LESSON 4

The Relative Priority of Actuality and Potency.

The Reduction of Natural Potencies to Actuality

  Chapter 5: 1047b 31-1048a 24

             761. And since among all potencies some are innate, as the senses, and some are acquired by practice, as the power of playing the flute, and some by learning, as artistic powers, those which are acquired by practice and by the use of reason must be acquired by previous exercise. But this is not necessary in the case of those which are not such and which involve passivity.

             762. Now that which is capable is capable of something at some time and in some way, and has all the other qualifications which must be included in the definition; and some things can cause motion according to a rational plan and their potencies are rational, whereas other things are devoid of any rational plan and their potencies are irrational. And the former potencies must exist in living things, whereas the latter exist in both kinds of things.

             763. And since this is so, then in the case of the latter potencies, when the thing that is capable of acting and the one that is capable of being acted upon come close to each other, the one must act and the other be acted upon; but in the case of the former potencies this is not necessary.

             764. For the latter are all productive of one effect, whereas the former are productive of contrary effects. Hence they would produce contrary effects at the same time, that is, if they were to act on a proximate patient without something determining them. But this is impossible.

             765. Therefore there must be some other thing which is the proper cause of this, and by this I mean appetite or choice. For whatever a thing chiefly desires this it will do, when, insofar as it is potential, it is present and comes close to the thing which is capable of being acted upon. Hence every potency endowed with reason, when it desires something of which it has the potency and insofar as it has it, must do this thing. And it has this potency when the thing capable of being acted upon is present and is disposed in a definite way; but if it is not, it will not be able to act.

             766. For it is unnecessary to add this qualification: when nothing external hinders it; for the agent has the potency insofar as it is a potency for acting. But this is not true of all things but only of those which are disposed in a definite way, in the case of which external obstacles will be excluded; for they remove some of the qualifications which are given in the definition of the capable or possible.

             767. And for this reason if such things wish or desire to do two things or contrary things at the same time, they will not do them; for they do not have the potency for doing both at the same time, nor is it possible to do them at the same time, since it is those things which they have the capacity of doing that they do.

COMMENTARY

             1815. Having rejected the false opinions about potency and actuality the Philosopher now establishes the truth about them; and in regard to this he does two things. First (761:C 1815), he shows how actuality is prior to potency in the same subject; and second (762:C 1816), how potency, when it is prior to actuality, is brought to a state of actuality ("Now that which").

             He accordingly says, first (761), that, since some potencies are innate in the things of which they are the potencies, as the sensory powers in animals; and some are acquired by practice, as the art of flute-playing and other operative arts of this kind; and some are acquired by teaching and learning, as medicine and other similar arts; all of the above-mentioned potencies which we have as a result of practice and the use of reason must first be exercised and their acts repeated before they are acquired. For example, one becomes a harpist by playing the harp, and one becomes a physician by studying medical matters. But other potencies which are not acquired by practice but which belong to us by nature and are passive, as is evident in the case of sensory powers, are not a result of exercise; for one does not acquire the sense of sight by seeing but actually sees because he has the power of sight.

             1816. Now that which (762).

             Here he shows how those potencies which are prior to actuality are brought to actuality; and in regard to this he does two things. First, he shows how different potencies--rational and irrational potencies--differ from each other in this respect. Second (765:C 1820), he shows how rational potencies are brought to a state of actuality ("Therefore, there must").

             In regard to the first he does three things. First (762), he lays down certain conditions required for the study of the aforesaid differences, and one of these is that it is necessary to consider several qualifications in the definition of the capable or potential. For the capable does not refer to just anything at all but to something definite. Hence the capable must be capable of something, such as to walk or to sit. And similarly what can act or be acted upon cannot act or be acted upon at any time whatever; for example, a tree can bear fruit only at some definite time. Therefore, when it is said that something is capable, it is necessary to determine when it is capable. And it is also necessary to determine in what way it is capable, for that which is capable can neither act nor be acted upon in every way; for example, one can walk in this way, namely, slowly, but not rapidly. And the same thing is true of the other qualifications which they are accustomed to give in the definitions of things, for example, by what instrument, in what place, and the like.

             1817. Another qualification which he lays down is that some things are capable of something because of a rational plan, and the potencies for these capabilities are rational. But some capabilities are irrational, and the potencies for these are irrational. Again, rational potencies can exist only in living things, whereas irrational potencies can exist in both, i.e., in both living and nonliving things. And they exist not only in plants and in brute animals, which lack reason, but also in men themselves, in whom are found certain principles both of acting and of being acted upon which are irrational; for example, the powers of nutrition and growth, and weight, and other accidents of this kind.

             1818. And since (763).

             Second, he gives the difference between the potencies in question. He says that in the case of irrational potencies when the thing capable of being acted upon comes close to the thing which is capable of acting, then in accordance with that disposition whereby that able to be acted upon can be acted upon and that capable of acting can act, it is necessary that the one be acted upon and that the other act. This is clear, for instance, when something combustible comes in contact with fire. But in the case of rational potencies this is not necessary; for no matter how close some material may be brought to a builder, it is not necessary that he build something.

             1819. For the latter (764).

             Third, he gives the reason for the difference pointed out. He says that irrational potencies are such that each is productive of only one effect, and, therefore, when such a potency is brought close to something that is capable of being acted upon, it must produce the one effect which it is capable of producing. But one and the same rational potency is capable of producing contrary effects, as was said above (747:C 1789-93). Therefore, if, when it is brought close to something capable of being acted upon, it would be necessary for it to bring about the effect which it is capable of producing, it would follow that it would produce contrary effects at the same time; but this is impossible. For example, it would follow that a physician would induce both health and sickness.

             1820. Therefore there must (765).

             He then shows what is necessary in order for rational potencies to begin to act, seeing that closeness to the thing capable of being acted upon is not sufficient. In regard to this he does three things.

             First, he reveals the principle by which a rational potency is made to act. He concludes from the above discussions that since a rational potency has a common relationship to two contrary effects, and since a definite effect proceeds from a common cause only if there is some proper principle which determines that common cause to produce one effect rather than the other, it follows that it is necessary to posit, in addition to the rational power which is common to two contrary effects, something else which particularizes it to one of them in order that it may proceed to act. And this "is appetite or choice," i.e., the choosing of one of the two, or the choice which involves reason; for it is what a man intends that he does, although this occurs only if he is in that state in which he is capable of acting and the patient is present. Hence, just as an irrational potency which is capable of acting must act when its passive object comes close to it, in a similar fashion every rational potency must act when it desires the object of which it has the potency, and in the way in which it has it. And it has the power of acting when the patient is present and is so disposed that it can be acted upon; otherwise it could not act.

             1821. For it is unnecessary (766).

             Second, he answers an implied question. For since he had said that everything capable of acting as a result of a rational plan, when it desires something of which it is the potency, acts of necessity on the patient before it, someone could ask why he did not add this qualification, namely, "when nothing external hinders it"; for it has been said that it must act if it has sufficient power to act. But this does not occur in any and every way, but only when the thing having the potency is disposed in some particular way; and in this statement external obstacles are excluded. For the things which hinder it externally remove some of the qualifications laid down in the common definition of the capable or possible, so that it is not capable at this time or in this way or the like.

             1822. And for this (767).

             Third, he instructs us to avoid the absurd conclusions which he first said would follow, namely, that a rational potency would produce contrary effects at the same time. For if it is necessary that a rational potency should do what it desires, and assuming that some should wish either by reason or by sense appetite to do two different or contrary things at the same time, it does not follow for this reason that they will do them. For they do not have power over contrary effects in such a way that they may do contrary things at the same time; but they act according to the way in which they have a potency, as has been explained (763-65:C 1816-20).