by Aristotle
3 · There are some who say, as the Megaric school does, that a thing can act only when it is acting, and when it is not acting it cannot act, e.g. he who is not [30] building cannot build, but only he who is building, when he is building; and so in all other cases. It is not hard to see the absurdities that attend this view.
For it is clear that on this view a man will not be a builder unless he is building (for to be a builder is to be able to build), and so with the other arts. If, then, it is [35] impossible to have such arts if one has not at some time learnt and acquired them, and it is then impossible not to have them if one has not sometime lost them (either by forgetfulness or by some accident or by time; for it cannot be by the destruction [1047a1] of the object itself, for that lasts for ever), a man will not have the art when he has ceased to use it, and yet he may immediately build again; how then will he have got the art? And similarly with regard to lifeless things; nothing will be either cold or hot or sweet or perceptible at all if people are not perceiving it; so that the upholders [5] of this view will have to maintain the doctrine of Protagoras. But, indeed, nothing will even have perception if it is not perceiving, i.e. exercising its perception. If, then, that is blind which has not sight though it would naturally have it, when it would naturally have it and when it still exists, the same people will be blind many times in the day—and deaf too. [10]
Again, if that which is deprived of potentiality is incapable, that which is not happening will be incapable of happening; but he who says of that which is incapable of happening that it is or will be will say what is untrue; for this is what incapacity meant. Therefore these views do away with both movement and becoming. For that which stands will always stand, and that which sits will always [15] sit; if it is sitting it will not get up; for that which cannot get up will be incapable of getting up. But we cannot say this, so that evidently potentiality and actuality are different; but these views make potentiality and actuality the same, so that it is no small thing they are seeking to annihilate. [20]
Therefore it is possible that a thing may be capable of being and not be, and capable of not being and yet be, and similarly with the other kinds of predicate; it may be capable of walking and yet not walk, or capable of not walking and yet walk. And a thing is capable of doing something if there is nothing impossible in its having the actuality of that of which it is said to have the capacity. I mean for instance, if a [25] thing is capable of sitting and it is open to it to sit, there will be nothing impossible in its actually sitting; and similarly if it is capable of being moved or moving or of standing or making to stand or of being or coming to be, or of not being or not coming to be.
The word ‘actuality’, which we connect with fulfillment, has, strictly speaking, [30] been extended from movements to other things; for actuality in the strict sense is identified with movement. And so people do not assign movement to non-existent things, though they do assign some other predicates. E.g. they say that non-existent things are objects of thought and desire, but not that they are moved; and this because, while they do not actually exist, they would have to exist actually if they [1047b1] were moved. For of non-existent things some exist potentially; but they do not exist, because they do not exist in fulfillment.
4 · If what we have described is the possible or a consequence of the possible, evidently it cannot be true to say ‘this is capable of being but will not be’,—a view [5] which leads to the conclusion that there is nothing incapable of being. Suppose, for instance, that a man (one who did not understand the meaning of ‘incapable of being’) were to say that the diagonal of the square is capable of being measured but will not be measured, because a thing may be capable of being or coming to be, and yet not be or be about to be. But from the premises this necessarily follows, that if [10] we actually suppose that which is not, but is capable of being, to be or to have come to be, there will be nothing impossible in this; but the result will be impossible, for the actual measuring of the diagonal is impossible. For the false and the impossible are not the same; that you are standing now is false, but not impossible.
[15] At the same time it is clear that if, when A is, B must be, then, when A is possible, B also must be possible. For if B need not be possible, there is nothing to prevent its not being possible. Now let A be supposed possible. Then, when A is possible, nothing impossible would follow if A were supposed to be; and then B must [20] of course be. But we supposed B to be impossible. Let it be impossible, then. If, then, B is impossible, A also must be so. But A was supposed possible; therefore B also is possible. If, then, A is possible, B also will be possible, if they were so related that if [25] A is, B must be. If, then, A and B being thus related, B is not possible on this condition, A and B will not be related as was supposed. And if when A is possible, B must be possible, then if A is, B must also be. For to say that B must be possible, if A is possible, means that if A is both at the time when and in the way in which it was [30] supposed capable of being, B also must then and in that way be.
5 · As all potentialities are either innate, like the senses, or come by practice, like the power of playing the flute, or by learning, like that of the arts, those which come by practice or by rational formula we must acquire by previous exercise, but [35] this is not necessary with those which are not of this nature and which imply passivity.
[1048a1] Since that which is capable is capable of something and at some time and in some way—with all the other qualifications which must be present in the definition—, and since some things can work according to a rational formula and their potentialities involve a formula, while other things are non-rational and their potentialities are non-rational, and the former potentialities must be in a living [5] thing, while the latter can be both in the living and in the lifeless; as regards potentialities of the latter kind, when the agent and the patient meet in the way appropriate to the potentiality in question, the one must act and the other be acted on, but with the former kind this is not necessary. For the non-rational potentialities are all productive of one effect each, but the rational produce contrary effects, so that they would produce contrary effects at the same time; but this is impossible. That which decides, then, must be something else; I mean by this, desire or choice. [10] For whichever of two things the animal desires decisively, it will do, when it is in the circumstances appropriate to the potentiality in question and meets the passive object. Therefore everything which has a rational potentiality, when it desires that for which it has a potentiality and in the circumstances in which it has it, must do this. And it has the potentiality in question when the passive object is present and is [15] in a certain state; if not it will not be able to act. To add the qualification ‘if nothing external prevents it’ is not further necessary; for it has the potentiality in so far as this is a potentiality of acting, and it is this not in all circumstances but on certain conditions, among which will be the exclusion of external hindrances; for these are barred by some of the positive qualifications. And so even if one has a rational wish, [20] or an appetite, to do two things or contrary things at the same time, one cannot do them; for it is not on these terms that one has the potentiality for them, nor is it a potentiality for doing both at the same time, since one will do just the things which it is a potentiality for doing.
6 · Since we have treated of the kind of potentiality which is related to [25] movement, let us discuss actuality, what and what sort of thing it is. In the course of our analysis it will also become clear, with regard to the potential, that we not only ascribe potentiality to that whose nature it is to move something else, either without qualification or in some particular way, but also use the word in another sense, in the pursuit of which we have discussed these previous senses. Actuality means the [30] existence of the thing, not in the way which we express by ‘potentially’; we say that potentially, for instance, a statue of Hermes is in the block of wood and the half-line is in the whole, because it might be separated out, and even the man who is not studying
we call a man of science, if he is capable of studying. Otherwise, actually. Our meaning can be seen in the particular cases by induction, and we must not seek [35] a definition of everything but be content to grasp the analogy,—that as that which is building is to that which is capable of building, so is the waking to the sleeping, [1048b1] and that which is seeing to that which has its eyes shut but has sight, and that which is shaped out of the matter to the matter, and that which has been wrought to the unwrought. Let actuality be defined by one member of this antithesis, and the [5] potential by the other. But all things are not said in the same sense to exist actually, but only by analogy—as A is in B or to B, C is in D or to D; for some are as movement to potentiality, and the others as substance to some sort of matter.
The infinite and the void and all similar things are said to exist potentially and [10] actually in a different sense from that in which many other things are said so to exist, e.g. that which sees or walks or is seen. For of the latter class these predicates can at some time be truly asserted without qualification; for the seen is so called sometimes because it is being seen, sometimes because it is capable of being seen. But the infinite does not exist potentially in the sense that it will ever actually have separate existence; its separateness is only in knowledge. For the fact that division [15] never ceases to be possible gives the result that this actuality exists potentially, but not that it exists separately.
Since of the actions which have a limit none is an end but all are relative to the end, e.g. the process of making thin is of this sort, and the things themselves when [20] one is making them thin are in movement in this way (i.e. without being already that at which the movement aims), this is not an action or at least not a complete one (for it is not an end); but that in which the end is present is an action. E.g. at the same time we are seeing and have seen, are understanding and have understood, are thinking and have thought: but it is not true that at the same time we are learning [25] and have learnt, or are being cured and have been cured. At the same time we are living well and have lived well, and are happy and have been happy. If not, the process would have had sometime to cease, as the process of making thin ceases: but, as it is, it does not cease; we are living and have lived. Of these processes, then, we must call the one set movements, and the other actualities. For every movement is incomplete—making thin, learning, walking, building; these are movements, and [30] incomplete movements. For it is not true that at the same time we are walking and have walked, or are building and have built, or are coming to be and have come to be—it is a different thing that is being moved and that has been moved, and that is moving and that has moved; but it is the same thing that at the same time has seen and is seeing, or is thinking and has thought. The latter sort of process, then, I call an actuality, and the former a movement.
[35] 7 · What and what sort of thing the actual is may be taken as explained by these and similar considerations. But we must distinguish when a thing is [1049a1] potentially and when it is not; for it is not at any and every time. E.g. is earth potentially a man? No—but rather when it has already become seed, and perhaps not even then, as not everything can be healed by the medical art or by chance, but there is a certain kind of thing which is capable of it, and only this is potentially [5] healthy. And the definition of that which as a result of thought comes to be in fulfillment from having been potentially is that when it has been wished it comes to pass if nothing external hinders it, while the condition on the other side—viz. in that which is healed—is that nothing in it hinders the result. Similarly there is potentially a house, if nothing in the thing acted on—i.e. in the matter—prevents it [10] from becoming a house, and if there is nothing which must be added or taken away or changed; this is potentially a house, and the same is true of all other things for which the source of their becoming is external. And in the cases in which the source of the becoming is in the very thing which suffers change, all those things are said to be potentially something else, which will be it of themselves if nothing external hinders them. E.g. the seed is not yet potentially a man; for it must further undergo [15] a change in a foreign medium.2 But when through its own motive principle it has already got such and such attributes, in this state it is already potentially a man; while in the former state it needs another principle, just as earth is not yet potentially a statue, for it must change in order to become bronze.
It seems that when we call a thing not something else but ‘of’ that something (e.g. a casket is not wood but of wood, and wood is not earth but made of earth, and [20] again perhaps in the same way earth is not something else but made of that something), that something is always potentially (in the full sense of that word) the thing which comes after it in this series. E.g. a casket is not earthen nor earth, but wooden; for wood is potentially a casket and is the matter of a casket, wood in general of a casket in general, and this particular wood of this particular casket. And if there is a first thing, which no longer is called after something else, and said [25] to be of it, this is prime matter; e.g. if earth is airy and air is not fire but fiery, fire then is prime matter, not being a ‘this’. For the subject and substratum differ by being or not being a ‘this’; the substratum of accidents is an individual such as a man, i.e. body and soul, while the accident is something like musical or white. (The [30] subject is called, when music is implanted in it, not music but musical, and the man is not whiteness but white, and not ambulation or movement but walking or moving,—as in the above examples of ‘of’ something.) Wherever this is so, then, the ultimate subject is a substance; but when this is not so but the predicate is a form or [35] a ‘this’, the ultimate subject is matter and material substance. And it is only right that the ‘of’ something locution should be used with reference both to the matter and to the accidents; for both are indeterminates. We have stated, then, when a [1049b1] thing is to be said to be potentially and when it is not.
8 · We have distinguished the various senses of ‘prior’, and it is clear that actuality is prior to potentiality. And I mean by potentiality not only that definite [5] kind which is said to be a principle of change in another thing or in the thing itself regarded as other, but in general every principle of movement or of rest. For nature also is in the same genus as potentiality; for it is a principle of movement—not, however, in something else but in the thing itself qua itself. To all such potentiality, [10] then, actuality is prior both in formula and in substance; and in time it is prior in one sense, and in another not.
Clearly it is prior in formula; for that which is in the primary sense potential is potential because it is possible for it to become actual, e.g. I mean by ‘capable of building’ that which can build, and by ‘capable of seeing’ that which can see, and by [15] ‘visible’ that which can be seen. And the same account applies to all other cases, so that the formula and the knowledge of the one must precede the knowledge of the other.
In time it is prior in this sense: the actual member of a species is prior to the potential member of the same species, though the individual is potential before it is actual. I mean that the matter and the seed and that which is capable of seeing, which are potentially a man and corn and seeing, but not yet actually so, are prior in [20] time to this particular man who now exists actually, and to the corn and to the seeing subject; but they are posterior in time to other actually existing things, from which they were produced. For from the potential the actual is always produced by [25] an actual thing, e.g. man by man, musician by musician; there is always a first mover, and the mover already exists actually. We have said in our account of substance that everything that is produced is something produced from something and by something, and is the same in species as it.
[30] This is why it is thought impossible to be a builder if one has built nothing or a harpist if one has never played the harp; for he who learns to play the harp learns to play it by playing it, and all other learners do similarly. And thence arose the sophistical quibble, that one who does
not know a science will be doing that which is the object of the science; for he who is learning it does not know it. But since, of that [35] which is coming to be, some part must have come to be, and, of that which, in general, is changing, some part must have changed (this is shown in the treatise on [1050a1] movement), he who is learning must, it would seem, know some part of the science. It is surely clear, then, in this way, that the actuality is in this sense also, viz. in order of becoming and of time, prior to the potentiality.
But it is also prior in substance; firstly, because the things that are posterior in [5] becoming are prior in form and in substance, e.g. man is prior to boy and human being to seed; for the one already has its form, and the other has not. Secondly, because everything that comes to be moves towards a principle, i.e. an end. For that for the sake of which a thing is, is its principle, and the becoming is for the sake of the end; and the actuality is the end, and it is for the sake of this that the potentiality [10] is acquired. For animals do not see in order that they may have sight, but they have sight that they may see. And similarly men have the art of building that they may build, and theoretical science that they may theorize; but they do not theorize that they may have theoretical science, except those who are learning by practice; and these do not theorize except in a limited sense, or else they have no need to theorize.3 [15] Further, matter exists in a potential state, just because it may attain to its form; and when it exists actually, then it is in its form.
And the same holds good in cases in which the end is a movement, as well as in all others. Therefore as teachers think they have achieved their end when they have exhibited the pupil at work, so also does nature. For if this is not the case, we shall [20] have Pauson’s Hermes over again; for it will be hard to say about the knowledge, as about the statue, whether it is within or without. For the action is the end, and the actuality is the action. Therefore even the word ‘actuality’ is derived from ‘action’, and points to the fulfillment.