practice of Socrates, which he takes to be the same as Plato's.
"[Socrates] was in the habit of drawing forth the opinions of those with whom he was arguing, in order to state his own view as a response to their answers. This practice was not kept up by his successors; but Arcesilaus revived it and prescribed that those who wanted to listen to him should not ask him questions but state their own opinions. When they had done so, he argued against them. But his listeners, so far as they could, would defend their own opinion" (de Finibus 2.2, translated by Long and Sedley, 68J, see also de Natura Deorum 1.11).
Arcesilaus had (selectively) derived the lesson from Plato's dialogues that nothing can be known with certainty, either by the senses or by the mind (de Oratore 3.67, on the topic of Plato and Socrates as proto-skeptics, see Annas [1992], Shields [1994] and Woodruff [1986]). He even refused to accept this conclusion; thus he did not claim to know that nothing could be known (Academica 45).
Attack on the Stoics
In general, the Stoics were the ideal target for the skeptics; for, their confidence in the areas of metaphysics, ethics and epistemology was supported by an elaborate and sophisticated set of arguments. And, the stronger the justification of some theory, the more impressive is its skeptical refutation. They were also an attractive target due to their prominence in the Hellenistic world. Arcesilaus especially targeted the founder of Stoicism, Zeno, for refutation. Zeno confidently claimed not only that knowledge is possible but that he had a correct account of what knowledge is, and he was willing to teach this to others. The foundation of this account is the notion of katalpsis: a mental grasping of a sense impression that guarantees the truth of what is grasped. If one assents to the proposition associated with a kataleptic impression, i.e. if one experiences katalepsis, then the associated proposition cannot fail to be true. The Stoic sage, as the perfection and fulfillment of human nature, is the one who assents only to kataleptic impressions and thus is infallible.
Arcesilaus argued against the possibility of there being any sense-impressions which we could not be mistaken about. In doing so, he paved the way for future Academic attacks on Stoicism. To summarize the attack: for any sense-impression S, received by some observer A, of some existing object O, and which is a precise representation of O, we can imagine circumstances in which there is another sense-impression S', which comes either (i) from something other than O, or (ii) from something non-existent, and which is such that S' is indistinguishable from S to A. The first possibility (i) is illustrated by cases of indistinguishable twins, eggs, statues or imprints in wax made by the same ring (Lucullus 84-87). The second possibility (ii) is illustrated by the illusions of dreams and madness (Lucullus 88-91). On the strength of these examples, Arcesilaus apparently concluded that we may, in principle, be deceived about any sense-impression, and consequently that the Stoic account of empirical knowledge fails. For the Stoics were thorough-going empiricists and believed that sense-impressions lie at the foundation of all of our knowledge. So if we could not be certain of ever having grasped any sense-impression, then we cannot be certain of any of the more complex impressions of the world, including what strikes us as valuable. Thus, along with the failure to establish the possibility of katalepsis goes the failure to establish the possibility of Stoic wisdom (see Hankinson [1995], Annas [1990] and Frede [1983/1987] for detailed discussions of this epistemological debate).
On suspending judgment
In response to this lack of knowledge (whether limited to the Stoic variety or knowledge in general), Arcesilaus claimed that we should suspend judgment. By arguing for and against every position that came up in discussion he presented equally weighty reasons on both sides of the issue and made it easier to accept neither side (Academica 45). Diogenes counts the suspension of judgment as another of Arcesilaus' innovations (DL4.28) and refers to this as the reason he never wrote any books (4.32). Sextus Empiricus (Outlines of Pyrrhonism [generally referred to by the initials of the title in Greek, PH] 1.232) and Plutarch (Adversus Colotes 1120C) also attribute the suspension of judgment about everything to him.
Determining precisely what cognitive attitude Arcesilaus intended by "suspending judgment" is difficult, primarily because we only have second and third hand reports of his views (if indeed he endorsed any views, see Dialectical Interpretation below). To suspend judgment seems to mean not to accept a proposition as true, i.e. not to believe it. It follows that if one suspends judgment regarding p, then he should neither believe that p nor should he believe that not-p (for this will commit him to the truth of not-p). But if believing p just means believing that p is true, then suspending judgment regarding everything is the same as not believing anything. If Arcesilaus endorsed this, then he could not consistently believe either that nothing can be known or that one should consequently suspend judgment.
Dialectical Interpretation
One way around this problem is to adopt the dialectical interpretation (advanced by Couissin [1929]). According to this interpretation, Arcesilaus merely showed the Stoics that they didn't have an adequate account of knowledge, not that knowledge in general is impossible. In other words, knowledge will only turn out to be impossible if we define it as the Stoics do. Furthermore, he did not show that everyone should suspend judgment, but rather only those who accept certain Stoic premises. In particular, he argued that if we accept the Stoic view that the Sage never errs, and since katalepsis is not possible, then the Sage (and the rest of us insofar as we emulate the Sage) should never give our assent to anything. Thus the only way to achieve sagehood, i.e. to consistently avoid error, is to suspend judgment regarding everything and never risk being wrong (Lucullus 66-67, 76-78, see also Sextus Empiricus, Against the Logicians [generally referred to by the initial M, for the name of the larger work from which it comes, Adversus Mathematikos] 7.150-57). But the dialectical Arcesilaus himself neither agrees nor disagrees with this.
Practical Criterion: to eulogon
The biggest obstacle to the dialectical interpretation is Arcesilaus' practical criterion, to eulogon. Arcesilaus presented this criterion in response to the Stoic objection that if we were to suspend judgment regarding everything, then we would not be able to continue to engage in day to day activities. For, the Stoics thought, any deliberate action presupposes some assent, which is to say that belief is necessary for action. Thus if we eliminate belief we will eliminate action (Plutarch, Adversus Colotes 1122A-F, LS 69A).
Sextus remarks that
"inasmuch as it was necessary . . . to investigate also the conduct of life, which cannot, naturally, be directed without a criterion, upon which happiness-that is, the end of life-depends for its assurance, Arcesilaus asserts that he who suspends judgment about everything will regulate his inclinations and aversion and his actions in general by the rule of 'the reasonable [to eulogon],' and by proceeding in accordance with this criterion he will act rightly; for happiness is attained by means of wisdom, and wisdom consists in right actions, and the right action is that which, when performed, possesses a reasonable justification. He, therefore, who attends to 'the reasonable' will act rightly and be happy" (M 7.158, translated by Bury).
There is a good deal of Stoic technical terminology in this passage, including the term eulogon itself, and this may seem to support the dialectical interpretation. On this view, Arcesilaus is simply showing the Stoics both that their account of knowledge is not necessary for virtue, and that they nonetheless already have a perfectly acceptable epistemic substitute, to eulogon (see Striker [1980/1996]). But this raises the question, why would Arcesilaus make such a gift to his Stoic adversaries? It would be as if, Maconi's words, "Arcesilaus first knocked his opponent to the ground and then gave him a hand up again" (1988: 248). Such generosity would seem to be incompatible with the purely dialectical purpose of refutation. Similarly, if he had been arguing dialectically all along, there seems to be no good reason for him to respond to Stoic objections, for he was not presenting his own views in the first place. On the other hand, the proponent of the dialectical view could maintain that Arcesilaus has not done any favors to the Stoics by giving them the gift of to eulogon; rather, this 'gift' may still be seen as a refutation of the Stoic view that a robust knowledge is necessary for virtue.
An alternative to the dialectical view is to interpret to eulogon as Arcesilaus' own considered opinion regarding how one may live well in the absence of certainty. This view then encounters the earlier difficulty of explaining how it is consistent for Arcesilaus to endorse suspending judgment on all matters while at the same time believing that one may attain wisdom and happiness by adhering to his practical criterion.
Carneades
Arcesilaus was succeeded by Lacydes (c. 243 B.C.E.), and then Evander and Hegesinus in turn took over as heads of the Academy. Following Hegesinus, Carneades of Cyrene (c. 213 to 129 B.C.E.), perhaps the most illustrious of the skeptical Academics, took charge. Rather than merely responding to the dogmatic positions that were currently held as Arcesilaus did, Carneades developed a wider array of skeptical arguments against any possible dogmatic position, including some that were not being defended. He also elaborated a more detailed practical criterion, to pithanon. As was the case with Arcesilaus, he left nothing in writing, except for a few letters, which are no longer extant (DL 4.65).
Socratic Dialectic
Carneades employed the same dialectical strategies as Arcesilaus (Academica 45, Lucullus 16), and similarly found his inspiration and model in Plato's Socrates. The Socratic practice which Carneades employed, according to Cicero, was to try to conceal his own private opinion, relieve others from deception and in every discussion to look for the most probable solution (Tusculan Disputations 5.11, see also de Natura Deorum 1.11).
In 155 B.C.E., nearly one hundred years after Arcesilaus' death in 243, Carneades is reported to have gone as an Athenian ambassador to Rome. There he presented arguments one day in favor of justice and the next he presented arguments against it. He did this not because he thought that justice should be disparaged but rather to show its defenders that they had no conclusive support for their view (Lactantius, LS 68M). Similarly, we find Carneades arguing against the Stoic conception of the gods, not in order to show that they do not exist, but rather to show that the Stoics had not firmly established anything regarding the divine (de Natura Deorum 3.43-44, see also 1.4). It seems then that Carneades was motivated primarily by the Socratic goal of relieving others of the false pretense to knowledge or wisdom and that he pursued this goal dialectically by arguing both for and against philosophical positions.
On ethical theory
But whereas Arcesilaus seemed to limit his targets to positions actually held by his interlocutors, Carneades generalized his skeptical attack, at least in ethics and epistemology. The main task of Hellenistic ethics was to determine the summum bonum, the goal at which all of our actions must aim if we are to live good, happy lives. Carneades listed all of the defensible candidates, including some that had not actually been defended, in order to argue for and against each one and show that no one in fact knows what the summum bonum is, if indeed there is one (de Finibus 5.16-21). He may have even intended the stronger conclusion that it is not possible to acquire knowledge of the summum bonum, assuming his list was exhaustive of all the serious candidates.
On the Stoic sage
As with Arcesilaus, Carneades also focused much of his skeptical energy on the Stoics, particularly the views of the scholarch Chrysippus (DL 4.62). The Stoics had developed a detailed view of wisdom as life in accordance with nature. The Stoic sage never errs, he never incorrectly values the goods of fortune, he never suffers from pathological emotions, and he always remains tranquil. His happiness is completely inviolable since everything he does and everything he experiences is precisely as it should be; and crucially, he knows this to be true. Even though the Stoics were extremely reluctant to admit that anyone had so far achieved this extraordinary virtue, they nonetheless insisted that it was a real possibility (Luc. 145, Tusc. 2.51, Seneca Ep. 42.1, M 9.133, DL 7.91).
As a dialectician, Carneades carefully examined this conception of the sage. Sometimes he argued, contrary to the Stoic view, that the sage would in fact assent to non-kataleptic impressions and thus that he was liable to error (Luc. 67); for he might form opinions even in the absence of katalepsis (Luc. 78). But he also apparently argued against the view that the sage will hold mere opinions in the absence of katalepsis (Luc. 112). Presumably he didn't himself endorse either position since the issue that had to be decided first was whether katalepsis was even possible. In other words, if certainty is possible, then of course the sage should not settle for mere opinion. But if it is not possible, then perhaps he will be entitled to hold mere opinions, provided they are thoroughly examined and considered.
On epistemology
Just as Carneades generalized his skeptical attack on ethical theories, he also argued against all of his predecessors' epistemological theories (M 7.159). The main task of Hellenistic epistemology was to determine the criterion (standard, measure or test) of truth. If the criterion of truth is taken to be a sort of sense-impression, as in the Stoic theory, then we will not be able to discover any such impression that could not in principle appear true to the most expertly trained and sensitive perceiver and yet still be false (M 7.161-65, see Arcesilaus' 'Attack on the Stoics' above). But if we can discover no criterial sense-impression, then neither will the faculty of