Aristotle · a new plain-English translation from the original language
1| It is clear, then, that what is hot would be what passes through. And what has fine parts is always of that kind. So it turns out that hot and cold differ by smallness and largeness, but not by shapes. Further, if the pyramids are unequal, the large ones would not be fire, nor would the shape be the cause of burning, but rather the cause of the opposite. That the elements, then, do not differ by their shapes is clear from what has been said. And since the most authoritative differences among bodies are those in their affections, functions, and powers (for we say that each of the things that exist by nature has functions, affections, and powers), it would be right to speak first about these, so that by examining them we may grasp the differences of each thing in relation to each other. Book 4.
2| Chapter 1. Concerning heavy and light, we must examine what each of them is and what their nature is, and for what cause they have these powers. For the inquiry about them belongs together with the accounts of motion; for we call a thing heavy and light by its being able to be moved in a certain natural way. No names are laid down for their actualities, unless one should think that "inclination" is such a name. And because natural philosophy is a study concerned with motion, and these things have in themselves, as it were, certain sparks of motion, 306a everyone makes use of their powers, yet no one has gone through them thoroughly, except a few. Having first looked, then, at what has been said by others, and having worked through the difficulties that must be distinguished for this inquiry, let us then also state what appears to us to be the case about them. Now the heavy and the light are spoken of in one sense without qualification, in another relative to something else; for of two things that have weight, we say one is lighter, the other heavier — for example bronze compared with wood. Concerning the things spoken of without qualification, then, nothing has been said by earlier thinkers, but only concerning things spoken of relatively; for they do not say what the heavy is and what the light is, but what is heavier and what is lighter among things that have weight.
3| What is meant will be clearer put this way. Some things are naturally constituted always to move away from the middle, others always toward the middle. Of these, what moves away from the middle I call moving upward, and what moves toward the middle, downward. For it is absurd not to think that there is an up and a down in the heaven, as some maintain — they say there is no up and no down, on the ground that the heaven is entirely alike in every direction, and that anyone walking around it will everywhere be his own antipode. But we say that the outermost limit of the whole is up, which is also up in position and first by nature; and since the heaven has both an outermost limit and a middle, it is clear that there will be both an up and a down, as indeed most people say, though not adequately. The reason for this is that they think the heaven is not alike in every direction, but that only the hemisphere above us is such — whereas if they went on to suppose that it is so all around in a circle as well, and that the middle stands in the same relation to the whole everywhere, they would call the outer part up and the middle down. Speaking without qualification, then, we call light what moves upward and toward the outer limit, and heavy without qualification what moves downward and toward the middle;
4| but relative to something else, we call a thing light and lighter when, of two things having weight and equal bulk, one is naturally moved downward more slowly than the other. Chapter 2. Of those who have previously come to the examination of these matters, most have spoken only about the heavy and light in this relative sense, in which, of two things both having weight, one is lighter than the other. And having gone through the subject in this way, they think they have also determined the matter of the heavy and light without qualification; but their account does not fit that case. This will become clearer as we proceed. Some say, as happens to be written in the Timaeus, that what is heavier is what is composed of more of the same elements, and what is lighter is what is composed of fewer — just as, of lead, the greater amount of lead is heavier, and of bronze, the greater amount of bronze. And likewise for each of the other things of the same kind: for in an excess of equal parts, each thing is heavier. And in the same way they say lead is heavier than wood; for all bodies, they say, are made of certain identical elements and a single matter, though they do not seem to be. Now on this determination, nothing has been said about the heavy and light without qualification; for as things stand, fire is always light and moves upward, while earth and all earthy things move downward and toward the middle. So it is not on account of a small number of triangles, out of which they say each of these bodies is composed, that fire is naturally moved upward;
5| for what is more would move less, and would be heavier, being composed of more triangles. But as it is, the opposite appears: the more there is of it, the lighter it is, and the faster it moves upward. And of fire moving from above downward, a small amount will move faster, a large amount more slowly. Besides this, since they say that what has fewer of the same-kind particles is lighter, and what has more is heavier, and that air, water, and fire are made of the same triangles, but differ in fewness and multitude — so that one of them is lighter, another heavier — then there will be some amount of air that will be heavier than water. But the very opposite happens: for a greater amount of air always moves upward more, and in general any portion whatever of air moves upward out of water. This, then, is the way in which some have determined the matter of light and heavy; but to others this distinction did not seem adequate, and though they were earlier than the men of the present age, they thought more innovatively about the matters now under discussion. For it appears that some bodies, though smaller in bulk, are heavier. It is clear, then, that it is not adequate to say that things of equal weight are composed of an equal number of primary particles;
6| For they would be equal in bulk. As for the primary and indivisible bodies, it is absurd to say — as some do — that they are planes, out of which the bodies that have weight are composed; but for those who say they are solids, it is more possible to say that the greater among them is the heavier. But as for the compounds, since each does not evidently behave in this way, and we see many things heavier though smaller in bulk — wool compared to bronze, for instance — some suppose and say that the cause is different: they say that void, taken in along with the body, makes bodies light, and sometimes makes the greater bodies the lighter ones, since they have more void. For this reason, they say, the bulk is often greater when the body is composed of an equal or even a smaller number of solid parts, and in general the cause of anything's being lighter is that it has more void within it. This, then, is how they speak; but it is necessary for those who draw the distinction in this way to add not only that the lighter thing has more void, if it is to be lighter, but also that it has less solid; for if it exceeds that proportion, it will not be lighter. And this, they say, is also why fire is lightest of all: because it has the most void. It will follow, then, that a little fire, having more void, will be lighter than a great deal of gold, unless the gold will also have many times more solid —
7| — so this too must be stated. Now some of those who deny that void exists drew no distinction at all about light and heavy — Anaxagoras and Empedocles, for example. Others drew a distinction but, while denying that void exists, said nothing about why some bodies are light without qualification and others heavy, and why some always move upward and others downward. Further, about the fact that some bodies, though greater in bulk, are lighter than smaller bodies, they said nothing at all, nor is it clear how, from what they have said, they will manage to say anything that agrees with the appearances. And it is necessary that those who attribute the lightness of fire to its having much void be caught in almost the same difficulties. For fire will have less solid than other bodies, and more void; but nevertheless there will be some quantity of fire in which the solid and the full exceeds the solid contained in some small quantity of earth. And if they say the void accounts for this too, how will they distinguish what is heavy without qualification? Either by its having more solid, or by its having less void. If then they will say this, there will be some quantity of earth so small that the solid in it 309b is less than the solid in a great quantity of fire.
8| Likewise, if they draw the distinction by means of the void, there will be something lighter than what is light without qualification and always moves upward, and yet this thing itself will always move downward. But this is impossible; for what is light without qualification is always lighter than things that have weight and move downward, whereas what is merely lighter is not always light, because one thing is also said to be lighter than another among things that have weight — earth than water, for instance. But surely it does not suffice, in order to resolve the difficulty now stated, to make the void proportional to the full. For it will turn out that speaking this way too leads to the same impossibility. For in the greater quantity of fire and in the lesser, the solid will bear the same ratio to the void. But the greater quantity of fire moves upward faster than the lesser, and likewise downward again the greater quantity of gold and of lead move faster than the lesser, and similarly each of the other bodies that have weight. But this ought not to happen, if it is by this ratio that heavy and light are distinguished. It is also absurd if bodies move upward because of the void they contain, while the void itself does not move upward. But surely if the void is naturally disposed to move upward and the full downward, and if this is the cause of motion for the other bodies, there was no need to inquire, concerning the compounds, why some bodies are light and others heavy; rather one should have said, concerning the void and the full themselves, why the one is light and the other has weight, and further what the cause is of the full and the void not always being separated from each other.
9| It is also unreasonable to assign a place to the void, as though the void did not itself already occupy some place; for if the void moves, it is necessary that it have some place of its own, out of which it changes and into which it changes. And besides this, what is the cause of its motion? For it is surely not the void itself that causes it; for it is not the void alone that moves, but the solid as well. The same result follows even if someone draws the distinction in some other way — making some things heavier and others lighter than one another by greatness and smallness, or constructing it in whatever other manner — while assigning the same matter to all things, or several matters but only contrary ones. For if the matter is one, there will be nothing heavy or light without qualification, as happens for those who construct bodies out of triangles; and if the matters are contrary, as with those who posit void and full, there will be no accounting for why the things intermediate between what is absolutely heavy and absolutely light are heavier and lighter than one another and than the simple bodies. To distinguish by greatness and smallness seems more contrived than the previous accounts, but because it allows one to make differentiae for each of the four elements, it stands more securely against the earlier difficulties. But for one who makes a single nature underlie the things that differ in magnitude, the same result is necessary as for those who posit a single matter: nothing will be light without qualification or move upward, except by lagging behind or being squeezed out, and many small things will be heavier than a few large ones.
10| And if this is so, it will follow that a great quantity of air and a great quantity of fire are heavier than water and than a small quantity of earth. But this is impossible. These, then, are the views stated by others, and stated in this way. 3 Let us now speak, first drawing a distinction concerning the point about which some are most puzzled: why some bodies always move upward by nature and others downward, while others move both upward and downward; and after this, concerning heavy and light and the affections that occur in connection with them, for what cause each of these comes about. Now concerning each thing's moving to its own place, one must suppose the same as concerning the other comings-to-be and changes. For since there are three kinds of motion — one in respect of magnitude, one in respect of form, one in respect of place — in each of these we see the change occurring from contraries into contraries and into the intermediates, and not being a change from anything whatever into anything whatever; and likewise not anything whatever is capable of moving anything whatever; but just as the alterable and the increasable are different from each other, so too the alterative and the increasative are different from each other. In the same way, then, one must suppose that what is motive and what is movable in respect of place are not anything whatever in relation to anything whatever. If then what is motive toward the upward and the downward is what makes heavy and what makes light, and what is movable is what is potentially heavy and potentially light, then for each thing to move to its own place is for it to move to its own form.
11| And in this way one might rather grasp what the ancients meant when they said that like moves toward like. For this does not hold without qualification in every case; for if one were to transpose the earth to where the moon now is, each of its parts would not move toward the moon, but to where they now move — precisely where they move now. In general, then, this must hold for things that are alike and undifferentiated and subject to the same motion, so that wherever one part is naturally disposed to move, the whole is disposed to move as well. But since place is the boundary of what contains, and what contains everything that moves up and down is both the extremity and the middle, and this is in a way the form of what is contained, to move to one's own place is to move toward what is like; for things that are next to one another in the series are like one another — water to air, for instance, and air to fire. And it is possible to state the likeness in reverse for the things in the middle, though not for the extremes — one can say air is like water, but not that water is like earth; for what is higher always stands to what is beneath it as form stands to matter, and that is how they stand to one another. And to ask why fire moves upward and earth downward is the same as to ask why what is capable of health, when it is moved and changes qua capable of health, arrives at health and not at whiteness.
12| The same holds for all the other things that undergo alteration. But when a thing capable of growth changes qua capable of growth, it does not arrive at health but at an increase in magnitude. Likewise, each of these changes, some in quality, some in quantity, and in place light things move upward, heavy things downward — except that some of these seem to have the principle of their change within themselves (I mean the heavy and the light), while others do not, but from outside, such as what is curable and what is capable of growth. And yet sometimes these too change from within themselves: when a small motion occurs in what is outside, one arrives at health, another at growth; and since what is curable is the same as what is receptive of disease, if it is moved qua curable it moves toward health, but if qua diseased, toward disease. But the heavy and the light appear, more than these, to have their principle within themselves, because their matter is closest to substance. A sign of this is that their motion is the motion of things set free, and it is last in coming to be among the motions, so that in respect of substance this motion would be first. So when air comes to be out of water, and something light out of something heavy, it moves toward what is above.
13| At the same time it is light, and it is no longer coming to be so, but is already there. It is clear, then, that being potentially light, it comes, on its way to actuality, to that place, and to such an amount and such a kind as that of which there is actuality — how much, of what sort, and where. And the same is the cause also of earth and fire, when they already exist as actual, being moved to their own places when nothing obstructs. For nourishment too, when what obstructs it is removed, and what is curable, when what is holding it back is absent, moves at once; and what moves it is both what originally caused it and what removed the obstruction, or that from which it sprang free, as has been said in our earlier discussions, in which we determined that none of these things moves itself. So then, the cause on account of which each of the things that move moves, and what it is for a thing to move to its own place, have been stated.
14| 4. Let us now speak of the differences among these and of what happens in connection with them. First, then, let it be laid down, as it appears to everyone, that what is heavy without qualification is what sinks below everything, and what is light without qualification is what floats on top of everything. And by "without qualification" I mean looking to the genus, and applying it to those things in which both do not belong: for instance, any amount whatever of fire is seen moving upward, unless something else happens to obstruct it, and any amount of earth moves downward — and in the same way, the more there is, the faster it moves. But heavy and light in another sense belong to things in which both are present; for such things float on some things and sink below others, as air and water do. Without qualification, neither of these is light or heavy: both are lighter than earth (for any portion whatever of them floats on it), and heavier than fire (for any portion whatever of them sinks below it); but relative to each other, without qualification, one is heavy and the other light — for air, however much of it there is, floats on water, and water, however much there is, sinks below air. And since, among the other things too, some have weight and some have lightness, it is clear that the cause of all these is the difference among the simple bodies; for according as they partake of those in a greater or lesser degree, bodies will be, some light, some heavy.
15| So it is about those first bodies that we must speak; for the rest follow upon the first, which is exactly what we said those who explain the heavy by the full and the light by the void ought to have done. Now it happens that the same things do not appear heavy and light everywhere, on account of the difference among the first bodies. I mean, for instance, that a talent's weight of wood will be heavier than a mina's weight of lead in air, but lighter in water; and the cause is that everything has weight except fire, and everything has lightness except earth. Earth, then, and whatever has most of earth in it, must have weight everywhere; water everywhere except in earth; and air everywhere except in water and earth — for in its own region everything has weight except fire, and air does too. A sign of this is that an inflated skin pulls down more than an empty one. So if something has more air in it than earth and water, it can be lighter than something else in water, but heavier in air; for it does not float on air, though it does float on water. That there is something light without qualification and something heavy without qualification is clear from the following (by light without qualification I mean what is naturally suited always to move upward, and heavy what is naturally suited always to move downward, when nothing obstructs it —
16| for such things exist, and it is not the case, as some suppose, that everything has weight; for some think that even the things others call light are heavy, and always move toward the middle; and light is similarly disputed) — for we see, as has been said before, that earthy things sink below everything and move toward the middle. But the middle has been determined. If, then, there is something that floats on everything, as fire clearly does, moving upward even within air itself, while the air stays still, it is clear that this moves toward the outermost limit. So it cannot possibly have any weight — for then it would sink below something else; and if it did, there would have to be some other thing again, which moves to the outermost limit, and on which everything that moves would float. But as it is, nothing of the sort appears. Fire, then, has no weight at all, nor does earth have any lightness whatever, given that it sinks below everything and what sinks below moves toward the middle. But that there is indeed a middle, toward which the motion of things having weight goes, and from which the motion of light things goes, is clear from many considerations — first, from the fact that nothing can move to infinity. For just as nothing is impossible, so too nothing of that sort comes to be —
17| and locomotion is a coming-to-be from somewhere to somewhere. Next, fire is clearly seen moving upward, and earth downward, and everything having weight, at similar angles. So it is necessary that they move toward the middle. But whether this happens toward the middle of the earth or toward the middle of the whole — since these are the same — is another discussion. Since what sinks below everything moves toward the middle, it is necessary that what floats on everything move toward the outermost limit of the region in which they carry out their motion; for the middle is opposite to the outermost limit, and what sinks below is always opposite to what floats on top. That is also why it is reasonable that the heavy and the light are two: for the places too are two, the middle and the outermost limit. But there is also something between these, which is called the one or the other relative to each of the two; for if the intermediate is, as it were, outermost relative to one and middle relative to the other, then on this account there is also another sort of heavy and light, such as water and air. And we say that the containing belongs to the form, and the contained belongs to the matter. This distinction holds in all the genera: for in quality too, and in quantity, one thing is more as form, another as matter.
18| And likewise with things classified by place: the up belongs to what is determinate, the down to matter. So too within the very matter of the heavy and the light: insofar as it is potentially of the one sort, it is matter of the heavy, and insofar as it is potentially of the other sort, it is matter of the light. And it is one and the same thing, though its being is not the same — just as with what is prone to disease and what is curable, the being is not the same; that is why to be diseased is not the same as to be healthy. So, then, what has this kind of matter is light and always moves upward, while what has the opposite kind is heavy and always moves downward. But things that have a matter different from these two — though standing to one another in the same relation as fire and earth do — are, without qualification, borne both upward and downward. That is why air and water each have both lightness and heaviness: water sinks below everything except earth, while air rises above everything except fire. Since there is only one thing that rises above everything and one thing that sinks below everything, there must necessarily be two others that both sink below something and rise above something. So the kinds of matter, too, must necessarily be as many as these — four — but four in the sense that there is one
19| common to them all, especially since they come to be out of one another, though their being is different in each case. For nothing prevents there being one or several intermediates between contraries, as with colors; for 'intermediate' and 'mean' are said in many ways. Now in its own place, each of the things that have both heaviness and lightness has heaviness (earth has heaviness in every place), but it does not have lightness except relative to those things above which it rises. That is why, when the body beneath is withdrawn, each is carried down into the place next below: air into the place of water, water into the place of earth. But upward, into the place of fire, when fire is removed, air will not be carried unless by force — just as water too is drawn upward, when the surface becomes one continuous surface and one draws it upward faster than the downward motion by which water naturally moves. Nor is water carried into the place of air, except in the way just described. Earth does not undergo this, because its surface does not become continuous with what draws it. That is why water is drawn up into a heated vessel, but earth is not. And just as earth does not go upward, so fire does not go downward when the air beneath it is taken away.
20| For fire has no heaviness even in its own place, just as earth has no lightness. The two intermediate bodies move downward when what is beneath them is withdrawn, because what is heavy without qualification sinks into the place below everything, while what is heavy only relative to something sinks into its own place, or into the place of the things above which it rises, on account of the likeness of its matter. That it is necessary to make their differentiae equal in number to them is clear. For if there were one matter for all of them — say the void, or the full, or magnitude, or triangles — then either all would be carried upward or all downward, and the opposite motion would no longer exist at all. So either nothing would be light without qualification, if everything tends downward more the larger the bodies it is made of, or the more numerous, or because they are full — but this we do in fact observe, and it has been shown that, alike, always and everywhere, motion occurs both downward and upward. Or, if it is the void, or something of that sort, that always moves upward, there will be nothing that always moves downward. And indeed some of the intermediate bodies will move downward faster than earth, for in a large volume of air there will be more triangles, or more solid particles, or more small ones, than in a small volume of earth. But not even a single portion of air is observed moving downward.
21| The same holds, likewise, for the light, if one makes it exceed the other by its matter. But if there are two kinds of matter, how will the intermediate bodies be able to do what air and water in fact do? Suppose, for example, one were to say there is void and full: fire, then, is void, and that is why it moves upward, while earth is full, and that is why it moves downward; and suppose one says that and suppose one says that air has more of fire in it, and water more of earth. Then there will be some quantity of water that has more fire in it than a small amount of air has, and a large amount of air more earth in it than a small amount of water has, so that a given quantity of air will have to move downward faster than a small amount of water. But this is never observed to happen anywhere. It is necessary, then — just as fire moves upward because it has this something, say the void, and the other bodies do not, and earth moves downward because it has the full — that air too moves to its own place, above water, because it has this particular something, and water moves downward because it has that particular something. But if both were reducible to some one thing, or to two, and both these belonged to each of the two bodies, there would be some quantity of each at which water would exceed a small amount of air in the upward direction, and air would exceed water in the downward direction, as has been said many times. Shapes are not the cause of moving upward or downward without qualification, but of moving faster or slower.
22| It is not hard to see the reasons why. For the puzzle now raised is why flat pieces of iron and lead float on water, while other things smaller and less heavy, if they are round or elongated — a needle, for instance — sink; and why some things float because of their smallness, gold-dust for example, and other earthy and dust-like things, on air. Now concerning all these cases, to hold the cause to be what Democritus supposed is not correct. For he says that the hot particles rising up out of the water hold up the flat bodies that have weight, while the narrow ones fall through, 313 b since there are few particles to strike against them. But this ought to happen even more in air, as he himself objects. But having raised the objection, he resolves it feebly; for he says that the 'thrust' does not move in one direction, calling 'thrust' the motion of bodies carried upward. But since, among continuous bodies, some are easily divided and others less so, and likewise some are divisive of others to a greater degree and some to a lesser, these must be reckoned the causes. Now what is easily bounded is easily divided, and the more easily bounded, the more easily divided; and air is more of this sort than water, and water more than earth.
23| And indeed, within each kind, the smaller quantity is more easily divided and is torn apart more readily. So bodies that have breadth remain on the surface because they enclose a large quantity of the medium, since a large quantity is not easily torn apart; but bodies whose shapes are the opposite sink downward, because they enclose only a small quantity and so divide it easily. And this happens far more in air, to the degree that air is more easily divided than water. Since weight has a certain force by which it is carried downward, and continuous bodies have a certain force for resisting being torn apart, these two must be weighed against each other: for if the force of the weight exceeds the force of resistance in the continuous body against being torn and divided, it will force its way downward faster; but if it is weaker, it will float on the surface. Let this, then, be our determination, in this manner, concerning the heavy and the light and the attributes connected with them.