Lecture 5 — Meanings of “act”

Since we have dealt with the kind of potency which is related to motion, let us now determine about act both what it is and what kind of thing it is.

For in our distinctions, it will become evident at the same time, with regard to the potential, not only that we speak of the potential as that which is disposed by nature to move another or to be moved by another, either in an unqualified sense or in some special way, but also that we use the word in another sense as well.

And for this reason, we will also come upon these points in making our investigations.

Now, act is the existence of a thing not in the sense in which we say that a thing exists potentially, as when we say that Mercury is potentially in the wood, and a half in the whole, because it can be separated from it; or as we say that one who is not theorizing is a man of science if he is able to theorize; but in the sense in which each of these exists actually.

What we mean becomes evident in particular cases by induction, and we should not look for the boundaries of every thing, but perceive what is proportional. For it is as one who is building to one capable of building, and as one who is awake to one who is asleep, and as one who sees to one whose eyes are closed but who has the power of sight, and as that which is separated out of matter to matter, and as that which has been worked on to that which has not. And let act be defined by one member of this division and potency by the other.

However, things are not all said to be actual in the same way, but proportionally, as this is in that or to that; indeed, some are as motion to potency, and others as substance to some matter.

But the infinite and the void and all other such things are said to exist potentially and actually in a different sense from that which applies to many beings—for example, from that which sees or walks or is visible.

For these things can be verified, and verified without qualification; for what is visible is so designated sometimes because it is being seen and sometimes because it is capable of being seen.

But the infinite does not exist potentially in the sense that it will ever have actual separate existence, but it exists potentially only in knowledge. For, since the process of division never comes to an end, this shows that this act exists potentially, but not that it ever exists separately. (The Moerbeke text omits 1048b18–35.)

Therefore, regarding act, both what it is and what kind of thing it is will be evident to us from these and similar considerations.

1823. Having drawn his conclusions about potency, Aristotle now establishes the truth about act; and this is divided into two parts.

In the first, he establishes what act is.

In the second (1048b37; [1832]), he establishes what is true when something is in potency to act, at however, we must determine.

In regard to the first, he does two things.

First, he links this up with the preceding discussion. He says that, since we have dealt with the kind of potency which is found in mobile things (that is, the kind which is an active or passive principle of motion), we must now explain what act is and how it is related to potency. For when we will have distinguished the kinds of act, the truth about potency will become evident from this at the same time. For act is found not only in mobile things but also in immobile ones.

Kinds of act

1824. And since potency is referred to act, it is evident from this that capability or potency taken in reference to action is attributed not only to something that is naturally disposed to move something else actively or be moved by something else passively. This is either in an unqualified sense, inasmuch as potency is referred alike to acting and being acted upon, or in some special way, inasmuch as potency is referred to what is able to act or be acted upon well. But capability or potency is also referred to that act which is devoid of motion. For although the word “act” is derived from motion, as was explained above [1805], it is still not motion alone that is designated as act. Hence, neither is potency referred only to motion. It is therefore necessary to inquire about these things in our investigations.

1825. Now, act is the existence (1048a30). Second, he establishes the truth about act.

First, he shows what act is;

second (1048b6; [1828]), how it is used in different senses in the case of different things, at however, things.

In regard to the first, he does two things.

First, he shows what act is. He says that a thing is actual when it exists but not in the way in which it exists when it is potential. For we say that the image of Mercury is in the wood potentially and not actually before the wood is carved; but once it has been carved, the image of Mercury is then said to be in the wood actually.

And in the same way, we say that any part of a continuous whole is in that whole, because any part (for example, the middle one) is present potentially inasmuch as it is possible for it to be separated from the whole by dividing the whole; but after the whole has been divided, that part will now be present actually.

The same thing is true of one who has a science and is not speculating, for he is capable of speculating even though he is not actually doing so; but to be speculating or contemplating is to be in a state of act.

1826. What we mean (1048a35). Here he answers an implied question, for someone could ask him to explain what act is by giving its definition. And he answers by saying that it is possible to show what we mean (that is, by “act”) in the case of singular things by proceeding inductively from examples, and we should not look for the boundaries of every thing, that is, the definition. For simple notions cannot be defined, since an infinite regress in definitions is impossible. But act is one of those first simple notions. Hence it cannot be defined.

1827. And he says that we can see what act is by means of the proportion existing between two things. For example, we may take the proportion of one who is building to one capable of building; and of one who is awake to one asleep; and of one who sees to one whose eyes are closed although he has the power of sight; and of that which is separated out of matter (that is, what is formed by means of the operation of art or of nature, and thus is separated out of unformed matter) to what is not separated out of unformed matter.

And similarly, we may take the proportion of what has been prepared to what has not been prepared, or of what has been worked on to what has not been worked on. But in each of these opposed pairs, one member will be actual and the other potential. And thus, by proceeding from particular cases, we can come to an understanding in a proportional way of what act and potency are.

1828. However, things (1048b6). Then he shows that the term “act” is used in different senses, and he gives two different senses in which it is used.

First, “act” means action or operation. And with a view to introducing the different senses of act, he first says that we do not say that all things are actual in the same way, but in different ones, and this difference can be considered according to different proportions. For a proportion can be taken as meaning that, just as one thing is in another, so a third is in a fourth—for example, just as sight is in the eye, so hearing is in the ear. And the relation of substance (that is, of form) to matter is taken according to this kind of proportion, for form is said to be in matter.

1829. There is another meaning of proportion inasmuch as we say that, just as this is related to that, so another thing is related to something else; for example, just as the power of sight is related to the act of seeing, so too the power of hearing is related to the act of hearing. And the relation of motion to motive power, or of any operation to an operative potency, is taken according to this kind of proportion.

1830. But the infinite (1048b9). Second, he gives the other sense in which the word “act” is used. He says that the infinite and the empty or the void, and all things of this kind, are said to exist potentially and actually in a different sense from many other beings (such as what sees and what walks and what is visible). For it is fitting that things of this kind should sometimes exist in an unqualified sense either only potentially or only actually. For example, the visible is only actual when it is seen, and it is only potential when it is capable of being seen but is not actually being seen.

1831. But the infinite is not said to exist potentially in the sense that it may sometimes have actual separate existence alone; but in the case of the infinite, act and potency are distinguished only in thought and in knowledge.

For example, in the case of the infinite in the sense of the infinitely divisible, act and potency are said to exist at the same time, because the capacity of the infinite for being divided never comes to an end. For when it is actually divided it is still potentially further divisible. However, it is never actually separated from potency in such a way that the whole is sometimes actually divided and is incapable of any further division. And the same thing is true of the void, for it is possible for a place to be emptied of a particular body, but not so as to be a complete void, for it continues to be filled by another body. Thus, in the void, potency always continues to be joined to act. The same thing is true of motion and time and other things of this kind which do not have complete being.

Then, at the end, he makes a summary of what has been said. This is evident in the text.