Translation: Aquinas on powers 3

Thomas Aquinas
Commentary on the Sentences
Book I, question 4, article 2

Are the powers of the mind its essence?

In response, it should be said that any proper and immediate effect must be proportionate to its cause. Whence, in all things in which the proximate source [principia] of its operation belongs in the genus of substance, its operation is its substance, and this is only true of God. For this reason, he alone does not act through the mediation of a power that differs from his substance. But for every other thing, its operation is an accident, and for this reason, the proximate source of its operation must be an accident too, just as we saw in bodies: the substantial form of fire [for instance] has no operation except through the mediation of its active and passive qualities, which are, as it were, forces or powers of it.

Similarly, I say that no operation comes forth from the mind, since it is a substance, except through the mediation of a power, nor does an operation come forth from a highly developed mental ability except through the mediation of a habit.

But these powers flow from the essence of the mind itself, like certain perfections of the body's parts, the operation of which is effected through the mediation of the body (e.g., the senses, the imagination, and so on), and as certain things that exist in the mind itself, the operation of which does not need the body (e.g., the intellect, will, and other such things).

For this reason, I say that the mind's powers are accidents. They are not common accidents, which flow not from the principles of the species but rather from the principles of the individual. On the contrary, they are proper accidents, which follow from the species and have their origin from its principles. At the same time though, they belong to the integrity of the mind, insofar as the mind is a 'whole made up of powers' [a 'totum potentiale', as Boethius calls it], having a certain perfection of power, which is made up of diverse powers.