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Dictionary of the History of Ideas

Studies of Selected Pivotal Ideas

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1. One of Pyrrho's achievements, according to
Timon (cf. DL IX.65) was to break the chains of false
opinion; what opinions he attacked, and by what
means, we do not know. Timon himself denounces
rather than refutes his adversaries; but the fragments
of his works indicate that he discussed appearance as
the limit of certainty (DL IX.105), the method of
hypothesis (AM III.2), and the divisibility of time (AM
VI.66, X.197). He also held, apparently, that nothing
is by nature good (AM XI.140). Our information, how-
ever, is too slight to permit the identification of his
opponents or the reconstruction of his arguments.

With Arcesilaus the picture is clearer but still far
from complete. He undertook to argue on either side
of any question (DL IV.28; cf. IX.51, where Protagoras
is said to have held that for every argument there is
a counterargument) and to refute whatever opinion
anyone expressed (Ac. I.45; ND I.11; Fin. II.2; Or.
III.67; PE XIV.7.15). The opinion that chiefly interested
him was the Stoic view that some appearances can of
themselves be apprehended as certainly true. In rebut-
tal he defended the thesis that no appearances can be
so apprehended. This thesis was known as akatalepsia
(“nonapprehension”) (cf. AM VII.153-55; PE XIV.7.4).
It was sometimes taken to be a statement of the skepti-
cal position, along with epochē, “suspension of judg-
ment” (Ac. II.59; Plutarch, Moralia 1121F-1122A). A
more cautious interpretation would be that the
polemical postures assumed by Arcesilaus in order to
refute the Stoics are not necessarily positions to which
he himself subscribed; otherwise he becomes liable to
the charge of holding “dogmatically” that nothing can
be known. Such an accusation was in fact made against
the Academy (cf. Ac. II.28-29; NA XI.5.8; PH I.226);
but Cicero says quite explicitly that the Academic
Skeptics suspended judgment on every question, as the
arguments on both sides were of equal weight (Ac.
I.45), and Sextus absolves Arcesilaus, at least, from the
charge of dogmatism (PH I.232).

A second view that Arcesilaus is said to have
attacked is the doctrine that pleasure is the highest
good (cf. Fin. II.2). This was the view of two contem-
porary schools, the Cyrenaic and the Epicurean. Here
Arcesilaus might well have drawn on Plato; but the
evidence is lacking.

With Carneades our knowledge of the nature and
range of skeptical polemic is greatly increased.
Carneades' discussion of the problem of knowledge was
broadened to refute not only the Stoics (who were still
the primary target) but all others who claimed to have
found an infallible test of truth. Some idea of his argu-
ments can be got from Cicero, Ac. II.79-98 and from
Sextus, AM VII.159-65. Similarly in his discussion of
ethical theory he gave an exhaustive enumeration of
possible views of the summum bonum, or “highest
good” (Fin. V.16-20). His practice of arguing both sides
of a question is illustrated by his two speeches on
justice delivered at Rome on the occasion of the em-
bassy from Athens in 155 B.C. His arguments against
natural justice can be recovered in part from the
fragmentary remains of Cicero, De republica III, where
Philus is his spokesman.

Carneades also developed arguments against philo-
sophical theology. The best-known are (1) that the
powers and activities assigned to divine beings are not
consistent with their being changeless and eternal (AM
IX.137-81; ND III.29-34); (2) that the evils in the
universe are not consistent with divine providence
(Plutarch, Moralia, frag. 193 ed. Sandbach, from
Porphyrius, De abstinentia III.20; Ac. II.120); (3) that
the occurrence of accidental designs, for example, a
rock that has the form of a head, invalidates the argu-
ment that a design implies a designer (Div. I.23); and
(4) that no clear boundary can be drawn between what
is divine and not divine (ND III.43-50; AM
VII.182-90). This last argument is an example of the
sorites, or “heap,” a device for obscuring boundaries
by pointing to continuous gradations. It was also used,
presumably by Carneades (cf. Ac. II.49 and 92-95), to
obscure the distinction between illusions and veridical
sense perceptions.

Carneades' methods exhibit certain tendencies that
became increasingly strong in later skepticism. One
such tendency is toward the schematic formulation of
alternatives, as exhibited in the discussion of the
summum bonum. Compare also his attack on divina-
tion (Div. II.9-12), where the possible objects of
divination are systematically enumerated and rejected.


It is tempting to assign also to Carneades the series
of propositions (PH III.10-11) on the power and provi-
dence of god, a scheme which Lactantius assigns to
Epicurus—rather improbably, inasmuch as it entails
the rejection of Epicurean theology; see Lactantius,
De ira Dei, 13.20-21 and De Lacy, Transactions of the
American Philological Association,
79 (1948), 18-19.
The tendency toward schematic analysis is seen also
in the argument on fate reported by Cicero, De fato
31; and it is commonly supposed that Carneades
formulated the “four heads” (Ac. II.83) from which it
follows that nothing can be apprehended through sense
perception. Carneades anticipates a later trend also in
his examination of the notion of the divine. Compara-
ble examinations were subsequently made of cause (AM
IX.195-266), body (ibid. 359-440), time (AM X.169-
247), and the like, the aim being in each case to show
that no consistent account of these concepts can be

The development of characteristically skeptical
analyses and arguments led to two levels of refutation,
one level employing arguments that dogmatists use
against each other, the other the distinctively skeptical
arguments. There is a hint of this already in Carneades,
who opposes to the Stoic doctrine of fate not only his
own dialectical refutation but also the Epicurean re-
jection of fatalism (Cicero, De fato 21-23). The mutual
support of Epicureans and skeptics against Stoics or
Platonists appears again in Div. II.51 and in Sextus'
attacks on the teachers of the arts and sciences (AM

A fairly good example of skeptical polemics in the
Carneadean tradition is the speech of Cicero in Ac.
II.64-146. It includes a historical sketch, arguments to
discredit both sense perception and reasoning as
sources of certain knowledge, a defense of Carneades'
doctrine of probability (see below, III, 3), and an ac-
count of the disagreements of the dogmatists in physics,
ethics, and logic.

At some time the scope of skeptical attack was
broadened to include among its targets the theoretical
arts and sciences. Medicine was among the first to be
involved in this controversy. The split between the
theoretical and empirical approaches to medicine is
evident already in the Hippocratic corpus (fifth century
B.C.); and an Empirical School of medicine, with strong
tendencies toward skepticism, was founded by Philinus
in the third century B.C. Members of this school in later
times praised Pyrrho for having followed appearances
in everyday activities and having suspended judgment
about all else (cf. Galen, Subfiguratio empirica, in
Deichgräber, p. 82). The statement that “Appearance
prevails wherever it goes” is indeed found in the frag-
ments of Timon (cf. AM VII.30), and it provides a basis
for the view that the arts and sciences which limit
themselves to the use of appearances are legitimate,
whereas those that claim to say something about the
real nature of things are not. This is the view that
Sextus adopts in AM I-VI. There are a few indications
that the Academic Skeptics also discussed the arts and
sciences. In Ac. II.122 Cicero mentions the empirical
physicians' conviction that the nature of the body
cannot be discovered by dissection, as the concealed
organs may be altered by the mere act of laying them
bare. Cicero also rejects the argument that the skeptic's
attack on knowledge is an attack also on the arts; some
arts, he says, admit that they use conjecture more than
knowledge, and others such as painting and sculpture
are guided by what appears rather than by what is
(Ac. II.22, 107, 146). There is no evidence, however,
that the Academic Skeptics attacked mathematics.

Aenesidemus is best known for the ten tropes (see
below, III, 2). Underlying the tropes is a formulation
of the epistemological problem in terms of signs: if
from the apparent we obtain knowledge of the non-
apparent, then the apparent serves as a sign, the
nonapparent as a thing signified (see Photius, III, 121).
But, Aenesidemus argues (cf. AM VIII.215-35), if signs
were apparent they would appear the same to all who
are in a similar state, that is, there would be no dis-
agreement about what they signify. But there is
disagreement; therefore signs are not apparent. Sextus
gives a much fuller account of this doctrine of signs.
He divides the nonapparent into three kinds: (1) the
absolutely nonapparent, e.g., the number of grains of
sand in Libya; (2) the nonapparent by nature, e.g., the
invisible pores in the skin, or the void outside the
universe; and (3) the nonapparent at the moment, e.g.,
the city of Athens. Things absolutely nonapparent may
be left out of consideration. Things by nature non-
apparent can be known only if there are appearances
which point to them unambiguously (indicative signs),
as the movements of the body are said to be signs of
the soul or motion a sign of void. Things nonapparent
at the moment can be signified by present appearances
that remind us of them (admonitive signs), as smoke
is the sign of fire, a scab is the sign of a wound (AM
VIII.141-55). Sextus does not challenge the possibility
of admonitive signs; they presuppose no necessary
connection between sign and thing signified, and they
are adequate to account for the connections that we
establish between things in everyday activities (AM
VIII.155-58). Reminding is, in fact, the skeptics' sub-
stitute for proof; see for example, PH III.20; De Lacy,
Phronesis, 3 (1958), 71. But about the indicative sign,
which is the invention of dogmatic philosophers and
theorizing physicians, the skeptic withholds judgment,
as he finds the arguments against it as strong as those


for it (AM VIII.159-298). Sextus includes the argument
of Aenesidemus mentioned above as a part of his attack
on the indicative sign.

The very length of Sextus' discussion of signs testifies
to their importance in skeptical polemic (cf. also DL
IX.96-97). His reference to theoretical medicine and
his use of medical examples suggest that the terms in
which he presents the problem may have been current
in medical controversy. A more widespread practice
was to distinguish between common signs, which are
ambiguous in their reference, and particular signs,
which signify one thing only. This distinction is found
in medical writers, who use it in the identification of
symptoms; see for example Galen, Commentary on
Hippocrates' De Officina Medici,
I.1 (ed. Kühn, XVIII,
2, 643-45). It appears also in rhetorical theory (cf.
Cicero, Partitiones oratoriae, 34) and in philosophical
controversy of the Hellenistic period (see Philodemus,
De signis, cols. 1 and 14). There is reason to suppose
that Carneades' attack on Stoic epistemology was at
some time stated in terms of this distinction: the Stoics
regarded some sense perceptions as particular signs,
others as common signs. Carneades challenged them
to show that any appearance is ever a particular sign
(Ac. II.33-34, 84, 103).

Another matter of major concern to Aenesidemus
was the notion of cause. Sextus reports an argument
that he used to show that one thing cannot cause, i.e.,
generate, another (AM IX.218-26). In addition, he
formulated eight ways of attacking dogmatic theories
of causation (the eight tropes; cf. PH I.180-84; Photius,
III, 122). Photius reports that Aenesidemus also dis-
cussed truth (cf. AM VIII.40-47), motion, the universe
and the gods, the objects of choice and avoidance, the
virtues and the summum bonum (cf. AM XI.42).

Sextus' treatises are by far the most extensive of the
ancient skeptical writings that have survived; and
although Sextus incorporates many items derived from
earlier skeptics, his presentation and elaboration seem
to be his own. For example, no model has been found
for his six books on the special disciplines (AM I-VI)
or for his discussion of ethics (AM XI, PH III.168-279).
He also gives a long and detailed treatment of cause
(AM IX.195-266; cf. DL IX.97-99). Of the many other
matters that he takes up, perhaps the most important
is his attack on Stoic and Peripatetic logic (PH
II.134-203; AM VIII.300-481). Sextus had a com-
mendable familiarity with early Greek philosophy, and
he ranks as an important source of information about
the pre-Socratics and others whose works have been
lost. He has, besides, an obvious enthusiasm for his
subject, which sometimes turns to playfulness (e.g., PH
I.62-63). It is perhaps because his writings were more
than mere compilations that they survived.