(436) rather say that one part of him is in motion while another is at rest. Very true. And suppose the objector to refine still further, and to draw the nice distinction that not only parts of tops, but whole tops, when they spin round with their pegs fixed on the spot, are at rest and in motion at the same time (and he may say the same of anything which revolves in the same spot), his objection would not be admitted by us, because in such cases things are not at rest and in motion in the same parts of themselves; we should rather say that they have both an axis and a circumference, and that the axis stands still, for there is no deviation from the perpendicular; and that the circumference goes round. But if, while revolving, the axis inclines either to the right or left, forwards or backwards, then in no point of view can they be at rest. That is the correct mode of describing them, he replied. Then none of these objections will confuse us, or incline us to believe that the same thing at the same time, in the same part or in relation to the same thing, can act or be acted upon in contrary ways. Certainly not, according to my way of thinking. Yet, I said, that we may not be compelled to examine all such objections, and prove at length that they are untrue, let us assume their absurdity, and go forward on the understanding that hereafter, if this assumption turn out to be untrue, all the consequences which follow shall be withdrawn. Yes, he said, that will be the best way.

(22) But suppose that we identify alteration with Motion on the ground that Motion itself results in difference: how then do we proceed to define Motion?

It may roughly be characterized as the passage from the potentiality to its realization. That is potential which can either pass into a Form- for example, the potential statue- or else pass into actuality- such as the ability to walk: whenever progress is made towards the statue, this progress is Motion; and when the ability to walk is actualized in walking, this walking is itself Motion: dancing is, similarly, the motion produced by the potential dancer taking his steps.

In the one type of Motion a new Form comes into existence created by the motion; the other constitutes, as it were, the pure Form of the potentiality, and leaves nothing behind it when once the motion has ceased. Accordingly, the view would not be unreasonable which, taking some Forms to be active, others inactive, regarded Motion as a dynamic Form in opposition to the other Forms which are static, and further as the cause of whatever new Form ensues upon it. To proceed to identify this bodily motion with life would however be unwarrantable; it must be considered as identical only in name with the motions of Intellect and Soul.

That Motion is a genus we may be all the more confident in virtue of the difficulty- the impossibility even- of confining it within a definition.

But how can it be a Form in cases where the motion leads to deterioration, or is purely passive? Motion, we may suggest, is like the heat of the sun causing some things to grow and withering others. In so far as Motion is a common property, it is identical in both conditions; its apparent difference is due to the objects moved.

Is, then, becoming ill identical with becoming well? As motions they are identical. In what respect, then, do they differ? In their substrates? or is there some other criterion?

This question may however be postponed until we come to consider alteration: at present we have to discover what is the constant element in every motion, for only on this basis can we establish the claim of Motion to be a genus.

Perhaps the one term covers many meanings; its claim to generic status would then correspond to that of Being.

As a solution of the problem we may suggest that motions conducing to the natural state or functioning in natural conditions should perhaps, as we have already asserted, be regarded as being in a sense Forms, while those whose direction is contrary to nature must be supposed to be assimilated to the results towards which they lead.

But what is the constant element in alteration, in growth and birth and their opposites, in local change? What is that which makes them all motions? Surely it is the fact that in every case the object is never in the same state before and after the motion, that it cannot remain still and in complete inactivity but, so long as the motion is present, is continually urged to take a new condition, never acquiescing in Identity but always courting Difference; deprived of Difference, Motion perishes.

Thus, Difference may be predicated of Motion, not merely in the sense that it arises and persists in a difference of conditions, but in the sense of being itself perpetual difference. It follows that Time, as being created by Motion, also entails perpetual difference: Time is the measure of unceasing Motion, accompanying its course and, as it were, carried along its stream.

In short, the common basis of all Motion is the existence of a progression and an urge from potentiality and the potential to actuality and the actual: everything which has any kind of motion whatsoever derives this motion from a pre-existent potentiality within itself of activity or passivity.

(16) If it be urged that Motion is but imperfect Act, there would be no objection to giving priority to Act and subordinating to it Motion with its imperfection as a species: Act would thus be predicated of Motion, but with the qualification "imperfect."

Motion is thought of as imperfect, not because it is not an Act, but because, entirely an Act, it yet entails repetition . It repeats, not in order that it may achieve actuality- it is already actual- but that it may attain a goal distinct from itself and posterior: it is not the motion itself that is then consummated but the result at which it aims. Walking is walking from the outset; when one should traverse a racecourse but has not yet done so, the deficiency lies not in the walking- not in the motion- but in the amount of walking accomplished; no matter what the amount, it is walking and motion already: a moving man has motion and a cutter cuts before there is any question of Quantity. And just as we can speak of Act without implying time, so we can of Motion, except in the sense of motion over a defined area; Act is timeless, and so is Motion pure and simple.

Are we told that Motion is necessarily in time, inasmuch as it involves continuity? But, at this, sight, never ceasing to see, will also be continuous and in time. Our critic, it is true, may find support in that principle of proportion which states that you may make a division of no matter what motion, and find that neither the motion nor its duration has any beginning but that the division may be continued indefinitely in the direction of the motion's origin: this would mean that a motion just begun has been in progress from an infinity of time, that it is infinite as regards its beginning.

Such then is the result of separating Act from Motion: Act, we aver, is timeless; yet we are forced to maintain not only that time is necessary to quantitative motion, but, unreservedly, that Motion is quantitative in its very nature; though indeed, if it were a case of motion occupying a day or some other quantity of time, the exponents of this view would be the first to admit that Quantity is present to Motion only by way of accident.

In sum, just as Act is timeless, so there is no reason why Motion also should not primarily be timeless, time attaching to it only in so far as it happens to have such and such an extension.

Timeless change is sanctioned in the expression, "as if change could not take place all at once"; if then change is timeless, why not Motion also?- Change, be it noted, is here distinguished from the result of change, the result being unnecessary to establish the change itself.

(23) The Motion which acts upon Sensible objects enters from without, and so shakes, drives, rouses and thrusts its participants that they may neither rest nor preserve their identity- and all to the end that they may be caught into that restlessness, that flustering excitability which is but an image of Life.

We must avoid identifying Motion with the objects moved: by walking we do not mean the feet but the activity springing from a potentiality in the feet. Since the potentiality is invisible, we see of necessity only the active feet- that is to say, not feet simply, as would be the case if they were at rest, but something besides feet, something invisible but indirectly seen as an accompaniment by the fact that we observe the feet to be in ever-changing positions and no longer at rest. We infer alteration, on the other hand, from the qualitative change in the thing altered.

Where, then, does Motion reside, when there is one thing that moves and another that passes from an inherent potentiality to actuality? In the mover? How then will the moved, the patient, participate in the motion? In the moved? Then why does not Motion remain in it, once having come? It would seem that Motion must neither be separated from the active principle nor allowed to reside in it; it must proceed from agent to patient without so inhering in the latter as to be severed from the former, passing from one to the other like a breath of wind.

Now, when the potentiality of Motion consists in an ability to walk, it may be imagined as thrusting a man forward and causing him to be continually adopting a different position; when it lies in the capacity to heat, it heats; when the potentiality takes hold of Matter and builds up the organism, we have growth; and when another potentiality demolishes the structure, the result is decay, that which has the potentiality of demolition experiencing the decay. Where the birth-giving principle is active, we find birth; where it is impotent and the power to destroy prevails, destruction takes place- not the destruction of what already exists, but that which intervenes upon the road to existence.

Health comes about in the same way- when the power which produces health is active and predominant; sickness is the result of the opposite power working in the opposite direction.

Thus, Motion is conditioned, not only by the objects in which it occurs, but also by its origins and its course, and it is a distinctive mark of Motion to be always qualified and to take its quality from the moved.

(7) Hence, too, the errant spheres, being moved contrarily to the inerrant one, are moved by one another by mutual contrariety, [and also] by the spable one through contrariety itself. And this can otherwise not be. The Bears up there , which neither set nor rise, think'st thou they rest or move? A: They move, Thrice-greatest one. H: And what their motion, my Asclepius? A: Motion that turns for ever round the same. H: But revolution - motion around same - is fixed by rest. For "round-the-same" doth stop "beyond-same". "Beyond-same" then, being stopped, if it be steadied in "round-same" - the contrary stands firm, being rendered ever stable by its contrariety.

(6) If space is, therefore, to be thought, [it should] not, [then, be thought as] God, but space. If God is also to be thought, [He should] not [be conceived] as space, but as energy that can contain [all space]. Further, all that is moved is moved not in the moved but in the stable. And that which moves [another] is of course stationary, for 'tis impossible that it should move with it. A: How is it, then, that things down here, Thrice-greatest one, are moved with those that are [already] moved? For thou hast said the errant spheres were moved by the inerrant one. H: This is not, O Asclepius, a moving with, but one against; they are not moved with one another, but one against the other. It is this contrariety which turneth the resistance of their motion into rest. For that resistance is the rest of motion.

(7) Now comes the question whether, in all this discussion, we are not merely helping to make out a case for some other order of Beings and talking of matters alien to ourselves.

But how could that be? What understanding can there be failing some point of contact? And what contact could there be with the utterly alien?

We must then have, ourselves, some part or share in Eternity.

Still, how is this possible to us who exist in Time?

The whole question turns on the distinction between being in Time and being in Eternity, and this will be best realized by probing to the Nature of Time. We must, therefore, descend from Eternity to the investigation of Time, to the realm of Time: till now we have been taking the upward way; we must now take the downward- not to the lowest levels but within the degree in which Time itself is a descent from Eternity.

If the venerable sages of former days had not treated of Time, our method would be to begin by linking to Eternity its Next , then setting forth the probable nature of such a Next and proceeding to show how the conception thus formed tallies with our own doctrine.

But, as things are, our best beginning is to range over the most noteworthy of the ancient opinions and see whether any of them accord with ours.

Existing explanations of Time seem to fall into three classes:

Time is variously identified with what we know as Movement, with a moved object, and with some phenomenon of Movement: obviously it cannot be Rest or a resting object or any phenomenon of rest, since, in its characteristic idea, it is concerned with change.

Of those that explain it as Movement, some identify it with Absolute Movement , others with that of the All. Those that make it a moved object would identify it with the orb of the All. Those that conceive it as some phenomenon, or some period, of Movement treat it, severally, either as a standard of measure or as something inevitably accompanying Movement, abstract or definite.

(21) The claim of Motion to be established as a genus will depend upon three conditions: first, that it cannot rightly be referred to any other genus; second, that nothing higher than itself can be predicated of it in respect of its essence; third, that by assuming differences it will produce species. These conditions satisfied, we may consider the nature of the genus to which we shall refer it.

Clearly it cannot be identified with either the Substance or the Quality of the things which possess it. It cannot, further, be consigned to Action, for Passivity also comprises a variety of motions; nor again to Passivity itself, because many motions are actions: on the contrary, actions and passions are to be referred to Motion.

Furthermore, it cannot lay claim to the category of Relation on the mere ground that it has an attributive and not a self-centred existence: on this ground, Quality too would find itself in that same category; for Quality is an attribute and contained in an external: and the same is true of Quantity.

If we are agreed that Quality and Quantity, though attributive, are real entities, and on the basis of this reality distinguishable as Quality and Quantity respectively: then, on the same principle, since Motion, though an attribute has a reality prior to its attribution, it is incumbent upon us to discover the intrinsic nature of this reality. We must never be content to regard as a relative something which exists prior to its attribution, but only that which is engendered by Relation and has no existence apart from the relation to which it owes its name: the double, strictly so called, takes birth and actuality in juxtaposition with a yard's length, and by this very process of being juxtaposed with a correlative acquires the name and exhibits the fact of being double.

What, then, is that entity, called Motion, which, though attributive, has an independent reality, which makes its attribution possible- the entity corresponding to Quality, Quantity and Substance?

But first, perhaps, we should make sure that there is nothing prior to Motion and predicated of it as its genus.

Change may be suggested as a prior. But, in the first place, either it is identical with Motion, or else, if change be claimed as a genus, it will stand distinct from the genera so far considered: secondly, Motion will evidently take rank as a species and have some other species opposed to it- becoming, say- which will be regarded as a change but not as a motion.

What, then, is the ground for denying that becoming is a motion? The fact, perhaps, that what comes to be does not yet exist, whereas Motion has no dealings with the non-existent. But, on that ground, becoming will not be a change either. If however it be alleged that becoming is merely a type of alteration or growth since it takes place when things alter and grow, the antecedents of becoming are being confused with becoming itself. Yet becoming, entailing as it does these antecedents, must necessarily be a distinct species; for the event and process of becoming cannot be identified with merely passive alteration, like turning hot or white: it is possible for the antecedents to take place without becoming as such being accomplished, except in so far as the actual alteration has "come to be"; where, however, an animal or a vegetal life is concerned, becoming takes place only upon its acquisition of a Form.

The contrary might be maintained: that change is more plausibly ranked as a species than is Motion, because change signifies merely the substitution of one thing for another, whereas Motion involves also the removal of a thing from the place to which it belongs, as is shown by locomotion. Even rejecting this distinction, we must accept as types of Motion knowledge and musical performance- in short, changes of condition: thus, alteration will come to be regarded as a species of Motion- namely, motion displacing.