It would be superfluous to receive by faith, things that can be known by natural reason

Given the sin of impiety through which they [the Romans] sinned against the divine nature [by idolatry], the punishment that led them to sin against their own nature followed.... I say, therefore, that since they changed into lies [by idolatry] the truth about God, He brought them to ignominious passions, that is, to sins against nature; not that God led them to evil, but only that he abandoned them to evil.

We set forth our petitions before God, not in order to make known to Him our needs and desires, but rather so that we ourselves may realize that in these things it is necessary to turn to God for help.

Grace does not destroy nature, it perfects it.

The truth of the Christian faith surpasses the capacity of reason.

It is altogether unlawful to kill oneself... Wherefore suicide is contrary to the inclination of nature, and to charity whereby every man should love himself... Life is God's gift to man, and is subject to His power, Who kills and makes to live. Hence whoever takes his own life, sins against God... for it belongs to God alone to pronounce sentence of death and life.

For it is necessary in every practical science to proceed in a composite (i.e. deductive) manner. On the contrary in speculative science, it is necessary to proceed in an analytical manner by breaking down the complex into elementary principles.