For the universe is governed not only by law, but by the law of reason, and we, in following our own rational nature, are ipso facto conforming ourselves to the laws of the larger world. In a sense, of course, there is no possibility of our disobeying the laws of nature, for we, like all else in the world, act of necessity. It is not to be supposed that a genuine solution of this difficulty is to be found in Stoic philosophy. They urged, however, that, though we will in any case do as the necessity of the world compels us, it is given to us alone, not merely to obey the law, but to assent to our own obedience, to follow the law consciously and deliberately, as only a rational being can. Virtue, then, is the life according to reason.
Morality is simply rational action.
It is the universal reason which is to govern our lives, not the caprice and self-will of the individual. The wise man consciously subordinates his life to the life of the whole universe, and recognizes himself as a cog in the great machine. Now the definition of morality as the life according to reason is not a principle peculiar to the Stoics. Both Plato and Aristotle taught the same. In fact, it is the basis of every ethic to found morality upon reason, and not upon the particular foibles, feelings, or intuitions, of the individual self.