Home Page

email us



Philosophy of the Skeptical Academy

Introduction by Charles Siegel

Volume 2 of the Rediscovered Philosophers series

new material in this edition copyright © 2016

The Academy was founded by Plato in about 387 BC. It was located less than a mile north of Athens' Diplon Gate, on a site that had been sacred since the Bronze Age. The site was associated with the hero Akademos. According to the myth, Theseus, the early king of Athens, abducted Helen when she was twelve years old, long before she caused the Trojan War. When her brothers, the twins Castor and Pollux, invaded Athens, Akademos told them where Theseus had hidden Helen, saving the city.

Conventional History of the Academy

The doctrines of the Academy changed so drastically over time that historians speak of several Academies. First, let's look at the conventional view of this history.

Plato (428/7 BC – 348/7 BC) founded the "Old Academy" or "First Academy," which was "dogmatic," meaning that it believed philosophers could discover the truth. Plato's ideas are well known. He believed there was a realm of pure ideas that are embodied imperfectly in the material world. For example, any triangle that we draw in this world is an imperfect imitation of the pure idea of a triangle, and any beauty, justice, or goodness we see in this world is an imperfect imitation of the pure ideas of beauty, justice, and goodness. Philosophers could find truths by understanding these pure ideas, just as mathematicians find truths about the triangle by understanding the idea of the triangle.

Plato's immediate successors as the head - or scholarch - of the Academy are less well known. Speusippus was scholarch from 347–339 BC, Xenocrates from 339–314 BC, Polemo (or Polemon) from 314–269 BC, and Crates from 269–266 BC. Little survives from their writings, and we know about them from occasional quotations and testimonies in other philosophers and from the Diogenes Laertius, who wrote a book of biographies of philosophers in the third century AD that included legends and rumors as well as facts. Yet they were considered important for centuries after their own time, and Cicero often mentions the writings of Polemo.

The Academy of Plato and these immediate successors is known as the "Old Academy" or "First Academy."

Things changed dramatically in about 266 BC, when Arcesilaus became scholarch and inaugurated what is called the "Middle Academy" or "Second Academy." Arcesilaus was a skeptic who believed that we cannot have any certain knowledge and that philosophers should suspend judgment rather than having beliefs that are not knowledge but just opinion. This suspension of judgment was called epochê in Greek.

In 155 BC, Carneades became scholarch and inaugurated what is called the "New Academy" or "Third Academy." Carneades retained some of Arcesilaus' skepticism, but he believe that, even though we could not have certain knowledge, we could have probable knowledge. Carneades wrote nothing, but his ideas are preserved by his follower Clitomachus, who was scholarch from 129 to 110 BC.

Philo of Larissa (who was scholarch from 110 to 84 BC) changed his opinions during his life and he came to believe even more strongly that we can have valid knowledge, leading some to say that he was so different from Carneades and Clitomachus that he founded a "Fourth Academy." In 88 BC, Philo left Athens and went to Rome to escape the war between Rome and King Mithridates VI of Pontus, who challenged Rome's increasing dominance over the Greek world. Here he wrote what scholars call his "Roman books," with his new opinions, but we know little about the content of these books, and even their titles have not survived.

In about 90 BC, Philo's student Antiochus of Ascalon began teaching his own version of Academic philosophy. He claimed to be returning to the original teachings of the Old Academy, but he was actually creating a fusion of the ideas of the Old Academy, the Peripatetics, and the Stoics. Antiochus rejected the skepticism of the New Academy and said we could have knowledge, and he is sometimes considered the founder of a "Fifth Academy."

Many scholars accept this conventional history, but it is based on revisionist histories of the Academy promoted by Antiochus and Clitomachus, who both had reasons to distort history in order to support their own beliefs.

Antiochus' Revisionist History

Antiochus was the first to divide the history of the Academy into phases, and he said simply that there was an "Old Academy" of Plato which was dogmatic, and a "New Academy" of Arcesilaus, Carneades, Clitomachus, and Philo, which was skeptical. Though he was actually synthesizing the teachings of several schools, Antiochus called his own school the Old Academy and claimed that he was restoring the original Platonist philosophy that the skeptics had abandoned.

But it is not plausible that the Old Academy shared Plato's dogmatism during its entire history. Both the Middle Academy and the New Academy focused on criticizing Stoic epistemology and ignored the equally dogmatic Platonist epistemology. This indicates that, by the time of the Middle Academy, Platonist epistemology had already dropped out of the debate and was not taken seriously.

There is historical evidence that the Old Academy gradually became more skeptical after Plato's death.

Speusippus, who was Plato's successor as scholarch, rejected the theory of ideas that was the basis of Plato's epistemology, though we do not know what he replaced it with.

Xenocrates, his successor, said there were three forms of cognition: knowledge (epistêmê) of mathematical objects, sensation (aisthêsis) of the phenomenal world, and opinion (doxa) about objects of both the reason and the senses, such as the stars. This seems to be a large step in the direction of skepticism, saying that we can have certain knowledge only in a limited realm.

We know very little about Xenocrates' two successors, Polemo and Crates, except that Polemo is said to have followed Xenocrates closely.

From the bit we know, it seems that there was a gradual movement toward skepticism among Plato's successors, and that Arcesilaus simply carried that movement to its logical conclusion. Arcesilaus did invent the idea of epochê, suspension of judgment, but there was not a sudden change from the dogmatism of the Old Academy to the skepticism of Arcesilaus, as Antiochus claimed.

Varro, speaking on behalf of Antiochus in Cicero's Academica, was clearly wrong to claim that "… Speusippus and Xenocrates, who were the earliest supporters of the system and authority of Plato, - and, after them, Polemo and Crates, and at the same time Crantor, - being all collected together in the Academy, diligently maintained those doctrines which they had received from their predecessors." Antiochus invented this history so he could claim that he was the successor to all of these early Platonists and that his Old Academy was rejecting the innovations of the skeptical New Academy.

Clitomachus' Revisionist History

Clitomachus claimed that he advocated the ideas of Carneades because Carneades was a very popular teacher. Some time later, Philo also claimed to be stating the ideas of Carneades, even where he disagreed with Clitomachus, and his motive was obviously the same: to boost the prestige of his ideas by attributing them to Carneades.

There were disputes at the time about whether Clitomachus spoke for Carneades. Metrodorus of Stratonicea, who had been a student of Carneades, said that he believed a wise man could hold opinions, and Philo of Larissa accepted this idea before the days of his Roman books. By contrast, Clitomachus said that Carneades claimed that the wise man could hold opinions not because he believed it but because he used the method of arguing all sides of a case. On this point, Cicero agreed with Clitomachus, saying:

"… it was quite possible for a man to perceive nothing, and nevertheless to be guided at times by opinion; which is said to have been admitted by Carneades. I, indeed, trusting rather to Clitomachus than to Philo or Metrodorus, believe that he [Carneades] argued this point rather than that he admitted it."

Yet there were other disagreements between the two, and Cicero said that Metrodorus generally was right. Cicero praised Clitomachus for his "industry, as the number of books which he composed testifies" and for his "brilliancy of genius," but he concluded his encomium of Clitomachus with this reservation: "But Metrodorus of Stratonice was thought to be the one who had the most thorough understanding of Carneades."

In addition to his dispute with Metrodorus, the way in which Clitomachus became scholarch also leads us to believe that there was a struggle within the Academy about who spoke for Carneades after his retirement.

In 140/39 BC, after studying with Carneades for nineteen years, Clitomachus left the Academy and formed his own school in the Palladium, attracting many students. Carneades retired in 137/6 BC, and he was replaced as scholarch by a philosopher with the same name whom he had chosen as his successor, Carneades, son of Polemarchus. This younger Carneades died in 131/0 BC and was succeeded as scholarch by Crates of Tarsus. During Crates' tenure, Clitomachus returned to the Academy and brought his students with him. Philodemus, who wrote a history of the Academy that survives in fragments, says that "Clitomachus stormed into the Academy with many pupils," using the metaphor of a military attack. This history is unclear about exactly when Clitomachus returned, but the most likely interpretation is that he returned near the end of Crates' tenure. Both Carneades and Crates died in 129/8 BC. When Crates died, Clitomachus was elected scholarch and held the position until his death in 110/09 BC.

We have only these bare facts about how Clitomachus became scholarch, and we have to imagine the reality behind them. It seems at least plausible that there was a struggle for control of the Academy after Carneades retired. Carneades picked a successor who reflected his views. Clitomachus' opportunity came when Carneades was either dead or close to death and could no longer influence who should be his successor, so he returned to the Academy with all his students, creating a new majority that could bring his faction into power. It seems plausible that competing factions tried to boost their chances of winning control by claiming that they were the true advocates of Carneades' beliefs.

Thus, the factions that disagreed with each other, Clitomachus and Metrodorus and perhaps others, all claimed to represent Carneades' beliefs. Later historians accepted these claims that the New Academy began with Carneades. For example, Sextus Empiricus (c. 160 – 210 AD) wrote:

Most people say that there were three Academies, the first and oldest one Plato's Academy, the second or Middle Academy of Acresilaos [the Greek spelling] the student of Polemo, and the third or New Academy of Carneades and Clitomachus. Some people add Philo and Charmidas' as Fourth Academy. Some also count Antiochus' as a Fifth Academy.

And Eusebius wrote essentially the same thing a century later.


Carneades becomes a mysterious figure once we realize that it is not necessarily true that Clitomachus spoke for him. Socrates taught orally, and after his death, several of his students claimed that they were carrying on his teachings - but these students all had different philosophies, so it is hard to tell what Socrates himself believed. Likewise, Carneades taught orally, and we know that at least two of his students who disagreed with each other (Clitomachus and Metrodorus) claimed that they were carrying on his teachings, so it is hard to tell what Carneades himself believed.

Most scholars do not realize that these claims about Carneades' beliefs are suspect. Some scholars attribute all of Clitomachus' ideas to Carneades; some rely on what Clitomachus said that Carneades believed; and some quote later sources, primarily Sextus Empiricus, who probably also believed that Clitomachus spoke for Carneades. If we ignore these uncertain testimonies, there is one key fact that we know about Carneades' philosophy: he argued for conflicting sides of an issue, showing that the conflicting arguments were all convincing in order to unsettle the belief that reasoning can lead us to truth.

One example of this tactic survives. In Rome, Carneades gave two lectures on two successive days, the first arguing that we can understand justice and should act justly, and the second arguing that justice is a social convention so that it is foolish to do what is just rather than what is in your self-interest. These lectures attracted the youth but scandalized the establishment. The second lecture was transcribed or reconstructed, and Cicero copied it into De Republica. We are publishing it here for the first time as a lecture of Carneades with all the available background material about it, which should make it more accessible than it has been in the past, buried in the text of De Republica.

We have other testimonies about this tactic of Carneades. For example, Cicero tells us, "Carneades passed in review all the opinions as of that Chief Good, not only that actually had been held by philosophers hitherto, but that it was possible to hold. He then pointed out that no science or art can supply its own starting-point." This review of all possible positions in ethics was influential, and Antiochus summarizes it in the work that we entitle "On Ethics," included in Philosophy of the Syncretic Academy. It is plausible that Carneades argued for all of these possible opinions to show that all the arguments were equally convincing and we could not know which to believe.

Cicero also tells us that Clitomachus himself said that he heard Carneades argue for so many different opinions that he did not know what his actual beliefs were. One of Cicero's speakers says "I may follow Callipho, whose opinion Carneades used to defend with such zeal, that he appeared wholly to approve of it; although Clitomachus affirmed that he never could understand what Carneades approved of," undermining Clitomachus' claim to speak for Carneades.

Arcesilaus used to use a similar tactic: Cicero tells us he "used to … pass most of his days in arguing against every one's opinion, in order that when equally important reasons were found for both sides of the same question, the judgment might more naturally be suspended, and prevented from giving assent to either."

Clitomachus did not use this tactic of Arcesilaus and Carneades. We can see in the selections from his writing in this book that he argued explicitly for and against specific beliefs. In this respect, at least, Carneades was closer to the Middle Academy of Arcesilaus than to the New Academy of Clitomachus.

This book includes the one surviving lecture of Carneades and several works of Clitomachus, so readers can decide for themselves whether Clitomachus was expounding Carneades' ideas.


Unlike Carneades, Clitomachus' opinions are easy to find. Many fragments of his writing survive, including the expositions of his opinions in Cicero's dialogs that are included in this book.
Of the three branches of Hellenistic philosophy, natural science, ethics, and epistemology, Clitomachus concentrated on epistemology, arguing against Stoic dogmatism and for a moderate form of skepticism.

The Stoics believed that some perceptions were self-evidently true and were the basis for knowing truth. They called this sort of perception phantasia katalêptikê. Phantasia means "perception" or "sense impression." Katalêpsis means "comprehension." We could translate phantasia katalêptikê as "comprehensible perception" (as Cicero did in Academica I:11), but because it is a technical term, many scholars use the Greek word and call it a "cataleptic perception" or "cataleptic impression." Cicero tells us that Zeno, the founder of Stoicism, said of this sort of impression, "That it was such as is impressed and stamped upon and figured in us, according to and conformably to something which exists." The Stoic view is discussed in more detail in the introduction to Philosophy of the Stoics.

Arcesilaus and Clitomachus both attacked the idea that we could know the truth through cataleptic perceptions. For example, they said that there is no difference in your perception if you (1) see the same person on two occasions or (2) see identical twins on two occasions. In both cases, you might have a strong conviction that you are seeing the same person twice, your conviction would be true in the first case and false in the second, and there is nothing about the perceptions themselves that lets you see that one is true and the other false. This is one of many arguments that they made against cataleptic perceptions.

Arcesilaus believed that, because we could not know the truth, we should practice epochê (suspension of judgment) and not assent to any beliefs. As Cicero says:

Arcesilaus asserted that there was nothing which could be known, … and that there was nothing which could be discerned or understood; for which reasons it was not right for anyone to profess or affirm anything, or sanction anything by his assent, but men ought always to restrain their rashness and to keep it in check so as to guard it against every fall. For … nothing could be more discreditable than for a man's assent and approbation to precede his knowledge and [cataleptic] perception of a fact.

Clitomachus agreed that we cannot have knowledge but he also said that we should act based on probability, writing:

…there is no appearance of such a character that [cataleptic] perception will follow it, but many such as to draw after them probability. … And, in truth, that wise man whom you are bringing on the stage, is often guided by what is probable, not being comprehended, nor perceived, nor assented to, but only likely; and unless a man acts on such circumstances there is an end to the whole system of life. For what must happen? Has the wise man, when he embarks on board ship, a positive comprehension and perception in his mind that he will have a successful voyage? How can he? But suppose he goes from this place to Puteoli, thirty furlongs, in a seaworthy vessel, with a good pilot, and in fine weather like this, it appears probable that he will arrive there safe. According to appearances of this kind, then, he will make up his mind to act or not to act…. the wise man does not assent to them, because it is possible that something false may exist of the same kind as this true thing.

Clitomachus used the Greek word pithanon; Cicero translated it as probabile, so it is usually translated into English as "probable," though some scholars say that "plausible" or "persuasive" would be better translations.

This debate was framed as the question of whether we should "assent" to our perceptions, and the term "assent" is used frequently in the selections in this book. This book includes part of Clitomachus' book On Withholding Assent, where he argued that we should not assent to our perceptions and believe that they are true, but that withholding assent did not prevent him from finding some perceptions probable or persuasive.

This epistemology seems naive to us today, since we know more about physics and the physiology of perception then they knew in Hellenistic times. Since the time of Locke, Berkeley, and Hume, philosophers have had to grapple with the qualitative difference between the ideas in our minds and the physical objects that we perceive, as they are described by modern physics. For example, there is a qualitative difference between the color red, as it exist in our perception, and electromagnetic radiation with a wavelength of 650 nm, which causes this perception. Aristotle dealt with this issue, but most Hellenistic philosophy misses it completely.

Nevertheless, this debate is important historically, because it is a major theme in Hellenistic philosophy, from the Stoics, who based their epistemology on cataleptic perceptions, to Arcesilaus, Clitomachus, and the Academic skeptics, who denied that there could be cataleptic perceptions, to Antiochus of Ascalon, who used the Stoics' epistemology to defend his own fusion of Academic, Peripatetic, and Stoic thought.

Philo of Larissa

Philo of Larissa succeed Clitomachus and was scholarch from 110 to 84 BC. There have been valuable attempts to reconstruct his ideas from the few testimonia that remain, saying that it seems he believed that we cannot know anything according to the criterion of cataleptic perception, but we can know something in fact. Yet so little remains that we probably will never know much about his thinking unless new manuscripts are discovered.

Cicero wrote a discourse expounding Philo's views at the end of Academica Book I, but only the introduction survives and the exposition of Philo's views is lost because of a gap in the manuscript. Early in Academica Book II, someone talks about "those two books of Philo which were yesterday mentioned by Catulus," but we do not know what those books said or what their titles were. This book has identified two selections that are probably by Philo (which we have named "Defenses of Skepticism" and "On Determinism and Freedom"), but they review and criticize the ideas of other philosophers and do not tell us much about his own beliefs.

Philo's beliefs changed radically during his life, and we know about this change largely because of his dispute with Antiochus of Ascalon.

Initially, he was a skeptic. He followed Metrodorus' interpretation of Carneades' epistemology rather than Clitomachus', but the difference seems to be small. It seems that perhaps Clitomachus said that we could act on probabilities but should not "assent" and form opinions, while Philo said that we could form opinions without claiming that they are knowledge. We looked earlier at this quotation from Cicero:

"… it was quite possible for a man to perceive nothing, and nevertheless to be guided at times by opinion; which is said to have been admitted by Carneades. I, indeed, trusting rather to Clitomachus than to Philo or Metrodorus, believe that he [Carneades] argued this point rather than that he admitted it."

which implies that Philo and Metrodorus attributed this idea to Carneades because they themselves believed it, while Clitomachus did not.

In the final paragraphs of Academica, Catulus says he is coming to believe that we should "assent" and form opinions while recognizing that they are only opinions (which sounds like Philo's view). Cicero, who studied with Philo agrees, and then Hortentius laughs off the entire debate:

I? said Catulus. I return to my father's opinion, which he used to say was derived from Carneades, and think that nothing can be perceived; but still I imagine that a wise man will assent to what is not actually perceived - that is to say, will form opinions: being, however, aware at the same time that they are only opinions, and knowing that there is nothing which can be comprehended and perceived. And, practicing that epochê so as to take probability for a guide in all things, I altogether assent to that other doctrine, that nothing can be perceived. I see your meaning, said I [Cicero]; and I do not very much object to it. But what is your opinion, Hortensius? He laughed, and said, I suspend my judgment. I understand, said I; for that is the peculiar principle of the Academy.

Thus, as far as we can see, it seems that Clitomachus said we should act based on probabilities without "assenting" and adopting opinions, while Philo (before the Roman books, when he still claimed to speak for Carneades) said we should adopt opinions based on probabilities while recognizing that they are opinions rather than knowledge. It seems that both claimed that they were still practicing epochê, like the more radical skeptic Arcesilaus.

This theoretical difference does not seem to have made much of a practical difference. Cicero said that, as a member of the New Academy, he was free to expound the beliefs of all the philosophers, retaining the mental reservation that he was only claiming they were probable, not that they were knowledge.

"It is their [the Stoics'] teachings that I am following in these books…. But our New Academy allows us wide liberty, so that it is within my right to defend any theory that presents itself to me as most probable."

It does not seem to make much of a practical difference whether he thought they were probable guides to life, like Clitomachus, or probable opinions, like Metrodorus and the early Philo.
Philo's beliefs changed when he went to Rome in 88 BC to escape the war between Rome and King Mithridates VI of Pontus, and he wrote what scholars call his "Roman books." These books led Antiochus to attack him, and this dispute is described in the introduction to Philosophy of the Syncretic Academy, which concludes that, in the Roman books, Philo probably adopted some other criterion for truth than cataleptic perceptions.

The End of the Academy

In about 90 BC, Antiochus, who had been Philo's student, began teaching his own version of Academic philosophy, rejecting the skepticism of the New Academy and creating a synthesis of Academic, Peripatetic and Stoic thought. Much of his thinking survives in Cicero's dialogs and is collected in the book, Philosophy of the Syncretic Academy.

Antiochus is often considered the founder of another Academy, but there is not a good name for his school. He himself called it the "Old Academy," saying that he was reverting to the original teachings of Plato and his immediate followers, but this is obviously not true. It is sometimes called the "Fifth Academy," but this numbering assumes that Philo founded a separate Fourth Academy, which many historians do not believe. He is sometimes called a "Middle Platonist," because he stands between Plato himself and the Neo-Platonists of the third to sixth century BC, but this term places him in the larger history of Platonism rather than in the history of the Academy. In these books, we will use a descriptive term and call his teaching "The Syncretic Academy," because he created a synthesis of Old Academic, Peripatetic, and Stoic thought.

The original site of the Academy, founded by Plato in about 387 BC, was destroyed by the Roman general and statesman Sulla in 86 BC, during the Mithridatic War, the war between Rome and King Mithridates VI of Pontus, who challenged Rome's dominance over the Greek world. During this war, Philo fled to Rome and wrote his Roman works. Antiochus was in Alexandria on a diplomatic mission with Lucullus and was so angered by the Roman works that he wrote the book Sosus, his first open criticism of his teacher Philo. Though both Philo and Antiochus claimed to speak for the Academy, the Academy itself did not survive as an institution after its buildings were destroyed in the Mithridatic War.

This internet preview does not include footnotes.