Whether the intellect can be false?
Objection 1: It would seem that the intellect can be false; for the Philosopher says (Metaph. vi, Did. v, 4) that "truth and falsehood are in the mind." But the mind and intellect are the same, as is shown above (Q 79, A 1). Therefore falsehood may be in the mind.
Objection 2: Further, opinion and reasoning belong to the intellect. But falsehood exists in both. Therefore falsehood can be in the intellect.
Objection 3: Further, sin is in the intellectual faculty. But sin involves falsehood: for "those err that work evil" (Prov. 14:22). Therefore falsehood can be in the intellect.
On the contrary, Augustine says (QQ. 83, qu. 32), that "everyone who is deceived, does not rightly understand that wherein he is deceived." And the Philosopher says (De Anima iii, 10), that "the intellect is always true."
I answer that, The Philosopher (De Anima iii, 6) compares intellect with sense on this point. For sense is not deceived in its proper object, as sight in regard to color; has accidentally through some hindrance occurring to the sensile organ---for example, the taste of a fever-stricken person judges a sweet thing to be bitter, through his tongue being vitiated by ill humors. Sense, however, may be deceived as regards common sensible objects, as size or figure; when, for example, it judges the sun to be only a foot in diameter, whereas in reality it exceeds the earth in size. Much more is sense deceived concerning accidental sensible objects, as when it judges that vinegar is honey by reason of the color being the same. The reason of this is evident; for every faculty, as such, is "per se" directed to its proper object; and things of this kind are always the same. Hence, as long as the faculty exists, its judgment concerning its own proper object does not fail. Now the proper object of the intellect is the "quiddity" of a material thing; and hence, properly speaking, the intellect is not at fault concerning this quiddity; whereas it may go astray as regards the surroundings of the thing in its essence or quiddity, in referring one thing to another, as regards composition or division, or also in the process of reasoning. Therefore, also in regard to those propositions, which are understood, the intellect cannot err, as in the case of first principles from which arises infallible truth in the certitude of scientific conclusions.
The intellect, however, may be accidentally deceived in the quiddity of composite things, not by the defect of its organ, for the intellect is a faculty that is independent of an organ; but on the part of the composition affecting the definition, when, for instance, the definition of a thing is false in relation to something else, as the definition of a circle applied to a triangle; or when a definition is false in itself as involving the composition of things incompatible; as, for instance, to describe anything as "a rational winged animal." Hence as regards simple objects not subject to composite definitions we cannot be deceived unless, indeed, we understand nothing whatever about them, as is said Metaph. ix, Did. viii, 10.
Reply to Objection 1: The Philosopher says that falsehood is in the intellect in regard to composition and division. The same answer applies to the Second Objection concerning opinion and reasoning, and to the Third Objection, concerning the error of the sinner, who errs in the practical judgment of the appetible object. But in the absolute consideration of the quiddity of a thing, and of those things which are known thereby, the intellect is never deceived. In this sense are to be understood the authorities quoted in proof of the opposite conclusion.
I · Q. 85, Art. 7: Whether one person can understand one and the same thing better than another can?
Whether one person can understand one and the same thing better than another can?
Objection 1: It would seem that one person cannot understand one and the same thing better than another can. For Augustine says (QQ. 83, qu. 32), "Whoever understands a thing otherwise than as it is, does not understand it at all. Hence it is clear that there is a perfect understanding, than which none other is more perfect: and therefore there are not infinite degrees of understanding a thing: nor can one person understand a thing better than another can."
Objection 2: Further, the intellect is true in its act of understanding. But truth, being a certain equality between thought and thing, is not subject to more or less; for a thing cannot be said to be more or less equal. Therefore a thing cannot be more or less understood.
Objection 3: Further, the intellect is the most formal of all that is in man. But different forms cause different species. Therefore if one man understands better than another, it would seem that they do not belong to the same species.
On the contrary, Experience shows that some understand more profoundly than do others; as one who carries a conclusion to its first principles and ultimate causes understands it better than the one who reduces it only to its proximate causes.
I answer that, A thing being understood more by one than by another may be taken in two senses. First, so that the word "more" be taken as determining the act of understanding as regards the thing understood; and thus, one cannot understand the same thing more than another, because to understand it otherwise than as it is, either better or worse, would entail being deceived, and such a one would not understand it, as Augustine argues (QQ. 83, qu. 32). In another sense the word "more" can be taken as determining the act of understanding on the part of him who understands; and so one may understand the same thing better than someone else, through having a greater power of understanding: just as a man may see a thing better with his bodily sight, whose power is greater, and whose sight is more perfect. The same applies to the intellect in two ways. First, as regards the intellect itself, which is more perfect. For it is plain that the better the disposition of a body, the better the soul allotted to it; which clearly appears in things of different species: and the reason thereof is that act and form are received into matter according to matter's capacity: thus because some men have bodies of better disposition, their souls have a greater power of understanding, wherefore it is said (De Anima ii, 9), that "it is to be observed that those who have soft flesh are of apt mind." Secondly, this occurs in regard to the lower powers of which the intellect has need in its operation: for those in whom the imaginative, cogitative, and memorative powers are of better disposition, are better disposed to understand.
The reply to the First Objection is clear from the above; likewise the reply to the Second, for the truth of the intellect consists in the intellect understanding a thing as it is.
Reply to Objection 3: The difference of form which is due only to the different disposition of matter, causes not a specific but only a numerical difference: for different individuals have different forms, diversified according to the difference of matter.