Chapter XVII. Question 17 of falsity

As opposed to truth, St. Thomas treats of falsity in its relation to things, to sense, to intellect, and to truth itself.

The first article shows that natural things, in so far as they are compared with the divine intellect, are not false, because in so far they exist, inasmuch as they are from God, and are from His idea to which they conform. Yet it is possible for moral actions even to withdraw themselves from God’s rule, and therefore sins are called lies. But in relation to the created intellect things can be called false, either because they are signified by what is false, or because of their resemblance to the truth, as brass is false gold.

In the second article it is decided that falsity, formally as such, is not formally in the senses as in one knowing falsity, because the senses do not compare one thing with another. Nevertheless there is an occasion of falsity or of false judgment from the senses apprehending the thing as being like what it truly is. As remarked in this article concerning proper sensibles (such as color, sound), the. senses have no false knowledge, except accidentally, because of a defect in the organ; but of the common sensibles (such as extension, distance) and of the accidental sensibles (such as substance, life) the senses, even rightly disposed, can have a false knowledge, because of the abnormal way in which the object is proposed to the faculty; for the senses are not directly and immediately referred to these. Thus a stick half submerged in the water appears to be broken.

The third article concludes that the intellect cannot be false in the simple apprehension of a thing, but in composition and division, or in judgment, inasmuch as it attributes to a thing what does not belong to it. Thus there can accidentally be falsity in the first act of the intellect, which is apprehension, in so far as composition of the intellect is mixed up in it, for instance, if in a definition parts are united which are mutually exclusive, such as “a reasonable four-footed animal.”

Finally, in the fourth article, St. Thomas teaches that truth and falsity, which are found in the intellect, are opposed as contraries and not merely as privations, because each consists in some act, or acceptance on the part of the intellect, which is truth, indeed, according to an adequate apprehension or conformity, and falsity according to an inadequate apprehension.

Thus the questions about truth and falsity are concluded as they concern God, which is the way they must be concluded in theology.