If a thing can be done adequately by means of one, it is superfluous to do it by means of several; for we observe that nature does not employ two instruments [if] one suffices.

There is but one Church in which men find salvation, just as outside the ark of Noah it was not possible for anyone to be saved.

The happy man in this life needs friends.

Better to illuminate than merely to shine; to deliver to others contemplated truths than merely to contemplate.

If there were some solitary or feral man, the passions of the soul would be sufficient for him; by them he would be conformed to things in order that he might have knowledge of them. But because man is naturally political and social, there is need for one man to make his conceptions known to others, which is done with speech. So significant speech was needed if men were to live together. Which is why those of different tongues do not easily live together.

It is possible to demonstrate God's existence, although not a priori, yet a posteriori from some work of His more surely known to us.

Good and evil are essential differences of the act of the will. For good and evil pertain essentially to the will; just as truth and falsehood pertain to the reason, the act of which is distinguished essentially by the difference of truth and falsehood (according as we say that an opinion is true or false.) Consequently, good and evil volition are acts differing in species.