Adapted from A Guide to Stoicism by George Stock (1915)

Among the Greeks and Romans of the classical age, philosophy occupied the place taken by religion in some later societies. Their appeal was to reason, not to revelation. To what, asks Cicero in his Offices, are we to look for training in virtue, if not to philosophy? Many people today are born into certain religions or religious denominations, but it was of his own free choice that the serious-minded young Greek or Roman embraced the tenets of one of the great sects which divided the world of philosophy. Conversions from one sect to another were of quite rare occurrence. A certain Dionysius of Heraclea, who went over from the Stoics to the Cyrenaics, was ever afterward known as "the deserter." It was as difficult to be independent in philosophy as it is with us to be independent in politics. When a young man joined a school, he committed himself to all its opinions, not only as to the end of life, which was the main point of division, but as to all questions on all subjects. The Stoic did not differ merely in his ethics from the Epicurean; he differed also in his theology and his physics and his metaphysics.

The life span of Zeno, the founder of Stoicism, was from B.C.E. 347 to 275. He did not begin teaching till 315, at the mature age of forty. Aristotle had passed away in 322, and with him closed the great constructive era of Greek thought. The Ionian philosophers had speculated on the physical constitution of the universe, the Pythagoreans on the mystical properties of numbers; Heraclitus had propounded his philosophy of fire, Democritus and Leucippus had struck out a rude form of the atomic theory, Socrates had raised questions relating to man, Plato had discussed them with all the freedom of the dialogue, while Aristotle had systematically worked them out. The later schools did not add much to the body of philosophy. What they did was to emphasize different sides of the doctrine of their predecessors and to drive views to their logical consequences. The great lesson of Greek philosophy is that it is worthwhile to do right irrespective of reward and punishment and regardless of the shortness of life. This lesson the Stoics so enforced by the earnestness of their lives and the influence of their moral teaching that it has become associated more particularly with them. 

The Greeks were all agreed that there was an end or aim of life, and that it was to be called "happiness," but at that point their agreement ended. As to the nature of happiness there was the utmost variety of opinion. Democritus had made it consist in mental serenity, Anaxagoras in speculation, Socrates in wisdom, Aristotle in the practice of virtue with some amount of favor from fortune, Aristippus simply in pleasure. Zeno's contribution to thought on the subject does not at first sight appear illuminating. He said that the end was "to live consistently," the implication doubtless being that no life but the passionless life of reason could ultimately be consistent with itself. Cleanthes, his immediate successor in the school, is credited with having added the words "with nature," thus completing the well-known Stoic formula that the end is "to live consistently with nature."

It was assumed by the Greeks that the ways of nature were "the ways of pleasantness," and that "all her paths" were "peace." This may seem to us a startling assumption, but that is because we do not mean by "nature" the same thing as they did. We connect the term with the origin of a thing, they connected it rather with the end; we mean by a thing's nature what it is or has been, they meant what it ought to become under the most favorable conditions. Hence we find Aristotle maintaining that the State is a natural product, because it is evolved out of social relations which exist by nature. Nature indeed was a highly ambiguous term to the Greeks no less than to ourselves, but in the sense with which we are now concerned, the nature of anything was defined by the Peripatetics as "the end of its becoming." Another definition of theirs puts the matter still more clearly. "What each thing is when its growth has been completed, that we declare to be the nature of each thing."

Following out this conception the Stoics identified a life in accordance with nature with a life in accordance with the highest perfection to which man could attain. Now, as man was essentially a rational animal, his work as man lay in living the rational life. And the perfection of reason was virtue. Hence the ways of nature were no other than the ways of virtue. And so it came about that the Stoic formula might be expressed in a number of different ways which yet all amounted to the same thing. The end was to live the virtuous life, or to live consistently, or to live in accordance with nature, or to live rationally.