against other bodies if the quickness of their motion did not compensate for their lack of size.8


  I add nothing concerning the direction in which each moves. For, if you consider that the power to move and the power that determines in what direction the motion should take place are two completely different things and can exist one without the other (as I have set out in the Dioptrics),9 you will easily judge that each part moves in the manner made least difficult for it by the disposition of the bodies surrounding it.10 Moreover, in the same flame there can be some parts going upward, and others downward, some in straight lines, and others in circles; indeed, they can go in all directions, without changing anything of the flame’s nature. Thus, if you see almost all of them tending upward, you need not think that this is for any other reason than that the other bodies touching them are almost always disposed to offer them greater resistance in any other direction.

  But, having recognized that the parts of the flame move in this manner, and that it suffices to conceive of their motions in order to understand how the flame has the power to consume the wood and to burn, pray let us examine if the same will not also suffice to make us understand how the flame heats us and how it sheds light for us. For, if that is the case, it will not be necessary for the flame to possess any other quality, and we will be able to say that it is this motion alone that is called now “heat” and now “light” according to the different effects it produces.