## 1. Life and Work



The external facts of Philo's career are largely undisputed. He
was born in 159/8 BCE (but see Fleischer 2017b). After eight years of
study with Callicles, a student of Carneades, in his native Larissa,
Philo moved to Athens in 134/3 BCE, where he spent fourteen years with
Clitomachus, another of Carneades' students, who was the
scholarch (or head) of the Academy from 129/8 (or perhaps 127/6) to
his death in 110/9 BCE. Philo was elected to replace Clitomachus in
that year, and remained the scholarch until his death in 84/3 BCE.



Philo's tenure as head of the Academy was troubled by two
events. First, in the late 90s BCE his authority was challenged by the
secession of his student Antiochus of Ascalon, who set up a rival
anti-skeptic "Old Academy". (A second student,
Aenesidemus, also left the Academy to found or revive the radically
skeptical Pyrrhonist school, probably in the 90s BCE; but the dating
of this secession to Philo's tenure as scholarch is insecure.)
Secondly, civil unrest in Athens and the threat of the Mithridatic war
led to an exodus of Academic philosophers to safer cities. Philo
himself moved to Rome in 89/8 BCE, where he continued to give lectures
and published his "Roman Books". It is unclear whether he
ever returned to Athens after its "pacification" by the
Romans in 86 BCE. The name of his successor as scholarch, who probably
oversaw the final demise of the Academy as an institution, is also
unclear. (The section of Philodemus' *Catalogue of Academic
Philosophers*--our main source for his
biography--dealing with Philo's death, his students, and
his successor, is at several points illegible; see Fleischer 2017c.)
None of Philo's written works survive, but we possess a summary
of a work on ethics, some direct evidence for his Roman Books and
earlier epistemological views, and indirect evidence for a work on
rhetoric.


## 2. The Evidence for the Development of Philo's Views



Since the evidence for Philo's various epistemological views is
philosophically rich but radically incomplete, their interpretation is
unsurprisingly controversial. The primary sources agree that
Philo's views evolved between his election as scholarch in 110/9
BCE and the publication of the Roman Books in 88 BCE; but the precise
stages of his epistemological evolution and the arguments that led
Philo to change his mind are not explicitly described in the texts we
have.



Our evidence indicates (and no scholar disputes this) that Philo began
as an adherent of the radical skepticism attributed to Carneades by
Clitomachus. The two central questions that the evidence appears to
leave open are:


1. Did Philo change his epistemological position in the period
preceding the Roman Books?
2. What was the epistemological position of the Roman Books?



In order to understand these questions it is important to know
something about the context in which Philo's views evolved.
Several sources make it clear that when Philo arrived in Athens in the
130s BCE, the Academy was sharply divided over the legacy of
Carneades. One side, led by Clitomachus, advocated radical skepticism
as the authentic Carneadean position, while another, led by Metrodorus
of Stratonicea, promoted some form of mitigated skepticism. We know,
however, that Philo was elected scholarch in 110/9 BCE as a
representative of the Clitomachian, i.e., radically skeptical, wing of
the Academy (see Numenius fragment 28). We also know that the
epistemological views in his Roman Books in 88 BCE were regarded as
shocking innovations by Academics of all kinds (see Cicero
*Academica* [*Ac*.] 2.18).



With respect to the first question, this suggests that, if Philo
abandoned radical skepticism prior to the Roman Books, then he adopted
the form of mitigated skepticism earlier attributed to Carneades by
Metrodorus. Otherwise he held the same view from the 130s BCE until
leaving Athens in 89/8 BCE.



On the second question, about the epistemological position of the
Roman Books, the limited textual evidence has elicited from
interpreters three answers: some form of mitigated skepticism,
fallibilism, or Platonism. The first answer implies that Philo's
view developed once, from radical to mitigated skepticism, whether
prior to (Sedley 1981; Vezzoli 2011; Tarrant 2018) or in the Roman
Books (Glucker 1978; Levy 1992, 2010). According to the second
answer, the Roman Books adopted a form of fallibilism. Philo's
innovation in the Roman Books may then be understood either as his
first departure from radical skepticism (Hankinson 1995; Thorsrud
2009) or as a second change of view, now from mitigated skepticism (M.
Frede 1987; Barnes 1989; Striker 1997; Brittain 2001). The third
answer, that the Roman Books advocated a form of Platonism, may
similarly presume Philo's views developed either once, from
radical skepticism directly to Platonism (Glidden 1996), or twice,
first from radical skepticism to mitigated skepticism and then to
Platonism (Tarrant 1985).



Given these two questions and the interpretive constraints on their
answers, we arrive at a schema of five accounts of Philo's
epistemological development:


* Radical Skepticism - Mitigated Skepticism
* Radical Skepticism - Fallibilism
* Radical Skepticism - Platonism
* Radical Skepticism - Mitigated Skepticism -
Fallibilism
* Radical Skepticism - Mitigated Skepticism -
Platonism



The resolution of these questions depends primarily on an
interpretation of Cicero's *Academica*, our principal,
and only first-hand, philosophical source for Academic skepticism. But
this text strongly suggests Philo held three epistemological positions
over his career, since Cicero identifies and distinguishes three
positions held by different Academics in Philo's lifetime: a
radical skepticism associated with Clitomachus (e.g., in *Ac*.
2.78, 2.108); a form of mitigated skepticism held by a group of
Academics who regarded it as incompatible with the Roman Books
(*Ac*. 2.148, 2.11-12 & 2.18); and the Roman
Book view (*Ac*. 2.18). So it is clear that the Roman
Books did represent a third distinct Academic position. It also seems
clear that they represented *Philo's* third
epistemological view, because the interpretation of Carneades that
generated the second view is explicitly tied to Philo and Metrodorus
(*Ac*. 2.78, cf. 2.148), while we know that the Roman Books
offered a novel interpretation of Arcesilaus and Carneades that was
contested by the proponents of the second view (*Ac*.
2.11-12, 2.18). We can thus safely infer, in response to the
first question above, that Philo advocated mitigated skepticism at
some point in the 90s BCE, prior to the Roman Books of 88 BCE and
after his election to the scholarchate as a Clitomachian radical
skeptic in 110/9 BCE. That this is correct is confirmed by the
criticisms of mitigated skepticism aimed at Philo by his student
Antiochus before the Roman Books (see
 section 3.4
 below), and by the fact that virtually all the generic references to
Academic skepticism in later writers assume that it was a form of
mitigated skepticism (see, e.g., Gellius *Attic Nights* 11.5.8,
Photius *Library* 212.170a, Plutarch *Stoic
Contradictions* ch. 10, and Sextus *Outlines of Skepticism*
[*PH*] 1.226-31). Since Metrodorus was regarded as
unorthodox, the only plausible candidate for the creation of this
received view of Academic skepticism is a work by Philo from the 90s
BCE.



The second question above is much simpler to dispose of once the first
has been resolved. If Philo had previously been a mitigated skeptic
and the Roman Books presented an epistemological innovation, his final
position was not mitigated skepticism. But we have excellent evidence
that it wasn't a (recognizable) form of Platonism, since
Antiochus and Numenius flatly rejected it, despite being avowed
revivers of Platonism. (The only evidence in favor of the Platonist
hypothesis is an explicitly unsupported fantasy in Augustine, to the
effect that Platonist doctrines were secretly taught in the Academy
throughout its skeptical phase [*Against the Academics*
3.37-43].) The fallibilist interpretation of the Roman Books is
thus at least *prima facie* the most plausible candidate
offered to date. Whether it is in fact a satisfying candidate will
depend on its ability to present a coherent philosophical
interpretation of the development of Philo's epistemological
views from the evidence we have.



The following sections thus offer an interpretation of Philo's
philosophical development on the hypothesis that he held three
distinct epistemological views, as proposed by the Radical Skepticism
- Mitigated Skepticism - Fallibilism account above. It is
worth stressing, however, that, given the uncertainties of our
evidence, the exegetical and historical arguments above cannot be
regarded as conclusive. The case is not closed (see, e.g., Glucker
2004 and Tarrant 2018).


## 3. Epistemological Views


### 3.1 Academics vs. Stoics



Philo's distinct epistemological views share one fundamental
feature: all of them deny the possibility of knowledge according to
the dominant Stoic conception of it. The essential context for
understanding Philo is thus the critique of Stoic epistemology offered
by Academic philosophers, and especially by Arcesilaus and Carneades,
over the preceding hundred and fifty years (c. 280-130 BCE).



The Stoics' epistemology was designed to accommodate their
belief that it must be possible, in principle, to achieve the sort of
inerrant wisdom Socrates had desired. The Stoic theory depends on
three innovations (see, e.g., Cicero *Ac.* 1.40-2.). (1)
They defined the formation of a belief as a matter of assenting to an
occurrent thought or impression that something is, or is not, the
case. (2) They isolated a certain kind of perceptual (and perhaps also
non-perceptual) impression as "cognitive"
(*cataleptic*), because it was self-warranting, such that
assenting to these impressions constituted a "cognition"
(*catalepsis*--lit. a "grasp") of the state of
affairs they represented. And (3) they took secure knowledge of the
sort Socrates sought to be the state of an agent whose beliefs are
constituted entirely by perceptual and non-perceptual cognitions. As a
result, given their ethical doctrine that secure knowledge was
necessary and sufficient for happiness, and since, according to (3),
such knowledge could be achieved by restricting one's assent to
cognitive impressions, the Stoics identified the avoidance of opinion
and error--i.e., assent to non-cognitive impressions, whether
inadequately warranted (opinion) or false (error)--as the
overriding principle of rationality.



The Academics attacked every part of this Stoic theory--their
practice was to argue against all philosophical positions--but
their criticism focused, unsurprisingly, on the central notion of the
cognitive impression. The Stoics standardly defined a cognitive
impression as one that came from what is, was stamped and impressed
exactly in accordance with it, and was, accordingly, such that it
couldn't be false (see, e.g., Sextus *Adversus
Mathematicos* [ *M*] 7.248 or Cicero
*Ac*. 2.77). They took this to mean, roughly, that an
impression is cognitive if and only if


1. its content is true
2. it is caused in the appropriate way for correctly representing its
object, and
3. its truth is warranted by the inimitable richness and detail of
representation guaranteed by its causal history (see M. Frede
1999).



The general Academic tactic against this view was to concede the
possibility that an impression might meet conditions [a] and [b], but
argue that condition [c] never obtained. They appealed to our
experience of twins etc. and in abnormal states such as dreams,
illusions and episodes of madness to show that it was always possible
to have a false impression with exactly the same richness and detail
of representation as a true one; it follows that meeting condition [b]
could never suffice to show that condition [c] obtains, with the
result that the warrant claimed in [c] is never available to us. (See,
e.g., Sextus *M* 7.402-10 & Cicero *Ac*.
2.84-90).



The Academics used these arguments to point out that if our
impressions are never self-warranting in the way cognitive impressions
are supposed to be, and if the Stoic definition of the cognitive
impression is correct, there is no cognition. Hence, if all knowledge
depends on cognitions, as the Stoics claim, nothing at all can be
known. The Academics also offered a corollary to this argument,
drawing on the Stoic principle of rationality mentioned above:


1. if there are no cognitive impressions (as the Academics have
argued)
2. and if the wise person never assents to a non-cognitive impression
(as the Stoics think)
3. then the wise person will never assent to anything, viz. she will
suspend her assent universally.



Thus, according to the Stoic theory, once it is shown that there are
no cognitive impressions as they define them, if there are any wise
people, they will have no beliefs; and, whether there are any wise
people or not, it is never rational to assent to any impression. (See,
e.g., Sextus *M* 7.150-7 & Cicero *Ac*.
2.66-8 & 2.77-8).



The Stoics, of course, came up with plenty of sophisticated
counter-arguments to the criticisms of the cognitive impression, to
which the Academics devised equally subtle responses. But one argument
in particular seems to have seriously troubled the Academic students
of Carneades: the Stoic "inactivity" objection. This was a
very simple practical *reductio*, connected to the corollary
argument given above: if the Academics were right it would be
impossible to act at all (let alone well), since voluntary action
depends on beliefs and thus on assent (see, e.g., Cicero *Ac*.
2.24-5 and 2.34-7). But since action (indeed, good action)
is possible, the Academics must be mistaken. The later Academics saw
three ways in which they could respond to this counter-argument
without giving up their arguments against cognitive impressions. They
could:


1. deny the connection the Stoics discerned between voluntary action
and belief or assent; or
2. reject the Stoic principle of rationality by allowing for
rationally defensible assent to non-cognitive impressions, i.e.,
opinions (thus rejecting premise [ii] above and the conclusion [iii]);
or
3. accept the force of the Stoic position by allowing that knowledge
must after all be possible, though on some weaker definition of
cognition than the Stoic one.



These three options turn out to define the three Academic positions
Philo held: position [1] was the core of Clitomachus' defense of
radical skepticism; position [2] was the basis of Philo's
defense of mitigated skepticism; and position [3] was the one Philo
defended in the Roman Books.


### 3.2 Radical Skepticism



The dialectic of Academic and Stoic argument and counter-argument
outlined above may give the impression that Carneades, and the earlier
Academic skeptics more generally, were committed to the conclusions
that they argued for, i.e., that there are no cognitive impressions,
that nothing can be known, that the wise person will suspend assent
universally, etc. But there are several reasons to doubt that
Carneades straightforwardly believed on the basis of these arguments
that nothing can be known and that it is irrational to assent to any
impression (see M. Frede 1987). First, such a position is obviously
inconsistent: since beliefs are assents on the Stoic view (and
Carneades' arguments rely on Stoic assumptions), the two
conclusions cannot be consistently held at one time by a rational
agent. Secondly, the arguments only work if one already accepts a
basically Stoic epistemological framework, i.e., their theory of
impressions, their empiricism, their conception of knowledge, their
psychological doctrine etc. But Carneades had no reason to accept any
of these highly contestable views rather than, e.g., the Platonic or
Epicurean alternatives. And, thirdly, we know that the Academic method
of argument was dialectical: Carneades made it his practice to argue
for and against any and all philosophical views. And, in this
particular case, there is good reason to think that his arguments were
designed to show the inadequacies of the Stoic view and their
apparently skeptical consequences for the Stoics themselves. This is
more or less directly attested in some sources (Numenius fr. 27,
Sextus *M* 7.159-64, cf. 7.150), as well as evident
from the fact that Carneades was happy to try several incompatible
responses to the Stoic *reductio* argument--viz. options
[1] and [2] above--both of which can easily be read as further
criticisms of Stoic epistemological views (see Striker 1980 [1996] and
Allen 1994).



So Carneades was not committed to the views that nothing can be known
and that it is always irrational to assent *on the basis of*
these anti-Stoic arguments: the latter do not give him *reasons to
believe* their conclusions. Nevertheless, it seems likely that he
was committed to them in some sense, since the Stoics and other
philosophers kept on arguing against these views as if they were his,
or the Academic, position, and some of his students clearly agreed.
(Carneades' actual position remains controversial; see Bett 1989
and Allen 2004 [2020].) Clitomachus, at any rate, advocated an
interpretation of Carneades' skepticism that saw his method of
argument on either side of all philosophical questions as motivated by
some sort of commitment to the view that it is irrational to assent to
anything less than what one knows to be true, and as resulting in a
similar kind of commitment to the view that nothing can be known. And
it was this interpretation of Carneades that Philo held at the start
of his Academic career (Numenius fr. 28).



Clitomachus defended the consistency of a radical skepticism of this
sort by denying that assent is necessary for action or belief, as the
Stoics had claimed in their inactivity objection to the Academic
corollary argument
 (section 3.1
 above). His defense came in two stages, both appealing to arguments
Carneades had used in response to the Stoic objection. The first stage
identified a way to discriminate between our thoughts without
appealing to their objective status as true or as
"cognitive" impressions (see Cicero *Ac*.
2.98-99, cf. 2.32). Here Clitomachus drew on Carneades'
"theory of probable [or, better, 'persuasive'
(*pithanon*)] impressions"--i.e., the description of
ordinary epistemic procedures that Carneades promoted as an
alternative to the Stoic theory of cognitive impressions (see Sextus
*M* 7. 166-89 and Allen 1994). In ordinary life,
Carneades argued, we proceed without assuming that a set of what the
Stoics call impressions is "cognitive" or immediately
warranted to be true. Rather, some "impressions" leave us
with no immediate inclination to accept them, while some strike us as
subjectively "persuasive", at least initially, owing to
their internal characteristics (e.g., the richness of their
representation). We can increase or diminish the initial
persuasiveness of our impressions by considering the perceptual
conditions under which we experience them (e.g., normal perceptual
conditions for perceiving the state of affairs they represent), and
their fit with our other impressions (e.g., normal coherence
conditions). And we accept and act on impressions when they reach the
level of persuasiveness we find appropriate to the situation we are
in. But, Clitomachus insisted, none of these procedures is sufficient
to establish that an impression is true or "cognitive",
since, as the Academics have argued, the representational features of
any true impression can always be replicated by a false one. (See
Cicero *Ac*. 2.98-99.) And there is no reason to think
that in ordinary life we assume that the procedures are sufficient
(see Plutarch *Common Conceptions* ch. 36).



This first stage gives the Academic a procedure that allows for
discrimination between impressions while preserving the Academic
thesis that nothing can be known. The second stage of
Clitomachus' defense drew on Carneades' criticisms of the
Stoic unitary notion of assent as simply a matter of taking an
impression (or its content) to be true. Carneades had argued that this
fails to account for the complexity of our cognitive life: many of our
actions are not the product of distinct acts of assent, but are rather
unconscious, or habitual, like animal action; and we sometimes
deliberately act without assent, for instance, when we follow
unendorsed hypotheses or act in conditions of uncertainty (see Bett
1990). On the basis of considerations of this sort, Clitomachus argued
that we should distinguish "assenting" to an impression,
in the Stoic sense of taking it to be true, from
"approving" an impression, in the sense of acting on it or
accepting it *as if* it were true. (See Cicero *Ac*.
2.104.)



This second stage gives the Academics a way of accepting impressions
and acting on them that preserves the thesis that rationality demands
that one should always suspend assent. Thus, by combining both stages,
Clitomachus was able to argue that the Academic is free to
"follow" or "approve" persuasive impressions
without assenting to them: the Academic has a "practical
criterion" that allows for action without presupposing the
cognitive access to objective truth required for rational assent
(Sextus *M* 7. 166; cf. Cicero *Ac*. 2.108).
Clitomachus, however, did not restrict the application of this
"practical" criterion to cases of ordinary action
(*pace* Gorler 1994). He also explicitly claimed that it
gave the radical skeptics a means to explain their philosophical
activities, i.e., their arguments and views (Cicero *Ac*.
2.104; cf. 2.32). He was thus in a position to explain the
Academics' apparent commitment to the theses that assent is
irrational and knowledge is unattainable. These are views that the
radical skeptic finds "persuasive"; but they are not
"beliefs", at least not in the Stoic sense, because the
Academic does not take them to be true.



One might plausibly question whether Carneades' resistance to
(straightforward Stoic) assent was the "heroic" defense of
rationality against opinion and error Clitomachus took it to be
(Cicero *Ac*. 2.108). It remains very controversial whether
there is a coherent distinction to be made between approving a view
and assenting to its truth (see the wider discussion in Burnyeat &
Frede [ed.] 1998). But a case can be made that acts of pretense,
imagination, and supposition require taking on views in a manner
distinct from that of belief and that the rational activities of the
radical skeptic are founded on supposition (see Striker 1980 [1996];
Bett 1990; Reinhardt 2018). Another way to support the distinction is
to note that the process of arguing for and against a thesis, in the
way Carneades did, can leave one stuck with a view one way or the
other, but without being aware of any rational ground for preferring
this view. After constant repetition of this process, one can see how
the Academics might have come to have the view that their views or
"beliefs" are all non-rational in the specific sense that
they were not actively formed in accordance with the explicit criteria
of rationality advocated by the dogmatic philosophers. And if they
remained committed--in the same attenuated or
"non-rational" sense--to the Socratic ideal of
inerrant knowledge, one can see why they might try to preserve their
rationality by not giving their assent to the views they found
themselves holding. A case along these lines is made in Brittain 2005
[2008]. Philo, at any rate, initially agreed with Clitomachus that
Carneades' ability to maintain something like these critical
stances towards all beliefs--his own as well as the theories of
his philosophical opponents--represented a paradigm of
self-conscious rationality (see Numenius fr. 28).


### 3.3 Mitigated Skepticism



Clitomachus' interpretation of Carneades' skepticism was
the dominant view in the Academy in the period c. 130-100 BCE.
But it was always contested, initially by Metrodorus, and later by
Philo himself. The basis for the alternative interpretation was a
second response Carneades had given to the Stoic inactivity objection
(position [2] in
 section 3.1
 above), arguing that it is sometimes rational to assent to
non-cognitive impressions (see Cicero *Ac*. 2.78, cf. 2.53).
Clitomachus had taken this as just an *ad hominem* argument,
designed to challenge the Stoic defense of the view that the
overriding principle of rationality is avoidance of any possibility of
error (see Cicero *Ac*. 2.67-8). Metrodorus and his
followers, however, thought that this was a statement of
Carneades' own view, and adopted it themselves.



There is no direct evidence to explain Philo's shift from
radical to mitigated skepticism. But we can learn something about the
general motivations he may have had for adopting his new position from
the ways in which some mitigated skeptics understood the Carneadean
notion of "persuasive impressions". In the case of
perceptual impressions, the difference between their view and the
Clitomachian position is clarified by a criticism from Philo's
former student Antiochus that some Academics took persuasive
impressions to be a criterion of *truth*, rather than just of
action and philosophical criticism (see Sextus
*M* 7.435-8 and Cicero *Ac*. 2.32-6).
This shows that these Academics understood the mechanisms Carneades
had outlined for increasing the persuasiveness of impressions to
provide a means of confirming or disconfirming--in various
degrees, though never ones that warranted them
conclusively--whether they were likely to be true or not. These
mitigated skeptics thus believed that the persuasiveness of perceptual
impressions under the right perceptual and coherence conditions as
defeasible, but rational, *evidence* for their truth. We find a
similar move in the case of non-perceptual impressions: some mitigated
skeptics formed tentative beliefs as to which positions are more
likely to be true (see, e.g., Cicero *Ac*. 2.148), after using
the standard Academic practice of arguing on either side of
philosophical questions as a means of rationally evaluating arguments
(see Cicero *Ac*. 2.7, 2.60 & *On the Nature of the
Gods* 1.11, Galen *On the Best Method of Teaching* ch. 1,
and Plutarch *Stoic Contradictions* ch. 10). These mitigated
skeptics thus changed the status of argument on either side from a
critical practice ending in suspension of assent into a positive
method for rationally confirming and, indirectly, teaching
philosophical beliefs.



It is not difficult to see how this shift in the understanding of
persuasive impressions might lead to a re-evaluation of the conception
of rationality shared by Stoics and, at least in part, by the radical
skeptics. Clitomachus had agreed with the Stoics that avoiding error
is a necessary condition for rationality, and consequently, given the
apparent unavailability of knowledge, advocated suspending assent
universally. But once Philo had begun to use persuasiveness as a
rational method for evaluating impressions, the radically skeptical
position started to look more like an abdication of rationality than
its paradigm. Granted that nothing can be known--a view the
mitigated skeptics continued to find extremely persuasive (see Cicero
*Ac*. 2.148)--it still seems that we are rationally
obliged to form the best beliefs we can, given the evidence available
to us. And while this will involve the possibility of error, the
refusal to use the evidence we have seems absurd when it is
generalized to every case--and immoral in the case of ethics,
since without some regulatory beliefs, it is unlikely that our lives
could be virtuous or happy (see
 section 4).



These reasons, then, or something like them, led Philo, along with
other mitigated skeptics, to the formal position that, while nothing
could be known (as shown by the Academic arguments against the
possibility of cognitive impressions), it is nevertheless rational to
assent under certain conditions, i.e., to hold beliefs based on
reasons (Cicero *Ac*. 2.78). The mitigated skeptics retained
the Stoic characterization of such beliefs as "opinions"
to mark the fact that, despite the rational grounds they had for
holding them, they were just rational *beliefs*--i.e.,
they did not amount to "cognitions" or knowledge (Cicero
*Ac*. 2.148). But they also distinguished *rational*
opinions of this sort from the general Stoic category of opinion as
any assent to a non-cognitive impression (and hence as always bad), by
qualifying their assent to them as "measured"--that
is, as provisional on their avowedly inconclusive evidence, rather
than as a straightforward commitment to their truth. (See the
anonymous *Introduction to Plato* ch. 7 and Gellius *Attic
Nights* 11.5.8. Sextus mis-ascribes this view to Clitomachus in
*PH* 1.226 & 1.229-30.)



The significant difference between this position and radical
skepticism is clear from the principal example of a mitigatedly
skeptical "opinion" that we have: the thesis that nothing
can be known (see, e.g., Cicero *Ac*. 2.148, Gellius *Attic
Nights* 11.5.8, Galen *On the Best Method for Teaching* ch.
1). The mitigated skeptics evidently believed this thesis *on the
basis of* the Academic arguments considered in
 section 3.1
 above. But this means that, despite their rejection of the existence
of cognitive impressions and their new principle of rationality, their
skepticism was heavily parasitic on Stoic epistemology: they accepted
a dogmatic epistemological framework, such that they believed the
Stoic theory of impressions, Stoic empiricism, the Stoic conception of
knowledge, and so on. One does not need to see this as a weakness to
notice that the ties between mitigated skepticism and its dogmatic
framework render it liable to redundancy, in a way radical skepticism
is not, if the philosophical conception of knowledge itself
changes.


### 3.4 Fallibilism



Philo's motivation for his final shift away from skepticism in
the Roman Books can be seen, at least in part, from the criticisms
directed at him by his ex-student Antiochus before their publication
in 88/7 BCE. These criticisms point to a kind of instability inherent
in mitigated skepticism: it seems to waver unhealthily between a
dogmatic position allowing for something approaching certainty about
some questions and a radical skepticism about our ability to make any
epistemic progress. More specifically, it suggests that we can take
persuasive impressions as evidence for the truth that is firm enough
to warrant assent--thus allowing for a life guided by reasoned
belief, and even ethical teaching--while simultaneously
maintaining that even the most perfect rational consideration of the
evidence is compatible with wholesale error. (See the argument in
Cicero *Ac*. 2.111, addressed explicitly to Philo prior to his
Roman view, and its elaboration in *Ac*. 2.34-6 &
2.43-44. These Antiochian criticisms are echoed almost verbatim
by Aenesidemus in Photius *Library* 212 170a 14-38.)



The outlines of Philo's response to this problem in the Roman
Books are fairly clear from the direct evidence we have for their
epistemological innovations (Cicero *Ac*. 2.18 and Sextus
*PH* 1.235). He argued, first, that the Stoic definition of the
cognitive impression ruled out the possibility of anything being
known--i.e., he restated the standard Academic arguments to this
effect--and, secondly, that this definition was therefore
misconceived, since at least some things could be known. His
elucidation of the second claim is unfortunately not explicit in the
surviving evidence. But its criticism by Antiochus (the context for
Cicero's report) very strongly suggests that Philo offered an
alternative and weaker definition of knowledge of single propositions.
For Antiochus both characterizes Philo's innovations as an
attempt to redefine "cognition" (*Ac*. 2.17 &
2.18 fin.) and attempts to refute them by arguing that an impression
that does not meet the condition given in the third clause of the
Stoic definition (see
 section 3.1
 above) cannot be "cognitive". Philo's new
definition thus amounted to something like the Stoic definition minus
its third clause (the clause the Academics had always disputed). If
so, Philo claimed that an impression is cognitive if it is both [a]
true and [b] caused in the appropriate way for correctly representing
its object--without adding the disputed Stoic rider [c], that its
truth is warranted by the inimitable richness and detail of
representation guaranteed by its causal history.



This bare outline of Philo's final position is sufficient to
show its novelty, and thus explain its poor reception by Antiochus and
the Academics alike (see *Ac*. 2.11-12, 2.18). His new
conception of knowledge was a radical innovation in three respects.
First, given his acceptance of the standard Academic arguments against
self-warranting cognitive impressions, it offered a fallibilist
theory, which allows for unqualified assent to knowledge claims on the
basis of impressions that might nonetheless be false. Antiochus'
criticism suggests that he defended this view by pointing out that the
theoretical or counterfactual possibility of error was epistemically
irrelevant in cases where the impression is in fact true and our
positive evidence for it is, in practice, conclusive (see Barnes
1989). But however he justified it, Philo's new conception of
knowledge challenged the fundamental epistemological principle of the
Hellenistic period that knowledge must be certain. Secondly,
Philo's new theory implied that there is in fact a good deal of
knowledge. It thus constituted an apparently radical rejection of the
basic thesis that all the skeptical Academics had shared, that nothing
can be known. And, thirdly, Philo's theory implied a revised
principle of rationality. The mitigated skeptics had responded to the
Stoic inactivity objection by identifying rationality with forming
defeasible beliefs on the basis of the available evidence. But, by
qualifying the assent of the rational agent as "measured"
or provisional, they insulated rationality itself from practical
error: whether or not the belief is false, an agent who forms it on
the appropriate grounds is never mistaken in holding it provisionally.
On Philo's new position, however, rationality is compatible with
outright error because it is rational to give straightforward,
unqualified assent to impressions that might nonetheless be false. The
Roman Books thus marked Philo's final rejection of the joint
Stoic and Academic thesis that the avoidance of error is an overriding
principle of rationality.



This sketch of their implications explains why Philo's
innovations were decisive enough to startle his contemporaries and,
eventually, to lead to the doxographical classification of his version
of Academicism as a distinct "Fourth Academy" (see, e.g.,
Sextus *PH* 1.220 & 1.235). But two facts imply that his
further elucidation in the Roman Books included some significant
limitations on the range of knowledge Philo came to accept, and hence
the sense in which he rejected the skepticism of his Academic
predecessors. The first is just that his contemporaries (and later
historians) continued to regard him, even at the end of his career, as
an Academic, i.e., in some way a follower of Arcesilaus and Carneades,
rather than a defector like Antiochus or Aenesidemus. The second is
that Philo asserted "the unity of the Academy" in the
Roman Books (see Cicero *Ac*. 1.13), i.e., claimed that his new
view was in fact the underlying view of all the Academics from
Socrates and Plato to himself. Exactly what he meant by this claim is
controversial, but the tenuous and complex evidence does not suggest
that it involved either accepting an anti-skeptical reading of Plato
or denying that the skeptical Academics were skeptical about the
possibility of achieving theoretical knowledge in philosophy (see
Brittain 2001: chs. 4-5 and Tarrant 2018: 86-87).



By combining these external constraints on our understanding of the
epistemological innovations of the Roman Books with their
philosophical context--Philo's prior position of mitigated
skepticism and the criticisms it faced--we can see, at least
roughly, how Philo may have given flesh to the basic outline above.
Taken together, these considerations suggest three constraints on the
range of the knowledge that Philo accepted. They suggest, first, that
Philo supplemented the externalist bones of his new definition of
cognition with the internalist constraints on assent that the
mitigated skeptics had already identified: assent to a Philonian
cognitive impression would only be warranted when the representational
"richness" guaranteed by its causal history (condition [b]
above) was confirmed by meeting the additional perceptual and
coherence conditions Carneades had identified for persuasive
impressions. Secondly, that Philo took Philonian cognition to apply
primarily to experiential knowledge, i.e., the kind that we ascribe to
ourselves in virtue of perception and to experts with practical
skills, or something like "ordinary knowledge". And
thirdly, that Philo accordingly did not assume that the results of
philosophical inquiry would often, or even usually, or perhaps ever,
amount to knowledge when subjected to rational criticism through
argument on either side. (The evidence that might support these three
claims is collected in Brittain 2001: ch. 3.)



The hypothesis that Philo's fleshed-out final theory of
knowledge was roughly along these lines makes sense of both the
context and the reception of his innovations. It also allows us to
offer a more philosophically satisfying explanation of his eventual
acceptance of the possibility of knowledge than Antiochus'
suggestion that he was unable to endure the criticisms he and other
Academics had dealt with for thirty years (Cicero *Ac*. 2.18).
By allowing for the existence of ordinary, fallible knowledge, Philo
challenged the epistemological framework of his era; but by limiting
knowledge so that it did not include most of the results of
philosophical inquiry, and by ascribing the acceptance of this view to
the entire Academic tradition, he sought to redefine the skeptical
Academy in terms of its original Socratic function as the non-dogmatic
critic of philosophical pretensions to theoretical knowledge. On this
view, Academic philosophy is not defined by an epistemological
position (as even Clitomachus' radical skepticism appears to
have been), but by the critical method of argument on either side.


## 4. Philosophy of Education



In defining the Academy only by its critical method, rather than also
by its acceptance of any epistemological positions, Philo recognized a
value in argument on either side that was independent of the
conclusions or acts of suspension it yielded: its ability to cultivate
in others autonomy in dialectical reasoning. In the periods of both
his mitigated skepticism and his fallibilism, Philo argued on either
side in order to judge whether some philosophical view merited his
assent (see
 sections 3.3-3.4).
 To this end he accepted rational norms of criticism (cf. D. Frede
1996), so that he was obliged to disregard illicit sources of
persuasion: e.g., performative aspects of a speaker's
presentation of arguments, or a speaker's reputation (unless
their reputation is cited as a reason for belief). Thus we find in
Philonian sources an analysis of the sources of authority and
arguments against epistemic deference (see Cicero *Ac*. 2.9,
2.115 and *Topica* 72-8; cf. Sextus *PH*
2.37-46 & *M* 7.314-42). The evidence
suggests that Philo sought to protect auditors from his own authority,
by concealing his judgments about arguments on either side. At any
rate, Academics who are associated with Philo or the mitigated
skepticism he popularized (e.g., Charmadas, Cicero, and Favorinus)
concealed their evaluations of arguments, on the grounds that their
auditors would be better situated to follow the rational norms of
criticism (see Cicero *On the Orator* 1.84, *Ac*. 2.60,
*On the Nature of the Gods* 1.10-11, *On
Divination* 2.150, *Tusculan Disputations* 5.11 & 5.83,
*On Fate* 1, and Galen *On the Best Method of
Teaching*).



Philo's interest in students' autonomy in dialectical
criticism is most often related to his mitigated skepticism (Long
& Sedley 1987, 1:449: Ioppolo 1993: 210; Brittain 2001:
111-4; Tarrant 2018). As mentioned above, Philo's
educational interests are shared by the Academics Charmadas (Cicero
*On the Orator* 1.84) and Favorinus (Galen *On the Best
Method of Teaching*), whom some identify as mitigated skeptics
(see Brittain 2001: 213-4; Tarrant 1985: ch. 2 & 2018: 83;
Brittain 2007: 302; Ioppolo 1993). And since the same concerns about
rational norms carry over from Philo's mitigated skepticism to
his reconstructed fallibilism (see
 section 3.4),
 it is likely Philo retained this pedagogical view in his Roman Books
(see also
 section 5).



Although Philo's philosophy of education is identified most
closely with mitigated skepticism, its origin may also be tied to
Clitomachean radical skepticism. Scholarship on Cicero, our best
source for the defense of argument on either side on educational
grounds, has increasingly defended radically skeptical interpretations
of some of his dialogues (Brittain 2016: Cappello 2019; Wynne 2018
& 2021), and Cicero himself associates it with Arcesilaus and
Carneades (see *On Divination* 2.150, *Tusculan
Disputations* 5.11 & 5.83). It may seem that radical skeptics
would not have justified argument on either side for educational
reasons because they argue for purely destructive ends. But one may
think that radical skepticism can ground a Socratic interest in
others' training in dialectic out of a hypothetical acceptance
of rational norms (see Brittain 2005 [2008]). If this is right, then
Philo in the Roman Books had further cause for identifying its
critical method as the defining mark of the Academy.


## 5. Ethics and Rhetoric



Our knowledge of Philo's work in ethics comes almost entirely
from an extended summary of an introductory book or lecture preserved
without any context in an anthology (Stobaeus *Anthology* 2.7).
The summary is puzzling because it presents a picture of Philonian
ethics that seems too dogmatic, and too ordinary, for an Academic,
even at the time of the Roman Books. The work presents a method for
teaching ethics in terms of an analogy between philosophy and
medicine. This yields a division of ethical teaching into three parts:
a protreptic stage (showing the need for philosophical guidance), a
therapeutic stage (adjusting the student's evaluative concepts),
and a preservative stage (outlining the life-styles and political
arrangements that promote or maintain happiness by reinforcing these
adjusted concepts). This is intriguing as an example of the way in
which late Hellenistic philosophers approached the teaching of
practical ethics (see Annas 1993: 95-96. But it does not look
innovative. The analogy between medicine and philosophy is a standard
one in Plato and in Hellenistic ethics. The focus on practical rules
and the application of technical divisions and sub-divisions is
derived from the Stoic tradition. And its theoretical claims--for
instance, that wisdom or knowledge is necessary for virtue, and that
virtue promotes the goal of happiness--do not identify it as an
exception to the mainstream tradition of weaker or stronger
"intellectualist" and "eudaemonist" virtue
ethics. In these respects, the summary suggests that Philo's
ethics was largely unaffected by the wide-ranging and penetrating
criticisms of Hellenistic ethics by his Academic predecessors, and
especially by Carneades (examined in Algra 1997).



But there is reason to think that the summary--which was probably
written five hundred years after Philo's work--gives a
misleading picture of Philonian ethics by not informing us directly of
the methods it used to enable and secure the possession of happiness.
It is perhaps natural to assume that his methods were the standard
dogmatic ones. Two aspects of the wider context omitted by the
excerptor, however, suggest that Philo's ethics were in fact
based on the Academic method of argument on either side. First, we
know that the mitigated skeptics had already come to see their method
of arguing for and against ethical theses as a way of
*teaching* ethics that allowed students to evaluate which views
were more persuasive, i.e., had better rational grounds (see
 section 4).
 This is clearest in the case of Philo's colleague Charmadas in
Cicero *On the Orator* 1.83-93. It is confirmed by the
criticisms of mitigated skepticism from Aenesidemus in Photius
*Library* 212 170a and Sextus *PH* 1.226. Secondly, we
know that Philo had developed a way to popularize the Academic method
by incorporating it into a technical system of rhetoric (see Cicero
*On the Orator* 3.110-118 and *Tusculan
Disputations* 2.9). But since the function of this system was to
provide students with forensic techniques for arguing about moral
issues, and given that teaching rhetoric in any form was a significant
departure for an Academic philosopher, this development must have had
some connection to Philo's ethical views (see Reinhardt 2000 and
Brittain 2001).



When the summary is read with this wider context in mind, three
apparently minor points stand out. First, the therapeutic stage,
dealing with the students' fundamental conceptions of value, is
described as the effort to replace "falsely *acquired*
beliefs" with ones "in a healthy state", rather than
just false with true beliefs (Stobaeus *Anthology* 2.7 p.
40.18-20). Secondly, the preservative stage, concerned with the
lifestyles that promote or secure happiness, is framed as an
*investigation* of a set of questions that correspond precisely
with the questions dealt with by argument on either side in
Philo's rhetoric (ibid. p. 41.7-14). And, thirdly, that
kind of general investigation is explicitly distinguished from the
provision of straightforwardly *prescriptive* advice about how
to behave, which is regarded as a temporary fix for busy people (ibid.
p. 41.16-25). These points can be explained in various ways. But
given the wider context, they suggest that the summary has obscured
the central point about Philo's ethics: its method of teaching
was not dogmatic, but the Academic one of argument on either side.



If this is right, the summary's apparent ordinariness and
dogmatic structure reflect only Philo's systematic approach to
ethical topics, not its methods or results: Philo did not propose a
dogmatic ethics, but rather a systematic technique for structuring
students' moral values into a coherent way of life through their
rational evaluation of arguments on either side. A philosophical
approach to ethics of this kind allows students to use their ethical
intuitions--the knowledge provided by their own
experience--to revise and structure their conceptions of value,
and, on that basis, critically evaluate their general social and
political roles, and select the appropriate actions in a particular
situation. An approach of this sort perhaps no longer seems striking
or innovative, but if Philo adopted it in the early 80s BCE, it
presented no less a challenge to Hellenistic ethics than his Roman
Books did to epistemology. Two reasons to think that Philo did adopt
this approach are, first, that it yields a conception of ethical
knowledge that fits the epistemology of the Roman Books--a
Philonian rational agent will have the sort of wisdom and happiness
that is available to ordinary people, i.e., something quite unlike the
illusory promise of inerrant knowledge and moral perfection promised
by the Stoics. And, secondly, Philo's student Cicero may have
adopted something like a mitigatedly skeptical version of this
approach both in his personal life (see Griffin 1989) and in his
philosophical works on ethics (see Schofield 2002).


## 6. Conclusion



On this reconstruction of his work, Philo eventually abandoned both
radical and mitigated skepticism for a form of fallibilism that he
described as the basis of the Academic tradition. His promotion of
Academic philosophy as open-ended critical inquiry had some impact on
the work of Cicero, Plutarch, Favorinus and Augustine, but his radical
innovations in epistemology and ethics sank almost without trace. The
skeptical tradition survived in the form of Pyrrhonism, but the
Academy did not. Like any interpretation of Philo's
philosophical development, this reconstruction is speculative in some
respects. But much of it can be confirmed or disconfirmed by further
work on ancient skepticism, and especially its Latin tradition, which
remains an open field for research.