The Ways to Wisdom

Aquinas Day By Day


Aquinas’s topic: the three acts of the mind and the parts of logic based on them

Scripture: “Thus do I pour out instruction like prophecy and bestow it on generations to come.” Sirach 24:31

Aquinas’s text: Exposition libri peryermenias, Bk. 1, lec. 1, no. 1

As the Philosopher says in On the Soul 3, there is a twofold operation of the intellect. One is the understanding of indivisibles, by which the intellect apprehends the essence of a each thing in itself; the other is the operation of the intellect composing and dividing. Then one must add a third operation, reasoning, by which reason proceeds from what is known to investigate the unknown. The first of these operations is ordered to the second, because there can be no composition and division without first apprehending simple things. And the second operation in turn is ordered to the third, because it is necessary to proceed from a truth known to which the intellect assents in order to attain certitude about things not known.

Since logic is called rational science, it must direct its consideration to what pertains to the three operations of reason just mentioned. Therefore, what pertains to the first operation of the intellect, that is, what is conceived by simple understanding, Aristotle treats in his book the Categories. What pertains to the second operation of the intellect, that is, the affirmative and negative proposition, the Philosopher treats in his book On Interpretation. And what pertains to the third operation he treats in his book Prior Analytics and in the books that follow it. There he treats the syllogism as such, the different kinds of syllogisms, and the species of argument reason uses to proceeds from one point to another. Therefore, following the order of the three operations, the book of Categories is ordered to the book On Interpretation, which in turn is ordered to the Prior Analytics, and so on.

Sicut dicit philosophus in III de anima, duplex est operatio intellectus: una quidem, quae dicitur indivisibilium intelligentia, per quam scilicet intellectus apprehendit essentiam uniuscuiusque rei in seipsa; alia est operatio intellectus scilicet componentis et dividentis. Additur autem et tertia operatio, scilicet ratiocinandi, secundum quod ratio procedit a notis ad inquisitionem ignotorum. Harum autem operationum prima ordinatur ad secundam: quia non potest esse compositio et divisio, nisi simplicium apprehensorum. Secunda vero ordinatur ad tertiam: quia videlicet oportet quod ex aliquo vero cognito, cui intellectus assentiat, procedatur ad certitudinem accipiendam de aliquibus ignotis.

Cum autem logica dicatur rationalis scientia, necesse est quod eius consideratio versetur circa ea quae pertinent ad tres praedictas operationes rationis. De his igitur quae pertinent ad primam operationem intellectus, idest de his quae simplici intellectu concipiuntur, determinat Aristoteles in libro praedicamentorum. De his vero, quae pertinent ad secundam operationem, scilicet de enunciatione affirmativa et negativa, determinat philosophus in libro perihermeneias. De his vero quae pertinent ad tertiam operationem determinat in libro priorum et in consequentibus, in quibus agitur de syllogismo simpliciter et de diversis syllogismorum et argumentationum speciebus, quibus ratio de uno procedit ad aliud. Et ideo secundum praedictum ordinem trium operationum, liber praedicamentorum ordinatur ad librum perihermeneias, qui ordinatur ad librum priorum et sequentes.

[Introductions and translations © R.E. Houser]

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The Center for Thomistic Studies at the University of St. Thomas is the only graduate philosophy program uniquely focused on the thought of St. Thomas Aquinas in the United States. The Center is founded on the Church’s insistence of the perennial value of the thought of Aquinas as the new millennium proceeds.
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