3. Third Way

32. [Exposition of the Opinion] - In a third way, by attributing somehow to the habit the idea of active principle in respect of the act, one can say that the habit is a partial active cause, along with the power itself (which is also a partial cause), in respect of a perfect act proceeding from the power and the habit, although the power itself could be the total cause in respect of an imperfect act preceding the generation of the habit. And then one would have to speak about the distinction of these two partial causes, and how they per se make one total cause, in the way spoken above in distinction 3 in the question ‘On the Cause of Generated Knowledge’ [I d.3 nn.495-498].

33. [A doubt] - But then there is a doubt. Since these two [sc. power and habit] are not causes of the same order, as are two people hauling a boat, - which of them has the idea of prior cause?

34. It seems that the habit does, because it belongs to the prior cause to determine the second and not conversely; but the habit determines the power toward act; and it gives inclination to it, and not conversely; but to give inclination belongs to the superior in respect of the inferior, and not conversely

35. But the opposite of this seems to be the case:

First, because the power uses the habit and not conversely, - because what uses another in acting is more principal than it, and that which it uses is as it were the instrument or the second cause with respect to it [I d.3. n.562]

36. Likewise, the power is more unlimited in acting than the habit, because it extends to more things; but the superior cause seems to be more unlimited in extent;     therefore etc     . [ibid. n.559].

37. Further, third, a habit is a natural cause. Therefore if it be the principal cause, which moves the power, it would move it by way of nature and consequently the power, since it acts in the way in which it is moved, would act by way of nature; for an agent that acts insofar as it is moved - if it be moved by way of nature - also acts further by way of nature, and so every action of an habituated power would be natural and none free (at any rate none would be in the power of the will), which is a unfitting result.

38. Again, fourth, the habit would be the power, because it would be that by which the possessor of it can first act.

39. Again, fifth, when there are two ordered causes one of which is cause of the other, that which is cause of the other is the superior cause; but the power is the cause of the habit - at any rate by the mediation of acts - and not in any way conversely;     therefore etc     .

40. [Clarification of the opinion] - I concede, for these reasons [nn.35-39] that, by holding the habit to be a partial cause with respect to the act [n.32], the habit would be second cause and not first, but the power itself would be the first cause and absolutely would not need the habit for operating; yet it operates less perfectly without the habit than with it (and that when an equal effort on the part of the power is posited), just as, when two causes come together for one effect, one cause alone does not have power per se for an effect as perfect as both together do. And in this way there is saved why the act is more intense when from the power and the habit than when from the power alone; not indeed that the power is the cause of the substance of the act and the habit the cause of the intensity of the act (as if there were two causes corresponding to the two caused things [n.27]), but that both causes coming together are able to produce a more perfect effect than one alone [I d.3 n.296], - which effect, however, being a whole in itself and as ‘per se one’ is from the two causes, but causing in diverse order [nn.32-33].

41. [Against the opinion] - Against this opinion there is the following argument:

No things distinct in species are equivocal agent causes for each other; habit and act are distinct in species; therefore they are not equivocal agent causes for each other; but an act is necessarily an equivocal cause in the generation of a habit, an acquired habit at least, - not therefore conversely.

42. The proof of the major is that an equivocal cause contains eminently in itself the perfection of the effect; but two things distinct in species cannot eminently contain each other. - Further, in comparing the same first cause to two effects, it seems that the second of the effects would have a determinate order, immediate or mediate, prior or posterior - and that when speaking of the whole species of the second of those effects. The point is evident by induction in passions that follow the same subject, wherein there is necessarily a determinate order, that one follows the subject more immediately than the other, and that according to its whole species, so that this order does not vary in any individuals whatever of the species. Therefore with respect to the power - which is the common cause of the act and the habit - the two effects will have a determinate order, so that either necessarily the act according to its whole species would precede the habit or conversely; and since some act of necessity precedes the habit as the cause of it, the habit would not precede any act.

43. Further, if the habit is a partial and equivocal cause with respect to the act, then the cause of this cause will be more perfect than the equivocal cause of the same act (the consequence is plain, because in equivocal causes the cause of the cause is a more perfect cause than the cause closer to the thing caused); but the act is the cause of the generation of the habit; therefore if the power along with the habit can perform a perfect act [nn.32, 40], it could much more perform the same perfect act if it were under the act that generates the habit, - which seems an unfitting result, because two perfect acts cannot exist in the same power, or at any rate, if they could, it does not seem that one of them could in any way be the active principle with respect to the other.

44. Further, if the habit is as it were the second cause [n.40], supplying some degree of causality that is lacking to the power, then the habit could become so perfect that it would supply the place of the whole power; for universally, in agents of the same nature, it seems that the virtue of one could be so intensified that it would equal the two [I d.3 n.497].

45. Further, if it be held that, in the process of making more or less intense, the preexisting individual is corrupted, it would be necessary to posit that the habit is not the cause of the act, because it is corrupted in the act whereby it is made more intense; but a cause is not a cause when it is corrupted, because what does not exist is not cause of anything.