He knows that adultery is wrong because it attacks the welfare of the family which is the basic unit of society. Lying is wrong because it misuses the faculty designed for human communication, which would become an impossibility unless we had the right to presume that our fellow men were telling us the truth. And so forth. Conclusions such as these are the basis of the laws by which man governs himself in every society and at all times in history. Reason can, by the same principle that it determines a thing to be right or wrong, also determine the degree to which it is right and wrong.
Some acts are, obviously, more contrary to man's rational nature than are some others.
This recognition of what is right and reasonable, what is in accordance with man's nature, is in itself another acknowledgment of the existence of God. We admit a moral order because we see that man and the world in which he lives exist to some order and purpose. They are not, therefore, simply their own explanation, but they have been given a direction by their Creator. It is for this reason that man is acting contrary to his nature when he takes his own life, for this life is not his to use in any way contrary to the purpose for which it was given him. Most of the things mentioned that are generally recognized as wrong are forbidden by the laws of civilized society.