Skepticism in the Academy
Academic Skepticism begins in 265 BC with Arcesilaus, who succeeded Crates as the sixth head of the Academy Plato founded almost a hundred years ago in 387 BC.
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 BC.
Arcesilaus, 315-240 (succeeded Crates as the sixth head of the Academy, changed the focus of the Academy, and initiated the "New" (Skeptical) Academy)
Carneades, 214-129 (Arcesilaus' most disguished successor)
Clitomachus, 187-110 (one of Carneades' students)
Philo of Larisa, 160-83 (last head of the New Academy)
Antiochus, 1st century BC (broke away from the New Academy, tried to reestablish the "Old" Academy)
Aenesidemus, 1st century BC (broke from the New Academy, founded new movement named after Pyrrho (who pursued a skeptical way of life but wrote nothing and established no school))
Most of what is known about Academic Skepticism depends on Cicero (106 - 43 BC) and the discussion in his Academica.
The Academica is a dialogue 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.
Skeptical and Dogmatic Assent
"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).
Arcesilaus tried to return to the skepticism he thought Socrates advocated and that had been misunderstood in the Academy, 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 argue for and assent to the impression that
(•) It is not permitted to assent.
This raised a question within the Academy about the nature of the skepticism that defined the school, since Arcesliaus seems to assent to (•).
Assent to the "plausible" or "probable" impression
Carneades, who was fourth in succession after Arcesilaus, tried to clarify Academic Skepticism and its position on assent and knowledge.
The Academic Skeptic does not assent to the impression that all assent is prohibited. This would make Academic Skepticism straightforwardly incoherent. Instead, the Academic Skeptic assents to the impression that the kind of assent the Stoics require for knowledge is prohibited. This has the consequence that there is more than one kind of assent.
"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" (Academica II.28-29).
What are these kinds of assent?
Carneades seems to have thought that one kind of assent is the assent that the Academic Skeptic gives to a "plausible" or "probable" impression. This is the kind of assent that Arcesilaus and other Academic Skeptics give to the impression that the kind of assent the Stoics require for knowledge is prohibited.
"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, plausible." 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 plausible impression (πιθανὴν φαντασίαν) and that which is at once plausible and irreversible and tested" (Sextus Empiricus, Against the Logicians I.166-167).
Skeptical assent: Clitomachus and Philo
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 of this "skeptical" assent.
What are these competing explanations?
The evidence is 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 Academic Skeptics do not think there are any cognitive impressions, but they too assent to and rely on some impressions and not others. They rely on what Carneades called the "plausible" or "probable impression." The question, to which Clitomachus and Philo seem to have given different answers, is why they are right to rely on these impressions.
The two conceptions of skeptical assent
"After setting out these points, he [Clitomachus] adds 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 (omnino eum rei nulli adsentiri), 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).
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 in the first way but not the second. He is "guided by probability (probabilitatem)" in his "approval" and "disapproval" of impressions.
"'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).
It seems that Philo (before his Roman Books) also thought that the Academic Skeptic gives "absolute assent to no impression at all," but the description of the way he assents appears different from the assent Clitomachus describes. The problem, though, is that given the surviving evidence, it is not at all easy to see exactly what this difference is supposed to be.
The difference between the two conceptions
There looks to be part of an answer in the following attack on the Academic Skeptics:
"What then is the probability that your school talk about? For if what a particular person happens to encounter, and almost at first glance thinks probable, is accepted as certain, what could be more frivolous than that? ... [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 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. For to enable them to trust their judgement, it will be necessary for the characteristic mark of truth to be known to them, and if this be obscured and suppressed, what truth pray will they suppose that they attain to" (Cicero, Academica II.36)?
The suggestion seems to be that it is rational to rely on "probability" because assenting to "probable" impressions is forming beliefs that "come as near to [the truth] as possible."
"[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. 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, which we can easily act upon but can scarcely advance as certain..." (Cicero, Academica II.7-8).
Clitomachus, it seems, does not advance this understanding of why the Academic Skeptic can "trust their judgement." His view is in a way even more skeptical.
"[The 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. 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 plausible, 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" in Essays in Ancient Philosophy, 213-214).
In his Roman Books, Philo consolidated his position in a way that seemed to narrow the ground between the Skeptics and their opponents.
"[T]hey had heard these doctrines from Philo at Rome...." (Cicero, Academica II.11).
The evidence of his view in the Roman Books is limited, but he 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 results in knowledge if the content of the "plausible" impression to which assent is given is true. Under pressure in questioning from someone like Socrates, rational means might convince one to withdraw his assent from a "plausible" impression whose propositional content is true. In itself, however, Philo (in his Roman Books) thought that this would not show that the person did not have knowledge up until the point he withdrew his assent to the impression.
"[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).
Now, since even members of the Academy allowed for the possibility of knowledge, it seemed to some in the Academy that their school had lost its way.
Aenesidemus (1st century BC) was one of the Academic
Skeptics who thought that the Academy had moved in the wrong direction under
Philo's leadership. In an attempt to return to the true
skepticism he thought was lost in the Philonian Academy,
founded a breakaway skeptical movement under the name of
This new skeptical movement continued into the 3rd century AD.