Academic Skepticism and Pyrrhonian Skepticism

Arcesilaus, 315-240 BCE. Arcesilaus succeeded Crates (the fifth head of the Academy), changed the focus of the Academy, and initiated the "New" Academy.

Carneades, 214-129 BCE. Carneades is Arcesilaus' most distinguished successor.

Clitomachus, 187-110 BCE. Clitomachus succeeded Carneades.

Philo of Larisa, 160-83 BCE. Philo was the last head of the New Academy.

Antiochus, 1st century BCE. Antiochus broke away from the New Academy, tried to reestablish the "Old" Academy.

Aenesidemus, 1st century BCE. Aenesidemus broke from the New Academy to found a new skeptical movement under the name of Pyrrho. (Pyrrho lived in the 4th to 3rd century BCE. He seems to have pursued a skeptical way of life but wrote nothing and established no school).
Academic skepticism begins in 265 BCE with Arcesilaus, who succeeded Crates as the sixth head of the Academy Plato founded almost a hundred years earlier in 387 BCE.

Arcesilaus refocused the Academy by interpreting Plato's dialogues in terms of the Socratic practice of exposing the pretense to wisdom. There were disputes about how to understand this skepticism. These disputes eventually give rise to the establishment of a new school under the name of "Pyrrhonian skepticism." This happened in about 100 BCE.

Academic Skepticism

Cicero's Academica. is reconstructed from fragments of two distinct works. The first (Academica Priora) consists in the now lost Catulus and the extant Lucullus. The second (Academica Posteriora) consists in the Academic Books, of which only part of the first book is extant. Book I of the Academica is what remains of the Academic Books. Book II is the Lucullus.
Most of what is known about Academic Skepticism depends on Cicero (106 - 43 BCE).

"It was entirely with Zeno, so we have been told, that Arcesilas set on foot his battle, not from obstinacy or desire for victory, as it seems to me at all events, but because of the obscurity of the facts that had led Socrates to a confession of ignorance.... Accordingly Arcesilas said that there is nothing that can be known, not even that residuum of knowledge that Socrates had left himself--the truth of this very dictum: so hidden in obscurity did he believe that everything lies, nor is there anything that can be perceived or understood, and for these reasons, he said, no one must make any positive statement or affirmation or give the approval of his assent to any proposition, and a man must always restrain his rashness and hold it back from every slip, as it would be glaring rashness to give assent either to a falsehood or to something not certainly known, and nothing is more disgraceful than for assent and approval to outstrip knowledge and perception" (Cicero, Academica I.45).
Zeno of Citium (the founder of Stoicism) introduced what Cicero describes as "new pronouncements" in epistemology (Academica I.40-42). Arcesilaus countered these pronouncements. In opposition to the Stoic position, he seems to have said that "that there is nothing that can be known" and that therefore "we should not assert or affirm anything, or approve it with assent" (Academica I.45). Given that Arcesilaus did say this and that in saying this he did not straightforwardly contradict himself, he cannot be understood to have assented to the view that no one should assent to any view. Still, because it remained unclear exactly how he should be understood, it became a problem within the Academy to understand his opposition to the Stoic pronouncements. This opposition had become a defining feature of the Academy, and there was a serious worry that the school would be undermined if the problem went unsolved.

A Problem in the School

Arcesilaus tried to return to the skepticism he thought Socrates advocated and that Plato had not understood, but in his attempt to return to the skepticism of Socrates, Arcesilaus seems to have done more than ask questions in the manner of Socrates. He seems to assent and believe, and this raised questions about the nature of the skepticism that defined the school.

The Academics and their opponents the Stoics looked back to Socrates, but they saw different things. Socrates' questioning seemed to show that nobody had the knowledge necessary to live a good life, but Socrates did not abandon his questioning. Moreover, according to the Stoics, he was right not to stop because although knowledge is difficult to obtain, it is not impossible.

The Stoics thought that knowledge is possible because there are "cognitive impressions." The thought that nature, in its providence, gives human beings the ability to restrict their assent to these impressions and thus allows them to have the knowledge they need. The beliefs they form by assenting to cognitive impressions are true. Moreover, in the absence of false beliefs, questioning cannot force assent to a cognitive impression to be withdrawn because no argument whose conclusion is the negation of the propositional content of the cognitive impression is valid.

"[Y]ou know the kind of man Chaerephon was, how impetuous in whatever he undertook. Well, once he went to Delphi and made so bold as to ask the oracle ... if there were anyone wiser than I. Now the Pythia replied that there was no one wiser. ... For when I heard this, I thought to myself: 'What in the world does the god mean, and what riddle is he propounding? For I am conscious that I am not wise either much or little. What then does he mean by declaring that I am the wisest? He certainly cannot be lying, for that is not possible for him.' And for a long time I was at a loss as to what he meant; then with great reluctance I proceeded to investigate him somewhat as follows. I went to one of those who had a reputation for wisdom, thinking that there, if anywhere, I should prove the utterance wrong and should show the oracle 'This man is wiser than I, but you said I was wisest' So examining this man--for I need not call him by name, but it was one of the public men with regard to whom I had this kind of experience, men of Athens--and conversing with him, this man seemed to me to seem to be wise to many other people and especially to himself, but not to be so" (Plato, Apology 20e). In countering the Stoics, the Academics take themselves to follow Socrates. To investigate the meaning of the oracle's response to Chaerephon, Socrates searched for someone with the knowledge necessary to live a good life. Because he thought that he himself lacked this knowledge, he needed a way to determine whether his interlocutors had this knowledge. His method was to question his interlocutors and to use their answers as premises in argument for a conclusion that they themselves thought was contrary to something they believed. If his interlocutors were refuted in this way, it seems that Socrates can conclude that they do not have knowledge and thus that they do not disprove the god. The Academics use this same method to investigate the Stoics and their "new pronouncements" in epistemology. The Stoics hold that it is not necessary to withhold assent from all impressions because some impressions are cognitive, and the Academics test them with the an argument whose conclusion is in conflict with this view about assent.

The Socratic method itself does not prevent the Academics from having beliefs or even knowledge. Nor does it prevent some of their beliefs from being about the force of the argument they press against the Stoics and their epistemology. The Socratic method does not prevent the Academics from believing, or even knowing, that the Stoics should accept the argument the Academics press against them and that the Stoics should withhold assent because they insist that assent should be restricted to cognitive impressions and there are no such impressions.

"From this sprang the demand put forward by Hortensius, that your school [= the New Academy] should say that the wise man has perceived [= has a "grasp" or cognition] at least [of] the mere fact that nothing can be perceived [= nothing is cognizable = there are no cognitive impressions = there are no impressions that allows to to "grasp" or cognize the fact the impression represents]. But when Antipater used to make the same demand, and to say that one who asserted that nothing could be perceived might yet consistently say that this single fact could be perceived, namely that nothing else could, Carneades with greater acumen used to oppose him; he used to declare that this was so far from being consistent that it was actually grossly inconsistent: for the man who said there was nothing that was perceived made no exception, and so not even the impossibility of perception could itself be grasped and perceived in any way, because it had not been excepted" (Cicero, Academica II.28-29). If, however, it is the position that defines the school that the Academic but not the Stoic can assent, the question arises as to how Academic skepticism is a consistent position.

Persuasive Impressions

"Carneades holds that there are two classifications of presentations [= impressions (φαντασίαι)], which under one are divided into those that can be perceived [= those impressions to which assent is cognition (κατάληψις)] and those that cannot, and under the other into those that are probable (probabilia) and those that are not probable.... [H]is view is that there is no presentation of such a sort as to result in perception, but many that result in a judgement of probability. For it is contrary to nature for nothing to be probable, and entails that entire subversion of life..." (Cicero, Academica II.99).

The Greek adjective πιθανόν means "persuasive." Cicero renders the Greek into Latin as probabile, "credible, probable."

"[Carneades] too, himself requires a criterion for the conduct of life and for the attainment of happiness, he is practically compelled on his own account to frame a theory about it, and to adopt both the persuasive impression (πιθανὴν φαντασίαν) and that which is at once persuasive and irreversible and tested" (Sextus Empiricus, Against the Logicians I.166-167).

"[J]ust as in ordinary life when we are investigating a small matter we question a single witness, but in a greater matter several, and when the matter investigated is still more important we cross-question each of the witnesses on the testimony of the others,--so likewise, says Carneades, in trivial matters we employ as criterion only the persuasive (πιθανῇ) impression, but in greater matters the irreversible, and in matters which contribute to happiness the tested impression (Sextus Empiricus, Against the Logicians1.184).
Carneades tried to clarify Academic skepticism and its position on assent and belief. He seems to have thought that the Academic can assent to "persuasive" impressions.

In this assent to impressions in terms of their persuasiveness, Carneades seems to have in mind the ordinary way in which human beings think about things and form beliefs once they have sufficient justification relative to the importance they attribute to the matter. Unless something intervenes to stop them, human beings ordinarily consider the matter in question until they have sufficient justification to decide it one way or another given the importance they attach to it. Once they have this justification, they ordinarily accept that the issue is as their thinking has shown it to be.

Although Carneades introduced some clarity into the nature of Academic Skepticism, it remained unclear exactly what the assent permitted to the Academic Skeptic is. Clitomachus and Philo, the subsequent heads of the Academy after Carneades, offered competing explanations.

The evidence is extremely limited, but the explanations seem to be about reliability. The Stoics thought that human beings assent to some impressions and not to others, that human beings assent to cognitive impressions, and that human beings take steps to get a cognitive impression (they look again, look under better light, and so on) if their initial impression is insufficiently clear. Human beings rely on cognitive impressions, and they are right to do so because nature in its providence arranges things so that assent to cognitive impressions results in true beliefs.

The Academics do not think there are any cognitive impressions, but they too assent to some impressions and not others. They do so in terms of what Carneades called the "persuasive" impression. The question, to which Clitomachus and Philo seem to have given different answers, is why they are permitted to rely on and give their assent in terms of these impressions.


Clitomachus distinguishes two ways to withhold assent. The first it to give "absolute assent to no impression at all." The second is not to reply "so as to convey approval or disapproval of something." According to Clitomachus, the Academic Skeptic withholds assent in the first way but not in the second. He is "guided by probability (probabilitatem)" in his "approval" and "disapproval" of impressions. The Academic Skeptic simply says 'yes' or 'no' to his impressions in such a way that he is following his impressions in terms of their persuasiveness.

"For believe [or: to be persuaded (πείθεσθαι)] is said in different ways: sometimes not to resist but simply to follow without any strong impulse or inclination, as the boy is said to believe [or: be persuaded (πείθεσθαι) by] his tutor; but sometimes to assent (συγκατατίθεσθαί) to a thing of by choice and with a kind of sympathy due to strong desire, as when the incontinent man believes [or: is persuaded (πείθεται) by] him who approves of an extravagant mode of life" (Sextus Empiricus, Outlines of Pyrrhonism I.230). "[Clitomachus says] that the formula 'the wise man withholds assent' is used in two ways, one when the meaning is that he gives absolute assent to no impression at all, the other when he restrains himself from replying so as to convey approval or disapproval of something, with the consequence that he neither makes a negation nor an affirmation; and that this being so, he holds the one plan in theory, so that he never assents, but the other in practice, so that he is guided by probability (probabilitatem), and wherever this confronts him or is wanting he can answer 'yes' or 'no' accordingly. In fact as we hold that he who restrains himself from assent about all things nevertheless does move and does act, the view is that there remain impressions of a sort that arouse us to action, and also answers that we can give in the affirmative or the negative in reply to questions, merely following a corresponding impression, provided that we answer without actual assent; but that nevertheless not all impressions of this character were actually approved, but those that nothing hindered" (Cicero, Academica II.104).

Philo of Larisa

"'My view [= Philo's view before his Roman Books]?' replied Catulus, 'I am coming round to the view of my father, which indeed he used to say was that of Carneades, and am beginning to think that nothing can be perceived [= nothing can be cognized], but to deem that the wise man will assent to something not perceived, that is, will hold an opinion, but with the qualification that he will understand (intellegat) that it is an opinion and will know (sciatque) that there is nothing that can be comprehended and perceived; and therefore although [in this way] agreeing with their rule of ἐποχήν [= holding back] as to everything, I assent emphatically to that second view, that nothing exists that can be perceived'" (Cicero, Academica II.148). The way Philo (in his Roman Books) describes the assent the Academic can give appears different from the assent Clitomachus describes. The problem, though, is that given the limited amount of surviving evidence, it is not at all easy to see exactly what this difference is supposed to be.

"[T]he sole object of our discussions is by arguing on both sides to draw out and give shape to some result that may be either true or the nearest possible approximation to the truth (aut verum sit aut ad id quam proxime accedat). Nor is there any difference between ourselves and those who think that they have positive knowledge except that they have no doubt that their tenets are true, whereas we hold many doctrines as probable (probabilia), which we can easily act upon but can scarcely advance as certain..." (Cicero, Academica II.7-8).

"What then is the probability (probabile) that your school [the New Academy] talk about? ... [W]hen they say that it can happen to the wise man that after he has taken every precaution and explored the position most carefully something may yet arise that while appearing to resemble truth (veri simile) is really very far remote from truth, they will be unable to trust themselves, even if they advance at all events a large part of the way, as they are in the habit of saying, towards the actual truth, or indeed come as near to it as possible" (Cicero, Academica II.36)?
One possibility is that Philo thought that the Academic can assent to persuasive impressions because this assent is a way to form beliefs that "come as near to [the truth] as possible."

This explanation is different from the one Cicero attributes to Clitomachus. Clitomachus has no story to tell about about arguments for and against and "resembling the truth." Nor does he think that such a story is necessary. In the Academic opposition to Zeno's "new pronouncements" epistemology, the question is whether the Stoic method of assent in terms of cognitive impressions is better than their method in terms of persuasive impressions. Since to the Academics the method of assent the Stoics propose appears unusable, it seems that the answer Clitomachus gives is that this "new" method is not better than the existing method the Academics use and hence that they will continue to follow their practice of saying 'yes' or 'no' to their impressions in such a way that they are following their impressions in terms of their persuasiveness. This is the ordinary way people form beliefs, and to the Academics the alternative the Stoics propose is not viable.

In this dispute, Philo prevailed. He became head of the Academy in about 110 BCE.

Pyrrhonian Skepticism

"[T]hey had heard these doctrines from Philo at Rome...." (Cicero, Academica II.11).
In his "Roman" Books (lectures he gave in Rome), Philo consolidated his position in a way that seemed to narrow the ground between the Academics and their opponents.

"[Philo had] maintained that there was nothing that could be grasped (that is the expression that we choose in rendering ἀκατάληπτον), if that 'presentation' of which he spoke (for we have by this time sufficiently habituated ourselves by our yesterday's conversation to this rendering of φαντασίᾳ) was, as Zeno defined it, a presentation impressed and moulded from the object from which it came in a form such as it could not have if it came from an object that was not the one that it actually did come from (we declare that this definition of Zeno's is absolutely correct, for how can anything be grasped in such a way as to make you absolutely confident that it has been perceived and known, if it has a form that could belong to it even if it were false?)--but when Philo weakens and abolishes this, he abolishes the criterion between the unknowable and the knowable; which leads to the inference that nothing can be grasped..." (Cicero, Academica II.18).
The evidence is limited, but Philo in his Roman Books seems to have argued that although there is no knowledge as the Stoics conceive of knowledge (in terms of assent to a cognitive impression such that no rational means can force its withdraw), the assent permitted to the Academic Skeptic does result in knowledge if the propositional content of the persuasive impression to which assent is given is true. Under pressure in questioning from someone like Socrates, rational means might convince one to withdraw assent from a persuasive impression whose propositional content is true. In itself, however, Philo seems to have thought that this would not show that the person did not have knowledge up until the point at which he withdrew his assent to the impression.

Now, since Philo (in his Roman Books) allows that even members of the Academy can have knowledge, it seemed to some in the Academy that their school had lost its way.

Aenesidemus (1st century BCE) was one of the Academics who thought that the Academy had moved in the wrong direction under Philo's leadership. In about 100 BCE, in an attempt to return to what thought of as the true skepticism that was lost in the Philonian Academy, Aenesidemus founded a breakaway skeptical movement under the name of "Pyrrhonian skepticism."

The Academy ceased to function after Philo, but the breakaway movement continued in into about the 3rd century CE. Sextus Empiricus (2nd or 3rd century CE) is the chief representative. He "describe[s] in outline the skeptical doctrine" in his Outlines of Pryrrhonism. Just what this "skeptical doctrine" is, and how it relates to Clitomachus's understanding of Carneades and the assent to persuasive impressions, is beyond the scope of this course.

Perseus Digital Library:

Henry George Liddell, Robert Scott, A Greek-English Lexicon: "[There is] an etymological and conceptual connection between pithanon (probable) and peithestai (to follow; cf. PHI, 230). It is this connection which Cicero tries to preserve when he renders pithanon by probabile to make it correspond to the verb for 'approve' or 'accept' which he likes to use, namely probare (Cic., Ac. pr. [Academica II].99; [Academica II.]139)..." (Michael Frede, "The Skeptic's Two Kinds of Assent and the Question of the Possibility of Knowledge," 215. Essays in Ancient Philosophy, Michael Frede (University of Minnesota Press, 1987), 201-222).

"[Carneades' view, says Clitomachus,] is that there is no presentation of such a sort as to result in perception, but many that result in a judgement of probability [or: many that allow for approval (probatio)]" (Cicero, Academica II.99).

πιθανός, pithanos, adjective, "persuasive, plausible,"
πείθω, peithō, verb, "persuade"

Charlton T. Lewis, Charles Short, A Latin Dictionary:
adensio, noun, "assent,"

"[L]et us say a few words on the subject of assent or approval (adsensione atque adprobatione), termed in Greek συγκατάθεσιν..." (Cicero, Academica II.37).

probabilis, adjective, "worthy of approval"
probatio, noun, "approval,"
probo, verb, "to be satisfied with, to approve,"
versimilis, adjective, (veri, noun, "true" + similis, adjective, "like"), "truth-like"

Arizona State University Library. Loeb Classical Library:
Cicero, Academica
Sextus Empiricus, Against the Logicians, Outlines of Pyrrhonism

"[The Academic reliance on the 'probable'] admits of two interpretations. It may be taken in just the sense that this is how human beings in general seem to proceed, or it may be taken in the sense that this is how one ought to proceed if one wants to get a reliable impression, one which if not true, at least has a good chance to be true. Whereas on the first interpretation it is just noted that human beings, as a matter of fact, go about considering matters in a certain way when in doubt, on the second interpretation proper consideration is regarded as conferring some epistemological status on the impression thus arrived at: it has a least a good chance of being true, to be like the truth (versimilis), or else be the truth itself (Cic., Ac. pr. [= Academica II] 7; 32; 66; 99; 107). On the other interpretation, the fact that something appears to be the case goes no way to show that it is true; however much it appears to be the case, this does not itself make it any more likely to be true. The probable is just the persuasive, and there is no reason to assume that plausibility and truth, or even evidence and truth, go hand in hand" (Michael Frede, "The Skeptic's Two Kinds of Assent and the Question of the Possibility of Knowledge," 213-214. Essays in Ancient Philosophy, Michael Frede (University of Minnesota Press, 1987), 201-222).

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