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.

On the Truth of the Catholic Faith: pts. 1-2. Providence (ed. 1956)