Was Aristo an Agnostic Stoic?

What we know about one of Zeno's most unorthodox students

Statue of unknown Greek philosopher, from Delphi Museum

It’s sometimes asserted that all ancient Stoics believed in Providence, and that this belief is necessary to justify the rest of their system of philosophy, especially their ethics. In fact, there’s no more reason for modern thinkers to conclude that belief in Providence is a necessary premise for Stoic Ethics than it is for more or less any other ethical system.

Their precursors, the Cynics, for instance, held similar ethical views to the Stoics but they did not typically study theology or attempt to justify their ethic by appeal to belief in Providence. Cicero, an Academic, broadly agreed with Stoic Ethics, but grounded his virtue ethic in human nature and reason rather than dogmatic belief in Providence. Today, some people, usually Christians or followers of other faiths, are convinced that you cannot have ethics without belief in God — they often say it’s simply inconceivable to them. Others, mostly agnostics or atheists, feel that you can derive ethical conclusions from principles based on human nature and reason, without any reference to God. In the ancient world, philosophical discussion about the existence of God (or the gods), and its ethical implications, was not at all unusual, although belief in the established pantheons of gods, and respect for the traditional religious customs of Greece and Rome was, typically, the norm.

As for what the ancient Stoics believed, given that so few of their original writings survive today, it seems impossible for us to make any meaningful generalizations in this regard. How could anyone claim to know what 100% of ancient Stoics believed about the gods based on less than 1% of their writings? The most we could reasonably assert is Zeno and some of his best-known followers, throughout the five centuries or so during which the school flourished, all shared a broadly similar belief in Providence, although we also have evidence of many theological disagreements between leading Stoic thinkers.

By agnostic, I mean, in the broad sense, “a person who is unwilling to commit to an opinion about something”, and more specifically, in the more narrow sense, “a person who believes that God is unknowable or one who is unwilling to commit to any opinion about the nature of God, or about God’s existence or nonexistence.” An atheist, by contrast, is someone who claims to know that God does not exist. We have no evidence that any ancient Stoics were atheists. There was, however, one Stoic philosopher, very well-known in antiquity, who appears to have adopted an agnostic position regarding the nature, and perhaps even the existence, of the gods.

Aristo of Chios was a student of Zeno of Citium, the founder of Stoicism, and therefore a fellow-student and subsequently a rival of Cleanthes, who succeeded Zeno as head of the school. His name is spelled Ariston in ancient Greek, but the final n is, by convention, usually dropped in English, although you will find it spelled both ways by different authors — the Greek name Platon is likewise more familiar to us as Plato. (I have amended several of the texts below for consistency in this regard.) Aristo was one of Zeno’s most highly-regarded students, and although none of his writings survive, his influence endured for centuries. We find references to his teachings in the writings of Cicero, Seneca, and Plutarch, among others, and an entire chapter of Diogenes Laertius’ Lives and Opinions of Eminent Philosophers is dedicated to his life and thought.

Surprisingly, one of the main controversies about Aristo is whether, in fact, he was a Stoic. He was certainly a student of Zeno’s, but came to disagree quite markedly with some of his teacher’s views. It’s unclear, though, to what extent this disagreement was perceived by them as marking an actual break from Stoicism. Diogenes Laertius has some nuanced things to say about Aristo’s relationship with other Stoics. However, he does label Aristo as a Stoic, albeit an unorthodox one.

It seems to me that Aristo’s break from Zeno was partial enough that later generations of philosophers appear to disagree as to whether he should be classed as an unorthodox Stoic or the founder of a distinct, but minor, school of his own. Cicero, for instance, sometimes contrasts the views of Aristo with those of the Stoics, which can be read as implying that he thinks of them as representing two different schools of philosophy. Our clearest evidence, however, comes from Seneca, himself a Stoic, who unequivocally considers Aristo to be a fellow Stoic. As we shall see, Seneca, and at least one other ancient author, referred to him as Ariston Stoicus or “Aristo the Stoic”.

In this article, I’ll look in depth at the evidence in relation to two questions:

1. Was Aristo a Stoic?

2. Did he reject the orthodox Stoic belief in a Provident God?

Marcus Aurelius on “Aristo”

Before I do so, however, it’s worth drawing attention to a famous passage from the private letters of Marcus Aurelius to his rhetoric tutor, Marcus Cornelius Fronto. Here the young Marcus, as Caesar, mentions the striking impact upon him of having read an author called Aristo.

Aristo’s books just now treat me well and at the same time make me feel ill. When they teach me a better way, then, I need not say, they treat me well; but when they shew me how far short my character comes of this better way, time and time again does your pupil blush and is angry with himself, for that, twenty-five years old as I am, no draught has my soul yet drunk of noble doctrines and purer principles. Therefore I do penance, am wroth with myself, am sad, compare myself with others, starve myself. A prey to these thoughts at this time, I have put off each day till the morrow the duty of writing. But now I will think out something, and as a certain Athenian orator once warned an assembly of his countrymen, that the laws must sometimes be allowed to sleep, I will make my peace with Aristo’s works and allow them to lie still awhile, and after reading some of Tully’s [i.e., Cicero’s] minor speeches I will devote myself entirely to your stage poet. However, I can only write on one side or the other, for as to my defending both sides of the question, Aristo will, I am sure, never sleep so soundly as to allow me to do that! — Marcus Aurelius to Fronto

Aristo was a fairly common Greek name, e.g., it is believed to have been the name of Plato’s father, and of at least one other famous philosopher, an Aristotelian called Aristo of Ceos, and a prominent Roman jurist called Titius Aristo. Scholars therefore disagree as to whether Marcus is referring to our Aristo or not in this letter. However, on reflection, for the reasons below, it seems probable to me that he was, indeed, talking about Aristo of Chios. (Pierre Hadot, in The Inner Citadel, also considers this question and arrives at the same conclusion, that Marcus is talking about Aristo of Chios.)

By this time in his life, aged twenty-five, Marcus Aurelius is already perceived by Fronto as a Stoic, although Marcus did read widely, and studied other schools of philosophy. Aristo of Chios was an important figure in the history of Stoicism, and one known for his brash and challenging nature.

When [Zeno’s] pupil Aristo discoursed at length in an uninspired manner, sometimes in a headstrong and over-confident way. "Your father," said he, "must have been drunk when he begat you." Hence he would call him a chatterbox, being himself concise in speech. — Diogenes Laertius

Diogenes Laertius also claims Aristo was nicknamed the Siren, presumably because of his captivating eloquence, and he remarks on Aristo’s uniquely persuasive and influential manner of speaking. Several books are attributed to him including a four-volume collection of his letters to Cleanthes, and many works the authenticity of which was in doubt, including a volume titled On Zeno's Doctrines and two volumes of Exhortations to philosophy. If Marcus was this shaken by whatever he read it seems most likely to have come from the “Aristo” most famous for possessing the ability to affect people in such a powerful way with his words. Marcus certainly resembles a man who has been filled with anguish, having heard the song of a Siren — the nickname we’re told Aristo of Chios had earned.

We can, moreover, find several parallels between the ideas for which Aristo was famous and certain themes in the Meditations of Marcus Aurelius. As we shall see, for instance, Aristo questioned the value of studying Logic and Physics. Marcus refers several times to concerns he has about having spent too much time on these subjects and not enough on Ethics. Aristo expresses agnosticism about the nature of God; Marcus Aurelius, about nine times, expresses a sort of methodological agnosticism, asserting that whether the universe is produced by God or atoms, i.e., Providence or randomness, either way, Stoic ethical principles are still valid. Marcus also seems to have been drawn to Cynicism earlier in his life, a tradition with which Aristo appears to have associated himself.

Although we cannot be certain, it seems plausible and indeed likely to me that Marcus was describing the powerful impact upon him of reading some books by Aristo of Chios, perhaps shared with him by his mentor, Junius Rusticus, or another Stoic teacher.

Aristo’s Stoicism

Diogenes Laertius’ Lives and Opinions of Eminent Philosophers is our most important source for information on Aristo. In the introductory chapter, Diogenes reviews the different sects of philosophy, and different ways of classifying them. Although he mentions Aristo of Chios here, Diogenes does not list him or his followers as constituting a distinct philosophical sect or school. Presumably, therefore, he must be lumping them in with the other Stoics in this part of the book.

Indeed, Lives and Opinions contains a whole section dedicated to the Stoics, which consists of seven chapters, each of which deals with the life and thought of a different member of their school. The preceding section, on the Cynics, concludes with the words:

So much, then, for the Cynics. We must now pass on to the Stoics, whose founder was Zeno, a disciple of Crates [of Thebes, the Cynic]. — Diogenes Laertius

The first chapter, of course, is about Zeno of Citium, the founder of the Stoic school. It is, by far, the longest chapter in this section because it includes a detailed summary of the doctrines of the Stoic school. However, it ends with the words “But the points on which some of them [i.e., some of the Stoics] differed are as follows." The following chapters therefore describe ways in which other Stoics departed from the original teachings of Zeno, and the first of those is the chapter concerning Aristo of Chios.

We’re told that Aristo began lecturing in the Cynosarges, although it’s not clear whether he did this while Zeno was still alive. After Zeno’s death, Cleanthes, author of the Hymn to Zeus, succeeded him as head of the Stoic school, and placed greater emphasis on worship of the gods. It’s therefore possible that when Cleanthes took over teaching at the Stoa, Aristo set up a rival branch of Stoicism at the Cynosarges, which, in contrast to the more theological teachings of Cleanthes, espoused a position closer to Cynicism, in which the study of Logic and Physics (including theology) are downplayed and Ethics takes centre stage.

Once Aristo became established as a teacher in his own right, he earned the reputation of being a αἱρετιστὴς (hairetistes), which literally means “one who chooses”, i.e., he choose a different approach to Zeno — it’s the etymological root of our English word “heretic”. It can potentially mean someone who has founded a new sect of philosophy but could also simply mean that he disagreed with Zeno, while remaining part of the broad Stoic movement. There’s no explicit reference to him joining another school of philosophy, or decisively breaking away from the Stoic school and, as we’ve seen, he was still referred to both by Diogenes and later authors as a Stoic.

The Cynosarges was one of the three main gymnasia of ancient Athens, along with the Academy and Lyceum, where the schools of Plato and Aristotle were located respectively. The Cynosarges was particularly known for being less exclusive than the Lyceum and Academy, because it was open to poorer citizens, resident foreigners, known as metics, and illegitimate children, who often had one foreign parent. It was associated with outsiders, in a sense, and those living on the fringes of Athenian society, which perhaps made it a suitable home for a renegade Stoic.

Whereas Zeno, and subsequently Cleanthes, only appear to have had a handful of students, Aristo attracted a large following:

Once when somebody reproached [Chrysippus] for not going with the multitude to hear Aristo, he rejoined, "If I had followed the multitude, I should not have studied philosophy."—Diogenes Laertius

One of our other sources claims that Aristo and Arcesilaus, the founder of Academic Skepticism, were the two rival philosophers of this period who attracted the largest following. This seems to confirm that Aristo was more famous and influential, during his lifetime, than his Stoic rival, Cleanthes.

Diogenes also described Aristo as being particularly “persuasive and influential with the crowd” or mob (ὄχλος), i.e., relatively large audiences, at the Cynosarges and perhaps elsewhere, including many poorer and less well-educated residents of Athens. That may help to explain Plutarch’s remark that “Aristo of Chios, when the sophists spoke ill of him for talking with all who wished it, said, ‘I wish even the beasts could understand words which incite to virtue’” (Plutarch, Table Talk, 10.1). In other words, Aristo took Stoicism from the Agora, in the centre of Athens, to the Cynosarges, outside the city walls, where he adopted a simpler, more austere, and populist approach, and drew large audiences including many foreigners and poorer citizens, perhaps eclipsing Zeno’s official successor, Cleanthes, in popularity. It may be that his nickname, The Siren, alludes to the fact that he lured many young Stoics away from Cleanthes, the implication being that they were ruined by joining him at the Cynosarges.

Indeed, another source, the geographer Strabo, who had trained in Stoic philosophy himself, cites Eratosthenes of Cyrene, a student of Zeno, as having said that Aristo and the Skeptic Arcesilaus were the two leading teachers at Athens during his lifetime, when philosophy peaked in popularity:

"For," he says, "never before at this time, under one enclosure and one city, were there so many philosophers flourishing as in the time of Aristo and Arcesilaus." He places Arcesilaus and Aristo as the leading figures among those who flourished in his own time. […] And --- he [Aristo] shared [scil. did not prohibit], so that the same young men might hear both him and Cleanthes.

At the Cynosarges, then, Aristo must have attracted a much larger following than the rival branch of Stoicism being taught in the Agora by Cleanthes.

We’re told that one of Socrates’ most influential followers, Antisthenes, was looked down on by some Athenians because his mother was Thracian and therefore classed as a “barbarian”. Almost a century before Aristo, Antisthenes had taught his austere form of Socratic philosophy in the Cynosarges. Antisthenes was considered by some ancient authors to be the founder, or at least precursor, of the Cynic school, and his views may well have had some influence on Aristo. As we shall see, there are certainly good reasons to compare Aristo to the Cynics.

As we’ve seen, Diogenes Laertius claims that some referred to Aristo as an αἱρετιστής, which can mean the founder of a philosophical sect or school. He also tells us the names of two philosophers who were called “Aristonians” (Ἀριστώνειοι), because they claimed to be followers of Aristo. From this we can infer that Aristo was not the only one who held the key philosophical doctrines attributed to him. If he can be described as an agnostic Stoic, for instance, he was apparently not alone, as we’re told he had many followers. At this point in history, therefore, Aristo’s brand of agnostic-sounding Stoicism, appears to have attracted more followers than the more overtly theological Stoicism of Cleanthes.

Some people have read that as meaning that Aristo could not have been a Stoic, based on the assumption that if a philosopher founded a sect or had students designated with his name in this way, they could no longer be considered members of broader school, such as Stoicism. However, that assumption is certainly false. It’s disproved by the the fact we know of others, including groups of Stoics, who were identified as members of a particular branch within a broader school of philosophy. Someone can, of course, be referred to both as a “Thomist” or an “Augustinian” and still be a “Christian”. We know that in the Roman Imperial period there were three branches of Stoicism whose followers were divided into disciples of the last three scholarchs of the Stoic school:

And there are many meetings of philosophers in the city, some called the pupils of Diogenes [of Babylon], and others, pupils of Antipater [of Tarsus], others again styled disciples of Panætius [of Rhodes]. — Athenaeus of Naucratis, Deipnosophists

They were all still Stoics, just followers of different branches of the philosophy. We may likewise conclude that Aristo’s followers could have been viewed as members of an Aristonian branch of Stoicism. This group of early Stoics could have been referred to, therefore, as Aristonians just as later Stoics were referred to as Diognitists, Antipatrists or Panaetians.

After concluding his discussion of Aristo, Herillus, and Dionysius, Diogenes writes:

These three, then, are the heterodox Stoics. The legitimate successor to Zeno, however, was Cleanthes: of whom we have now to speak.

Here the word used to refer to Aristo and the others is διενεχθείς, meaning simply “one who disagreed”, i.e., with Zeno’s original Stoicism, and presumably also with Cleanthes. It is usually translated as referring to “heterodox” Stoics. All three of these men disagreed with Zeno’s original teachings but we cannot conclude from that alone that they all broke away from the Stoic school. Indeed, of the three, Diogenes the Renegade, is the only one whom we’re told decisively broke from the Stoic school, in his case to become a follower of the Cyrenaics instead.

Athenaeus of Naucratis, writing in the late 2nd or early 3rd century CE, explicitly refers to “Aristo of Chios, who was one of the sect of the Stoics”, in order to criticize him for allegedly sacrificing virtue for certain pleasures (Deipnosophists). By contrast, in the same passage, Athenaeus refers to Dionysius of Heraclea, who “apostatized from the doctrines of the Stoics, and passed over to the school of Epicurus”. In other words he explicitly states, like Diogenes Laertius, that Dionysius abandoned the Stoic school to join the Cyrenaic or perhaps Epicurean school of philosophy. Athenaeus would surely have likewise referred to Aristo having “apostatized”, or broken away, from the Stoic school, if he had actually done so, but instead he continues to refer to him here as a Stoic.

Diogenes Laertius refers collectively to the “heterodox Stoics”, whereas nobody refers to Aristotle and Zeno, for instance, as “heterodox Platonists”. This, and the fact that Diogenes includes chapters about them alongside the more orthodox Stoics, makes it clear that despite their disagreements with Zeno, these three philosophers were still classified primarily as Stoics. It could, of course, be that some of these men considered themselves, or were considered by Zeno and his followers, as representing distinct schools of philosophy from Stoicism but nevertheless that later authors, such as Diogenes Laertius, lumped them together for convenience, because they had enough in common to justify doing so.

Moreover, in another chapter, on Arcesilaus, the Academic Skeptic, Diogenes Laertius clearly refers to Aristo’s followers as Stoics.

Hence the Stoics around Aristo of Chios used to reproach him, calling him a corrupter of the youth, a seducer, and shameless.

So from the fact that Diogenes Laertius refers to Aristo as a “heterodox Stoics” and to his followers as “Stoics”, it seems clear that he did not mean that Aristo had broken away from the Stoic school but that he continued to be viewed as a Stoic, albeit one representing a distinct branch of the philosophy from Zeno and Cleanthes.

It’s worth noting that Aristo is never referred to as a Cynic, despite the obvious similarities between their doctrines and the fact he based himself at the Cynosarges. Why was he not simply classed as a Cynic, though? Perhaps because we don’t find any reference to him embracing the austere ascetic lifestyle for which Cynics were typically known. In fact, we’re told he was criticized by some for his love of pleasure and luxury. We’re told one of his students, called Eratosthenes the Cyrenean, wrote a book titled Aristo, in which he portrayed his master as having become, over time, addicted to luxury:

And before now, I have at times discovered him breaking down, as it were, the partition wall between pleasure and virtue, and appearing on the side of pleasure. — quoted in Athenaeus, Deipnosophists

Incidentally, Aristo’s rejection of Stoic Physics appears to be directly related to his rejection of Zeno and Cleanthes’ concept of “preferred” indifferents. If we cannot be certain about the nature of the universe and the study of Physics is dogged with uncertainty, we cannot appeal to what is “in accord with Nature” as a criterion for saying whether health is intrinsically preferable to disease, beauty to ugliness, friends to enemies, and so on. Aristo appeals instead to human reason, and argues that externals are absolutely indifferent and only of instrumental value, depending on our circumstances, as means of exercising wisdom and other virtues.

Ariston Stoicus

Seneca, himself a Stoic, actually refers, unequivocally, as we shall see, to Aristo as a fellow Stoic. This suggests that it was not unusual for later philosophers to classify Aristo merely as an unorthodox Stoic, rather than someone who actually broke away decisively from the Stoic school, and this is probably also what Diogenes Laertius meant by referring to him as a “heterdox Stoic”.

Seneca, speaking of the division of philosophy concerned with “supplying precepts appropriate to the individual case”, such as practical advice about how to raise one’s children, writes:

But Aristo the Stoic, on the contrary, believes the above-mentioned department to be of slight import – he holds that it does not sink into the mind, having in it nothing but old wives’ precepts, and that the greatest benefit is derived from the actual dogmas of philosophy and from the definition of the Supreme Good. When a man has gained a complete understanding of this definition and has thoroughly learned it, he can frame for himself a precept directing what is to be done in a given case. — Seneca, Letters 94

In other words, if you really grasp that virtue is the only true good, then you don’t need philosophers to spell out in fine detail exactly how to raise your children, run your business, conduct yourself in public office, and so on. Aristo, again, is depicted as simplifying Stoicism, in order to focus on its basic ethical principles.

In the original Latin, Seneca calls him Ariston Stoicus, which literally means “Aristo the Stoic”. We find the same phrase used in the late 2nd or early 3rd century AD, by the Christian apologist Minucius Felix in Octavian, where he writes:

For Xenophon the Socratic says that the form of the true God cannot be seen and therefore should not be inquired into; Aristo the Stoic [says] that it cannot be comprehended at all: both realized that the majesty of God is the despair of understanding. — Minucius Felix, 19.12-3

We’ll return to Aristo’s claim that the nature of God is unknowable later. For now, the key part of this passage is that fact that Minucius Felix follows Seneca in referring to him unequivocally as Ariston Stoiconus or “Aristo the Stoic”. Neither Seneca nor Minucius Felix feel the need to qualify or explain this designation — they assume their readers will find it uncontroversial. It’s likely, based on the evidence from Seneca and this later Christian apologist, therefore, that Aristo, at least in the imperial period, was viewed unequivocally as a Stoic.

Aristo and the Cynics

One reason why Aristo may have been referred to as a Stoic, while disagreeing with Zeno, is that whereas others may have been drawn more in the direction of opposing philosophers such as Platonism or Cyrenaicism, Aristo appears to have been more inclined toward Cynicism. Zeno himself was originally a Cynic for many years, and the Stoics were often seen as closely-related to the Cynics. Aristo’s disagreement with Zeno may, therefore, have been perceived not as a break from the school but rather as a return to Stoicism’s Cynic roots. For instance, Diogenes Laertius concludes his discussion of the Cynic philosophers, including Antisthenes, by comparing their teachings, particularly their neglect of Logic and Physics in favour of Ethics, to the philosophy of Aristo of Chios.

Such are the lives of the several Cynics. But we will go on to append the doctrines which they held in common--if, that is, we decide that Cynicism is really a philosophy, and not, as some maintain, just a way of life. They are content then, like Aristo of Chios, to do away with the subjects of Logic and Physics and to devote their whole attention to Ethics. — Diogenes Laertius

As Physics includes theology, this means that the Cynics in general abandoned the study of theology, and that Aristo, the Stoic, came to resemble the Cynics in also abandoning the study of theology, in order to focus exclusively on ethics. This focus on ethics was also traditionally associated with Socrates. We’re told more about Ariston’s reasoning here in a fragment from Stobaeus:

Ariston said that of the things investigated by philosophers, some are up to us, some are not up to us, and some are beyond us. Ethics is up to us, dialectic is not up to us (for it does not contribute to the correction of life), and physics is beyond us, for it is impossible to know and is of no use. — Stobaeus, Eclogues II 8, 13 W

Once again, if Aristo taught his Stoic students that the whole of Physics, including theology, is simply “beyond us” (ὑπὲρ ἡμᾶς) in the sense of being “impossible to know”, that does appear, literally, to make him agnostic. He caps that by saying that theology is therefore completely useless to us, including himself and his students.

We’re likewise told that Aristo resembled the Cynics with regard to his central Ethical doctrines.

Whatever is intermediate between Virtue and Vice they [Antisthenes and the Cynics], in agreement with Aristo of Chios, account indifferent. — Diogenes Laertius

Seneca also portrays Aristo as someone who emphasized the worthless nature of external goods:

Then it will be in our power to understand how contemptible are the things we admire – like children who regard every toy as a thing of value, who cherish necklaces bought at the price of a mere penny as more dear than their parents or than their brothers. And what, then, as Aristo says, is the difference between ourselves and these children, except that we elders go crazy over paintings and sculpture, and that our folly costs us dearer? — Seneca, Letters 115

One way of viewing this is that Cynicism was originally viewed more as a philosophical way of life rather than a system of philosophical teachings. Diogenes Laertius implies that there was some difference of opinion as to whether “Cynicism is really a philosophy, and not, as some maintain, just a way of life”, for instance. Aristo, having been a student of Zeno, may have set up teaching a form of Stoicism in the Cynosarges, which more closely resembled Cynicism, in its simplicity, but was more than just a way of life, and went beyond Cynicism in presenting a systematic approach to ethics, based on philosophical arguments, which were indebted to Stoicism.

Aristo’s Agnosticism

Zeno’s Stoic philosophy consisted in a set of doctrines divided into three broad topics: Ethics, Physics, and Logic.

[Aristo] wished to discard both Logic and Physics, saying that Physics was beyond our reach and Logic did not concern us: all that did concern us was Ethics. — Diogenes Laertius

As we have seen, discarding Stoic Physics would mean, among other things, discarding Stoic theology. (I will set aside, for the purposes of this discussion, his reference to Logic.)

What we’re told here can be understood in relation to what Diogenes Laertius said, at the opening of his chapter on Aristo, about the goal of life being “perfect indifference to everything which is neither virtue nor vice.” Aristo must have viewed the study of theology as one of the things that are absolutely indifferent, being neither, in itself, a virtue nor a vice. We can imagine Aristo saying that studying Zeno’s theology, in itself, will not make you virtuous.

Living in accord with virtue and studying theology are not the same thing, and should not be equated. Indeed, either love or hatred of theology could be forms of vice, if they lead us to place too much value on something external to our own moral character. This reminds me of the Buddhist doctrine that the question as to whether or not the gods exist is “indifferent” — rather than answering the Buddha would simply raise one finger to signal to his followers that they were asking him the wrong sort of question.

Seneca also highlights the fact that Aristo abandoned Logic and theology as superfluous, adding that he viewed them, in some regard, as providing contradictory guidance in life.

Aristo of Chios remarked that the natural and the rational were not only superfluous, but were also contradictory. He even limited the “moral,” which was all that was left to him; for he abolished that heading which embraced advice, maintaining that it was the business of the pedagogue, and not of the philosopher – as if the wise man were anything else than the pedagogue of the human race! — Seneca, Letters 89

Cicero makes it clear that Aristo did suspend judgement and adopt a sort of agnosticism with regard to many questions about Physics, including what at the time appeared unfathomable mysteries of nature such as how large or small the sun was.

Socrates, then, is free from this ridicule, and so is Aristo of Chios, who thinks that none of these matters can be known. — Cicero, De Finibus, 2.39

Specifically with regard to theology, Cicero states in another text:

Aristo holds equally mistaken views. He thinks that the form of the deity cannot be comprehended, and he denies the gods sensation, and in fact is uncertain whether the god is a living being at all. — Cicero, De Natura Deorum, 1.14

(This key passage in Latin: Cuius discipuli Aristonis non minus magno in errore sententia est, qui neque formam dei intellegi posse censeat neque in deis sensum esse dicat, dubitetque omnino deus animans necne sit. — where dubitetque omnino, which could be translated “doubts altogether” seems to emphasise his profound uncertainty.)  

Moreover, Aristo cannot believe that God is Provident because he denies that the gods have any sensation, his point perhaps being that as the gods lack physical eyes and ears they can neither see humans nor hear their prayers.

It’s difficult to read these words without being reminded of the notorious opening lines of Protagoras’ work On the Gods:

As to the gods, I have no means of knowing either that they exist or that they do not exist. For many are the obstacles that impede knowledge, both the obscurity of the question and the shortness of human life. — Protagoras, On the Gods

Aristo’s agnosticism about the nature of God clearly follows from his more general belief that the study of Physics, or the Nature of the universe, of which theology was deemed a part by the Stoics, is simply “beyond” mortal comprehension.

It may seems unclear whether Aristo meant that the existence of God (or the gods) is uncertain or merely that his Nature is completely unknowable, and therefore indifferent to us. A few lines earlier, however, Cicero had said that Zeno of Citium wanted to call the law of nature divine, to which he objects: “How he makes out this law to be alive passes our comprehension; yet we undoubtedly expect god to be a living being.” At least for Cicero, therefore, Aristo’s being uncertain whether or not God is a living being is tantamount to being uncertain whether or not he exists.

Indeed, if the nature of the gods is completely incomprehensible, it is difficult to imagine how anyone could know for certain that they exist. It appears to me, therefore, that Aristo in addition to being agnostic about the Nature of God was probably also agnostic about God’s existence. How can we claim to know that something exists if we know nothing whatsoever about its nature? The fact that Aristo abandoned theological studies as worthless appears to confirm that he believed theological questions were beyond human comprehension, which suggests he was more like a straightforward agnostic than a proponent of some subtle mystical theology.

Conclusion

Aristo is a fascinating but somewhat mysterious figure, in the history of philosophy. He was clearly an important follower of Zeno, who, perhaps after his teacher died and Cleanthes took over the Stoic school, set up in the Cynosarges teaching a hybrid of Stoicism and Cynicism to a larger and more mixed audience. He was known as a Siren, a powerful and compelling speaker, who converted many others to follow philosophy as a way of life.

Although Aristo certainly disagreed with Zeno, Cleanthes, and other early Stoics, and attracted his own group of followers, he was still referred to by the historian of philosophy, Diogenes Laertius, and by fellow-Stoic Seneca, among others, as a Stoic, albeit an unorthodox one. Diogenes Laertius calls him a “heterodox Stoic” and refers to his followers as “Stoics”. Seneca and the apologist Minucius Felix both refer to him unequivocally as Ariston Stoicus — “Aristo the Stoic”. It seems to me that he was probably widely regarded as a Stoic who, in key regards, sought to return to the Cynic roots of the philosophy.

Several ancient authors claim that Aristo and Cleanthes, though leading rival philosophical schools influenced by the Stoic teachings of Zeno, were actually on relatively friendly terms with one another.

But when the truth has appeared and shone forth in philosophy, all who have grasped the work enjoy it without bloodshed. For this reason, Aristo embraced Cleanthes and shared his students. — Themistius or. 21 p. 255

The fact that students were attending the lectures of both Aristo and Cleanthes at the same time lends weight to the notion that they probably saw themselves as part of a single Stoic tradition.

Aristo was well-known for teaching that the study of theology was unnecessary, and for abandoning Physics and Logic to focus on Ethics. This is confirmed in several ancient sources. We’re told that he said theology was literally “impossible to know”, and therefore “of no use” whatsoever, which definitely makes him sound broadly agnostic. We’re told that he was agnostic about the Nature of God, which he viewed as incomprehensible to mortals. We’re not specifically told that he was agnostic about the existence of God but this seems to follow from his abandonment of theology and assertion that God’s nature is utterly unknowable. I believe Aristo is very likely, therefore, to have been agnostic about the existence of God. Moreover, he was far from being unique in that regard. We’re told he attracted larger audiences, and perhaps had more followers, than Zeno or Cleanthes. On that basis, it seems possible that, at one time, the majority of Stoics were actually agnostics who followed Aristo’s branch of the philosophy.

Moreover , from the fact that Aristo believed study of theology was impossible and of no value, it seems to follow that some of his Stoic students may have been agnostics. He clearly didn’t expect them to study theological arguments for the existence of God and appeals to the existence of God seem to play no role in his Ethics. So there doesn’t seem to be any requirement or expectation for his Stoic students to believe in God. To put it crudely, if an agnostic approached Aristo and said “Can I become a follower of your brand of Stoicism?”, it’s impossible to imagine him replying “No, you would have to be certain of the existence of God, you can’t be agnostic, even though I said studying theology is worthless.” His school was presumably, therefore, open to a diverse range of students regardless of their religious or theological views. Indeed, the large and diverse audience he reputedly attracted at the Cynosarges, including many of foreign descent, would likely have included a number of individuals who followed different religious traditions or held different theological views.

Aristo certainly thought that theological speculation was a distraction from the fundamental ethical questions in life. We just need to grasp that virtue is the only true good and live accordingly. We should be wary of overcomplicating ethics. When Marcus Aurelius says, for instance, that we should stop arguing about what a good man is and just be one (Meditations, 10.16), he sounds like he could be paraphrasing Aristo of Chios.

Moreover, we’re told that Aristo defined the telos or supreme goal of life as ἀδιαφορία or indifference (Clement of Alexandria, Stromata, 2.21). Although Marcus Aurelius frequently repeats the more orthodox Stoic doctrine that we must distinguish the relative value of indifferent things, nevertheless, at times he portrays the goal of life as a form of indifference, synonymous with virtue. (Note: Pierre Hadot, in The Inner Citadel, says he originally saw the influence of Aristo in this first passage but later changed his mind.)

As to living in the best way, this power is in the soul, if it be indifferent to things which are indifferent. —Meditations, 11.16

Elsewhere, Marcus repeats this point:

Adorn yourself with simplicity and modesty, and with indifference towards the things which lie between virtue and vice. — Meditations, 7.31

His language in this passage (despite subtle differences in the original Greek) seems to me to echo Aristo’s definition of the supreme goal of life:

[Aristo] declared the goal [telos] to be a life of indifference towards the things which lie between virtue and vice. — Diogenes Laertius

As Prof. Brad Inwood mentions Aristo of Chios in his recent book Stoicism, A Very Short Introduction.

Modern Stoics aiming primarily to improve human lives through moral betterment, setting aside physics and logic, can see themselves as the heirs of Aristo’s tradition, one that goes back to the early days of the school. It’s not just our modern reliance on Marcus, Epictetus, and Seneca that feeds this movement; a narrow focus on ethical improvement is also an authentic component of ancient Stoicism.

There’s nothing inauthentic, therefore, about a form of Stoicism that makes ethics the priority, and accepts some degree of uncertainty, or agnosticism, about theological questions.