“It was necessary for man’s salvation that there should be a knowledge revealed by God besides philosophical science built up by human reason” (Aquinas). However, “to the natural law belongs those things to which a man is inclined naturally: and among these it is proper to man to be inclined to act according to reason” (Aquinas)
It is necessary to have an understanding of the natural law for many reasons. Certainly, if Aquinas meant by “ it is proper to man to be inclined to act according to reason” simply to mean that everyone should follow their first thought in every act, he would be misunderstood. Man’s purpose is to seek and know truth, and this is the purpose of his ability to reason. Therefore, to act according to reason must mean to seek some objective truth towards which our acts must be directed.
Understanding this and the foundation behind it helps one to a deeper understanding of the truths revealed in Scripture, showing us that the “law” of God is not some merely arbitrary and positive law of Ockham’s and Calvin’s nominalist God.
We can answer the question of Socrates towards Euthyphro, as to whether things are good because the god(s) command them or if the god(s) command them because they are good is at the heart of our study. If we take a realist metaphysic and see human nature as something that truly exists (rejecting Sartre’s existentialism, etc), we will see that not only is it not an either/or question, but that Thomas is right: “ it is proper to man to be inclined to act according to reason,” and that reason will lead us to objective truths about what is right and wrong.
We will see that, indeed, “is” implies “ought.” We can know, to a great extent therefore, what we should and should not do, completely apart from revelation. This will serve at least three great purposes:
- It will give us a path to deeper insight into the purpose of the revealed moral law
- It will help us to defend the faith (at least by removing obstacles to the faith) without having to have those we witness to accept the Scripture and Tradition a priori
- It can help us toward a better understanding of revealed truth, as any interpretation that conflicts with right reasoned natural law will be untenable. (see Fr. Ashley, O.P. Living the Truth in Love, pg. 31 if you think that natural law interpreting Scripture and Scripture clarifying natural law is circular reasoning)
In studying natural law, therefore, one hopes to gain greater insight into the truth of what man should do based on what man is. And one should also better see how the theory works in practice, for after all, moral philosophy, while it certainly has is theoretical basis, is a practical discipline.