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.

A person is disposed to an act of choice by an angel ... in two ways. Sometimes, a man's understanding is enlightened by an angel to know what is good, but it is not instructed as to the reason why ... But sometimes he is instructed by angelic illumination, both that this act is good and as to the reason why it is good.

Faith has to do with things that are not seen and hope with things that are not at hand.

He suddenly announced that he could not write any more since "All that I have written seems like straw to me."

For those with faith, no evidence is necessary; for those without it, no evidence will suffice.

It must be understood that prime matter, and form as well, is neither generated nor corrupted, because every generation is from something to something. Now that from which generation proceeds is matter, and that to which it proceeds is form. So that, if matter or form were generated, there would be a matter for matter and a form for form, endlessly. Whence, there is generation only of the composite, properly speaking.

All the efforts of the human mind cannot exhaust the essence of a single fly.