To the converse question, whether intelligent cognition comes from things of sense, Thomas answers, following Aristotle: “One cannot say that sense perception is the whole cause of intellectual cognition, but rather in a certain way is the matter of the cause (materia causae).” On the other hand,
“it is impossible that the mind, in the state of the present life, wherein it is joined to the passive body (passibili corpori), should know anything actually (actu) except by turning itself to images (phantasmata). And this appears from two arguments. In the first place, since the mind itself is a power (vis) using no bodily organ, its action would not be interrupted by an injury to any bodily organ, if for its action there was not needed the action of some faculty using a bodily organ. Sense and imagination use a bodily organ. Hence as to what the mind knows actually (actu), there is needed the action of the imagination and other faculties, both in receiving new knowledge and in using knowledge already acquired. For we see that when the action of the imaginative faculty is interrupted by injury to an organ, as with the delirious, the man is prevented from actually knowing those things of which he has knowledge. Secondly (as any one may observe in himself), whenever he attempts to know (intelligere) anything, he forms images by way of example, in which he may contemplate what he is trying to know. And whenever we wish to make any one else understand, we suggest examples, from which he may make for himself images to know by.
“The reason of this is that the knowing faculty is suited to the knowable (potentia cognoscitiva proportionatur cognoscibili). The appropriate object of the intelligence of an angel, who is separate from all body, is intelligible immaterial substance (substantia intelligibilis a corpore separata); through this kind of intelligible he cognizes also material things. But the appropriate object of the human mind, which is joined to a body, is the essence or nature (quidditas sive natura) existing in material body; and through the natures of visible things of this sort it ascends to some cognition of invisible things. It belongs to the idea (ratio) of this nature that it should exist in some individual having corporeal matter, as it is of the concept (ratio) of the nature of stone or horse that it should be in this stone or this horse. Hence the nature of a stone or any material thing cannot be known completely and truly, unless it is known as existing in some particular [instance]. We apprehend the particular through sense and imagination; and so it is necessary, in order that the mind should know its appropriate object, that it should turn itself to images, in order to behold the universal nature existing in the particular. If, indeed, the appropriate object of our intelligence were the separate form, or if the form of sensible things did not subsist in the particular [instances], as the Platonists say, our mind in knowing would have no need always to turn itself to images” (Qu. lxxxiv. Art. 7).
It is next queried whether the judgment of the mind is impeded through binding (per ligamentum) the senses. In view of the preceding argument the answer is, that since “all that we know in our present state, becomes known to us through comparison with sensible things, it is impossible that there should be in us perfect mental judgment when the senses are tied, through which we take cognizance of sensible things” (Qu. lxxxiv. Art. 8).
This entire argument shows in what firm Aristotelian manner, scholasticism, in the person of Thomas, set itself upon a basis of sense perception; through which it still pressed to a knowledge of the supersensible and abstract. In this argument we also see, as always with Thomas, that knowledge is perfect and blessed, the more immaterial and abstract are its modes. All of which will continue to impress us as we follow Thomas, briefly, through his exposition of the modus and ordo of knowing (intelligendi) (Qu. lxxxv.).
The first question is whether our mind knows corporeal things by abstracting the species from the images—the type from the particular. There are three grades of the cognizing faculty (virtutis cognoscitivae). The lowest is sensation, which is the act of a bodily organ. Its appropriate object is form as existing in matter. And since matter is the principle of individuation (i.e. the particularizing principle from which results the particular or individual), sense perception is confined to the particular. The highest grade of the cognitient faculty is that which is independent of bodily organs and separate from matter, as the angelic intelligence; and its object is form subsisting without matter. For though angels know material things, they view them only in the immaterial, to wit, themselves or God. Between the two is the human mind, which
“is the forma of the body. So it naturally knows form existing individually in corporeal matter, and yet not as form is in such matter. But to know form, which is in concrete matter, and yet know it not as it is in such matter, is to abstract it from this particular matter which the images represent. It follows that our intelligence knows material things by abstracting them from images; and through reflecting on these material abstractions we reach some cognition of the immaterial, just as conversely the angels know the material through the immaterial” (Qu. lxxxv. Art. 1).
It is next proved that the soul, through the intelligible species or forms abstracted from particulars, knows things which are outside the soul. In a way, intellection arises from sense perception; therefore the sense perception of the particular precedes the intellectual knowledge of universals. But, on the other hand, the intelligence, in coming to perfect cognition, proceeds from the undistinguished to the distinguished, from the more to the less general, and so knows animal before it knows homo, and homo before it knows Socrates. The next conclusion reads very neatly in scholastic Latin, but is difficult to paraphrase: it is that the intelligence may know many things at once (simul) per modum unius, but not per modum multorum; that is to say, the mind may grasp at once whatever it may grasp under one species, but cannot know a number of things at once which fall under different species.
Next as to what our mind knows in material things (Qu. lxxxvi.). It does not know the particular or singular (singularia) in them directly; for the principle of singularity in material things is the particular matter. But our mind knows by abstracting from such the species, that is, the universal. This it knows directly. But it knows singularia indirectly, inasmuch as, when it has abstracted the intelligible species, it must still, in order to know completely (actu), turn itself to the images in which it knows the species.
How does the anima intellectiva know itself, and those things which are in it (Qu. lxxxvii.)? Everything is knowable in so far as it is actually (in actu) and not merely potentially. So the human intelligence knows itself not through its essence, which is still but potential, but in so far as it has actually realized itself; knows itself, that is, through its actuality. The permanent qualities (habitus) of the soul exist in a condition between potentiality and actuality. The mind knows them when they are actually present or operative.