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11 Descartes, Principles II.1-23 Descartes’s goal in the opening articles of the second part of the Principles is to establish, first, that we can be certain of the existence of material things, and second, that the only qualities that these things can be supposed to possess are those that arise from their being extended: their shape, size, motion, and order. Material things are, in other words, nothing other than bounded regions of space, and this identification is so strict that we can say both that there is nothing more to material things than what arises from their being considered to occupy space and that there is no such thing as empty space, any region of space being all that there is to a body. Not only do bodies have no sensible qualities like colour or taste, they have no mass, solidity, impenetrability, hardness, solidity, fluidity, salinity, acidity, etc. And not only are bodies spaces, there is no space where there is no body. QUESTIONS ON THE
1. Why
would God be a deceiver if material things did not exist?
2. What
do pain and other sensations teach us?
3. What
is hardness, as far as our senses are concerned?
4. Why
does the nature of body not depend on weight, hardness, colour, or other such
qualities?
5. Why
do preconceived opinions about rarefaction and empty space confuse the truth
that the nature of body is just extension?
6. What
makes some bodies denser than others?
7. Why
should we think that the extension constituting a body is exactly the same
with that constituting a space?
8. What
are we thinking of when we think of the extension of the place that a body
occupied after it has moved away from that place?
9. What
is the point of Descartes’s example of the man on the ship? 10.
Distinguish between internal and
external place. 11.
Why can there be no such thing as a
vacuum? 12.
Why could even God not remove all body
from a vessel while preventing any other body from taking the place those
contents had occupied? 13.
Why can there be no more matter in a
vessel filled with lead or gold than in one filled with air? 14.
What do Descartes’s claims about space
have to do with his argument against the possibility of atoms? (The title of the article claims that the
argument depends on the position on space, but the article itself only talks
about what follows from the power of God.) 15.
They are all made of the same thing,
namely extension. The only differences
arise from how this extension is cut up into parts, and how these parts are
shaped, ordered, and moving. NOTES ON THE Descartes’s argument for the external existence of material things. Descartes’s argument for the existence of material things is, like his earlier arguments for the existence of God, a causal argument. As he had earlier argued that God must exist in order to account for how I could come to have an idea of God, so he here argued that, given that God is no deceiver, material things must exist in order to account for how I could have come to have ideas of material things. This is not to say that these things must be exactly like what my ideas represent them as being. We know for a fact that things often are not exactly as they appear to be. In these cases, however, we are able to discover our error and learn from that error how to draw correct inferences from the information presented to our senses. All Descartes was concerned to argue is that the things that cause our ideas of material things must be something like those things — like them to the extent that they share the same nature with those things, even if that nature is not modified in precisely the same way. Now, the nature of material things, Descartes argued, is extension. The causes of material things ought, therefore, to be things that are also extended, even if not extended in exactly the same way (not placed in exactly the position they appear to be, not of exactly the size and shape they appear to be, or not moving at exactly the rate they appear to be). In somewhat more detail, Descartes’s argument proceeds by elimination. There are four possible causes of my ideas of material things. I might cause them, God might cause them, other immaterial spirits might cause them, or material things might cause them. I can eliminate the first possibility on the ground that I have no consciousness of myself as causing them. If there were something in myself that nonetheless caused them, this thing would be distinct from anything I conceive myself to be and hence would be a distinct substance (given that whatever can be conceived separately can exist separately and I can conceive of myself without conceiving anything that causes my ideas of sense — indeed, can’t conceive of what in me possibly could cause my ideas of sense). The cause of my ideas of sensation must therefore be one of the three remaining ones. This raises the question of why I have a sensory faculty at all — a faculty that gives me ideas I often don’t want to have (whether in dreams or when awake). There seem to be only two possibilities: either I inhabit a material world containing objects that can somehow harm me, and these sensory ideas are given to me to tell me something about them (specifically, where they are and whether or not they are the kinds of things that are beneficial or harmful), or I inhabit no such world and the ideas are all a hoax. I can eliminate the latter possibility because, firstly, I feel a strong natural impulse to consider my ideas of material things to be caused by external objects that resemble them to some degree. And, secondly, were this impulse misleading, I would have no way of discovering my error. Since God is no deceiver he would not make me naturally disposed to draw an incorrect inference without giving me some way of detecting the truth, nor would he allow any other spirit to deceive me in such a way. The only remaining alternative is the fourth one. Given that we have ideas of material things, and given that these ideas must have some cause, it only remains that they are caused by things that are something like them. This is not a very strong argument, and not very many people have found it convincing. Even later Cartesians, like Nicolas Malebranche, who followed Descartes in many other things, declared that it is extremely difficult to prove that material things must exist and that in the end our best reason for believing that they do is drawn from revelation. We might wonder, for instance, why God allows other spirits to perform so many other wicked deeds and yet would not permit them to commit this one. Or we might object to Descartes’s all too convenient appeal to a natural impulse to suppose that the causes of our ideas of material things must resemble them. The natural impulse that leads us to believe in an external world resembling our ideas should not be confused with what is clearly and distinctly perceived to be the case “in the light of nature.” What is seen in the natural light is seen so clearly that it determines the will, so that we cannot but assent to it. But we can quite easily exercise our wills to withhold assent to the proposition that there is an external world. The dreaming argument even provides us with a good reason for doing so. So when Descartes appealed to a “natural impulse” to believe in an external world, he was appealing to something less than a clear and distinct perception and inflating (without explicit notice or argument) his earlier claim that God would not deceive us about what we very clearly and distinctly perceive into a claim that God would not deceive us about what we have some strong natural impulse to accept. If we are going to think what whatever we have a strong natural impulse to believe must be true, because God would be a deceiver were it to turn out false, then the door seems opened to accepting any sort of fancy, as long as you can convince yourself that you are naturally impelled to accept it. To be fair, Descartes would have wanted to stipulate that we must not only feel a strong natural impulse to believe something, but also have no way of detecting our error. Just having the natural impulse is not enough. You also need to be unable, by proceeding methodically, to uncover any mistake in your inference. But it is not clear that this gets him out of the woods. As Simon Foucher and Pierre Bayle observed only a few years later, people have universally had a strong natural impulse to suppose that external objects are not only extended, but also coloured, solid, scented, and so on. This was believed without question for thousands of years, even by the most profound philosophers. It was only recently that philosophers like Galileo, Descartes, and Hobbes had discovered that there are reasons to doubt this (the sort of reasons Descartes gave over Principles IV.196-198, discussed in the previous lecture). If it took so many thousands of years to make this discovery, perhaps in a few more thousand years someone else will discover a reason for denying that external objects must be extended. The fact that we can’t now see any reason to think this doesn’t prove there couldn’t be one, just as the fact that Aristotle couldn’t see any reason to doubt that bodies are coloured doesn’t prove that there isn’t one. If God could permit us to be mistaken about the one point and not be a deceiver, he could allow us to be mistaken about the other, and if he would be a deceiver for allowing us to feel impelled to suppose that the causes of our ideas are extended when really they are not, then he ought to be just as much a deceiver for having allowed so many past generations to feel impelled to suppose that the causes of our ideas are coloured when they are not. All the same, rejecting Descartes’s argument for the existence of an external world is hardly an auspicious outcome, however, particularly if no better argument is forthcoming. Foucher and Bayle were sceptics, who were only too happy to seize on Descartes failure as an indication of the weakness of our cognitive powers and a lesson to us of how little we can presume to know with certainty, even about the most basic and important things. Others have not been so happy to accept that lesson. Some, possibly including Locke, believed that the true lesson to be drawn from Descartes’s failure (if it is one) is that there are some things that are so basic that they cannot and should not stand in need of proof. If we seek to demonstrate everything beyond any shadow of a doubt, our failure to do so only demonstrates the absurdity of the project of expecting to be able to find absolutely certain foundations for our most basic beliefs. The body and the nature of material things. Whatever difficulties others have subsequently found with his arguments, Descartes was satisfied that he had adequately demonstrated that there must be a material world. However, he attached a number of caveats to his argument. He maintained that all that we are entitled to affirm is that material things contain what we clearly and distinctly perceive to be contained in our ideas of material things. And, as has already been discussed at some length in the previous lecture, he did not think that we clearly and distinctly perceive material things to contain colour, pain, taste, smell, mass, solidity, hardness, viscosity, fluidity, salinity, etc. We do clearly conceive them to contain extension and its modes of size, shape, motion, and position. But even on this score, we cannot affirm them to be sized, shaped, positioned, or moving in exactly the way we perceive them to be. All that we can affirm is that they are sized, shaped, positioned, and moving somehow. There is one important thing we can know in rather more detail. Descartes took his argument to establish that among the bodies that exist in the material world there is one that is especially intimately related to me. I am able to move it merely through willing to do so, and my ideas of sensation are given to me from its perspective (I see the world from where it is located). Moreover, the states of this body affect me with pleasures or pains, so that when it is damaged or benefited, I feel distress or pleasure. This is in fact the reason for all sensations. Though we are essentially minds, which do not exist in space and therefore are not subject to division or dissolution (and hence naturally immortal), because we have been joined to bodies which are divisible and subject to dissolution and decay, there are various things that can harm our union with these bodies by attacking the structure of our bodies and their connection with us. Sensations were given us to give us a very ready means to tell different bodies apart, so we could readily recognize them on future occasions, and also to indicate to us which are beneficial and which are harmful. For this purpose it is not necessary that the sensations depict what it is in the mechanism of external bodies that interacts with the mechanism of our bodies in a beneficial or a harmful way. It would take us too long to discern a complex mechanism and figure out how it would act on the mechanism of our body. To survive we need almost instantaneous information about what is beneficial or harmful and we don’t need to know why. Accordingly, our sensations merely serve to tell us what is beneficial or harmful to us, not to tell us what qualities bodies have. They do this by being pleasant or unpleasant, as is particularly the case with smells, tastes, and tactile sensations, though also to a lesser extent with the colours of edible, rotten, or inedible objects and the sounds emitted by dangerous animals. Our ideas of such qualities as weight, solidity, hardness, fluidity, ductility, salinity, acidity, and so on are no different. These are either nothing more than ideas of how bodies tend to move under certain circumstances, and so only have to do with complex modes of extension, or they are just sensations of taste and touch masquerading as mechanical or chemical properties of bodies. The identification of body with space. In part II of the Principles the reasons for taking bodies to have only those qualities that arise from being extended in space are given in articles 4 and 11. According to those arguments, we should not suppose that bodies have sensible qualities or qualities like weight or hardness because we find by experience that there are bodies that lack these qualities. There are some stones that are so transparent as to lack all colour. There are some powders that are so fine as to have no hardness or viscosity or resistance to the touch. There are things like fire that have no weight. And so on. Since there is no sensible quality that some body cannot exist without, none are necessary for the existence of bodies, and therefore none can confidently be affirmed to be in bodies beyond any shadow of a doubt. Extension, on the other hand, cannot be conceived to be separated from a body, because as soon as we consider something to not be extended, we no longer consider it to be a body. And since whatever is extended must be extended somehow, bodies must have some size, shape, position and motion, even if it is not determinate which ones. This argument was critically examined in the previous lecture, so I will not repeat what I said there. However, two objections need to considered because Descartes himself was concerned to address them over Principles II.1-23. According to the first, bodies can vary in the amount of extension they take up just as they can vary in whether they are coloured, or heavy, or solid. Wax, for example, expands when heated. So the same sorts of experiences that tell us that the other properties are not essential to body might be used to prove that extension is not essential to body. According to the second argument, there can be space where there is no body, so body cannot just be cut up bits of space. Rarefaction and condensation. When a body is supposed to expand or spring out to fill a larger space without having anything added to it, it is said to be rarefied. (So compressed air, when released, is rarefied.) When it is compressed into a smaller volume, without having anything cut out of it, it is said to be condensed. The wax that expands when heated is an example of rarefaction and, in general, cases of rarefaction and condensation — cases where a body appears to be made to occupy a larger or smaller space without losing or gaining parts — might be taken to suggest that body is something distinct from the space it occupies. The two are not to be identified because the same body can take up different volumes depending on the degree of compression. Descartes needed to reject this way of understanding things to sustain his identification of body with space. He did so by insisting that the only intelligible way of accounting for rarefaction and condensation is by appeal to expansion and contraction of pores or gaps. As a body expands, pores open within it. As it is compressed those pores are forced shut. Change in volume is therefore really just change in shape, as he put it. The expanded body does not actually occupy any more space than it did when compressed. Some holes within it have just opened up. We might object that to claim that the only way a body can come to occupy more or less space is by opening or closing pores is to beg the question by presuming precisely what needs to be proven: that the only way to increase or decrease the amount of space a body occupies without opening or closing pores is by adding parts into or cutting parts out of the body and so changing the quantity of matter that is present in the body. However, Descartes was nonetheless right that there were no intelligible alternative explanations of rarefaction and condensation at the time. To suppose that a body might completely fill the space it occupies and yet be such that it could be further compressed without any diminution of the quantity of matter present, or expanded without opening up any gaps, defied the 17th century imagination, though dynamical views of matter as constituted by repulsive forces were not long in coming. Descartes can be forgiven for thinking that the only way there could be an increase without an opening of gaps would be through a creation of new matter ex nihilo, and the only way there could be a decrease in the volume of a material that completely filled its space would be by annihilation of matter. There is another problem that deserves mention, however. While 17th century natural philosophers believed that rarefaction and condensation are to be accounted for by the opening and closing of pores, they were divided over whether the pores opened on empty space or whether the pores would have to be filled with something else. Given his identification of all extension with body, Descartes would have had to view the former opinion as an error. Yet his discussion of rarefaction and condensation does little to combat it. The real challenge here is posed by empirical evidence that bodies continue to weigh as much before and after rarefaction and condensation. If the weight of the body is the same both before and after compression, then that suggests that nothing got squeezed out of it when its pores collapsed. Either, therefore, the pores enclosed a weightless empty space or the body completely filled the space before compression and somehow came to occupy a smaller volume without any loss of matter. Conversely, either pores opened in the body around empty spaces when it was rarefied, or extra materials from the surroundings flowed into the pores as it expanded, which ought to have made the aggregate heavier. Neither horn of the dilemma would be acceptable to Descartes, yet he only gave reasons for rejecting the second alternative without explaining how weight could remain constant through rarefaction and condensation if there is no such thing as void space. Obviously, he would have been assisted by his view that weight is merely a sensation and not a real quality of bodies. But even granting that weight is a sensation, why would this sensation not change with changes in the body, as when compressing it forces other matter out of its pores or inflating it forces new matter in? Weight is not just something felt but also something that manifests itself in causal interactions. One body tips the scale when balanced against another. This is not a matter of sensation (at least not of sensations of touch, as opposed to visual sensations of position and motion which are supposed to be informative about the external world). To really make his case Descartes would have needed to appeal to the claim of Principles II.23, that all the variety in materials is ultimately due to motion. To say that gold is heavier than lead is just to say that it is moving more in a certain direction, perhaps because it contains fewer pores through which the surrounding aetherial material can pass and so gets squeezed down more (imagine the opposite of the way submerged pieces of wood shoot up in water). Pores cannot open without the entry of new matter, but the matter might be moving in a very different direction through those pores and so may not contribute to the weight of the body. The identification of space with body. Granting that body is just extension, we might wonder why Descartes also wanted to maintain that there can be no space where there is no body, and so no such thing as a vacuum or empty space. The underlying reason is that his mechanics requires it. However his actual argument for this conclusion was blunt: Extension is a real, positive thing. But nothingness cannot have any positive qualities. So where there is extension there must be some thing that has that extension. Blunt and simple arguments for conclusions that have been widely rejected cannot stand on their own. However sound they may be, they raise the question of how it could be that people have been misled about such an apparently simple point. Descartes was concerned to answer that question. He proceeded to note that people tend to draw a distinction between the extension of a body — its specific size and shape — and the place it occupies. Descartes referred to these as the “internal place” and the “external place” of a body, respectively. Internal place is a property of a body — the way its extension is specifically modified. But external place seems separable from a body. We think that a body can move out of its place, leaving the place behind, as it were. This in turn leads us to imagine that the body might be able to move out of the place without replacement, leaving an empty place behind it. Even if, for some reason, that doesn’t happen, we think that it could be made to happen, if only by the power of God. It seems possible, for instance, that God could cause all the matter contained in a jar to pour out of it while not allowing any other matter to enter the jar, thus creating an unoccupied place or vacuum. Descartes tried to show that this way of thinking of things is mistaken. The mistake arises because “external place” is not anything real. As originally conceived, an external place is the surface shared in common by a body and the bodies that immediately surround it. But we are able to think of that surface apart from the body. We do that by imagining the body to move away while the surrounding bodies remain immobile and then just considering the surface defined by those immobile surrounding bodies, which is precisely the same surface that was there before. The thing is, the surface can even be conceived to remain while the surrounding bodies change. Descartes gave the example of a ship that is sailing with the wind against a current and getting nowhere. The current is flowing past the lower parts of the hull in one direction, the air past the upper parts of the hull in the opposite direction, and the ship is staying where it is relative to the shore. In this case, the external place remains the same, even though all the surrounding bodies change. Even if we imagine the ship removed, we can imagine a ship-shaped place that remains behind. But what exactly is remaining behind in this case and where is it remaining? Not the ship. Not any of the surrounding bodies. Just something that is only “conceptually distinct” from the ship — a ship shape, that we are only able to conceive by reference to a prior conception of the ship. And where is this ship shape, exactly? Really, nowhere, according to Descartes. We think the ship shape is in a certain place. But that place is only defined relative to certain remote bodies that are supposed to be at rest: the shore. What if we think of the Earth as moving? Then, we would have to think of the ship-shape as moving out of its ship shaped “place” and leaving it behind. But behind where? In some place that is defined relative to certain yet more remote objects such as the fixed stars? But then what if they are moving? Descartes thought that the extension of the universe in space is indefinite, and accordingly that there can be no limit to how far out you can go and what bodies you might find moving relative to what other bodies. This means that ultimately, there are no absolute places relative to which bodies move. Bodies only move relative to other bodies which are merely taken to be fixed points with reference to which motion is defined. Others could just as well have been picked instead. So when a body moves, there is no real place that it leaves behind. There is only a conceptually distinct shape defined relative to certain other bodies — a place that would not exist apart from those other bodies and so is nothing absolute or existing in itself and apart from any body. Having explained the grounds of the error in thinking that there is empty space, Descartes concluded with a capstone argument against the notion, the argument from the vessel. We speak of things like jars, cups, or barrels as being empty all the time, but Descartes insisted that all we ever mean by this is that these things do not contain what they were built to contain, even though they do contain something else. A cup is said to be empty if it contains no coffee even though it is full of air. No vessel could ever be totally empty of all matter as that would be a contradiction in terms. For, to say that a vessel is totally empty of all matter whatsoever is to say that there is nothing between the walls of that vessel. But if there is nothing between the walls of a vessel, then they must be together. Conversely, for there to be concavity within a vessel or jar there must be space. Since space just is body the only way there can be any concavity between the walls of a jar is if there is body between those walls. Descartes’s rivals thought otherwise. Gassendi (the author of the fifth set of objections to Descartes’s Meditations) had argued that since God is all-powerful, it ought to be possible for him to hold the Moon in its orbit above the Earth, and annihilate all the matter between the Earth and the Moon without allowing the Moon to move an inch towards the Earth. But Descartes maintained that to suppose that God could evacuate a jar, leaving nothing between its walls, while holding the walls apart would be tantamount to asking God to make a round square or to make a concavity without making a concavity. If there is nothing between the walls of a vessel they must be together. If they are apart it is only because there is something between them. Consequences. Descartes drew two conclusions from his rejection of the possibility of empty space. First, if there can be no space that is not the extension of some body, then it makes no sense to conceive of there being more or less body in a space, or to think of body as being something that “fills” a of space to a certain degree. After all, the limit of “less” is “none,” and to suppose that a body only fills some of the space that it occupies is to suppose that the remainder remains unoccupied. If the quantity of body in a space could be lessened, it could be lessened to nothing, leaving an empty space. If it filled a space to a certain degree, it would be one thing and the space it fills would be something else, which is a distinction that cannot properly be drawn. Consequently, weight or what was later called “mass” or “specific gravity” cannot be a real property of different kinds of material. Materials do not differ in mass or weight. They only differ in shape and direction of motion, some of them moving downwards while others move upwards through their pores, making them feel heavier than others that have larger pores. Descartes extended this conclusion to any other quality that is not a modification of extension. If body just is space then any property of body that is not a property of space — and here we can include things like charge, polarity, solidity, hardness, brittleness, malleability, elasticity or “spring,” fluidity, astringency, salinity, etc. as well as the sensible qualities of colour, heat, taste, and so on — must be either a consequence of the way the particles making bodies up are shaped or moving or it must be merely a sensation experienced by minds. There are no fundamentally different kinds of “elements” in nature. Earth, air, fire, water, salt, sulphur, mercury, tin, iron, lead, oxygen, hydrogen, and so on are all made of the same stuff. Such differences as there are between them arise exclusively from the way that the particles that make them up are shaped, arranged, and moving. For Bacon and Boyle, this had been a promising “hypothesis” worthy of testing and adopting as a guide to research. For Descartes, it is unquestionably true, being a supposedly assured consequence from what we clearly and distinctly perceive concerning the nature of body. A second conclusion concerns the extent of the universe in both the outward and the inward directions. Because we cannot conceive of a boundary without conceiving space on either side of it, and all space is body, it follows that the universe cannot be conceived to be even possibly bounded. It must extend, indefinitely, beyond any limit that can be imagined, though Descartes carefully maintained that this is not to say that it must be infinite in size. That would suppose that we can grasp the notion of infinity, which we cannot. All the same, he drew the consequence that there could not be another physical world, particularly another physical world composed of some radically different sort of material. Space is the only kind of physical material that there is, and since it extends indefinitely, this one world must contain all the bodies that there are or could be. And just as we can set no bounds to the extent of the universe outwards in space, so we can set no limits to the extent of its divisibility. The notion of an atom — of an indivisible body — must be rejected as incoherent. However far a space is divided, it is always divided into smaller and smaller spaces, not into indivisible points. Since there is no limit to the division of space, and body just is space, there can be no limit to the division of body either. Any body, however small, takes up some space and so has a left side that is distinct from its right side. Even if no power in nature could separate the two, God could, since the one can be conceived apart from the other and whatever is conceivable is possible to the power of God. These consequences make Descartes’s mechanical philosophy rather different from the mechanical philosophy of philosophers like Gassendi and Boyle, who had been more influenced by the ancient atomism of Epicurus and Democritus. They believed in indivisible atoms and empty space, which Descartes utterly rejected. Even among the revolutionary mechanist philosophers of the early modern period, Descartes was a revolutionary. ESSAY QUESTIONS AND RESEARCH PROJECTS
1. Is
Descartes entitled to affirm the separability principle? That is, from the fact that I can clearly
and distinctly perceive one thing without another, does it have to follow
that the one thing must be capable of existing apart from one another?
2. Has
Descartes made a convincing case for the claim that minds could exist apart
from bodies and that thought and feeling do not have to involve any operation
of an extended thing?
3. According
to Descartes, I can be sure that external objects exist because I find in
myself a strong inclination to suppose that my ideas of sense are caused by
such objects, and God would be a deceiver for giving me such an inclination
were there no such objects in existence. But, by the same token, I find in
myself a strong inclination to suppose that bodies possess colour and other
sensible qualities. Yet Descartes
appears not to have wanted to conclude that external objects must therefore
be coloured and possessed of the other sensible qualities. How can this
be? Is Descartes’s position on the demonstrability
of the existence of extended objects but the undemonstrability of the
existence of coloured objects consistent?
If so, say why. If not, say why
not.
4. One
of Descartes’s most astute critics was Princess Elizabeth of
5. Descartes’s
position that there is no such thing as space, but just extended bodies in a
plenum, was challenged in his own day by Pierre Gassendi, and in the
generation after by Isaac Newton. Both
Gassendi and Newton maintained that space is something in its own right, that
would continue to exist even if bodies were annihilated, and Newton maintained
that an “absolute space” (a space that is not defined relative to bodies but
is supposed to be separate from them and immovable) must be presupposed as an
ultimate reference frame for inertial motion.
6. Descartes’s
position that the essence of body consists just of extension, so that
whatever other real qualities a body might in fact have are ones that would
have to be merely accidental to it and that it could stand to lose without
ceasing to be a body, was in perfect accord with the mechanistic outlook of
the early seventeenth century, but it was challenged in the later part of the
century. Locke maintained, in
opposition to Descartes, that bodies must have a real quality of solidity in
addition to extension. |