Appendix 18. - (250)

St. Thomas states the problem in all its force:

This passage means: 'You maintain that the intellect, when it perceives a particular object, merely perceives exactly what the senses perceive, except that it divides in the particular what is common from what is individual. Then, setting aside what is individual by abstracting it, it perceives only what is common. This way of explaining how the term of sense becomes the object of the intellect would not meet with any objection if this division, which you assume the mind makes, were real. In other words, there would be no objection were we dealing with a real being where what is common and what is individual could be divided up as a cake or a pie is cut in two, with one half being cast on one side and the other being used for some purpose. It has to be said, however, that the division made by the understanding between what is proper and what is common is not a real division but a metaphorical division, so to speak. The understanding does not, in fact, extract what is individual from a real being, leaving behind only what is common in the way we extract lees from wine, leaving behind pure wine. We are not dealing with any real abstraction and division. When a particular ens is perceived by the understanding, it does not undergo any alteration.'

Anyone who thinks he has explained how our understanding perceives what sense puts before us by saying simply that the understanding abstracts the universal from the particulars may be quite happy to accept such an analogy or a likeness despite its unsuitableness. But he has not put forward any real explanation for perceptions and intellectual intuitions. The word abstraction, therefore, is a metaphor which may satisfy the shallowminded but it does not contain any new light likely to clarify the workings of the understanding. But if we abandon this analogy of abstraction and division, which cannot properly be applied to any particular sensible thing, from which nothing can be abstracted, nothing divided, what remains to be said about the way in which the understanding perceives things?

The following points are certain:
1. No particular sensible entity undergoes any alteration or division of any kind when perceived by the understanding. Consequently, the word abstraction does not throw any new light on the explanation of intellectual acts when it is understood as an operation dividing what is common from what is proper, in any particular sensible thing.
2. An ens, in so far as it is in the understanding, has a completely (not partly) different existence from that which it has in real nature.
3. The existence which an ens has in the understanding is universal although in its own nature what is real is particular.
4. Consequently, any object, insofar as it is universal, exists solely in the understanding; this object of the understanding, this universality, is entirely different from and has no connection with the terms of sense, which are particulars. Stated in this way, the difficulty of explaining how the mind can receive its objects from sense, in the way Locke and Condillac understand this, receives its full force. St. Thomas saw the difference between the terms of sense and the objects of understanding so clearly that in refuting the error of those who accepted that the acting intellect was external to us and communicated with us by means of sensible phantasms, he was able to show the impossibility of the error. The object of the intellect is in no way part of these phantasms, as the word abstraction might implicate. It is an object completely immune from phantasms and consequently completely different from them. There is, therefore, no true communication between the idea of this intellect and the sensible phantasm. This shows the shrewdness of the holy Doctor. He was not deceived, as the Arabs were, by the metaphorical connotations of the word abstraction (See comment of St. Thomas on the book De Anima, lect. 7, 10).