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 Obj. 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.
_______________________

SEVENTH ARTICLE [I, Q. 85, Art. 7]

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."

Obj. 2: Further, the intellect is true in its act