Theaetetus
may be remarked by the way. The attempt to discover the definition
of knowledge is in accordance with the character of Socrates as he
is described in the Memorabilia, asking What is justice? what is
temperance? and the like. But there is no reason to suppose that he
would have analyzed the nature of perception, or traced the connexion
of Protagoras and Heracleitus, or have raised the difficulty respecting
false opinion. The humorous illustrations, as well as the serious
thoughts, run through the dialogue. The snubnosedness of Theaetetus, a
characteristic which he shares with Socrates, and the man-midwifery
of Socrates, are not forgotten in the closing words. At the end of the
dialogue, as in the Euthyphro, he is expecting to meet Meletus at the
porch of the king Archon; but with the same indifference to the result
which is everywhere displayed by him, he proposes that they shall
reassemble on the following day at the same spot. The day comes, and
in the Sophist the three friends again meet, but no further allusion is
made to the trial, and the principal share in the argument is assigned,
not to Socrates, but to an Eleatic stranger; the youthful Theaetetus
also plays a different and less independent part. And there is no
allusion in the Introduction to the second and third dialogues, which
are afterwards appended. There seems, therefore, reason to think that
there is a real change, both in the characters and in the design.
The dialogue is an enquiry into the nature of knowledge, which is
interrupted by two digressions. The first is the digression about the
midwives, which is also a leading thought or continuous image, like the
wave in the Republic, appearing and reappearing at intervals. Again and
again we are reminded that the successive conceptions of knowledge are
extracted from Theaetetus, who in his turn truly declares that Socrates
has got a great deal more out of him than ever was in him. Socrates is
never weary of working out the image in humorous details,--discerning
the symptoms of labour, carrying the child round the hearth, fearing
that Theaetetus will bite him, comparing his conceptions to wind-eggs,
asserting an hereditary right to the occupation. There is also a serious
side to the image, which is an apt similitude of the Socratic theory
of education (compare Republic, Sophist), and accords with the ironical
spirit in which the wisest of men delights to speak of himself.
The other digression is the famous contrast of the lawyer and
philosopher. This is a sort of landing-place or break in the middle of
the dialogue. At the commencement of a great discussion, the reflection
naturally arises, How happy are they who, like the philosopher, have
time for such discussions (compare Republic)! There is no reason for the
introduction of such a digression; nor is a reason always needed, any
more than for the introduction of an episode in a poem, or of a topic in
conversation. That which is given by Socrates is quite sufficient, viz.
that the philosopher may talk and write as he pleases. But though not
very closely connected, neither is the digression out of keeping with
the rest of the dialogue. The philosopher naturally desires to pour
forth the thoughts which are always present to him, and to discourse of
the higher life. The idea of knowledge, although hard to be defined, is
realised in the life of philosophy. And the contrast is the favourite
antithesis between the world, in the various characters of sophist,
lawyer, statesman, speaker, and the philosopher,--between opinion and
knowledge,--between the conventional and the true.
The greater part of the dialogue is devoted to setting up and throwing
down definitions of science and knowledge. Proceeding from the lower to
the higher by three stages, in which perception, opinion, reasoning are
successively examined, we first get rid of the confusion of the idea of
knowledge and specific kinds of knowledge,--a confusion which has been
already noticed in the Lysis, Laches, Meno, and other dialogues. In
the infancy of logic, a form of thought has to be invented before the
content can be filled up. We cannot define knowledge until the nature of
definition has been ascertained. Having succeeded in making his meaning
plain, Socrates proceeds to analyze (1) the first definition which
Theaetetus proposes: 'Knowledge is sensible perception.' This is
speedily identified with the Protagorean saying, 'Man is the measure
of all things;' and of this again the foundation is discovered in the
perpetual flux of Heracleitus. The relativeness of sensation is then
developed at length, and for a moment the definition appears to be
accepted. But soon the Protagorean thesis is pronounced to be suicidal;
for the adversaries of Protagoras are as good a measure as he is, and
they deny his doctrine. He is then supposed to reply that the perception
may be true at any given instant. But the reply is in the end shown to
be inconsistent with the Heraclitean foundation, on which the doctrine
has been affirmed to rest. For if the Heraclitean flux is extended to
every sort of change in every instant of time, how can any thought
or word be detained even for an instant? Sensible perception, like
everything else, is tumbling to pieces. Nor can Protagoras himself
maintain that one man is as good as another in his knowledge of the
future; and 'the expedient,' if not 'the just and true,' belongs to the
sphere of the future.
And so we must ask again, What is knowledge? The comparison of
sensations with one another implies a principle which is above
sensation, and which resides in the mind itself. We are thus led to look
for knowledge in a higher sphere, and accordingly Theaetetus, when again
interrogated, replies (2) that 'knowledge is true opinion.' But how is
false opinion possible? The Megarian or Eristic spirit within us revives
the question, which has been already asked and indirectly answered in
the Meno: 'How can a man be ignorant of that which he knows?' No answer
is given to this not unanswerable question. The comparison of the mind
to a block of wax, or to a decoy of birds, is found wanting.
But are we not inverting the natural order in looking for opinion before
we have found knowledge? And knowledge is not true opinion; for the
Athenian dicasts have true opinion but not knowledge. What then
is knowledge? We answer (3), 'True opinion, with definition or
explanation.' But all the different ways in which this statement may be
understood are set aside, like the definitions of courage in the Laches,
or of friendship in the Lysis, or of temperance in the Charmides. At
length we arrive at the conclusion, in which nothing is concluded.
There are two special difficulties which beset the student of the
Theaetetus: (1) he is uncertain how far he can trust Plato's account of
the theory of Protagoras; and he is also uncertain (2) how far, and in
what parts of the dialogue, Plato is expressing his own opinion.
The dramatic character of the work renders the answer to both these
questions difficult.
1. In reply to the first, we have only probabilities to offer. Three
main points have to be decided: (a) Would Protagoras have identified
his own thesis, 'Man is the measure of all things,' with the other,
'All knowledge is sensible perception'? (b) Would he have based the
relativity of knowledge on the Heraclitean flux? (c) Would he have
asserted the absoluteness of sensation at each instant? Of the work of
Protagoras on 'Truth' we know nothing, with the exception of the two
famous fragments, which are cited in this dialogue, 'Man is the measure
of all things,' and, 'Whether there are gods or not, I cannot tell.' Nor
have we any other trustworthy evidence of the tenets of Protagoras, or
of the sense in which his words are used. For later writers, including
Aristotle in his Metaphysics, have mixed up the Protagoras of Plato, as
they have the Socrates of Plato, with the real person.
Returning then to the Theaetetus, as the only possible source from which
an answer to these questions can be obtained, we may remark, that Plato
had 'The Truth' of Protagoras before him, and frequently refers to the
book. He seems to say expressly, that in this work the doctrine of the
Heraclitean flux was not to be found; 'he told the real truth' (not
in the book, which is so entitled, but) 'privately to his
disciples,'--words which imply that the connexion between the doctrines
of Protagoras and Heracleitus was not generally recognized in Greece,
but was really discovered or invented by Plato. On the other hand,
the doctrine that 'Man is the measure of all things,' is expressly
identified by Socrates with the other statement, that 'What appears to
each man is to him;' and a reference is made to the books in which the
statement occurs;--this Theaetetus, who has 'often read the books,' is
supposed to acknowledge (so Cratylus). And Protagoras, in the speech
attributed to him, never says that he has been misunderstood: he rather
seems to imply that the absoluteness of sensation at each instant was
to be found in his words. He is only indignant at the 'reductio ad
absurdum' devised by Socrates for his 'homo mensura,' which Theodorus
also considers to be 'really too bad.'
The question may be raised, how far Plato in the Theaetetus could
have misrepresented Protagoras without violating the laws of dramatic
probability. Could he have pretended to cite from a well-known writing
what was not to be found there? But such a shadowy enquiry is not worth
pursuing further. We need only remember that in the criticism which
follows of the thesis of Protagoras, we are criticizing the Protagoras
of Plato, and not attempting to draw a precise line between his real
sentiments and those which Plato has attributed to him.
2. The other difficulty is a more subtle, and also a more important one,
because bearing on the general character of the Platonic dialogues. On
a first reading of them, we are apt to imagine that the truth is only
spoken by Socrates, who is never guilty of a fallacy himself, and is the
great detector of the errors and fallacies of others. But this natural
presumption is disturbed by the discovery that the Sophists are
sometimes in the right and Socrates in the wrong. Like the hero of a
novel, he is not to be supposed always to represent the sentiments
of the author. There are few modern readers who do not side with
Protagoras, rather than with Socrates, in the dialogue which is
called by his name. The Cratylus presents a similar difficulty: in
his etymologies, as in the number of the State, we cannot tell how
far Socrates is serious; for the Socratic irony will not allow him
to distinguish between his real and his assumed wisdom. No one is the
superior of the invincible Socrates in argument (except in the first
part of the Parmenides, where he is introduced as a youth); but he is by
no means supposed to be in possession of the whole truth. Arguments are
often put into his mouth (compare Introduction to the Gorgias) which
must have seemed quite as untenable to Plato as to a modern writer.
In this dialogue a great part of the answer of Protagoras is just
and sound; remarks are made by him on verbal criticism, and on the
importance of understanding an opponent's meaning, which are conceived
in the true spirit of philosophy. And the distinction which he is
supposed to draw between Eristic and Dialectic, is really a criticism of
Plato on himself and his own criticism of Protagoras.
The difficulty seems to arise from not attending to the dramatic
character of the writings of Plato. There are two, or more, sides to
questions; and these are parted among the different speakers. Sometimes
one view or aspect of a question is made to predominate over the rest,