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
