Knowledge Is Warranted, True Belief
Classic Philosophical Questions Part 5 - Knowledge
Plato, from the Theaetetus
Kem Stone - 8 October 2007
To present the basic, commonly held definition of knowledge as warranted, true belief, it is ironic that the text the
editors have chosen is actually an argument for why warranted, true belief is not a sufficient definition for
knowledge. Plato’s Theaetetus was perhaps the earliest example of this definition being offered, but it ultimately
rejects the definition and in classic Socratic fashion, leaves us understanding that we not only lack knowledge, but
are ignorant as to the nature of knowledge itself.
In this dialogue, Socrates makes an inquiry regarding the object of learning, which is to acquire wisdom.
Knowledge and wisdom being the synonymous in this context, it is important to establish just what we are after
when we seek to acquire knowledge. Theaetetus responds that it is judgment, but because there are true
judgments and false judgments, knowledge can only be regarded as judgment that is true.
The most obvious objection that can be levelled against this definition is that it is insufficient, that its scope is too
wide. But Socrates first attacks it on purely formal grounds, asking Theaetetus to consider the consequences of
replacing “knowing or not knowing” with “being or not being”. He asks, “May it not simply be that one who
thinks what is not about anything cannot but be thinking what is false, whatever his state of mind may be in other
respects?” Theaetetus agrees that when a man believes something and it is not true, he thinks what is not. But
Socrates argues that to think what is not is an absurd notion, as one cannot see what is not or hear what is not.
To think what is not is to think nothing, which must be something different than thinking falsely.
Theaetetus agrees with this, but when Socrates presses him for a new definition, he merely offers the same one as
before—that knowledge is true belief. It is here that Socrates levels the objection that the scope of this definition
is too broad, pointing out that the entire profession of oratory demonstrates that true belief is not knowledge.
“There you have men who use their skill to produce conviction, not by instruction, but by making people believe
whatever they want them to believe…And when a jury is rightly convinced of facts which can be known only by
an eye-witness, then, judging by hearsay and accepting a true belief, they are judging without knowledge,
although, if they did find the right verdict, their conviction is correct” (240). To define knowledge purely as “true
belief” would allow for any belief, no matter how poorly justified, to constitute knowledge if it just happens to be
true. If I believe the criminal is guilty purely by gut instinct, and he turns out to actually be guilty, my belief would
have to be called “knowledge” by this definition although I clearly did not know he was guilty.
To save his definition, Theaetetus adds a third criterion: that knowledge is true belief with the addition of an
account. This definition has survived for thousands of years, though today we do not use the term “account” but
“warrant” or “justification” though in essence they mean the same thing: a belief is knowledge if it is true and we
have a sufficient reason for believing it to be true. As to what constitutes a sufficient reason, a whole new field of
argument opens up, but here we are only concerned with the validity of the definition offered by Theaetetus, which
rests on what is meant by the term “account”.
Socrates believes that an account must be one of three things, and he examines them one by one. He brushes
over the first very quickly, as an account may simply mean “giving an overt expression to one’s thought by means
of vocal sound with names and verbs, casting an image of one’s notion on the stream that flows through the lips”
(241). Since any man can signify what he thinks on any subject, it is clearly not in this sense of the term that the
definition will suffice.
The next possible definition of an account is “being able to reply to the question, what any given thing is, by
enumerating its elements” (241). I confess that Socrates’ refutation of this definition greatly confuses me, though I
will do my best to re-state it. When considering a wagon, we may be content to say that it is something with
wheels, axle, body, rails, and yoke. But we would not have complete knowledge of the wagon as would one who
could give a complete account of the hundreds of parts that constitute it. In the same vain, we could not have the
same knowledge of our name as a grammarian would simply by telling the syllables. Yet when we write our
name, by knowing all the letters and syllables we are in possession of a complete catalogue of the elements of the
name, together with a correct belief. But since we have already established that we still do not have knowledge
of the name, knowledge must be something other than correct belief together with an account.
What confuses me is why Theaetetus agrees that we do not have knowledge of our names even if we know all of
the letters and syllables that compose it. What more is there to a name than this? Socrates claims it is not
knowledge if we think that one and the same thing is sometimes a part of one thing and sometimes part of another,
as is the case when we learn to write our names as schoolchildren, and Theaetetus agrees that in this condition we
do not have knowledge. But unless I misunderstand completely, which is quite likely because I am sure Plato has
given this a lot more thought than me, I would think that knowing how to write one’s name—even as a young
child—would mean that we do indeed have knowledge of our name. Perhaps the answer lies in the distinction
between the three types of knowledge—we may know how to write our name, we may be familiar with our
name, but we may still not have knowledge as to the true nature of the name. But if this is the case, it is still very
unclear within the text.
The final definition of an account is “being able to name some mark by which the thing one is asked about differs
from everything else” (243). The example Socrates gives is that we can give an account of the Sun by saying it is
the brightest of the heavenly bodies that go round the earth (ironically, this is a false definition, but I will not hold
Plato’s ignorance of future astronomical discoveries against him). So according to this definition, we have only a
notion of a thing until we have touched upon what it is that makes it different from all other things. But “If that was
so, how could I possibly be having a notion of you rather than of anyone else? Suppose I was thinking:
Theaetetus is one who is a man and has a nose and eyes and a mouth and so forth, enumerating every part of the
body. Will thinking in that way result in my thinking of Theaetetus rather than of Theodorus or, as they say, of the
man in the street?” (243). Even if he thinks of a man with a snub nose, the notion will not be of Theaetetus
specifically until his notion includes the snubness of the nose particular to Theaetetus. Therefore, he can not even
have a notion of Theaetetus until he has a notion of what makes him different from all other things.
So of this third possible definition of knowledge, “When we have a correct notion of the way in which certain
things differ from other things, it tells us to add a correct notion of the way in which they differ from other things.
On this showing, the most vicious of circles would be nothing to this injunction” (244). Socrates has shown that
this is a circular definition, as it essentially defines knowledge as “correct belief together with knowledge of a
differentness” and it is unacceptable for a term being defined to appear in the definition of that term.
Having exhausted all possible definitions for an “account” Socrates and Theaetetus abandon their inquiry into the
nature of knowledge, lamenting over this insurmountable ignorance yet recognising its benefit: “You will be gentler
and more agreeable to your companions, having the good sense not to fancy you know what you do not know”
(245). It is rather extraordinary to think that over two millennia since this dialogue was written, we are no closer
to a satisfactory definition of knowledge than Plato. We still consider “warranted, true belief” to be the most
adequate definition, yet the arguments rage on over whether this is sufficient, what exactly constitutes a “warrant”,
and whether we can really have actual knowledge at all.