The Stoic logic (including epistemology) and physics are a prelude to their ethical theory. The ultimate concern of the Stoics, as with the Epicureans, was the question of how life ought to be lived. Moreover, both the Stoics and the Epicureans tried to answer that question by appealing to humans as natural beings. Their theory is naturalistic, in the sense that every evaluative claim they make is based entirely on their conception of the natural constitution of the human being.
The Psycho-Physical Foundations of Ethics
The Stoics claimed that the human being is a rational animal. As an animal, a human being has a body and a soul. The soul is just as corporeal as is the body, and indeed it penetrates or thoroughly intermixes with the body. The parts of the soul are to be found in different parts of the body. The "leading part" (hegemonikon) of the soul, which is the rational part, is found in the heart, and the other parts radiate out from it like the tentacles of an octopus; for example, the visual part of the soul connects the heart with the eyes, the reproductive part connects it with the reproductive organs, etc. It is the leading part which is relevant to ethics. It is the seat of "presentations and impulses, and from it rational discourse is emitted" (Diogenes Laertius Lives of Eminent Philosophers, 7.159 [II-20]).
In a sense, presentations and impulses are primordial, for all animals have them. However, because they are located in the leading part of the human soul, presentations and impulses are under the control of human reason. The most important difference is that humans have the power of assent both to presentations and to impulses: each can lead us astray. Human action, then, is to a great extent rational. Stoic ethics concerns the right use of reason. The ultimate rational agent, the "wise man" or "sage," is fully rational in everything he does, assenting only to those presentations that are true and acting only in ways that reasonable.
Non-human animals act according to impulse, according to what is suitable to their constitution. That animals pursue what is suitable, what is congenial to their own nature, was obvious to the Stoics: nature makes an animal congenial to itself. "For it is not likely that nature would make an animal alienated from itself, nor having made the animal, to make it neither congenial to nor alienated from itself" (Diogenes Laertius Lives of Eminent Philosophers, 7.85 [II-20]). This claim conflicts with the observations of the Epicureans that animals naturally seek pleasure as an end in itself, since "pleasure is, if anything, a byproduct which supervenes when nature itself, on its own, seeks out and acquires what is suitable to [the animal's] constitution" (Diogenes Laertius Lives of Eminent Philosophers, 7.86 [II-20])
Rational animals, as animals, must be assumed to behave in the same way. Since our constitution as human beings is to be rational, what is natural to us is "the life according to reason." There may have been disagreement among the Stoics about what such a life entails. John Stobaeus (Anthology 2, 6a [II-95]) lists the following accounts of the goal of life:
There is a great difference between these two, for the later Stoics clearly believed that there is a specific rational principle with which one should live in agreement, namely, the rational principle that governs the cosmos. Diogenes describes Chrysippus' position as follows:
For our natures are parts of the nature of the universe. Therefore, the goal becomes "to live consistently with nature," i.e., according to one's own nature and that of the universe, doing nothing which is forbidden by the common law, which is right reason, penetrating all things, being the same as Zeus who is the leader of the administration of things. (Diogenes Laertius, Lives of Eminent Philosophers 7.88 [II-94])What is suitable to our own nature is suitable to that of the universe, because the universe has the same constitution as do we: it is a rational animal. When the "daimon" (god) in us harmonizes with the will of the universe, the goal has been attained.
An important distinction between the earlier and later formulations of the goal is that the last two stress success in doing what is natural, while the others do not. To say that reason is used rightly could mean either that one makes appropriate use of reason given the information one has, or that one makes decisions which turn out to be the correct ones. For the most part, the Stoics believed that the use of reason itself, rather than the outcome of its use, which determines the worth of human action.
To live according to virtue just is to live in agreement with nature. That virtue is the single goal of life had been taught by the Cynic Antisthenes, whose view according to Diogenes was that "'Life according to Virtue' is the End to be sought," to which he adds, "exactly like the Stoics. For indeed there is a certain close relationship between the two schools." (Lives of Eminent Philosophers 6.104). Zeno himself was a disciple of the Cynic Crates. The identification of virtue with the goal is reasonable in that the ancient Greeks conceived of virtue as excellence, and living according to nature is the highest form of rational activity, given that it follows the divine law of the cosmos, and nothing can be better than that.
Like the Cynics, the Stoics held that virtue as well as vice exist. Our failure to live a virtuous life consists in our living contrary to divine law, due to corruption: "sometimes because of the persuasiveness of external activities and sometimes because of the influence of companions" (Diogenes Laertius, Lives of Eminent Philosophers 7.89 [II-94]). There is a close connection between virtue and knowledge, as was taught by Socrates. The Stoics believed that virtue can be taught because people do become more virtuous. The key connection is that living according to nature requires a knowledge of nature, which can only come through education. It is no accident that the perfectly virtuous person is the "wise man."
Aside from virtue conceived abstractly, the Stoics discussed the individual virtues, producing a bewildering series of classifications of virtues. The four primary virtues are described by John Stobeaus (Anthology, 2, 5b1-2 [II-95]) as follows:
An extreme doctrine held by the Stoics is that there is nothing between the base and the virtuous. The argument for this is that virtue itself is a kind of completion, so that by nature it cannot be incomplete. Thus anyone falling short of of a fully virtuous life is base, and only the wise man is virtuous, since he "does everything in accordance with all the virtues; for his every action is perfect, and so bereft of none of the virtues" (Stobaeus 5b8).
It is characteristic of Greek philosophers to maintain that there is a close connection between virtue and happiness. With the Stoics, as usual, the connection is necessary: the virtuous person is happy just by being virtuous. This is not surprising, because the Greeks understood happiness as a kind of optimal or "flourishing" state of the human being. As virtue is living a perfectly rational life, the virtuous person achieves the best condition possible for a rational animal. Chrysippus is said to have held that living consistently with nature "is the virtue of the happy man and a smooth flow of life" (Diogenes, 7.88). Hecaton is quoted as giving a more specific argument in terms of one of the virtues: "magnanimity is sufficient for making one superior to everything and if it is a part of virtue, virtue too is sufficient for happiness, holding in contempt even those things which seem to be bothersome" (Diogenes, 7.128).
Just as virtue is identified with the goal of life, the good is identified with the virtuous. The Stoics understood goodness to be that which confers benefit. "Good is in general that from which there is something beneficial" (Diogenes Laertius, Lives of Eminent Philosophers, 7.94 [II-94]). What is beneficial to the rational animal is that he live in accordance with nature, i.e., to be virtuous. The inseparability of goodness from virtue is brought out in another "particular" definition of the good, which guarantees that it be identical to the virtuous: "that which is perfectly in accord with nature for a rational being, qua rational. And virtue is such a thing" (Diogenes, 7.94). What is bad is the opposite of good, and hence it is always some vice or other. We are told that joy and good spirits are supervenient byproducts of good, while low spirit and depression are product of of bad things. (Joy itself is called a virtue, and it must be distinguished from pleasure, to be discussed below.)
As with virtue, there is an elaborate classification of kinds of goods and relation of them to specific virtues. One sentence gives the flavor of this scheme: "Every good is advantageous and binding and profitable and useful and well-used and honourable and beneficial and worth choosing and just" (Diogenes, 7.98). One of the more interesting aspects of the Stoic doctrine of the good is its treatment of "things indifferent." Some indifferent things are those which simply do not provoke impulse, such as whether one has an odd or even number of hairs on one's head. Others are those which do not necessarily contribute to happiness or unhappiness, including wealth, health, strength, beauty, reputation. "For it is possible to be happy even without these things, since it is a certain kind of use of them which brings happiness or unhappiness" (Diogenes, 7.104).
This classification of apparent goods as "indifferent" is mitigated by their division into the "preferred," the "rejected" and what is neither. Thus, wealth, health, strength, etc. are generally to be preferred, either because they are "according to nature" or because they have a certain degree of utility. As far as actions are concerned, some are "appropriate," others "inappropriate," and yet others neither of the two. Appropriate actions are those which we are constrained to do by reason. Living according to virtue is always appropriate, while other actions are appropriate only sometimes. Generally, there is a close correlation between appropriate actions and preferred indifferents, though there are times when one might appropriately sacrifice what might be a preferred state, such as one's health, for a good reason.
One the most famous aspects of the Stoic ethical theory is its advocacy of rational control over the passions. What is unique about the Stoic theory is that it describes the passions--pain, pleasure, fear, desire--as judgments. For example, pleasure is "an irrational elation over what seems to be worth choosing" (Diogenes, 7.114). The judgmental aspect might best be brought out by contrasting pleasure with the "good state" of joy, which is "a reasonable elation" (Diogenes, 7.116). So pleasure shares with joy a certain feeling, but it involves a mistaken judgment that something not worth choosing is really worth choosing. So by making only reasonable judgments, one eliminates the passions altogether. "They say that the wise man is also free of passions, because he is not disposed to them" (Diogenes, 7.11). The Stoic psychology made it possible to hold this as an ideal, since our judgments are one and all products of the leading part of the soul, which is rational. (By contrast, Plato (Republic, 436ff) had postulated that the soul has a separate, irrational, part which is the seat of desire.) As with virtue and the good, the Stoics tried to give a systematic accounting for all the passions.
Unlike the Epicureans, the Stoics promoted participation in the life of society as a whole. The wise man is well-suited for civic life, due to his overall excellence. (Diogenes, 7.121-2) His rationality makes him lawful and suitable as a ruler (Stobaeus, 11i). Among the virtues are "public-spiritedness" which is "knowledge of fairness in a community," and "fair-dealing," a "knowledge of how to deal with one's neighbors blamelessly" (Stobaeus, 5b2). In general, the good concerns nature as a whole, which makes the benefit of all worth promoting. This kind of thinking was taken to some extremes, as with the doctrine that wives should be held in common by wise men. Another unusual aspect of their doctrine was that, in the interests of what is beneficial, it is sometimes permissible to eat human flesh. Thus there is a distinct utilitarian streak in the Stoic ethics--so strong that it can lead to prescriptions that violate strongly-held conventional beliefs about appropriate behavior. But it is important to remember that the only end is that of the universe as a whole, and certainly not the pleasure of large numbers of individual human beings, most (if not all) of whom are base.