## 1. Introduction




The *Theaetetus,* which probably dates from about 369 BC, is
arguably Plato's greatest work on epistemology. (Arguably, it is his
greatest work on anything.) Plato (c.427-347 BC) has much to say about
the nature of knowledge elsewhere. But only the *Theaetetus*
offers a set-piece discussion of the question "What is
knowledge?"




Like many other Platonic dialogues, the *Theaetetus* is
dominated by question-and-answer exchanges, with Socrates as main
questioner. His two respondents are Theaetetus, a brilliant young
mathematician, and Theaetetus' tutor Theodorus, who is rather less
young (and rather less brilliant).




Also like other Platonic dialogues, the main discussion of the
*Theaetetus* is set within a framing conversation (142a-143c)
between Eucleides and Terpsion (cp. *Phaedo* 59c). This frame
may be meant as a dedication of the work to the memory of the
man Theaetetus. Sedley 2004 (6-8) has argued that it is meant to set
some distance between Plato's authorial voice and the various other
voices (including Socrates') that are heard in the dialogue.
Alternatively, or also, it may be intended, like *Symposium*
172-3, to prompt questions about the reliability of knowledge based on
testimony. (Cp. the law-court passage (*Theaetetus* 201a-c),
and Socrates' dream (*Theaetetus* 201c-202c).)




The *Theaetetus*' most important similarity to other
Platonic dialogues is that it is *aporetic*--it is a
dialogue that ends in an *impasse*. The *Theaetetus*
reviews three definitions of knowledge in turn; plus, in a preliminary
discussion, one would-be definition which, it is said, does not really
count. Each of these proposals is rejected, and no alternative is
explicitly offered. Thus we complete the dialogue without discovering
what knowledge is. We discover only three things that knowledge is
*not* (*Theaetetus* 210c; cp. 183a5,
187a1).




This matters, given the place that the *Theaetetus* is normally
assigned in the chronology of Plato's writings. Most scholars agree
that Plato's first writings were the "Socratic" dialogues
(as they are often called), which ask questions of the "What
is...?" form and typically fail to find answers:
"What is courage?" (*Laches*), "What is
self-control?" (*Charmides*), "What is
justice?" (*Alcibiades I*; *Republic* 1),
"What is holiness?" (*Euthyphro*), "What is
friendship?" (*Lysis*), "What is virtue?"
(*Meno*), "What is nobility?" (*Hippias
Major*). After some transitional works (*Protagoras, Gorgias,
Cratylus, Euthydemus*) comes a series of dialogues in which Plato
writes to a less tightly-defined format, not always focusing on a
"What is...?" question, nor using the
question-and-answer interrogative method that he himself depicts as
strictly Socratic: the *Phaedo*, the *Phaedrus*, the
*Symposium,* and the *Republic*. In these dialogues
Plato shows a much greater willingness to put positive and ambitious
metaphysical views in Socrates' mouth, and to make Socrates the
spokesman for what we call "Plato's theory of Forms."




After these, it is normally supposed that Plato's next two works were
the *Parmenides* and the *Theaetetus*, probably in that
order. If so, and if we take as seriously as Plato seems to the
important criticisms of the theory of Forms that are made in the
*Parmenides*, then the significance of the
*Theaetetus*'s return to the aporetic method looks obvious.
Apparently Plato has abandoned the certainties of his middle-period
works, such as the theory of Forms, and returned to the
almost-sceptical manner of the early dialogues. In the
*Theaetetus*, the Forms that so dominated the
*Republic*'s discussions of epistemology are hardly mentioned
at all. A good understanding of the dialogue must make sense of this
fact.


## 2. Summary of the Dialogue




At the gates of the city of Megara in 369 BC, Eucleides and Terpsion
hear a slave read out Eucleides' memoir of a philosophical discussion
that took place in 399 BC, shortly before Socrates' trial and
execution (142a-143c). In this, the young Theaetetus is introduced to
Socrates by his mathematics tutor, Theodorus. Socrates questions
Theaetetus about the nature of expertise, and this leads him to pose
the key question of the dialogue: "What is knowledge?"
(143d-145e). Theaetetus' first response (D0) is to
give examples of knowledge such as geometry, astronomy, harmony,
arithmetic (146a-c). Socrates objects that, for any *x*,
examples of *x* are neither necessary nor sufficient for a
definition of *x* (146d-147e). Theaetetus admits this, and
contrasts the ease with which he and his classmates define
mathematical terms with his inability to define knowledge
(147c-148e). Socrates offers to explain Theaetetus' bewilderment about
the question "What is knowledge?" by comparing himself
with a midwife: Theaetetus, he suggests, is in discomfort because he
is in intellectual labour (148e-151d).




Thus prompted, Theaetetus states his first acceptable definition,
which is the proposal (D1) that "Knowledge is
perception" (151d-e). Socrates does not respond to this
directly. Instead he claims that D1 entails two other
theories (Protagoras' and Heracleitus'), which he expounds (151e-160e)
and then criticises (160e-183c). Socrates eventually presents no fewer
than eleven arguments, not all of which seem seriously intended,
against the Protagorean and Heracleitean views. If any of these
arguments hit its target, then by *modus tollens*
D1 is also false. A more direct argument against
D1 is eventually given at 184-7.




In 187b4-8, Theaetetus proposes a second definition of knowledge:
(D2) "Knowledge is true belief."
D2 provokes Socrates to ask: how can there be any
such thing as *false* belief? There follows a five-phase
discussion which attempts to come up with an account of false
belief. All five of these attempts fail, and that appears to be the
end of the topic of false belief. Finally, at 200d-201c, Socrates
returns to D2 itself. He dismisses
D2 just by arguing that accidental true beliefs
cannot be called *knowledge*, giving Athenian jurymen as an
example of accidental true belief.




Theaetetus tries a third time. His final proposal
(D3) defines knowledge as *"*true belief
with an account (*logos*)" (201c-d). The ensuing
discussion attempts to spell out what it might be like for
D3 to be true, then makes three attempts to spell out
what a *logos* is.




In 201d-202d, the famous passage known as *The Dream of
Socrates*, a two-part ontology of elements and complexes is
proposed. Parallel to this ontology runs a theory of explanation that
claims that to explain, to offer a *logos,* is to analyse
complexes into their elements, i.e., those parts which cannot be
further analysed. Crucially, the Dream Theory says that knowledge of
*O* is true belief about *O* plus an account of
*O*'s composition. If *O* is not composite, *O*
cannot be known, but only "perceived" (202b6). When
Socrates argues against the Dream Theory (202d8-206b11), it is this
entailment that he focuses on.




Socrates then turns to consider, and reject, three attempts to spell
out what a *logos* is--to give an account of
"account." The first attempt takes *logos* just to
mean "speech" or "statement" (206c-e). The
second account (206e4-208b12) of "*logos* of
*O*" takes it as "enumeration of the elements of
*O*." The third and last proposal (208c1-210a9) is that
to give the *logos* of *O* is to cite the
*semeion* or *diaphora* of *O*, the
"sign" or diagnostic feature wherein *O* differs
from everything else.




All three attempts to give an account of "account"
fail. The day's discussion, and the dialogue, end in *aporia.*
Socrates leaves to face his enemies in the courtroom.


## 3. Overall Interpretations of the *Theaetetus*




The *Theaetetus* is a principal field of battle for one of the
main disputes between Plato's interpreters. This is the dispute
between *Unitarians* and *Revisionists*.




Unitarians argue that Plato's works display a unity of doctrine and a
continuity of purpose throughout. Unitarians include Aristotle,
Proclus, and all the ancient and mediaeval commentators; Bishop
Berkeley; and in the modern era, Schleiermacher, Ast, Shorey,
Dies, Ross, Cornford, and Cherniss.




Revisionists retort that Plato's works are full of revisions,
retractations, and changes of direction. Eminent Revisionists include
Lutoslawski, Ryle, Robinson, Runciman, Owen, McDowell, Bostock, and
many recent commentators.




Unitarianism is historically the dominant interpretive tradition.
Revisionism, it appears, was not invented until the text-critical
methods, such as stylometry, that were developed in early
nineteenth-century German biblical studies were transferred to
Plato.




In the twentieth century, a different brand of Revisionism has
dominated English-speaking Platonic studies. This owes its impetus to a
desire to read Plato as charitably as possible, and a belief that a
charitable reading of Plato's works will minimise their dependence on
the theory of Forms. (Corollary: Unitarians are likelier than
Revisionists to be sympathetic to the theory of Forms.)




Unitarianism *could* be the thesis that all of Plato's work is,
really, Socratic in method and inspiration, and that Plato should be
credited with no view that is not endorsed in the early dialogues.
(In some recent writers, Unitarianism *is* this thesis: see
Penner and Rowe (2005).) But this is not the most usual form of
Unitarianism, which is more likely to "read back" the
concerns of the *Phaedo* and the *Republic* into the
Socratic dialogues, than to "read forward" the studied
agnosticism of the early works into these more ambitious later
dialogues. Likewise, Revisionism *could* be evidenced by the
obvious changes of outlook that occur, e.g., between the
*Charmides* and the *Phaedo*, or again between the
*Protagoras* and the *Gorgias*. But the main focus of
the Revisionist/Unitarian debate has never been on these
dialogues. The contrasts between the *Charmides* and the
*Phaedo*, and the *Protagoras* and the *Gorgias,*
tell us little about the question whether Plato ever abandoned the
theory of Forms. And that has usually been the key dispute between
Revisionists and Unitarians.




Hence the debate has typically focused on the contrast between the
"the Middle Period dialogues" and "the Late
dialogues." Revisionists say that the Middle Period dialogues
enounce positive doctrines, above all the theory of Forms, which the
Late dialogues criticise, reject, or simply bypass. The main place
where Revisionists (e.g., Ryle 1939) suppose that Plato criticises the
theory of Forms is in the *Parmenides* (though some
Revisionists find criticism of the theory of Forms in the
*Theaetetus* and *Sophist* as well). The main places
where Revisionists look to see Plato managing without the theory of
Forms are the *Theaetetus* and *Sophist*.




Ryle's Revisionism was soon supported by other Oxford Plato scholars
such as Robinson 1950 and Runciman 1962 (28). Revisionism was also
defended by G.E.L. Owen. More recently, McDowell 1976, Bostock 1988,
and Burnyeat 1990 are three classic books on the *Theaetetus*
of a decidedly Revisionist tendency. (McDowell shows a
particularly marked reluctance to bring in the theory of Forms
anywhere where he is not absolutely compelled to.)




Revisionists are committed by their overall stance to a number of more
particular views*.* They are more or less bound to say that the
late Plato takes the *Parmenides'* critique of the theory of
Forms to be cogent, or at least impressive; that the
*Sophist'*s theory of "the five greatest
kinds" (*Sophist* 254b-258e) is not a development of the
theory of Forms; and that the *Timaeus* was written before the
*Parmenides,* because of the *Timaeus'* apparent defence
of theses from the theory of Forms. Their line on the
*Theaetetus* will be that its argument does not support the
theory of Forms; that the *Theaetetus* is interesting precisely
because it shows us how good at epistemology Plato is once he
*frees* himself from his obsession with the Forms.




Some of these Revisionist claims look easier for Unitarians to dispute
than others. For example, Plato does not think that the arguments of
*Parmenides* 130b-135c actually *disprove* the theory of
Forms. Rather, it is obviously Plato's view that Parmenides' arguments
against the Forms can be refuted. See *Parmenides* 135a-d,
where Plato explicitly says--using Parmenides as his
mouthpiece--that these arguments *will* be refuted by
anyone of adequate philosophical training. (Whether anyone "of
adequate philosophical training" is available is, of course,
another question.)




Another problem for the Revisionist concerns Owen 1965's proposal,
adopted by Bostock 1988, to redate the *Timaeus* to the Middle
Period, thus escaping the conclusion that Plato still accepted the
theory of Forms at the end of his philosophical career. The trouble
with this is that it is not only the *Timaeus* that the
Revisionist needs to redate. In quite a number of apparently Late
dialogues, Plato seems sympathetic to the theory of Forms: see e.g.,
*Philebus* 61e and *Laws* 965c.




On the other hand, the Revisionist claim that the *Theaetetus*
shows Plato doing more or less completely without the theory of Forms
is very plausible. There are no explicit mentions of the Forms at all
in the *Theaetetus*, except possibly (and even this much is
disputed) in what many take to be the philosophical backwater of the
Digression. The main argument of the dialogue seems to get along
without even implicit appeal to the theory of Forms. In the
*Theaetetus*, Revisionism seems to be on its strongest ground
of all.




The usual Unitarian answer is that this silence is studied. In the
*Theaetetus,* Unitarians suggest, Plato is showing what
knowledge *is not*. His argument is designed to show that
certain sorts of alternatives to Plato's own account of knowledge must
fail. Plato demonstrates this failure by the 'maieutic'
method of developing those accounts *until* they fail. Thus the
*Theaetetus* shows the impossibility of a successful account of
knowledge that does not invoke the Forms. 




The fault-line between Unitarians and Revisionists is the deepest
fissure separating interpreters of the *Theaetetus*. It is not
the only distinction among overall interpretations of the dialogue. It
has also been suggested, both in the ancient and the modern eras, that
the *Theaetetus* is a sceptical work; that the
*Theaetetus* is a genuinely aporetic work; and that the
*Theaetetus* is a disjointed work. However, there is no space
to review these possibilities here. It is time to look more closely at
the detail of the arguments that Plato gives in the distinct sections
of the dialogue.


## 4. The Introduction to the Dialogue: 142a-145e




We should not miss the three philosophical theses that are explicitly
advanced in the Introduction. They are offered without argument by
Socrates, and agreed to without argument by Theaetetus, at
145d7-145e5: 


1. The wise are wise *sophiai* (= by/ because of/ in
respect of/ as a result of wisdom:145d11).
2. To learn is to become wiser about the topic you are learning
about (145d8-9).
3. Wisdom (*sophia*) and knowledge
(*episteme*) are the same thing (145e5).




All three theses might seem contentious today. (1) seems to allude to
*Phaedo* 100e's notorious thesis about the role of the Form of
*F*-ness in any *x*'s being *F*--that
*x* is *F* "*by* the Form of
*F*-ness." (2) looks contentious because it implies (3);
and (3) brings me to a second question about 142a-145e (which is also
an important question about the whole dialogue): What is the meaning
of the Greek word that I am translating as "knowledge,"
*episteme*?




Much has been written about Plato's words for knowledge. One important
question raised by Runciman 1962 is the question whether Plato was
aware of the commonplace modern distinction between knowing that,
knowing how, and knowing what (or whom). Nothing is more natural for
modern philosophers than to contrast knowledge of
objects (knowledge by acquaintance or objectual knowledge;
French *connaitre*) with knowledge of how to do
things (technique knowledge), and with knowledge of
propositions or facts (propositional knowledge; French
*savoir*). Runciman doubts that Plato is aware of this
threefold distinction (1962, 17): "At the time of writing the
*Theaetetus* Plato had made no clear distinction [between]
knowing that, knowing how, and knowing by acquaintance."




Against this, Plato's word for knowing how is surely
*tekhne*, from which we get the English word
"technique." Plato obviously thinks *tekhne*
incidental to a serious discussion of *episteme*.
This is part of the point of the argument against definition by
examples that begins at 146d (cp. 177c-179b).




As for the difference between knowing that and knowledge by
acquaintance: the *Theaetetus* does mix passages that discuss
the one sort of knowledge with passages that discuss the other. This
does not imply that Plato was unaware of the difference. Perhaps he
wants to discuss theories of knowledge that find deep conceptual
connections between the two sorts of knowledge.




A grammatical point is relevant here. The objectual "I know
Socrates" in classical Greek is *oida* (or
*gignosko*) *ton Sokraten*; the
propositional "I know Socrates is wise" is *oida*
(or *gignosko*) *ton Sokraten sophon
onta*, literally "I know Socrates being wise" or,
colloquially, just *oida ton Sokraten sophon*,
literally "I know Socrates wise". Thus the Greek
idiom can readily treat the object of propositional knowledge, which
in English would most naturally be a that-clause, as a *thing
considered as having a quality*. We might almost say that Greek
treats what is known in propositional knowledge as just one special
case of what is known in objectual knowledge. This suggests that the
ancient Greeks naturally saw propositional and objectual knowledge as
more closely related than we do (though not necessarily as
indistinguishable). If so, Plato may have felt able to offer a single
treatment for the two kinds of knowledge without thereby confusing
them. The point will be relevant to the whole of the
*Theaetetus*.


## 5. Definition by Examples: 146a-151d




At 145d Socrates states the "one little question that
puzzles" him: "What is knowledge?" Theaetetus' first
response (D0) is to offer examples of knowledge
(146c). Socrates rejects this response, arguing that, for any
*x*, examples of *x* are neither necessary nor
sufficient for a definition of *x*. They are not necessary,
because they are irrelevant (146e). They are not sufficient, because
they presuppose the understanding that a definition is meant to
provide (147a-b). Moreover (147c), a definition could be briefly
stated, whereas talking about examples is "an interminable
diversion" (*aperanton hodon*).




Does Socrates produce good arguments against definition by examples?
Many philosophers think not (McDowell 1976 (115), Geach 1966, Santas
1972, Burnyeat 1977). They often argue this by appealing to the
authority of Wittgenstein, who famously complains (*The Blue and
Brown Books*, 20) that "When Socrates asks the question,
'What is knowledge?', he does not regard it even as a
*preliminary* answer to enumerate cases of knowledge."
For arguments against this modern consensus, see Chappell 2005
(36-37).




Some commentators have taken Socrates' critique of definition by
examples to be an implicit critique of the *Republic*'s
procedure of distinguishing knowledge, belief, and ignorance by
distinguishing their objects. The suggestion was first made by Ryle
1990 (23), who points out that "Socrates makes it clear that
what he wants discussed is not a list of things that people
know," "but an elucidation of the concept of
knowledge." Ryle suggests that "Attention to this simple
point might have saved Cornford from saying that the implicit
conclusion of the dialogue is that 'true knowledge has for its
objects things of a different order'." Ryle thinks it
"silly" to suggest that knowledge can be defined merely by
specifying its objects.




However, 145e-147c cannot be read as a critique of the
*Republic*'s procedure of distinguishing knowledge from belief
by their objects. 145e-147c is not against defining knowledge by
examples of *objects* of knowledge; it is against
defining knowledge by examples of *kinds* of
knowledge. (See e.g., 146e7, "We weren't wanting to
make a list of kinds of knowledge.") This is a different
matter.




Why, anyway, would the Platonist of the *Republic* think that
examples of the objects of knowledge are enough for a definition of
knowledge? He is surely the last person to think that. The person who
*will* think this is the empiricist, who thinks that we acquire
all our concepts by exposure to examples of their application: Locke,
*Essay* II.1, Aristotle, *Posterior Analytics* 100a4-9.
For the Platonist, definition by examples is never even possible; for
the empiricist, definition by examples is the natural method in every
case. This suggests that empiricism is a principal target of the
argument of the *Theaetetus*. More about this in sections
6-8.




Theaetetus is puzzled by his own inability to answer Socrates' request
for a definition of knowledge, and contrasts it with the ease with
which he can provide mathematical definitions. He gives an example of
a mathematical definition; scholars are divided about the aptness of
the parallel between this, and what would be needed for a definition
of knowledge. Socrates' response, when Theaetetus still protests his
inability to define knowledge, is to compare himself to a midwife in a
long and intricate analogy.




Many ancient Platonists read the midwife analogy, and more recently
Cornford 1935 has read it, as alluding to the theory of recollection.
But it is better not to import metaphysical assumptions into the text
without good reason, and it is hard to see what the reason would be
beyond a determination to insist that Plato always maintained the
theory of recollection. With or without this speculation, the midwife
passage does tell us something important about how
the *Theaetetus* is going to proceed. In line with the
classification that the ancient editors set at the front of the
dialogue, it is going to be *peirastikos*,
an *experimental* dialogue. It will try out a number of
suggestions about the nature of knowledge. As in the aporetic
dialogues, there is no guarantee that any of these suggestions will be
successful (and every chance that none of them will be).




So read, the midwife passage can also tell us something important
about the limitations of the *Theaetetus'* inquiry. The
limitations of the inquiry are the limitations of the main inquirers,
and neither (the historical) Socrates nor Theaetetus was a
card-carrying adherent of Plato's theory of Forms. Perhaps the
dialogue brings us only as far as the threshold of the theory of Forms
precisely because, on Socratic principles, one can get no further. To
get beyond where the *Theaetetus* leaves off, you have to be a
Platonist. (For book-length developments of this reading of the
*Theaetetus,* see Sedley 2004 and Chappell 2005.)


## 6. First Definition (D1): "Knowledge is Perception": 151e-187a




Between Stephanus pages 151 and 187, and leaving aside the Digression,
172-177 (section 6d), 31 pages of close and complex argument state,
discuss, and eventually refute the first of Theaetetus' three serious
attempts at a definition of knowledge (D1):
"Knowledge is perception."




As before, there are two main alternative readings of 151-187: the
Unitarian and the Revisionist. On the Unitarian reading, Plato's
purpose is to salvage as much as possible of the theories of
Protagoras and Heracleitus (each respectfully described as *ou
phaulon*: 151e8, 152d2). Plato's strategy is to show that these
theories have their own distinctive area of application, the
perceptible or sensible world, within which they are true. However,
the sensible world is not the whole world, and so these theories are
not the whole truth. We get absurdities if we try to take them as
unrestrictedly true. To avoid these absurdities it is necessary to
posit the *intelligible world* (the world of the Forms)
alongside the *sensible world* (the world of perception). When
this is done, Platonism subsumes the theories of Protagoras and
Heracleitus as partial truths. On this reading, the strategy of the
discussion of D1 is to transcend Protagoras and
Heracleitus: to explain their views by showing how they are, not the
truth, but parts of a larger truth. In the process the discussion
reveals logical pressures that may push us towards the two-worlds
Platonism that many readers, e.g., Ross and Cornford, find in the
*Republic* and *Timaeus.*




On the Revisionist reading, Plato's purpose is to refute the theories
of Protagoras and Heracleitus. He thinks that the absurdities those
theories give rise to, come not from trying to take the theories as
*unrestrictedly* true, but from trying to take them as true
*at all*, even of the sensible world. Anyone who tries to take
seriously the thesis that knowledge is perception has to adopt
theories of knowledge and perception like Protagoras' and
Heracleitus'. But their theories are untenable. By *modus
tollens* this shows that D1 itself is
untenable. On this reading, the strategy of the discussion of
D1 is to move us towards the view that sensible
phenomena have to fall under the same general metaphysical theory as
intelligible phenomena.




This outline of the two main alternatives for 151-187 shows how
strategic and tactical issues of Plato interpretation interlock. For
instance, the outline shows how important it is for an overall
understanding of the *Theaetetus* to have a view on the
following questions of detail (more about them later): 


1. At 156a-157c, is Socrates just reporting, or also endorsing, a
Heracleitean flux theory of perception?
2. What is the date of the *Timaeus*, which seems (28-29, 45b-46c,
49e) to present a very similar theory of perception to that found in
*Theaetetus* 156-7?
3. What does Plato take to be the logical relations between the three
positions under discussion in 151-184 (D1,
Protagoras' theory, and Heracleitus' theory)? The closer he takes them
to be, the more support that seems to give to the Revisionist view
that the whole of 151-187 is one gigantic *modus tollens*. The
more separate they are, the better for those versions of Unitarianism
that suggest that Plato wants to pick and choose among the positions
offered in 151-187.



 
So much for the overall structure of 151-187; now for the parts.


### 6.1 The Definition of Knowledge as Perception: 151d-e




At 151d7-e3 Theaetetus proposes D1: "Knowledge
is *nothing other than* perception"
(*aisthesis*). This proposal is immediately equated by
Socrates with Protagoras's thesis that "man is the measure of
all things" (Hm for *homomensura*),
which in turn entails the thesis that things are to any human just as
they appear to that human (PS for phenomenal
subjectivism). Socrates then adds that, in its turn,
PS entails Heracleitus' view that "All is
flux," that there are no stably existing *objects* with
stably enduring *qualities*.




The first of these deft exchanges struck the Anonymous Commentator as
disingenuous: "Plato himself knew that Protagoras' opinion about
knowledge was not the same as Theaetetus'" (Anon, *ad
loc.*). Certainly it is easy to see counter-examples to the
alleged entailment. Take, for instance, the thesis that knowledge is
*awareness* (which is often the right way to translate
*aisthesis*). Or take the thesis that to know is to
perceive things as God, or the Ideal Observer, perceives them, and
that we fail to know (or to perceive) just insofar as our opinions are
other than God's or the Ideal Observer's. These theses are both
versions of D1. Neither entails Hm,
the claim that "man is the measure of all things"; nor the
Protagoreanism that lies behind that slogan.




So how, if at all, does D1 entail all the things
that Socrates apparently makes it entail in 151-184? And does Plato
think it has all these entailments? Evidently the answer to that
depends on how we understand D1. In particular, it
depends on the meaning of the word *aisthesis*,
"perception," in D1. If the slogan
"Knowledge is perception" equates knowledge with what ordinary
speakers of classical Greek would have meant by
*aisthesis*, then D1 does not entail
Protagoras' and Heracleitus' views. In the ordinary sense of
*aisthesis*, there are (as just pointed out) too many
other possible ways of spelling out D1 for the move
from D1 to Hm to be logically
obligatory. But if the slogan "Knowledge is perception" equates
knowledge with what Protagoras and Heracleitus meant by
*aisthesis*, D1 *does* entail
Protagoras' and Heracleitus' views. Of course it does; for then
D1 simply says that knowledge is just what Protagoras
and Heracleitus say knowledge is.


### 6.2 The "Cold Wind" Argument; and the Theory of Flux: 152a-160e




At 152b1-152c8 Socrates begins his presentation of Protagoras' view
that things are to any human just as they appear to that human by
taking the example of a wind which affects two people
differently. Such cases, he says, support Protagoras'
analysis: "that the wind is cold *to the one who feels
cold*, but not cold *to the one who does not feel
cold.*"




Some scholars (Cornford 1935, 33-4; Waterlow 1977) think that the
point of the argument is that *both* "the wind in itself
is cold" and "the wind in itself is not cold (but
warm)" are true: "'Warm' and
'cold' are two properties which can co-exist in the same
physical object. I perceive the one, you perceive the other."
The trouble with this suggestion is that much of the detail of the
Protagorean/Heracleitean position in 151-184 seems to be generated by
Protagoras' desire to *avoid* contradiction. If Cornford thinks
that Protagoras is *not* concerned to avoid contradicting
himself, then he has a huge task of reinterpretation ahead of him.




Rather, perhaps, the point of the argument is this: Neither "The
wind in itself is cold" nor "The wind in itself is
warm" is true. If we had grounds for affirming either, we would
have equally good grounds for affirming both; but the conjunction
"The wind in itself is cold and the wind in itself is
warm" is a contradiction. This contradiction, says Protagoras,
obliges us to give up all talk about "the wind in itself,"
and switch to relativised talk about the wind as it seems *to
me* or *to you,* etc. (The same contradiction pushes the
Plato of the *Republic* in the opposite direction: it leads him
to place no further trust in *any* relativised talk, precisely
because such talk cannot get us beyond such
contradictions.)




So we have moved from D1, to Hm, to
PS. At 152c8-152e1 Socrates adds
that, in its turn, PS entails Heracleitus' view that
"All is flux," that there are no stably existing
*objects* with stably enduring *qualities.* The reason
given for this is the same thought as the one at the centre of the
cold-wind argument: that everything to which any predicate can be
applied, according to one perception, can also have the negation of
that predicate applied to it, according to an opposite perception with
equally good credentials.




After a passage (152e1-153d5) in which Socrates presents what seem to
be deliberately bad arguments, eight of them, for Heracleitus' flux
thesis, Socrates notes three shocking theses which the flux theory
implies:


1. Qualities have no independent existence in time and space
(153d6-e1).
2. Qualities do not exist except in perceptions of them
(153e3-154a8).
3. (The dice paradox:) changes in a thing's qualities are not so much
changes in that thing as in perceptions of that thing
(154a9-155c6).




These shocking implications, Socrates says, give the phenomenal
subjectivist his reason to reject the entire object/quality
metaphysics, and to replace it with a metaphysics of flux.




In 155c-157c the flux theory is used to develop a
Protagorean/Heracleitean account of perception, to replace accounts
based on the object/property ontology of common sense. Socrates notes
the subversive implications of the theory of flux for the
meaningfulness and truth-aptness of most of our language as it
stands. (He returns to this point at 183a-b.) The ontology of the flux
theory distinguishes kinds of "process"
(*kinesis*), i.e., of flux, in two ways: as fast or slow,
and as active or passive. Hence there are four such processes. On
these the flux theory's account of perception rests.




A rather similar theory of perception is given by Plato in
*Timaeus* 45b-46c, 67c-68d. This fact has much exercised
scholars, since it relates closely to the question whether Plato
himself accepts the flux theory of perception (cp. *Theaetetus*
157c5). The question is important because it connects with the
question of whether the Revisionist or Unitarian reading of 151-187 is
right. (For more on this issue, see Cornford 1935 (49-50); Crombie
1963, II (21-22); Burnyeat 1990 (17-18); McDowell 1973 (139-140),
Chappell 2005 (74-78).)




At 157c-160c Socrates states a first objection to the flux theory.
This asks how the flux theorist is to distinguish false (deceptive)
appearances such as dreams from the true (undeceptive) appearances of
the waking world. The flux theorist's answer is that such appearances
should not be described as 'true' and 'false'
appearances to the same person. Rather they should be described as
different appearances to different people. According to the flux
theorist, we have the same person if and only if we have the same
combination of a perception and a perceiving (159c-d). So there is no
need to call any appearances *false*. Thus we preserve the
claim that all appearances are true--a claim which must be true
if knowledge is perception in the sense that Socrates has taken that
definition.




160b-d summarises the whole of 151-160. Socrates shows how the
exploration of Theaetetus' identification of knowledge with perception
has led us to develop a whole battery of views: in particular, a
Protagorean doctrine of the incorrigibility of perception, and a
Heracleitean account of what perception is. Thus "perception has
one of the two marks of knowledge, infallibility" (Cornford
1935, 58); "and, if we can accept Protagoras' identification of
what appears to me with what is, ignoring the addition 'for
me' and the distinction between being and becoming, the case
will be complete."


### 6.3 The Refutation of the Thesis that Knowledge is Perception: 160e5-186e12




160e marks the transition from the statement and exposition of the
definition of knowledge as perception (D1), to the
criticism and eventual refutation of that definition.




Scholars have divided about the overall purpose of 160e-186e. Mostly
they have divided along the lines described in section 3, taking
either a Revisionist or a Unitarian view of Part One of the
*Theaetetus*.




Revisionists say that the target of the critique of 160e-186e is
everything that has been said in support and development of
D1 ever since 151. Unitarians argue that Plato's
criticism of D1 in 160e-186e is more selective.
Obviously his aim is to refute D1, the equation of
knowledge with perception. But that does not oblige him to reject the
account of perception that has been offered in support of
D1. And Plato does not reject this account: he
accepts it.




Thus the Unitarian Cornford argues that Plato is not rejecting the
Heracleitean flux theory of perception. He is rejecting only
D1's claim that *knowledge* is that sort of
perception. It remains possible that perception is just as Heracleitus
describes it. Likewise, Cornford suggests, the Protagorean doctrine
that "man is the measure of all things" is true provided
it is taken to mean only "all things *that we
perceive*."




If some form of Unitarianism is correct, an examination of 160-186
should show that Plato's strategy in the critique of
D1 highlights two distinctions:


1. A distinction between the claim that *the* *objects of
perception* are in flux, and the claim that *everything* is
in flux.
2. A distinction between bare sensory awareness, and judgement on
the basis of such awareness.




One vital passage for distinction (1) is 181b-183b. If Unitarianism is
right, this passage should be an attack on the Heracleitean thesis
that *everything* is in flux, but not an attack on the
Heracleitean thesis that *the objects of perception* are in
flux. According to Unitarians, the thesis that the objects of
perception are in flux is a Platonic thesis too. Readers should ask
themselves whether this is the right way to read 181b -183b.




Distinction (2) seems to be explicitly stated at 179c. There also
seems to be clear evidence of distinction (2) in the final argument
against D1, at 184-187. Distinction (2) is also at
work, apparently, in the discussion of some of the nine objections
addressed to the Protagorean theory. Some of these objections can
plausibly be read as points about the unattractive consequences of
failing to distinguish the Protagorean claim that bare sense-awareness
is incorrigible (as the Unitarian Plato agrees) from the further
Protagorean claim that *judgements about* sense-awareness are
incorrigible (which the Unitarian Plato denies).




The criticism of D1 breaks down into twelve separate
arguments, interrupted by the Digression (172c-177c: translated and
discussed separately in section 6d). There is no space here to comment
in detail on every one of these arguments, some of which, as noted
above, have often been thought frivolous or comically intended
(cp. 152e1-153d5). Some brief notes on the earlier objections will
show what the serious point of each might be.




The first objection to Protagoras (160e-161d) observes that if all
perceptions are true, then there is no reason to think that animal
perceptions are inferior to human ones: a situation which Socrates
finds absurd.




If this objection is really concerned with perceptions strictly so
called, then it obviously fails. Protagoras just accepts this
supposedly absurd consequence; and apparently he is right to do so. If
we consider animals and humans just as perceivers, there is no
automatic reason to prefer human perceptions. Many animal perceptions
are *superior* to human perceptions (dogs' hearing, hawks'
eyesight, dolphins' echolocatory ability, most mammals' sense of
smell, etc.), and the Greeks knew it, cf. Homer's commonplace remarks
about "far-sighted eagles", or indeed Aristotle, in the
*Eudemian Ethics*, 1231a5-6. The objection works much better
rephrased as an objection about
*judgements about* perceptions, rather than about
*perceptions* strictly so called. Humans are no more and no
less *perceivers* than pigs, baboons, or tadpoles. But they are
different in their powers of judgement about perceptions. 




This distinction between arguments against a Protagorean view about
perception and a Protagorean view about judgement about perception is
relevant to the second objection too (161d-162a). This objection (cp.
*Cratylus* 386c) makes the point that Protagoras' theory
implies that no one is wiser than anyone else. Notably, the argument
does not attack the idea that *perception* is
infallible. Rather, it attacks the idea that the opinion or judgement
that anyone forms *on the basis of* perception is infallible
(161d3). (This is an important piece of support for Unitarianism:
cp. distinction (2) above.)




A third objection to Protagoras' thesis is very quickly stated in
Socrates' two rhetorical questions at 162c2-6. Since Protagoras'
thesis implies that all perceptions are true, it not only has the
allegedly absurd consequence that animals' perceptions are not
inferior to humans. It also has the consequence that humans'
perceptions are not inferior to the gods'. This consequence too is now
said to be absurd.




As with the first two objections, so here. If we consider divinities
and humans just as perceivers, there is no automatic reason to prefer
divine perceptions, and hence no absurdity. Plato may well want us to
infer that the Greek gods are not different just in respect of being
*perceivers* from humans. But they *are* different in
their powers of judgement about perceptions.




The next four arguments (163a-168c) present counter-examples to the
alleged equivalence of knowledge and perception. The fourth observes
that, if perception = knowledge, then anyone who perceives an
utterance in a given language should have knowledge of that utterance,
i.e., understand it--which plainly doesn't happen. The fifth
raises a similar problem about memory and perception: remembering
things is *knowing* them, but not *perceiving* them. The
sixth (the "covered eye") objection contrasts *not
perceiving* an object (in one sensory modality) with *not
knowing it*. If perception = knowledge, seeing an object with one
eye and not seeing it with the other would appear to be a case of the
contradictory state of both knowing it and not knowing it. The seventh
points out that one can perceive dimly or faintly, clearly or
unclearly, but that these adverbial distinctions do not apply to ways
of knowing--as they must if knowing *is* perceiving.




In 165e4-168c5, Socrates sketches Protagoras's response to these seven
objections. Protagoras makes two main points. First, he can meet some
of the objections by distinguishing types and occasions of
perception. Second, teaching as he understands it is not a matter of
getting the pupil to have true rather than false beliefs. Since there
are no false beliefs, the change that a teacher can effect is not a
change from false belief to true belief or knowledge. Rather,
Protagoras' model of teaching is a *therapeutic* model. What a
good teacher does, according to him, is use arguments (or discourses:
*logoi*) as a good doctor uses drugs, to replace the state of
the soul in which "bad things are and appear" with one in
which "good things are and appear." While all
beliefs are *true*, not all beliefs are
*beneficial*.




A difficulty for Protagoras' position here is that, if all beliefs are
true, then all beliefs about which beliefs are beneficial must be
true. But surely, some beliefs about which beliefs are beneficial
contradict other beliefs about which beliefs are beneficial;
especially if some people are better than others at bringing about
beneficial beliefs. (For example, no doubt Plato's and Protagoras'
beliefs conflict at this point.) This means that Protagoras' view
entails a contradiction of the same sort as the next
objection-the famous *peritrope*--seems to be
meant to bring out.




The *peritrope* ("table-turning") objection
(171a-b) is this. Suppose I believe, as Protagoras does, that
"All beliefs are true," but also admit that "There
is a belief that 'Not all beliefs are true'." If all
beliefs are true, the belief that "Not all beliefs are
true" must be true too. But if that belief is true, then by
disquotation, not all beliefs are true. So I refute myself by
contradicting myself; and the same holds for Protagoras.




The validity of the objection has been much
disputed. Burnyeat, Denyer and Sedley all offer reconstructions of the
objection that make it come out valid. McDowell and Bostock suggest
that although the objection does not prove what it is meant to prove
(self-contradiction), it does prove a different point (about
self-defeat) which is equally worth making. 




Socrates' ninth objection presents Protagoras' theory with a
dilemma. If the theory is completely general in its application, then
it must say that not only what counts as *justice* in cities,
but also what *benefits* cities, is a relative matter. As
Protagoras has already admitted (167a3), it is implausible to say that
benefit is a relative notion. But the alternative, which Protagoras
apparently prefers, is a conceptual divorce between the notions of
justice and benefit, which restrict the application of Protagoras'
theory to the notion of justice. Socrates obviously finds this
conceptual divorce unattractive, though he does not, directly, say
why. Instead, he offers us the Digression.


### 6.4 The Digression: 172c1-177b7




An obvious question: what is the Digression for? One answer (defended
in Chappell 2004, ad loc.) would be that it is a critique of the
society that produces the conceptual divorce between justice and
benefit that has just emerged. Socrates draws an extended parallel
between two types of character, the philosophical man and the man of
rhetoric, to show that it is better to be the philosophical type.




The Digression is "philosophically quite pointless,"
according to Ryle 1966: 158. Less dismissively, McDowell 1976: 174
suggests that the Digression serves "a purpose which, in a
modern book, might be served by footnotes or an appendix."
Similarly, Cornford 1935 (83) suggests that Plato aims to give the
reader some references for anti-relativist arguments that he presents
elsewhere: "To argue explicitly against it would perhaps take
him too far from the original topic of perception. Instead, he inserts
[the Digression], which contains allusions to such arguments in other
works of his."




Perhaps the Digression paints a picture of what it is like to
*live* in accordance with the two different accounts of
knowledge, the Protagorean and the Platonist, that Plato is
comparing. Thus the Digression shows us what is ethically at stake in
the often abstruse debates found elsewhere in the *Theaetetus*.
Its point is that we can't make a decision about what account of
knowledge to accept without making all sorts of other decisions, not
only about the technical, logical and metaphysical matters that are to
the fore in the rest of the *Theaetetus*, but also about
questions of deep ethical significance. So, for instance, it can
hardly be an accident that, at 176c2, the difference between justice
and injustice is said to be a difference between knowledge
(*gnosis*) and ignorance (*agnoia*).




Another common question about the Digression is: does it introduce or
mention the Platonic Forms? Certainly the Digression uses phrases that
are indisputably part of the Middle-Period language for the Forms. If
Plato uses the language of the theory of Forms in a passage which is
admitted on all sides to allude to the themes of the
*Republic*, it strains credulity to imagine that Plato is not
intentionally referring to the Forms in that passage.




On the other hand, as the Revisionist will point out, the
*Theaetetus* does not seem to *do* much with the Forms
that are thus allegedly introduced. But perhaps it would undermine the
Unitarian reading of the *Theaetetus* if the Forms
*were* present in the Digression in the role of paradigm
objects of knowledge. For the Unitarian reading, at least on the
version that strikes me as most plausible, says that the aim of
the *Theaetetus* is to show that, in the end, we cannot
construct a theory of knowledge without the Forms--a claim which is to
be proved by trying and failing, three times, to do so. So if the
Forms were there in the Digression, perhaps that would be a case of
"giving the game away."


### 6.5 Last Objection to Protagoras: 177c6-179b5




After the Digression Socrates returns to criticising Protagoras'
relativism. His last objection is that there is no coherent way of
applying Protagoras' relativism to judgements about the future.




How might Protagoras counter this objection? Protagoras has already
suggested that the past may now be no more than whatever I now
remember it to have been (166b). Perhaps he can also suggest that the
future is now no more than I now believe it will be. No prediction is
ever proved wrong, just as no memory is ever inaccurate. All that
happens is it seems to one self at one time that something *will
be* true (or *has been* true), and seems to another self at
another time that something different *is* true.




But these appeals to distinctions between Protagorean
selves--future or past--do not help. Suppose we grant to
Protagoras that, when I make a claim about how the future will be,
this claim concerns how things will be *for my future self*. It
is just irrelevant to add that my future self and I are different
beings. Claims about the future still have a form that makes them
refutable by *someone's* future experience. If I predict on
Monday that on Tuesday my head will hurt, that claim is falsified
either if I have no headache on Tuesday, or if, on Tuesday, there is
someone who is by convention picked out as my continuant whose head
does not hurt.



 
Similarly with the past. Suppose I know on Tuesday that on Monday I
predicted that on Tuesday my head would hurt. It is no help against
the present objection for me to reflect, on Tuesday, that I am a
different person now from who I was then. My Monday-self can only have
meant either that *his* head would hurt on Tuesday, which was a
false belief on his part if he no longer exists on Tuesday; or else
that the Tuesday-self would have a sore head. But if the Tuesday-self
has no sore head, then my Monday-self made a false prediction, and so
must have had a false belief. Either way, the relativist does not
escape the objection.




Moreover, this defence of Protagoras does not evade the following
dilemma. Either what I mean by claiming (to take an example of
Bostock's) that "The wine will taste raw to me in five years'
time" is literally that. Or else what I mean is just
"*It seems to me* that the wine will taste raw to me in
five years' time."




Suppose I mean the former assertion. If the wine turns out not to
taste raw five years hence, Protagoras has no defence from the
conclusion that I made a false prediction about how things would seem
to me in five years. Or suppose I meant the latter assertion. Then I
did not make a *prediction*, strictly speaking, at all; merely
a remark about what presently seems to me. Either way, Protagoras
loses.


### 6.6 Last Objection to Heracleitus: 179c1-183c2




Socrates argues that if Heracleitus' doctrine of flux is true, then no
assertion whatever can properly be made. Therefore (a) Heracleitus'
theory of flux no more helps to prove that knowledge *is*
perception than that knowledge *is* *not* perception,
and (b) Heracleiteans cannot coherently say anything at all, not even
to state their own doctrine.




There are two variants of the argument. On the first of these
variants, evident in 181c2-e10, Socrates distinguishes just
*two* kinds of flux or process, namely qualitative alteration
and spatial motion, and insists that the Heracleiteans are committed
to saying that both are continual. On the second variant, evident
perhaps at 182a1, 182e4-5, Socrates distinguishes indefinitely many
kinds of flux or process, not just qualitative alteration and motion
through space, and insists that the Heracleiteans are committed to
saying that *every* kind of flux is continual.




Now the view that everything is always changing in every way might
seem a rather foolish view to take about everyday objects. But, as
182a2-b8 shows, the present argument is not about everyday objects
anyway. Plato does not apply his distinction between kinds of change
to every sort of object whatever, including everyday objects. He
applies it specifically to the objects (if that is the word) of
Heracleitean metaphysics. These items are supposed by the Heracleitean
to be the reality underlying all talk of everyday objects. It is at
the level of these Heracleitean perceivings and perceivers that
Plato's argument against Heracleitus is pitched. And it is not
obviously silly to suppose that Heracleitean perceivings and
perceivers are constantly changing in every way.




The argument that Socrates presents on the Heracleiteans' behalf
infers from "Everything is always changing in every way"
that "No description of anything is excluded." How does
this follow? McDowell 1976: 181-2 finds the missing link in the
impossibility of *identifications*. We cannot (says McDowell)
identify a moving sample of whiteness, or of seeing, *any
longer* once it has changed into some other colour, or
perception.




But this only excludes *re*identifications: presumably I can
identify the moving whiteness or the moving seeing *until* it
changes, even if this only gives me an instant in which to identify
it. This point renders McDowell's version, as it stands, an invalid
argument. If it is on his account possible to identify the moving
whiteness *until it changes*, then it is on his account
possible to identify the moving whiteness. But if that is possible,
then his argument contradicts itself: for it goes on to deny this
possibility.




Some other accounts of the argument also commit this fallacy. Compare
Sayre's account (1969: 94): "If no statement, either affirmative
or negative, can remain true for longer than the time taken in its
utterance, then no statement can be treated as either true or false,
and the cause of communicating with one's fellow beings must be given
up as hopeless." 




Sayre's argument aims at the conclusion "No statement can be
treated as either true or false." But Sayre goes via the premiss
"Any statement remains true no longer than the time taken in its
utterance." If there are statements which *are* true,
even if they are not true for very long, it is not clear why these
statements cannot be *treated* *as* true, at least in
principle (and in practice too, given creatures with the right sensory
equipment and sense of time).




McDowell's and Sayre's versions of the argument also face the
following objection. It is obvious how, given flux, a present-tense
claim like "Item *X* is present" can quickly cease
to be true, because e.g., "Item *Y* is present"
comes to replace it. But it isn't obvious why flux should exclude the
possibility of past-tense statements like "Item *X*
flowed into item *Y* between *t*1 and
*t*2," or of tenseless statements like
"Item *X* is present at *t*1, item
*Y* is present at *t*2." As Bostock
1988: 105-6 points out, "So long as we do have a language with
stable meanings, and the ability to make temporal distinctions, there
is no difficulty at all about describing an ever-changing
world."



*"So long as"*: to make the argument workable, we
may suggest that its point is that the *meanings of words* are
exempt from flux. If meanings are not in flux, and if we have access
to those meanings, nothing stops us from identifying the whiteness at
least until it flows away. But if meanings are in flux too, we will
have the result that the argument against Heracleitus actually
produces at 183a5: anything at all will count equally well as
identifying or not identifying the whiteness. "Unless we
recognise some class of knowable entities exempt from the Heracleitean
flux and so capable of standing as the fixed meanings of words, no
definition of knowledge can be any more true than its
contradictory. Plato is determined to make us feel the need of his
Forms without mentioning them" (Cornford 1935, 99).


### 6.7 The Final Refutation of D1: 183c4-187a8




Socrates completes his refutation of the thesis that knowledge is
perception by bringing a twelfth and final objection, directed against
D1 itself rather than its Protagorean or Heracleitean
interpretations. This objection says that the mind makes use of a
range of concepts which it could not have acquired, and which do not
operate, through the senses: e.g., "existence,"
"sameness," "difference." So there is a part
of thought, and hence of knowledge, which has nothing to do with
perception. Therefore knowledge is not perception.




Unitarians and Revisionists will read this last argument against
D1 in line with their general
orientations. Unitarians will suggest that Socrates' range of concepts
common to the senses is a list of Forms. They will point to the
similarities between the image of the senses as soldiers in a wooden
horse that Socrates offers at 184d1 ff., and the picture of a
Heracleitean self, existing only in its awareness of particular
perceptions, that he drew at 156-160.




Revisionists will retort that there are important differences between
the Heracleitean self and the wooden-horse self, differences that show
that Heracleiteanism is no longer in force in 184-187. They will
insist that the view of perception in play in 184-187 is Plato's own
non-Heracleitean view of perception. Thus Burnyeat 1990: 55-56 argues
that, since Heracleiteanism has been refuted by 184, "the organs
and subjects dealt with [in the Wooden Horse passage] are the ordinary
stable kind which continue in being from one moment to the
next." On the other hand, notice that Plato's equivalent for
Burnyeat's "organs and subjects" is the single word
*aistheseis* (184d2). On its own, the word can mean
either "senses" or "sensings"; but it seems
significant that it was the word Plato used at 156b1 for one of the
two sorts of Heracleitean "offspring." Plato speaks of the
*aistheseis* concealed "as if within a Wooden
Horse" as *pollai tines* (184d1), "indefinitely
many." But while there are indefinitely many Heracleitean
*sensings*, there are not, of course, indefinitely many
*senses*. Indeed even the claim that we have *many*
senses (*pollai*), rather than *several*
(*enioi*, *tines*), does not sound quite right, either
in English or in Greek. This is perhaps why most translators, assuming
that *aistheseis* means "senses," put
"a number of senses" for *pollai tines
aistheseis*. Perhaps this is a mistake, and what
*aistheseis* means here is "Heracleitean
sensings." If so, this explains how the
*aistheseis* inside any given Wooden Horse can be
*pollai tines.*




If the *aistheseis* in the Wooden Horse are Heracleitean
*sensings*, not ordinary, un-Heracleitean *senses*, this
supports the Unitarian idea that 184-187 is contrasting Heracleitean
perceiving of particulars with Platonic knowing of the Forms (or
knowing of particulars *via*, and *in terms of*, the
Forms).




Another piece of evidence pointing in the same direction is the
similarity between Plato's list of the "common notions" at
*Theaetetus* 186a and closely contemporary lists that he gives
of the Forms, such as the list of Forms (*likeness*,
*multitude*, *rest* and their opposites) given at
*Parmenides* 129d, with ethical additions at
*Parmenides* 130b. There are also the *megista
gene* ("greatest kinds") of *Sophist*
254b-258e (*being*, *sameness*, *otherness*,
*rest* and *change*); though whether these
*gene* are Forms is controversial.


## 7. Second Definition (D2): "Knowledge is True Judgement": 187b-201c




151-187 has considered and rejected the proposal that knowledge is
perception. Sometimes in 151-187 "perception" seems to
mean "immediate sensory awareness"; at other times it
seems to mean "judgements made *about* immediate sensory
awareness." The proposal that "Knowledge is immediate
sensory awareness" is rejected as incoherent: "Knowledge
is not to be found in our bodily experiences, but in our reasonings
about those experiences" (186d2). The proposal that
"Knowledge is judgement about immediate sensory awareness"
raises the question *how* judgements, or beliefs, can emerge
from immediate sensory awareness. Answering this question is the
main aim in 187-201.




Empiricists claim that sensation, which in itself has no cognitive
content, is the source of all beliefs, which essentially have
cognitive content--which are by their very nature candidates for
truth or falsity. So unless we can explain how beliefs can be true or
false, we cannot explain how there can be beliefs at all. Hence
Plato's interest in the question of false belief. What Plato wants to
show in 187-201 is that there is no way for the empiricist to
construct contentful belief from contentless sensory awareness
alone. The corollary is, of course, that we need something else
besides sensory awareness to explain belief. In modern terms, we need
irreducible *semantic properties.* In Plato's terms, we need
the Forms.




In pursuit of this strategy of argument in 187-201, Plato rejects in
turn five possible empiricist explanations of how there can be false
belief. In the First Puzzle (188a-c) he proposes a basic 
difficulty for any empiricist. Then he argues that no move available
to the empiricist circumvents this basic difficulty, however much
complexity it may introduce (the other four Puzzles: 188d-201b). The
Fifth Puzzle collapses back into the Third Puzzle, and the Third
Puzzle collapses back into the First. The proposal that gives us the
Fourth Puzzle is disproved by the counter-examples that make the Fifth
Puzzle necessary. As for the Second Puzzle, Plato deploys this to show
how empiricism has the disabling drawback that it turns an outrageous
sophistical argument into a valid disproof of the possibility of at
least some sorts of false belief.




Thus 187-201 continues the critique of perception-based accounts of
knowledge that 151-187 began. Contrary to what some--for instance
Cornford--have thought, it is no digression from the main path of the
*Theaetetus*. On the contrary, the discussion of false belief
is the most obvious way forward.




As Plato stresses throughout the dialogue, it is Theaetetus who is
caught in this problem about false belief. It is not Socrates, nor
Plato. There is clear evidence at *Philebus* 38c ff. that false
belief (at least of some sorts) was no problem at all to Plato himself
(at least at some points in his career). Plato's question is not
"How on earth can there be false judgement?" Rather it is
"What sort of background assumptions about knowledge must
Theaetetus be making, given that he is puzzled by the question how
there can be false judgement?"




Is it only false judgements of *identity* that are at issue in
187-201, or is it *any* false judgement? One interpretation of
187-201 says that it is only about false judgements of
misidentification. Call this view *misidentificationism*. The
main alternative interpretation of 187-201 says that it is about any
and every false judgement. Call this view
*anti-misidentificationism*. The present discussion assumes the truth of
anti-misidentificationism; see Chappell 2005: 154-157 for the
arguments.




I turn to the detail of the five proposals about how to explain false
belief that occupy Stephanus pages 187 to 200 of the dialogue.


### 7.1 The Puzzle of Misidentification: 187e5-188c8




The first proposal about how to explain the possibility of false
belief is the proposal that false belief occurs when someone
misidentifies one thing as another. To believe or judge falsely is to
judge, for some two objects *O1* and *O2*, that
*O1* is *O2*.




How can such confusions even occur? Plato presents a dilemma that
seems to show that they can't. The objects of the judgement,
*O1* and *O2*, must either be known or unknown to the
judger *x*. Suppose one of the objects, say *O1*, is
unknown to *x*. In that case, *O1* cannot figure in
*x*'s thoughts at all, since *x* can only form
judgements using objects that he knows. So if *O1* is not an
object known to *x*, *x* cannot make *any*
judgement about *O1*. *A fortiori,* then, *x* can
make no *false* judgement about *O1* either.




If, on the other hand, both *O1* and *O2* are known to
*x*, then *x* can perhaps make *some* judgements
about *O1* and *O2*; but not the false judgement that
"*O1* is *O2*." If *x* *knows*
*O1* and *O2*, *x* must know that *O1* is
*O1* and *O2* is *O2*, and that it would be a
confusion to identify them. So apparently false belief is impossible
if the judger does not know both *O1* and *O2*; but also
impossible if he does know both *O1* and *O2*. 




I cannot mistake *X* for *Y* unless I am able to
formulate thoughts about *X* and *Y*. But I will not be
able to formulate thoughts about *X* and *Y* unless I am
*acquainted* with *X* and *Y*. Being acquainted
with *X* and *Y* means *knowing* *X* and
*Y*; and anyone who knows *X* and *Y* will not
mistake them for each other.




Why think this a genuine puzzle? There seem to be plenty of everyday
cases where knowing some thing in no way prevents us from sometimes
mistaking that thing for something else. One example in the dialogue
itself is at 191b (cp. 144c5). It is perfectly possible for someone
who knows Socrates to see Theaetetus in the distance, and wrongly
think that Theaetetus is Socrates. The First Puzzle does not even get
off the ground, unless we can see why our knowledge of *X* and
*Y* should guarantee us against mistakes about *X* and
*Y*. Who is the puzzle of 188a-c supposed to be a puzzle
*for*?




Some authors, such as Bostock, Crombie, McDowell, and White, think
that Plato himself is puzzled by this puzzle. Thus Crombie 1963: 111
thinks that Plato advances the claim that any knowledge at all of an
object *O* is sufficient for infallibility about *O*
because he fails to see the difference between "being acquainted
with *X*" and "being familiar with
*X*." But to confuse knowing *everything* about
*X* with knowing enough about *X* to use the name
'*X*' is really a very simple mistake. Plato would
not be much of a philosopher if he made this mistake.




If (as is suggested in e.g. Chappell 2004, ad loc.) 187-201 is an
indirect demonstration that false belief cannot be explained by
empiricism (whether this means a developed philosophical theory, or
the instinctive empiricism of some people's common sense), then it is
likely that the First Puzzle states the basic difficulty for
empiricism, to which the other four Puzzles look for alternative
solutions. The nature of this basic difficulty is not fully, or indeed
at all, explained by the First Puzzle. We have to read on and watch
the development of the argument of 187-201 to see exactly what the
problem is that gives the First Puzzle its bite.


### 7.2 Second Puzzle About False Belief: "Believing What is Not": 188c10-189b9




The second proposal says that false judgement is believing or judging
*ta* *me onta*, "things that are
not" or "what is not." Socrates observes that if
"what is not" is understood as it often was by Greek
thinkers, as meaning "nothing," then this proposal leads
us straight into the sophistical absurdity that false beliefs are the
same thing as beliefs about nothing (i.e., contentless beliefs). But
there can be no beliefs about nothing; and there are false beliefs; so
false belief isn't the same thing as believing what is not.




Some think the Second Puzzle a mere sophistry. Bostock 1988: 165
distinguishes two versions of the sophistry: "On one version, to
believe falsely is... to believe what is not 'just by
itself'; on the other version, it is to believe what is not
'about one of the things which are'". The argument
of the first version, according to Bostock, "is just that there
is no such thing as what is not (the case); it is a mere
nonentity. But just as you cannot perceive a nonentity, so equally you
cannot believe one either." Bostock proposes the following
solution to this problem: "We may find it natural to reply to
this argument by distinguishing... propositions [from] facts,
situations, states of affairs, and so on. Then we shall say that the
things that are believed are propositions, not facts... so a
false belief is not directed at a non-existent."




This raises the question whether a consistent empiricist can admit the
existence of propositions. At least one great modern empiricist, Quine
1953: 156-7, thinks not. Plato agrees: he regards a commitment to the
existence of propositions as evidence of *Platonism,*
acceptance of the claim that abstract objects (and plenty of them)
genuinely exist. So an explanation of false judgement that invoked
entities called propositions would be unavailable to the sort of
empiricist that Plato has in his sights.




Bostock's second version of the puzzle makes it an even more
transparent sophistry, turning on a simple confusion between the
"is" of predication and the "is" of
existence. As pointed out above, we can reasonably ask whether Plato
made this distinction, or made it as we make it.




If the structure of the Second Puzzle is really as Bostock suggests,
then the Second Puzzle is just the old sophistry about believing what
is not (cp. Parmenides DK 29B8*, Euthydemus* 283e ff.,
*Cratylus* 429d, *Republic* 477a, *Sophist* 263e
ff.). Moreover, on this interpretation of the Second Puzzle, Plato is
committed, in his own person and with full generality, to accepting
(at least provisionally) a very bad argument for the conclusion that
there can be no false belief. It would be nice if an interpretation of
the Second Puzzle were available that saw it differently: e.g., as
accepted by him only in a context where special reasons make the
Second Puzzle very plausible in that context.




One such interpretation is defended e.g., by Burnyeat 1990: 78, who
suggests that the Second Puzzle can only work if we accept the
"scandalous analogy between judging what is not and seeing or
touching what is not there to be seen or touched": "A
model on which judgements relate to the world in the same sort of
unstructured way as perceiving or (we may add) naming, will tie anyone
in knots when it comes to the question 'What is a false
judgement the judgement/ name of?'. The only available answer,
when the judgement is taken as an unstructured whole, appears to be:
Nothing."




Notice that it is the empiricist who will most naturally tend to rely
on this analogy. It is the empiricist who finds it natural to
assimilate judgement and knowledge to perception, so far as he can. So
we may suggest that the Second Puzzle is a mere sophistry for any
decent account of false judgement, but a good argument against the
empiricist account of false judgement that Plato is attacking. The
moral of the Second Puzzle is that empiricism validates the old
sophistry *because* it treats believing or judging as too
closely analogous to seeing: 188e4-7. For empiricism judgement, and
thought in general, consists in awareness of the ideas that are
present to our minds, exactly *as* they are present to our
minds. It cannot consist in awareness of those ideas *as they are
not*; because (according to empiricism) we are immediately and
incorrigibly aware of our own ideas, it can only consist in awareness
of those ideas *as they are*. Nor can judgement consist in
awareness of ideas that are *not* present to our minds, for
(according to empiricism) what is not present to our minds cannot be a
part of our thoughts. Still less can judgement consist in awareness of
ideas that do not exist at all.




The old sophists took false belief as "judging what is
not"; they then fallaciously slid from "judging what is
not," to "judging nothing," to "not judging at
all," and hence concluded that no judgement that was ever
actually made was a false judgement. The empiricism that Plato attacks
not only repeats this logical slide; it makes it look almost
reasonable. The point of the Second Puzzle is to draw out this
scandalous consequence.


### 7.3 Third Puzzle About False Belief: *Allodoxia*: 189b10-190e4




Literally translated, the third proposal about how to explain the
possibility of false belief says that false belief occurs "when
someone exchanges (*antallaxamenos*) in his understanding one
of the things that are with another of the things that are, and says
*is*" (189b12-c2).




Perhaps the best way to read this very unclear statement is as meaning
that the distinctive addition in the third proposal is the notion of
*inadvertency*. The point of Socrates' argument is that this
addition does not help us to obtain an adequate account of false
belief because thought (*dianoia*) has to be understood as an
inner process, with objects that we are always fully and explicitly
conscious of. If we are fully and explicitly conscious of all the
objects of our thoughts, and if the objects of our thoughts are as
simple as empiricism takes them to be, there is simply no room for
inadvertency. But without inadvertency, the third proposal simply
collapses back into the first proposal, which has already been
refuted.




The empiricist conception of knowledge that Theaetetus unwittingly
brings forth, and which Socrates is scrutinising, takes the objects of
thought to be simple mental images which are either straightforwardly
available to be thought about, or straightforwardly absent. The First
Puzzle showed that there is a general problem for the empiricist about
explaining how such images can be confused with each other, or indeed
semantically conjoined in any way at all. The Second Puzzle showed
that, because the empiricist lacks clear alternatives other than that
someone should *have* a mental image or *lack* it, he is
wide open to the sophistical argument which identifies
*believing* with *having a mental image*, and then
identifies *believing what is* with *having a mental
image*, too--and so "proves" the impossibility of
false belief. The Third Puzzle restricts itself (at least up to 190d7)
to someone who *has* the requisite mental images, and adds the
suggestion that he manages to confuse them by a piece of inadvertency.
Socrates' rejoinder is that nothing has been done to show *how*
there can be inadvertent confusions of things that are as simple and
unstructured, and as simply grasped or *not* grasped, as the
empiricist takes mental images to be. Just as speech is explicit
*outer* dialogue, so thought is explicit *inner*
dialogue. What the empiricist needs to do to show the possibility of
such a confusion is to explain how, on his principles, either speech
or thought can fail to be fully explicit and fully "in
touch" with its objects, if it is "in touch" with
them at all.




In the discussion of the Fourth and Fifth Puzzles, Socrates and
Theaetetus together work out the detail of two empiricist attempts to
explain just this. It then becomes clearer why Plato does not think
that the empiricist can explain the difference between fully explicit
and not-fully-explicit speech or thought. Plato thinks that, to
explain this, we have to abandon altogether the empiricist conception
of thought as the concatenation (somehow) of semantically inert simple
mental images. Instead, we have to understand thought as the syntactic
concatenation of the genuine semantic entities, the *Forms*.
Mistakes in thought will then be comprehensible as mistakes either
about the logical interrelations of the Forms, or about the correct
application of the Forms to the sensory phenomena.


### 7.4 Fourth Puzzle About False Belief: the Wax Tablet: 190e5-196c5




The Wax Tablet passage offers us a more explicit account of the nature
of thought, and its relationship with perception. The story now on
offer says explicitly that perception relates to thought roughly as
Humean "impressions" relate to Humean "ideas"
(191d; compare Hume, *First Enquiry* II). The objects of
perception, as before, are a succession of constantly-changing
immediate awarenesses. The objects of thought, it is now added, are
those objects of perception to which we have chosen to give a measure
of stability by imprinting them on the wax tablets in our minds. (The
image of memory as writing in the mind had currency in Greek thought
well before Plato's time: see e.g. Aeschylus, *Eumenides*
275.)




This new spelling-out of the empiricist account of thought seems to
offer new resources for explaining the possibility of false
belief. The new explanation can say that false belief occurs when
there is a mismatch, not between two objects of *thought*, nor
between two objects of *perception*, but between one object of
each type.




This proposal faces a simple and decisive objection. No one disputes
that there are false beliefs that *cannot* be explained as
mismatches of thought and perception: e.g., false beliefs about
arithmetic. The Wax Tablet does not explain how such false beliefs
happen; indeed it entails that they *can't* happen. Such
mistakes are confusions of two objects of thought, and the Wax Tablet
model does not dispute the earlier finding that there can be no such
confusions. So the Wax Tablet model fails.




There is of course plenty more that Plato *could* have said in
criticism of the Wax Tablet model. Most obviously, he could have
pointed out the absurdity of identifying any number with any
individual's *thought* of that number (195e9 ff.); especially
when the numerical thought in question is no more than an ossified
perception. In the present passage Plato is content to refute the Wax
Tablet by the simplest and shortest argument available: so he does not
make this point. But perhaps the point is meant to occur to the
reader; for the same absurdity reappears in an even more glaring form
in the Aviary passage.


### 7.5 Fifth Puzzle About False Belief: the Aviary: 196d1-200d4




If we had a solution to the very basic problem about how the
empiricist can get any content at all out of sensation, then the
fourth proposal might show how the empiricist could explain false
belief involving perception. The fifth and last proposal about how to
explain the possibility of false belief attempts to remedy the fourth
proposal's incapacity--which Plato says refutes it,
196c5-7--to deal with cases of false belief involving no
perception, such as false arithmetical beliefs. 




It attempts this by deploying a distinction between knowledge that
someone merely *has* (latent knowledge) and knowledge that he
is actually *using* (active knowledge)*.* (Perhaps Plato
is now exploring "the intermediate stages between knowing and
not knowing" mentioned at 188a2-3.) The suggestion is that false
belief occurs when someone wants to use some item of latent knowledge
in his active thought, but makes a wrong selection from among the
items that he knows latently.




If this proposal worked it would cover false arithmetical belief. But
the proposal does not work, because it is regressive. If there is a
problem about the very possibility of confusing two things, it is no
answer to this problem to suppose that for each thing there is a
corresponding item of knowledge, and that what happens when two
*things* are confused is really that the two corresponding
*items* *of* *knowledge* are confused
(200a-b).




The Aviary rightly tries to explain false belief by complicating our
picture of belief. But it complicates in the wrong way and the wrong
place. It is no help to complicate the story by throwing in further
objects of the same sort as the objects that created the difficulty
about false belief in the first place. What is needed is a different
sort of object for thought: a kind of object that can be thought of
under different aspects (say, as "the sum of 5 and 7," or
as "the integer 12"). There are no such aspects to the
"items of knowledge" that the Aviary deals in. As with the
conception of the objects of thought and knowledge that we found in
the Wax Tablet, it is this lack of aspects that dooms the Aviary's
conception of the objects of knowledge too. Like the Wax Tablet, the
Aviary founders on its own inability to accommodate the point that
thought cannot consist merely in the presentation of a series of inert
"objects of thought." Whether these objects of thought
are mental images drawn from perception or something else, the
thinking is not so much in the objects of thought as in what is
*done* with those objects (186d2-4).




We may illustrate this by asking: When the dunce who supposes that 5 +
7 = 11 decides to activate some item of knowledge to be the answer to
"What is the sum of 5 and 7?," *which* item of
knowledge does he thus decide to activate? At first only two answers
seem possible: either he decides to activate 12, or he decides to
activate 11. If he decides to activate 12, then we cannot explain the
fact that what he actually does is activate 11, except by saying that
he mistakes the item of knowledge which is 11 for the item of
knowledge which is 12. But this mistake is the very mistake ruled out
as impossible right at the beginning of the inquiry into false belief
(188a-c). Alternatively, if he decides to activate 11, then we have
to ask *why* he decides to do this. The most plausible answer
to that question is: "Because he believes falsely that 5 + 7 =
11." But as noted above, if he has already formed this false
belief, *within* the account that is supposed to explain false
belief, then a regress looms.




In fact, the correct answer to the question "Which item of
knowledge does the dunce decide to activate?" is neither
"12" nor "11." It is "*that
number* which is the sum of 5 and 7." But this answer does
not save the Aviary theorist from the dilemma just pointed out; for it
is not available to him. To be able to give this answer, the Aviary
theorist would have to be able to distinguish "that
number which is the sum of 5 and 7" from
"12." But since "12" *is "*that
number which is the sum of 5 and 7," this distinction
cannot be made by anyone who takes the objects of thought to be simple
in the way that the Aviary theorist seems to.




At 199e1 ff. Theaetetus suggests an amendment to the Aviary. This is
that we might have items of *ignorance* in our heads as well as
items of knowledge. As Socrates remarks, these ignorance-birds can be
confused with knowledge-birds in just the same way as knowledge-birds
can be confused with each other. So the addition does not help.


### 7.6 The Final Refutation of D2: 200d5-201c7




At 200d-201c Socrates argues more directly against
D2. He offers a counter-example to the thesis that
knowledge is true belief. A skilled lawyer can bring jurymen into a
state of true belief without bringing them into a state of knowledge;
so knowledge and true belief are different states.




McDowell 1976: 227-8 suggests that this swift argument
"contradicts the most characteristic expositions of the Theory
of Forms, which indicate that the title 'knowledge' should
be reserved for a relation between the mind and the Forms untainted by
any reliance on perception." By contrast Plato here tells us,
quite unambiguously, that the jury are persuaded into a state of true
belief "about things which only someone who sees them can
know" (201b8). This implies that there can be knowledge which is
entirely reliant on perception. (One way out of this is to deny that
Plato ever thought that knowledge is *only* of the Forms, as
opposed to thinking that knowledge is *paradigmatically* of the
Forms. For this more tolerant Platonist view about perception see e.g.
*Philebus* 58d-62d, and *Timaeus* 27d ff.)




The jury argument seems to be a counter-example not only to
D2 but also to D3, the thesis that
knowledge is true belief *with an account* (provided we allow
that the jury "have an account").




A third problem about the jury argument is that Plato seems to offer
two incompatible explanations of why the jury don't know: first that
they have only a limited time to hear the arguments (201b3, 172e1);
and second that their judgement is second-hand (201b9).


## 8. Third Definition (D3): "Knowledge is True Judgement With an Account": 201d-210a




Theaetetus' third proposal about how to knowledge is
(D3) that it is true belief with an account (*meta
logou alethe doxan*).




D3 apparently does nothing at all to solve the main
problems that D2 faced. Besides the jurymen
counter-example just noted, 187-201 showed that we could not define
knowledge as *true* belief unless we had an account of
*false* belief. This problem has not just evaporated in
201-210. It will remain as long as we propose to define knowledge as
true belief plus anything. Significantly, this does not seem to bother
Plato--as we might expect if Plato is not even trying to offer an
acceptable definition of knowledge, but is rather undermining
unacceptable definitions.




One crucial question about *Theaetetus* 201-210 is the question
whether the argument is concerned with objectual or propositional
knowledge. This is a basic and central division among interpretations
of the whole passage 201-210, but it is hard to discuss it properly
without getting into the detail of the Dream Theory: see section
8a.




A second question, which arises often elsewhere in the
*Theaetetus*, is whether the argument's appearance of
*aporia* reflects genuine uncertainty on Plato's part, or is
rather a kind of literary device. Is Plato thinking aloud, trying to
clarify his own view about the nature of knowledge, as Revisionists
suspect? Or is he using an aporetic argument only to smoke out his
opponents, as Unitarians think?




The evidence favours the latter reading. There are a significant
number of other passages where something very like Theaetetus' claim
(D3) that knowledge is "true belief with an
account" is not only discussed, but actually defended: for
instance, *Meno* 98a2, *Phaedo* 76b5-6, *Phaedo*
97d-99d2, *Symposium* 202a5-9, *Republic* 534b3-7, and
*Timaeus* 51e5. So it appears that, in the *Theaetetus*,
Plato cannot be genuinely puzzled about what knowledge can be. Nor can
he genuinely doubt his own former confidence in one version of
D3. If he does have a genuine doubt or puzzle of this
sort, it is simply incredible that he should say what he does say in
201-210 without also expressing it.




What Plato does in 201-210 is: present a picture (Socrates' Dream) of
how things may be if D3 is true (201c-202c); raise
objections to the Dream theory which are said (206b12) to be decisive
(202c-206c); and present and reject three further suggestions about
the meaning of *logos*, and so three more versions of
D3 (206c-210a). But none of these four
interpretations of D3 is Plato's own earlier version
of D3, which says that knowledge = true belief with
an account *of the reason why the true belief is true*. If what
Plato wants to tell us in *Theaetetus* 201-210 is that he no
longer accepts *any* version of D3, not even
his own version, then it is extraordinary that he does not even
mention his own version, concentrating instead on versions of
D3 so different from Plato's version as to be
obviously irrelevant to its refutation.




Unitarians can suggest that Plato's strategy is to refute what he
takes to be false versions of D3 so as to increase
the logical pressure on anyone who rejects Plato's version of
D3. In particular, he wants to put pressure on the
empiricist theories of knowledge that seem to be the main target of
the *Theaetetus*. What Plato wants to show is, not only that no
definition of knowledge except his own, D3, is
acceptable, but also that no version of D3 except his
own is acceptable.


### 8.1 The Dream of Socrates: 201d8-202d7




Rather as Socrates offered to develop D1 in all sorts
of surprising directions, so now he offers to develop
D3 into a sophisticated theory of knowledge. This
theory, usually known as the "Dream of Socrates" or the
"Dream Theory," posits two kinds of existents, complexes
and simples, and proposes that "an account" means
"an account of the complexes that analyses them into their
simple components." Thus "knowledge of *x*"
turns out to mean "true belief about *x* with an account
of *x* that analyses *x* into its simple
components."




Taken as a general account of knowledge, the Dream Theory implies that
knowledge is only of complexes, and that there can be no knowledge of
simples. Socrates attacks this implication.




A common question about the Dream Theory is whether it is concerned
with objectual or propositional knowledge. Those who take the Dream
Theory to be concerned with *propositional* knowledge include
Ryle 1990: 27-30: "from 201 onwards Plato concentrates on
'know' (*connaitre*): [Socrates' Dream] is a
logician's theory, a theory about the composition of truths and
falsehoods." Those who take the Dream Theory to be concerned
with *objectual* knowledge include White 1976: 177, and Crombie
1963: II: 41-42; also Bostock 1988. A third way of taking the Dream
Theory, which may well be the most promising interpretation, is to
take it as a *Logical Atomism*: as a theory which founds an
account of propositional structure on an account of the concatenation
of simple objects of experience or acquaintance such as "sense
data."




The Logical-Atomist reading of the Dream Theory undercuts the
propositional/objectual distinction. On this reading, the Dream
Theory claims that simple, private objects of experience are the
elements of the proposition; thus, the Dream Theory is *both* a
theory about the structure of propositions *and* a theory about
simple and complex objects. It claims in effect that a proposition's
structure is that of a complex object made up out of simple objects,
where these simple objects are conceived in the Russellian manner as
objects of inner perception or acquaintance, and the complexes which
they compose are conceived in the phenomenalist manner as
(epistemological and/ or semantic) constructs out of those simple
objects.




This supposition makes good sense of the claim that we ourselves are
examples of complexes (201e2: "the primary elements
(*prota stoikheia*) of which we and everything else are
composed..."). If the Dream theorist is a Logical Atomist,
he will think that there is a clear sense in which people, and
everything else, are composed out of sense data. He will also think
that descriptions of objects, too, are complexes constructed in
another way out of the immediately available simples of sensation.




For such a theorist, epistemology and semantics alike rest upon the
foundation provided by the simple objects of acquaintance. Both
thought and meaning consist in the construction of complex objects out
of those simple objects. Philosophical analysis, meanwhile, consists
in *stating how* the complexes involved in thought and meaning
are constructed out of simples. This statement involves, amongst other
things, dividing down to and enumerating the (simple) parts of such
complexes.




What then is the relation of the Dream Theory to the problems posed
for empiricism by the discussion of D2 in 187-201? The fundamental
problem for empiricism, as we saw, is the problem how to get *from
sensation to content*: the problem of how we could start with bare
sense-data, and build up out of them anything that deserved to be
called *meaning*. Plato thinks that there is a good answer to
this, though it is not an empiricist answer. Sense experience becomes
contentful when it is understood and arranged according to the
structures that the Forms give it. So to understand sense experience
is, in the truest sense, "to give an account" for it.




The empiricist cannot offer this answer to the problem of how to get
from sensation to content without ceasing to be an empiricist. What
the empiricist *can* do is propose that content arises out of
sets of sense experiences. We get to the level of belief and knowledge
only when we start to consider such sets: before that we are at the
level only of perception. Our beliefs, couched in expressions that
refer to and quantify over such sets, will then become knowledge (a)
when they are true, and (b) when we understand the full story of their
composition out of such sets.




If this is the point of the Dream Theory, then the best answer to the
question "Whose is the Dream Theory?" is "It belongs
to the empiricist whom Plato is attacking."


### 8.2 Critique of the Dream Theory: 202d8-206c2




The Dream Theory says that knowledge of *O* is true belief
about *O* plus an account of *O*'s composition. If
*O* is not composite, *O* cannot be known, but only
"perceived" (202b6).




Socrates' main strategy in 202d8-206c2 is to attack the Dream's claim
that complexes and elements are distinguishable in respect of
knowability. To this end he deploys a dilemma. A complex, say a
syllable, is either (a) no more than its elements (its letters), or
(b) something over and above those elements.




202d8-203e1 shows that unacceptable consequences follow from
alternative (a), that a complex is no more than its elements. If I am
to know a syllable *SO*, and that syllable is no more than its
elements, then I cannot know the syllable *SO* without also
knowing its elements *S* and *O*. Indeed, it seems that
coming to know the parts *S* and *O* is both necessary
and sufficient for coming to know the syllable *SO*. But if
that is right, and if the letter/syllable relation models the
element/complex relation, then if any complex is *knowable*,
its elements will be knowable too; and if any complex's elements
are
*unknowable*, then the complex will be unknowable too. This
result contradicts the Dream Theory.




203e2-205e8 shows that unacceptable consequences follow from
alternative (b), that a complex is something over and above its
elements. In that case, to know the syllable is to know something for
which knowledge of the elements is not sufficient. The syllable turns
out to be "a single Idea that comes to be out of the
fitted-together elements" (204a1-2). But then the syllable does
not have the elements as parts: if it did, that would compromise its
singularity. And if the elements are not the parts of the syllable,
nothing else can be. So the syllable has no parts, which makes it as
simple as an element. Thus if the element is unknowable, the syllable
must be unknowable too. This result contradicts the Dream Theory
too.




Finally, in 206a1-c2, Plato makes a further, very simple, point
against the Dream Theory. Our own experience of learning letters and
syllables shows that it is both more basic and more important to know
elements than complexes, not *vice versa* as the Dream Theory
implies. The thesis that the complexes are knowable, the elements
unknowable, is false to our experience, in which "knowledge of
the elements is primary" (Burnyeat 1990:192).


### 8.3 Three Attempts to Understand *Logos*: 206c2-210a9




The refutation of the Dream Theory's attempt to spell out what it
might be like for D3 to be true is followed by three
attempts to give an account of what a *logos* is. The first
attempt to give an account of "account" takes
*logos* just to mean "speech" or
"statement." This is deemed obviously insufficient
(206c1-206e3).




A second attempted explanation of "*logos* of O"
takes it as "enumeration of the elements of
*O*." The *logos* is a statement of the
*elements* of the object of knowledge. You have knowledge of
something when, in addition to your true belief about it, you are able
also to "go through the elements" of that thing.




Plato's objection to this proposal (208b) is that it leaves open the
possibility that someone could count as having knowledge of the name
"Theaetetus" even if they could do no more than write out
the letters of the name "Theaetetus" in the right
order. Since such a person can enumerate the elements of the complex,
i.e., the letters of the name (207c8-d1), he has an account. Since he
can arrange those letters in their correct order (208a9-10), he also
has true belief. For all that, insists Plato, he does not have
knowledge of the name "Theaetetus."




Why not, we might ask? To see the answer we should bring in what Plato
says about syllables at 207d8-208a3. Suppose someone could enumerate
the letters of "Theaetetus," and could give their correct
order, and yet knew nothing about syllables. This person wouldn't
count as knowing "Theaetetus" because he would have no
understanding of the principles that get us from ordered letters to
names. Those principles are principles about *how* letters form
syllables, and *how* syllables form names. A person who can
state only the letters of "Theaetetus" and their order has
no awareness of these principles.




To put it a modern way, a robot or an automatic typewriter might be
able to reproduce or print the letters of "Theaetetus"
correctly and in order. It might even be able to store such a correct
ordering in its electronic memory. That would not show that such a
machine *understood* how to spell "Theaetetus," any
more than the symbol-manipulating capacities of the man in Searle's
Chinese Room show that he understands Chinese. What is missing is an
awareness of bridging or structuring principles, rules explaining
*how* we get from strings of symbols, *via* syllables,
to representations of Greek names. 




Knowledge of such bridging principles can reasonably be called
knowledge of *why* the letters of "Theaetetus" are
what they are. So it is plausible to suggest that the moral of the
argument is to point us to the need for an account in the sense of an
explanation "Why?," and so to the version of
D3 that Plato himself accepts.




The third proposed account of *logos* says that to give the
*logos* of *O* is to cite the *semeion* or
*diaphora* of *O*. In the Wax Tablet passage,
*semeion* meant 'imprint'; in the present
passage, it means the 'sign' or diagnostic feature wherein
*x* differs from everything else, or everything else of
*O*'s own kind. So, presumably, knowledge of (say) Theaetetus
consists in true belief about Theaetetus plus an account of what
differentiates Theaetetus from every other human.




Socrates offers two objections to this proposal. First, if knowledge
of Theaetetus requires a mention of his *semeion*, so
does true belief about Theaetetus. Second, to *possess*
"an account of Theaetetus' *semeion*" must
mean either (a) having true belief about that *semeion,*
or else (b) having knowledge of it. But it has already been pointed
out that any true belief, if it is to qualify as being about
Theaetetus at all, must already be true belief about his
*semeion.* So interpretation (a) has the result that
knowledge of Theaetetus = true belief about Theaetetus'
*semeion* + true belief about Theaetetus'
*semeion*. As for (b): if we want to know what knowledge
is, it is no help to be told that knowledge of *O* = something
else + *knowledge* of the *semeion* of
*O*. We still need to know what knowledge of the
*semeion* of *O* is. Nor will it help us to be
launched on a vicious regress: as we will be if we are told that
knowledge of the *semeion* of *O* = something else
+ knowledge of the *semeion* of the
*semeion* of *O*. 




This is where the argument ends, and Socrates leaves to meet his
accusers.


## 9. Conclusion




The *Theaetetus* is an extended attack on certain assumptions
and intuitions about knowledge that the intelligent
man-in-the-street--Theaetetus, for instance--might find
initially attractive, and which some philosophers known to
Plato--Protagoras and Heracleitus, for instance--had worked
up into complex and sophisticated philosophical theories. Basic to all
these assumptions and intuitions, which here have been grouped together under
the name "empiricism," is the idea that knowledge is
constructed out of perception and perception alone.




The first part of the *Theaetetus* attacks the idea that
knowledge could be simply *identified* with perception.
Perceptions alone have no semantic structure. So if this thesis was
true, it would be impossible to state it.




The second part attacks the suggestion that knowledge can be defined
as true belief, where beliefs are supposed to be
semantically-structured concatenations of sensory impressions. Against
this Plato argues that, unless something can be said to explain
*how* impressions can be concatenated so as to give them
semantic structure, there is no reason to grant that the distinction
between true and false applies to such beliefs any more than it does
to perceptions.




Finally, in the third part of the *Theaetetus*, an attempt is
made to meet this challenge, and present some explanation of how
semantic structures can arise out of mere perceptions or impressions.
The proposed explanation is the Dream Theory, a theory interestingly
comparable to Russellian Logical Atomism, which takes both
propositions and objects to be complexes "logically
constructed" out of simple sensory impressions. On this
conception, knowledge will come about when someone is capable not only
of using such logical constructions in thought, but of understanding
how they arise from perception.




Socrates' basic objection to this theory is that it still gives no
proper explanation of *how* this logical construction takes
place. Without such an explanation, there is no good reason to treat
the complexes that are thus logically constructed as anything other
than simples in their own right. We need to know how it can be that,
merely by conjoining perceptions in the right way, we manage to
achieve a degree of semantic structure that (for instance) makes it
possible to *refer to things in the world*, such as
Theaetetus. But this is not explained simply by listing all the simple
perceptions that are so conjoined. Nor--and this is where we
reach the third proposal of 208b11-210a9--is it explained by
fixing on any of those perceptions in particular, and taking it to be
the special mark of Theaetetus whereby reference to Theaetetus is
fixed.




The third proposal about how to understand *logos* faces the
difficulty that, if it adds anything at all to differentiate knowledge
of *O* from true belief about *O*, then what it adds is
a diagnostic quality of *O*. If there is a problem about how to
identify *O*, there is a problem about how to identify the
diagnostic quality too. This launches a vicious regress.




One way of preventing this regress is to argue that the regress is
caused by the attempt to work up a definition of knowledge exclusively out of
empiricist materials. Hence there is no way of avoiding such a vicious
regress if you are determined to try to define knowledge on an exclusively
empiricist basis. The right response is to abandon that attempt.
Knowledge is indeed indefinable in empiricist terms. In *those*
terms, it has no *logos*. In *those* terms, therefore,
knowledge itself is unknowable.




The official conclusion of the *Theaetetus* is that we still do
not know how to define knowledge. Even on the most sceptical reading,
this is not to say that we have not learned anything about what
knowledge is like. As Theaetetus says (210b6), he has given birth to
far more than he had in him.




And as many interpreters have seen, there may be much more to the
ending than that. It may even be that, in the last two pages of the
*Theaetetus*, we have seen hints of Plato's own answer to the
puzzle. Perhaps *understanding* has emerged from the last
discussion, as *wisdom* did from 145d-e, as the key ingredient
without which no true beliefs alone can even begin to look like they
might count as knowledge. Perhaps it is only when we, the readers,
understand this point--that epistemological success in the last
resort depends on having epistemological virtue--that we begin
not only to have true beliefs about what knowledge is, but to
understand knowledge.