Stoicism was one of the new philosophical movements of the Hellenistic period. The name derives from the decorated porch (stoa poikelê) in the Agora at Athens where the members of the school congregated. Unlike `epicurean', the sense of the English adjective `stoical' is not utterly misleading with regard to its philosophical origins. The Stoics did, in fact, believe that emotions like fear or envy either were, or arose from, false judgements and that the Stoic sage---a person who had attained moral and intellectual perfection---would not undergo them. The later Roman Stoics, Seneca and Epictetus, emphasise the doctrines that the Stoic sage is utterly immune to misfortune and that virtue is sufficient for happiness. Our phrase `stoic calm' perhaps encapsulates the general drift of these claims. It does not, however, hint at the even more radical ethical views which the Stoics defended, e.g. that only the sage is free while all others are slaves, or that all those who are morally vicious are equally so. Though it seems clear that some Stoics took a kind of perverse joy in advocating views which seem so at odds with common sense, they did not do so simply to shock. Stoic ethics achieves a certain plausibility within the context of their physical theory and psychology. It seems that they were well aware of the mutually interdependent nature of their philosophical views, likening Stoic philosophy to a living animal in which logic is bones and sinews; ethics, the flesh; and physics, the soul.

Sources of our information on the Stoics

Since the Stoics themselves stress the systematic nature of their philosophy, the ideal way to evaluate the Stoics' distinctive ethical views would be to study them within the context of a full exposition of their philosophy. Here, however, we meet with the problem about the sources of our knowledge about Stoicism. We do not possess a single complete work by any of the first three heads of the Stoic school: Zeno of Citium (344--262 BC), Cleanthes (d. 232 BC) or Chrysippus (d. 206 BC). Chrysippus was particularly prolific, writing over 400 books in 199 titles, but we have only fragments of his works. The only complete works by Stoic philosophers that we possess are those by the later Roman writers, Seneca (4 BC--65 AD), Epictetus (c. 55--135) and the Emperor Marcus Aurelius (121--180) and these works are principally focused on ethics. They tend to be long on moral exhortation but give only clues to the theoretical bases of the moral system. For detailed information about the Old Stoa (i.e. the first three heads of the school and their associates) we have to depend on either doxographers, like Diogenes Laertius (3rd c. AD) and Stobaeus (5th c. AD), or other philosophers who discuss the Stoics for their own purposes. Nearly all of the latter group are hostile witnesses. Among them are the Aristotelian commentator Alexander Aphrodisias (2nd c. AD) who criticises the Stoics in On Mixture and On Fate; the Platonist Plutarch of Chaeronia (1st-2nd c. AD) who authored works such as On Stoic Self-Contradictions and Against the Stoics on Common Conceptions; the medical writer Galen (2nd c. AD), whose outlook is roughly Platonist; the Pyhrronian skeptic, Sextus Empiricus (2nd c. AD); Plotinus (3rd c. AD) and the sixth century neoplatonist, Simplicius. Another important source is Cicero. Though his own philosophical views often seem to incline toward those of Philo of Larissa and the New Academy, he is not without sympathy for what he sees as the high moral tone of Stoicism. In works like Academics and On the Nature of the Gods he attempts to provide summaries in Latin of the views of the major Hellenistic schools of thought.

From these sources, scholars have attempted to piece together a picture of the content, and in some cases, the development of Stoic doctrine. In some areas, there is a fair bit of consensus about what the Stoics thought and we can even attach names to some particular innovations. However, in other areas the proper interpretation of our meagre evidence is hotly contested. Until recently, non-specialists have been largely excluded from the debate because many important source were not translated into modern languages. Fragments of Stoic works and testimonia in their original Greek and Latin were collected into a three-volume set in 1903--5 by H. von Arnim, entitled Stoicorum Veterum Fragmenta. In writings on the Stoics, fragments and testimonia are still often referred to by von Arnim's volume numbers and text numeration; e.g. SVF I.345 = Diogenes Laertius, Lives 4.40. In 1987, A. A. Long and David Sedley brought out the first volume of The Hellenistic Philosophers which contains English translations and commentary of many important texts on Stoics, Epicureans and Skeptics. In what follows, I will refer to texts by or about Stoics using Long and Sedley's notation, i.e. 47G = section 47 of their work, text G, unless otherwise specifically noted.

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Philosophy and Life

When considering the doctrines of the Stoics, it is important to remember that they think of philosophy not merely as an interesting pastime or a particular body of knowledge, but as a way of life. They define philosophy as a kind of practice or exercise (askêsis) in the expertise concerning what is beneficial (26A). Once we come to know what we and the world around us are really like, and especially the nature of value, we will be utterly transformed. This soteriological element is common to their main competitors, the Epicureans, and perhaps helps to explain why both were eventually eclipsed by Christianity. The Meditations of Marcus Aurelius provide a fascinating picture of a would-be Stoic sage at work on himself. The book, also called To Himself, is the emperor's diary. In it, he not only reminds himself of the content of important Stoic teaching but also reproaches himself when he realises that he has failed to incorporate this teaching into his life in some particular instance. For the influence of Stoic philosophy on a life in our times, see Admiral James Stockdale's account of his use of the philosophy of Epictetus as a prisoner of war in Vietnam (In Love and War, New York, 1984).

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Physical Theory

An examination of Stoic ontology might profitably begin with a passage from Plato's Sophist. In it, Plato asks for a mark or indication of what is real or what has being. One answer which is mooted is that the capacity to act or be acted upon is the distinctive mark of real existence or `that which is'. The Stoics accept this criterion and add the rider that only bodies can act or be acted upon. Thus, only bodies exist. However, they allow that there are other ways of being part of nature than by virtue of existing. Incorporeal things like time, place or sayables (lekta, see below) are `subsistent' (huphestos, 27G). Moreover, all existent things are particular. The Stoics call universals `figments of the mind' and seem to offer a conceptualist treatment akin to Locke's, treating an apparent predication like "man is a rational, mortal animal" as the disguised conditional, "if something is a man, then it is a rational mortal animal" (30I).

In accord with this ontology, the Stoics, like the Epicureans, make God material. But while the Epicureans think the Gods are too busy being blessed and happy to be bothered with the governance of the universe, the Stoic God is immanent throughout the whole of creation and directs its development down to the smallest detail. God is identical with one of the two ungenerated and indestructible first principles (archai) of the universe. One principle is matter which is they regard as utterly unqualified and inert. It is that which is acted upon. God is identified with an eternal reason (logos, 44B ) or intelligent designing fire (46A) which structures matter in accordance with It's plan. This plan is enacted time and time again, beginning from a state in which all is fire, through the generation of the elements, to the creation of the world we are familiar and eventually back to fire in a cycle of endless recurrence. The designing fire of the conflagration is likened to a sperm which contains the principles or stories of all the things which will subsequently develop (46G). Under this guise, God is also called `fate.' It is important to realise that the Stoic God does not craft its world in accordance with its plan from the outside, as the demiurge in Plato's Timaeus (seemingly) does. Rather, God is the universe and it's history is determined by God's internal activity. The biological conception of God as a kind of living heat or seed from which things grow seems to be fully intended.

The first thing to develop from the conflagration are the elements. Of the four elements, the Stoics identify two as active (fire and air) and two as passive (water and earth). The active elements, or at least the principles of hot and cold, combine to form breath or pneuma. Pneuma, in turn, is the sustaining cause of all existing bodies and guides the growth and development of animate bodies. What is a sustaining cause? The Stoics think that the universe is a plenum. Like Aristotle, they reject the existence of empty space or void (except that universe as a whole is surrounded by it). Thus, one might reasonably ask, `What keeps an object from simply falling apart as it rubs elbows with other things in the crowd?' Within pneuma, there is a simultaneous movement inward and outward which gives it tension. (Perhaps this was suggested by the expansion and contraction associated with heat and cold.) Pneuma passes through all bodies and in its outward motion gives them the qualities that they have, and in its inward motion makes them unified objects (47J). In this respect, pneuma plays something of the role of substantial form in Aristotle for this too makes the thing of which it is the form both `some this', i.e. an individual, and `what it is' (Metaph. VII, 17). Because pneuma acts, it must be a body and it appears that the Stoics stressed the fact that it's blending with matter is `through and through' (47H, 48C). Perhaps as a result of this, they developed a theory of mixture which allowed for two bodies to be in the same place at the same time. It should be noted, however, that this is one of the areas of scholarly dispute. Some historians think that the claim that pneuma is blended through the totality of matter is a conclusion that the Stoics' critics drew about what their view committed them to. They propose that pneuma just is matter at a different level of description.

Pneuma comes in gradations and endows the bodies which it pervades with different qualities as a result. The pneuma which sustains an inanimate object is called tenor (hexis). Pneuma in plants is physique (phusis). In animals, pneuma gets called soul (psychê) and in rational animals the pneuma is the commanding faculty (hegemenikon). The Stoic account of the human soul is strongly monistic. Though they speak of the soul's faculties, these are parts of the commanding faculty associated with the physical sense organs. Unlike the Platonic tri-partite soul, all impulses or desires are functions of the rational part of the soul. This strongly monistic conception of the human soul has serious implications for Stoic epistemology and ethics. In the first case, our impressions of sense are affections of the commanding faculty. In rational animals, these impressions are thoughts, or representations with propositional content. Though the agent may have no choice about whether she has a particular rational impression, there is another power of the commanding faculty which the Stoics call `assent' and whether one assents to a rational impression is a matter of volition. To assent to an impression is to take its content as true. To withhold assent is to suspend judgement about whether it is true. Because both impression and assent are part of one and the same commanding faculty, there can be no conflict between separate and distinct rational and irrational elements within oneself---a fight which reason might lose. Compare this situation with Plato's description of the conflict between the inferior soul within us which is taken in by sensory illusions and the calculating part which is not (Rep. X, 602E). There is no reason to think that the calculating part can always win the civil war which Plato imagines to take place within us. But because the impression and assent are both aspects of one and the same soul according to the Stoics, they think that it is possible that we can always avoid falling into error if only our reason is sufficiently disciplined. In a similar fashion, impulses or desires are movements of the soul toward something. In a rational creature, these are exercises of the rational faculty which do not arise without assent. Thus, it might be thought that the movement of the soul toward X is automatically consequent upon the impression that X is desirable. Indeed, this is just what the Stoic's opponents, the Skeptics, argue (69A.) The Stoics, however, claim that there will be no impulse---much less an action---toward X unless one assents to the impression (53S). The upshot of this is that all desires are not only (at least potentially) under the control of reason, they are acts of reason. Thus, for the sage at least, there could be no gap between forming the judgement that one ought to do X and desiring to do X.

Since pneuma is a body, there is a sense in which the Stoics have a materialist theory of mind. The pneuma which is a person's soul is subject to generation and destruction (53 C, W). Unlike the Epicureans, however, it does not follow from this that my soul will be destroyed at the time at which my body dies. Chrysippus alleged that the souls of the wise would not perish until the next conflagration (SVF 2.811, not in LS). Is this simply a failure of nerve on the part of an otherwise thorough-going materialist? Recall that the distinctive movement of pneuma is its simultaneous inward and outward motion. It is this which makes it tensile and capable of preserving, organising and, in some cases, animating the bodies which it interpenetrates. The Stoics equate virtue with wisdom and both with a kind of firmness or tensile strength within the commanding faculty of the soul (41H, 61B, 65T). Perhaps the thought was that the souls of the wise had a sufficient tensile strength that they could subsist as a distinct body on their own. Later Stoics like Panaetius and Posidonius seem to have abandoned Chrysippus' view.

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For the Stoics, the scope of logic is very wide, including not only the analysis of argument forms, but also rhetoric, grammar, and what we would call epistemology and philosophy of language. Much has been written about the Stoics' advances in logic. In general, one may say that theirs is a logic of propositions rather than a logic of terms, like the Aristotelian syllogistic. One of the accounts they offer of validity is that an argument is valid if, through the use of certain ground rules (themata), it is possible to reduce it to one of the five indemonstrable forms. These five indemonstrables are the familiar forms:

  • if p then q; p; therefore q (modus ponens);
  • if p then q; not q; therefore not-p (modus tolens);
  • it is not the case that p and q; p; therefore not-q;
  • either p or q; p; therefore not-q;
  • either p or q; not p; therefore q

Though these and other developments in logic are interesting in their own right, the Stoic treatment of certain problems about modality and bivalence are more significant for the shape of Stoicism as a whole. Chrysippus in particular was convinced that the bivalence and the law of excluded middle applied even to contingent statements about the future. (The law of excluded middle says that `(p or not-p)' is necessarily true while bivalence insists that the truth table that defines a connective like `or' contains only two values.) Aristotle's discussion in chapter 12 of On Interpretation of a hypothetical sea battle which either will or will not happen tomorrow seems to deny this. (The proper interpretation of Aristotle's position is disputed, but let that pass for the moment.) He reasons that if it is either true or false now that there will be a sea battle tomorrow (and let us suppose for the sake of argument that it is not true), then our present deliberation about whether we should go out and fight tomorrow is pointless for it is already true now that, whatever we decide, we won't fight. Perhaps there are causal factors at work which will determine this, e.g. we may decide to fight but today's high temperatures will cause the wind to be against us tomorrow. At least on one reading, Aristotle's response to this is to deny the principle of bivalence for future contingent statements: it is now neither true nor false that there will be a sea battle tomorrow. Chrysippus apparently could not agree to making such an exception and he took the price of consistency to be a strict causal determinism: all things happen through antecedent causes (38G). Above I noted that the Stoics thought that God or designing fire contained within itself the plan of all that is to happen between conflagrations and that it brings this plan to fruition in its action upon matter. Viewed in isolation from Stoic logic, this might have seemed arbitrary but clearly it was not.

The Stoics express their commitment to casual determinism in a potentially misleading way. They treat the claim that "all things happen through antecedent causes" as an alternative formulation of the claim that `all things happen through fate' (kath heimarmenên). But, in fact, the Stoics do not accept the doctrine that modern philosophers call fatalism. The matter is doubly confused, because the modern arguments for fatalism often emerge from the very considerations about bivalence that Aristotle discusses in On Interpretation. The classic example is Richard Taylor's argument in Metaphysics (2nd edition, Englewood Cliffs, NJ, 1974). One way to see the difference between Taylor's fatalism and Chrysippus' causal determinism, is to ask, "What makes it the case that we won't have a sea battle tomorrow?" The causal determinist can say, "the lack of wind" or perhaps even "our decision not to go out and fight" and these things could all have been different, if only things had been different at some earlier time. So, though the present state of affairs determines that the future will only be one way, nonetheless there is a sense in which other things are possible (58H).  The fatalist responds that what makes it the case that we will not fight tomorrow is the fact that the proposition S, "There will not be a sea battle on such and such a date", has always been true. Much turns on what one says about the modal status of this truth. Is the proposition "It is true that not-S" itself necessary?  Diodorus Cronus, against whom Chrysippus argued, claimed that truths about the past are necessary: it is not merely that they aren't other than they are, they can't be other than they are, for we have no power to change the past (38A). He also claimed that what is impossible does not follow from what is possible. In the so-called Master Argument, he attempted to show that these two theses were incompatible with the claim that there is something which is possible, but yet does not happen. The details of the Master Argument are a matter of much dispute. We know that it was alleged to show that these three propositions formed an inconsistent triad, but exactly how it did this remains uncertain. We also know that Diodorus' manner of resolving this inconsistency was to reject that latter and to define the possible as that which is or will be the case. Now consider our sea battle which will not take place tomorrow. If "there will be a sea battle on such and such a date" is not true and will not be true, then by Diodorus' lights, it is impossible! (38C). Chrysippus felt the need to preserve the thesis that there are things which are possible but which do not happen. Toward this end, he rejected the proposition that what is impossible does not follow from what is possible with the following example: consider the conditional "if Dion is dead, then this one is dead" when ostensive reference is being made to Dion. The antecedent is possible, since Dion will one day be dead. However, the consequent is impossible since one cannot make the requisite ostensive reference to a dead man so as to make it true that "this one [i.e. the man I'm pointing to] is dead", for a dead man isn't a man (38F). On the surface this appears utterly ad hoc. While it is clearly wrong, given the Stoics' views about `sayables' (lekta), it is exactly the response that they should make and once again simply illustrates the systematic character of Stoic philosophy.

With respect to language, the Stoics distinguish between the signification, the signifier and the name bearer. Two of these are bodies: the signifier which is the utterance and the name bearer which gets signified. The signification, however, is an incorporeal thing called a lekton, or `sayable', and it, not the other two, is what is true or false (33B). They define a sayable as "that which subsists in accordance with a rational impression." Rational impressions are those alterations of the commanding faculty whose content can be exhibited in language. Presumably `graphei Sôcratês' and `Socrates writes' exhibit the contents of one and the same rational impression in different languages. At first glance, this looks very like a modern theory of propositions. But propositions (axiômata) are only one subspecies of sayables. They also include questions and commands on the one hand, and, in a category of sayables called `incomplete', the Stoics include predicates and incomplete expressions like `graphei' (he or she writes) (33F). An incomplete sayable like `writes' gets transformed into a proposition by being attached to a nominative case (ptôsis, 33G). One might expect a case to be the reference of a proper name or a noun, e.g. Socrates or the man, but it seems to mean the inflected word, `Socrates' or `ho anthrôpos'---the nominative case of the Greek word `man'. The Stoic doctrine of case is one of those areas where there is as yet little consensus. Stoic propositions are unlike contemporary theories of propositions in another way too: Stoic sayables are not timelessly true or false. If it is now daytime, the lekton corresponding to the utterance `it is day' is true. Tonight, however, it will be false (34F). Finally, the Stoic theory gives a certain kind of priority to propositions involving demonstratives. `This one is writing' is definite, while `someone is writing' is indefinite. Strangely, `Socrates is writing' is said to be intermediate between these two. The reasons for this are not clear, though they may be connected with the mysterious business of case (34K). When there is a failure of reference, the Stoics say that the lekton is destroyed and this is supposed to provide the reason why `this one is dead' (spoken in relation to Dion) is impossible.

Perhaps the most famous topic considered under the Stoic heading of logic is the matter of the criterion of truth and their disputes with the skeptical New Academy about it.

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