Capítulo 10. Chapter X.—Concerning Transient Motion
[3.10.64] Now those who are reputed to have given the most complete classification of Motion assert that six kinds of it exist—local transition, physical change, increase, decrease, becoming, perishing.[382] We, then, shall deal with each of the aforesaid kinds of motion separately beginning with local transition. According, then, to the Dogmatists, this is the motion by which the moving object passes on from place to place, either wholly or partially—wholly as in the case of men walking, partially as when a globe is moving round a central axis, for while as a whole it remains in the same place, its parts change their places.
[3.10.65] The main views held about motion are, I imagine, three. It is assumed by ordinary people[383] and by some philosophers that motion exists, but by Parmenides, Melissus and certain others[384] that it does not exist; while the Sceptics have declared that it is ‟no more” existent than non-existent; for so far as the evidence of phenomena goes it seems that motion exists, whereas to judge by the philosophic argument it would seem not to exist. So when we have exposed the contradiction which lies between those who believe in the existence of motion and those who maintain that motion is naught, if we shall find the counter-arguments of equal weight,[385] we shall be compelled to declare that, so far as these arguments go, motion is ‟no more” existent than non-existent.
[3.10.66] We shall begin with those who affirm its real existence.
These base their view mainly on ‟evidence.”[386] If, say they, motion does not exist, how does the sun move from east to west, and how does it produce the seasons of the year, which are brought about by its approximations to us and its recessions from us? Or how do ships put out from harbours and cast anchor in other harbours very far distant from the first?, And in what fashion does the denier of motion proceed from his house and return to it again? These facts are perfectly incontestable. Consequently, when one of the Cynics[387] had an argument against motion put to him, he made no reply but stood up and began to walk, thus demonstrating by his action and by ‟evidence” that motion is capable of real existence.
So these men attempt in this way to put to shame those who hold the contrary opinion;
[3.10.67] but those who deny the existence of motion allege such arguments as these: If a thing is moved, it is moved either by itself or by another thing. But if it is moved by another, it will be moved either causelessly or owing to some cause. Nothing, they assert, is moved causelessly; but if it is moved owing to some cause, the cause owing to which it moves will be what makes it move, and thus we are involved in an infinite regress, according to the criticism stated a little while ago.
[3.10.68] Moreover, if the movent thing is active, and what is active is moved, that movent thing will need another movent thing, and the second a third, and so on ad infinitum, so that the motion comes to have no beginning; which is absurd. Therefore the thing that moves is not always moved by another. Nor yet by itself. Since every movent causes motion either by pushing forward or by drawing after or by pushing up or by thrusting down, what is self-movent must move itself in one of the aforesaid ways.
[3.10.69] But if it moves itself propulsively, it will be behind itself; and if by pulling after, it will be in front of itself; and if by pushing up, it will be below itself; and if by thrusting down, it will be above itself. But it is impossible for anything to be above or before or beneath or behind its own self; therefore it is impossible for anything to be moved by itself. But if nothing is moved either by itself or by another, then nothing is moved at all.
[3.10.70] And if anyone should seek refuge in the notions of ‟impulse” and ‟purpose” we must remind him of the controversy about ‟what is in our power,”[388] and how it is still unsettled, since hitherto we have failed to find a criterion of truth.[389]
[3.10.71] Further, there is this also to be said. If a thing moves, it moves either in the place where it is or in that where it is not. But it does not move in the place where it is, for if it is in it, it remains in it; nor yet does it move in the place where it is not; for where a thing is not, there it can neither effect nor suffer anything. Therefore nothing moves. This argument is, in fact, that of Diodorus Cronos,[390] but it has been the subject of many attacks, of which we shall describe, owing to the character of our treatise, only the more formidable, together with a judgement of their value, as it seems to us.
[3.10.72] Some, then, assert that a thing can move in the place where it is; at any rate the globes which revolve round their axes move while remaining in the same place.[391] Against these men we should transfer the argument which applies to each of the parts of the globe, and, reminding them that, to judge by this argument, it does not move even in respect of its parts, draw the conclusion that nothing moves in the place where it is.
[3.10.73] And we shall take the same course in replying to those who declare that the moving thing occupies two places, that wherein it is and that whereto it shifts. For we shall ask them when the moving object shifts from the place wherein it is to the other place—whether while it is in the first place or while it is in the second. But when it is in the first place it does not pass over into the second, for it is still in the first; and when it is not in this, it is not passing from it.
[3.10.74] And besides, the question is being begged; for where it is not, there it cannot be active.For surely no one will allow that any object to which he does not grant motion at all can shift to any place.
[3.10.75] Some, however, make this statement: Place is used in two senses, the broad sense, as for example ‟my house,” and the exact sense,[392] as for instance ‟the air which enfolds the surface of my body.” So the moving object is said to move in place, ‟place” being used not in the exact sense but in the broad sense. To these we can reply by dividing up ‟place” in the broad sense, and saying that in one part of it the body said to be moved properly exists, this being its own ‟place” in the exact sense, and in the other part it does not exist, this being the remaining portions of ‟place” in the extended sense; next we shall argue that an object can move neither in the place where it is nor in that where it is not, and so conclude that nothing can move even in what is perversely termed ‟place” in the broad sense; for this is composed of the place wherein it is in the exact sense and the place wherein it is not, and it has been proved that a thing cannot move in either of these.
[3.10.76] We should also propound the following argument.[393] If a thing moves it moves either by way of orderly, or gradual, progression or by occupying the divisible interval all at once; but in neither of these ways can a thing move, as we shall prove; so that it does not move at all.
Now that a thing can not move in orderly progression is plain on the face of it. For if bodies, and also the places and the times in which the bodies are said to move, are divided to infinity, motion will not occur, it being impossible to discover amongst the infinite any first thing wherefrom the object said to move will derive its initial movement.
[3.10.77] And if the aforesaid objects are reducible to atomic parts, and each of the moving things passes equally in an atomic period of time with its own first atom into the first atomic point of space, then all moving things are of equal velocity —the speediest horse, for instance, and the tortoise;[394] which is a result even more absurd than the former. Therefore motion does not take place by way of orderly progression.
Nor yet by way of immediate occupation of the divisible interval.
[3.10.78] For if one ought, as they declare, to take the apparent as evidence for the non-apparent, since, in order to complete the distance of a stade a man must first complete the first portion of the stade, and secondly the second portion, and so on with the rest, so likewise everything that moves ought to move by way of orderly progression; for surely if we should assert that the moving thing passes all at once through all the portions of the place wherein it is said to move, it will be in all the portions thereof at once, and if one portion of the place through which it has its motion should be cold, another hot, or, mayhap, one black, another white, so as to be able also to colour things in contact,—then the moving thing will be at once hot and cold and black and white, which is absurd.
[3.10.79] Next let them tell us how much space the moving thing passes through all at once. For if they shall assert that it is limitless, they will be granting that a thing moves through the whole of the earth all at once; while if they shirk this conclusion, let them define for us the extent of the space. But, on the one hand, the attempt to define precisely the space or interval beyond which the thing moving all at once will be unable to advance so much as a hair’s-breadth is probably not merely presumptuous and rash or even ridiculous, but plunges us again into the original difficulty;[395] for all things will be of equal velocity, if each of them alike has its transitional movements over definite intervals of space.
[3.10.80] And if, on the other go hand, they shall assert that the moving thing moves all at once through a space that is small but not precisely determined, it will be open to us to adopt the sorites argument[396] and keep constantly adding a hair’s-breadth of space to the breadth assumed. And if, then, they shall make a halt anywhere while we are pursuing this argument, they will be reverting to the monstrous theory of precise definition as before; while if they shall assent to the process of addition, we shall force them to grant that a thing can move all at once through the whole of the earth. Consequently, objects said to be in motion do not move by occupying a divisible interval all at once.
[3.10.81] But if a thing moves neither thus instantaneously nor by way of gradual progression, it does not move at all.
These, and yet more than these, are the arguments used by those who reject transient motion. But we, being unable to refute either these arguments or the apparent facts on which the view of the reality of motion is based, suspend our judgement—in view of the contradiction between appearances and arguments—regarding the question as to the existence or non-existence of motion.