Thomas Aquinas, Disputed Questions on Truth (De Veritate)

1. Anselm says: "Truth is a correctness perceivable only by the mind." But sense does not have the same nature as the mind. Hence, truth is not in sense.

2. Augustine proves that truth is not known by the bodily senses, and his reasons were set down above. Hence, truth is not in sense.

To the Contrary:

Augustine says: "Truth manifests that which is." But that which is, is manifested not only to the intellect, but also to sense. Therefore.

REPLY:

Truth is both in intellect and in sense, but not in the same way. It is in intellect as a consequence of the act of the intellect and as known by the intellect. Truth follows the operation of the intellect inasmuch as it belongs to the intellect to judge about a thing as it is. And truth is known by the intellect in view of the fact that the intellect reflects upon its own act--not merely as knowing its own act, but as knowing the proportion of its act to the thing. Now, this proportion cannot be known without knowing the nature of the act; and the nature of the act cannot be known without knowing the nature of the active principle, that is, the intellect itself, to whose nature it belongs to be conformed to things. Consequently, it is because the intellect reflects upon itself that it knows truth.

Truth is in sense also as a consequence of its act, for sense judges of things as they are. Truth is not in sense, however, as something known by sense; for, although sense judges truly about things, it does not know the truth by which it truly judges. Although sense knows that it senses, it does not know its own nature; consequently, it knows neither the nature of its act nor the proportion of this act to things. As a result, it does not know its truth.

The reason for this is that the most perfect beings, such as, for example, intellectual substances, return to their essence with a complete return: knowing something external to themselves, in a certain sense they go outside of themselves; but by knowing that they know, they are already beginning to return to themselves, because the act of cognition mediates between the knower and the thing known. That return is completed inasmuch as they know their own essences. Hence, it is said in The Causes: "A being which is such as to know its own essence returns to it by a complete return."

Since sense is closer to an intellectual substance than other things are, it begins to return to its essence; it not only knows the sensible, but it also knows that it senses. Its return, however, is not complete, since it does not know its own essence. Avicenna has given the reason for this by pointing out that the sense knows nothing except through a bodily organ, and a bodily organ cannot be a medium between a sensing power and itself. But powers without any ability to sense cannot return to themselves in any way, for they do not know that they are acting. For example, fire does not know that it is heating.

From this discussion the solutions to the difficulties are clear.