Thomas Aquinas

“ Any proposition is said to be self-evident in itself, if its predicate is contained in the notion of the subject: although, to one who knows not the definition of the subject, it happens that such a proposition is not self-evident. For instance, this proposition, "Man is a rational being," is, in its very nature, self-evident, since who says "man," says "a rational being": and yet to one who knows not what a man is, this proposition is not self-evident. ”

“ Consequently, by the command of God, death can be inflicted on any man, guilty or innocent, without any injustice whatever. In like manner adultery is intercourse with another's wife; who is allotted to him by the law emanating from God. Consequently intercourse with any woman, by the command of God, is neither adultery nor fornication. The same applies to theft, which is the taking of another's property. For whatever is taken by the command of God, to Whom all things belong, is not taken against the will of its owner, whereas it is in this that theft consists. ”

“ For it is owing to the various conditions of men, that certain acts are virtuous for some, as being proportionate and becoming to them, while they are vicious for others, as being out of proportion to them. ”

“ Further, that which is established by law is made just. But many things are enacted by men, which are contrary to the law of nature. Therefore the law of nature can be abolished from the heart of man. ”

“ The saying of the Philosopher is to be understood of things that are naturally just, not as general principles, but as conclusions drawn from them, having rectitude in the majority of cases, but failing in a few.
Reply to Objection 3: As, in man, reason rules and commands the other powers, so all the natural inclinations belonging to the other powers must needs be directed according to reason. Wherefore it is universally right for all men, that all their inclinations should be directed according to reason.
Art. 5 - Whether the natural law can be changed? ”

“ All the inclinations of any parts whatsoever of human nature, e.g. of the concupiscible and irascible parts, in so far as they are ruled by reason, belong to the natural law, and are reduced to one first precept, as stated above: so that the precepts of the natural law are many in themselves, but are based on one common foundation. ”

“ The practical reason, on the other hand, is busied with contingent matters, about which human actions are concerned: and consequently, although there is necessity in the general principles, the more we descend to matters of detail, the more frequently we encounter defects. ”

“ The Philosopher proposes there to discover the genus of virtue; and since it is evident that virtue is a principle of action, he mentions only those things which are principles of human acts, viz. powers, habits and passions. ”

“ Now a certain order is to be found in those things that are apprehended universally. For that which, before aught else, falls under apprehension, is "being," the notion of which is included in all things whatsoever a man apprehends. ”