Thomas Aquinas, Summa Theologiae

Objection 1: It seems that falsity is not in the intellect. For Augustine says (Qq. lxxxiii, 32), "Everyone who is deceived, understands not that in which he is deceived." But falsity is said to exist in any knowledge in so far as we are deceived therein. Therefore falsity does not exist in the intellect.

Objection 2: Further, the Philosopher says (De Anima iii, 51) that the intellect is always right. Therefore there is no falsity in the intellect.

On the contrary, It is said in De Anima iii, 21,22 that "where there is composition of objects understood, there is truth and falsehood." But such composition is in the intellect. Therefore truth and falsehood exist in the intellect.

I answer that, Just as a thing has being by its proper form, so the knowing faculty has knowledge by the likeness of the thing known. Hence, as natural things cannot fall short of the being that belongs to them by their form, but may fall short of accidental or consequent qualities, even as a man may fail to possess two feet, but not fail to be a man; so the faculty of knowing cannot fail in knowledge of the thing with the likeness of which it is informed; but may fail with regard to something consequent upon that form, or accidental thereto. For it has been said (Article 2) that sight is not deceived in its proper sensible, but about common sensibles that are consequent to that object; or about accidental objects of sense. Now as the sense is directly informed by the likeness of its proper object, so is the intellect by the likeness of the essence of a thing. Hence the intellect is not deceived about the essence of a thing, as neither the sense about its proper object. But in affirming and denying, the intellect may be deceived, by attributing to the thing of which it understands the essence, something which is not consequent upon it, or is opposed to it. For the intellect is in the same position as regards judging of such things, as sense is as to judging of common, or accidental, sensible objects. There is, however, this difference, as before mentioned regarding truth (Question 16, Article 2), that falsity can exist in the intellect not only because the intellect is conscious of that knowledge, as it is conscious of truth; whereas in sense falsity does not exist as known, as stated above (Article 2).

But because falsity of the intellect is concerned essentially only with the composition of the intellect, falsity occurs also accidentally in that operation of the intellect whereby it knows the essence of a thing, in so far as composition of the intellect is mixed up in it. This can take place in two ways. In one way, by the intellect applying to one thing the definition proper to another; as that of a circle to a man. Wherefore the definition of one thing is false of another. In another way, by composing a definition of parts which are mutually exclusive. For thus the definition is not only false of the thing, but false in itself. A definition such as " a reasonable four-footed animal" would be of this kind, and the intellect false in making it; for such a statement as "some reasonable animals are four-footed" is false in itself. For this reason the intellect cannot be false in its knowledge of simple essences; but it is either true, or it understands nothing at all.

Reply to Objection 1: Because the essence of a thing is the proper object of the intellect, we are properly said to understand a thing when we reduce it to its essence, and judge of it thereby; as takes place in demonstrations, in which there is no falsity. In this sense Augustine's words must be understood, "that he who is deceived, understands not that wherein he is deceived;" and not in the sense that no one is ever deceived in any operation of the intellect.

Reply to Objection 2: The intellect is always right as regards first principles; since it is not deceived about them for the same reason that it is not deceived about what a thing is. For self-known principles are such as are known as soon as the terms are understood, from the fact that the predicate is contained in the definition of the subject.

Articulus 3

Argumentum 1

Ad tertium sic proceditur. Videtur quod falsitas non sit in intellectu.

Dicit enim Augustinus, in libro octoginta trium quaest., omnis qui fallitur, id in quo fallitur, non intelligit.

Sed falsum dicitur esse in aliqua cognitione, secundum quod per eam fallimur. Ergo in intellectu non est falsitas.

Argumentum 2

Praeterea, philosophus dicit, in III de anima, quod intellectus semper est rectus.

Non ergo in intellectu est falsitas.

Sed Contra

Sed contra est quod dicitur in III de anima, quod ubi compositio intellectuum est, ibi verum et falsum est.

Sed compositio intellectuum est in intellectu.

Ergo verum et falsum est in intellectu.

Corpus

Respondeo dicendum quod, sicut res habet esse per propriam formam, ita virtus cognoscitiva habet cognoscere per similitudinem rei cognitae. Unde, sicut res naturalis non deficit ab esse quod sibi competit secundum suam formam, potest autem deficere ab aliquibus accidentalibus vel consequentibus; sicut homo ab hoc quod est habere duos pedes, non autem ab hoc quod est esse hominem, ita virtus cognoscitiva non deficit in cognoscendo respectu illius rei cuius similitudine informatur; potest autem deficere circa aliquid consequens ad ipsam, vel accidens ei.

Sicut est dictum quod visus non decipitur circa sensibile proprium, sed circa sensibilia communia, quae consequenter se habent ad illud, et circa sensibilia per accidens.

Sicut autem sensus informatur directe similitudine propriorum sensibilium, ita intellectus informatur similitudine quidditatis rei. Unde circa quod quid est intellectus non decipitur, sicut neque sensus circa sensibilia propria. In componendo vero vel dividendo potest decipi, dum attribuit rei cuius quidditatem intelligit, aliquid quod eam non consequitur, vel quod ei opponitur. Sic enim se habet intellectus ad iudicandum de huiusmodi, sicut sensus ad iudicandum de sensibilibus communibus vel per accidens. Hac tamen differentia servata, quae supra circa veritatem dicta est, quod falsitas in intellectu esse potest, non solum quia cognitio intellectus falsa est, sed quia intellectus eam cognoscit, sicut et veritatem, in sensu autem falsitas non est ut cognita, ut dictum est.

Quia vero falsitas intellectus per se solum circa compositionem intellectus est, per accidens etiam in operatione intellectus qua cognoscit quod quid est, potest esse falsitas, inquantum ibi compositio intellectus admiscetur. Quod potest esse dupliciter.

Uno modo, secundum quod intellectus definitionem unius attribuit alteri; ut si definitionem circuli attribuat homini. Unde definitio unius rei est falsa de altera. Alio modo, secundum quod partes definitionis componit ad invicem, quae simul sociari non possunt, sic enim definitio non est solum falsa respectu alicuius rei, sed est falsa in se. Ut si formet talem definitionem, animal rationale quadrupes, falsus est intellectus sic definiendo, propterea quod falsus est in formando hanc compositionem, aliquod animal rationale est quadrupes. Et propter hoc, in cognoscendo quidditates simplices non potest esse intellectus falsus, sed vel est verus, vel totaliter nihil intelligit.

Ad 1

Ad primum ergo dicendum quod, quia quidditas rei est proprium obiectum intellectus, propter hoc tunc proprie dicimur aliquid intelligere, quando, reducentes illud in quod quid est, sic de eo iudicamus, sicut accidit in demonstrationibus, in quibus non est falsitas.

Et hoc modo intelligitur verbum Augustini, quod omnis qui fallitur, non intelligit id in quo fallitur, non autem ita, quod in nulla operatione intellectus aliquis fallatur.

Ad 2

Ad secundum dicendum quod intellectus semper est rectus, secundum quod intellectus est principiorum, circa quae non decipitur, ex eadem causa qua non decipitur circa quod quid est. Nam principia per se nota sunt illa quae statim, intellectis terminis, cognoscuntur, ex eo quod praedicatum ponitur in definitione subiecti.