LECTIO TWELVE

             § 373. After distinguishing between potency and act, and elucidating in terms of intellectual activity the transit from one state to the other, the Philosopher now applies what he has said to the case of sensation. First, he shows how there is a transit from potency to act in sensing. Secondly, at 'They differ, however' he explains the difference between the two cases. Thirdly, at 'For the present it is sufficiently established', he recapitulates what has been said about sensation.

             Regarding the first point, we must take into account that, as in intellectual cognition, so too in sensation, potency and act are each two-fold. For what so far possesses no sense-faculty but is due by nature to have one, is in potency to sensation; and what has the sense-faculty, but does not yet sense, is in potency to actual sensation in the same way as we have seen in the case of acquired intellectual knowledge. Now, as a subject moves from primary potency into primary actuality when it acquires knowledge through teaching, so too a subject's primary potency to the possession of a sense-faculty is actualised by his birth. But whereas a sense-faculty is natural to every animal,--so that in the act of being generated it acquires a sense-faculty along with its own specific nature--the case is not the same with intellectual knowledge; this is not naturally inborn in man; it has to be acquired through application and discipline.

             § 374. This is what he means by saying that 'the first change in the sensitive being' is caused by the parent. This 'first change', he explains, is from sheer potency to the primary actuality; and it is due to the parent; because there is a power in the semen to actualise the sensitive soul with all its capacities. Once an animal has been generated it has its senses in the same way as a man who has been taught possesses knowledge. And when it actually senses it corresponds to the man who actually exercises his knowledge by thinking.

             § 375. Then at 'They differ, however', he sets himself to discriminate between actual sensation and thinking; and he finds the first reason for distinguishing these activities in the difference between their objects, i.e. the sense-objects and intelligible objects which are attained by actual sensation and actual thinking respectively. The sense-objects which actuate sensitive activities--the visible, the audible, etc.--exist outside the soul; the reason being that actual sensation attains to the individual things which exist externally; whereas rational knowledge is of universals which exist somehow within the soul. Whence it is clear that the man who already has scientific knowledge about certain things does not need to seek such things outside himself; he already possesses them inwardly, and is able, unless prevented by some incidental cause, to reflect on them whenever he pleases. But a man cannot sense whatever he pleases; not possessing sense-objects inwardly, he is forced to receive them from outside.

             § 376. And as with sense-activities, so with the sciences of sense-objects; for the latter are individual things existing outside the soul. Therefore a man cannot speculate scientifically on any sense-objects, but only on such as he perceives in sensation. But there will be time to treat conclusively of this matter later on, in Book III, where we discuss the intellect and its relation to the senses.

             § 377. Concerning what is said here, we have to ask ourselves (a) why sensation is of individual things, whereas science is of universals; and (b) how exactly universals exist in the soul.

             As to (a) we should note that while the sense-faculty is always the function of a bodily organ, intellect is an immaterial power--it is not the actuality of any bodily organ. Now everything received is received in the mode of the recipient. If then all knowledge implies that the thing known is somehow present in the knower (present by its similitude), the knower's actuality as such being the actuality of the thing known, it follows that the sense-faculty receives a similitude of the thing sensed in a bodily and material way, whilst the intellect receives a similitude of the thing understood in an incorporeal and immaterial way. Now in material and corporeal beings the common nature derives its individuation from matter existing within specified dimensions, whereas the universal comes into being by abstraction from such matter and all the individuating material conditions. Clearly, then, a thing's similitude as received in sensation represents the thing as an individual; as received, however, by the intellect it represents the thing in terms of a universal nature. That is why individuals are known by the senses, and universals (of which are the sciences) by the intellect.

             § 378. As to (b), note that the term 'universal' can be taken in two senses. It can refer to the nature itself, common to several things, in so far as this common nature is regarded in relation to those several things; or it can refer to the nature taken simply in itself. Similarly, in a 'white thing' we can consider either the thing that happens to be white or the thing precisely as white. Now a nature--say, human nature,--which can be thought of universally, has two modes of existence: one, material, in the matter supplied by nature; the other, immaterial, in the intellect. As in the material mode of existence it cannot be represented in a universal notion, for in that mode it is individuated by its matter; this notion only applies to it, therefore, as abstracted from individuating matter. But it cannot, as so abstracted, have a real existence, as the Platonists thought; man in reality only exists (as is proved in the Metaphysics, Book VII) in this flesh and these bones. Therefore it is only in the intellect that human nature has any being apart from the principles which individuate it.

             § 379. Nevertheless, there is no deception when the mind apprehends a common nature apart from its individuating principles; for in this apprehension the mind does not judge that the nature exists apart; it merely apprehends this nature without apprehending the individuating principles; and in this there is no falsehood. The alternative would indeed be false--as though I were so to discriminate whiteness from a white man as to understand him not to be white. This would be false; but not if I discriminate the two in such wise as to think of the man without giving a thought to his whiteness. For the truth of our conceptions does not require that, merely apprehending anything, we apprehend everything in it. Hence the mind abstracts, without any falsehood, a genus from a species when it understands the generic nature without considering the differences; or it may abstract the species from individuals when it understands the specific nature, without considering the individuating principles.

             § 380. It is clear, then, that universality can be predicated of a common nature only in so far as it exists in the mind: for a unity to be predicable of many things it must first be conceived apart from the principles by which it is divided into many things. Universals as such exist only in the soul; but the natures themselves, which are conceivable universally, exist in things. That is why the common names that denote these natures are predicated of individuals; but not the names that denote abstract ideas. Socrates is a 'man', not a 'species'--although 'man' is a 'species'.

             § 381. Finally, at 'For the present etc.' he recapitulates his remarks on sensation and observes that only now has it become clear that what we call potency has more than one meaning. It is in one sense that we say that a boy can be a soldier, i.e. by a remote potentiality. But in another sense we say that a grown man can be a soldier, i.e. by proximate potentiality. And the same distinction applies to sense-perception; as we have seen, there are two ways of being in potency to sense anything. Though we have found no terms to express this difference, we have seen, nevertheless, that the two kinds of potency differ, and how they differ.

             § 382. And in spite of the fact that a thing which passes from the second stage of potency into act, through actualising its sense-faculty, ought not, strictly speaking, to be said to be 'altered' or 'acted upon', we cannot help using these terms; and this because the sense-faculty is potentially such as the sense-object is actually. It follows that, whilst at the start of the process of being acted upon the faculty is not like its object, at the term of the process it has this likeness. It was because they failed to make this distinction that the earlier philosophers thought that sense-faculties were composed of the same elements as their objects.

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