Using Logic
Edmund L. Gettier. Is Justified True Belief Knowledge? From Analysis 23 (1963): 121-123.
Various attempts
have been made in recent years to state necessary and
sufficient conditions
for someone's knowing a given proposition. The attempts have
often been such
that they can be stated in a form similar to the following: 1
a. S knows that P
IFF
i. P is true,
ii. S believes that P, and
iii. S is justified in believing that P.
For example,
Chisholm has held that the following gives the necessary and sufficient
conditions for
knowledge: 2
b. S knows that P
IFF
i. S accepts P,
ii. S has adequate evidence for P, and
iii. P is true.
Ayer has stated
the necessary and sufficient conditions for knowledge as follows:
3
c. S knows that P
IFF
i. P is true,
ii. S is sure that P is true, and
iii. S has the right to [be] sure that P is true.
I shall argue
that (a) is false in that the conditions stated therein do not constitute
a
sufficient condition
for the truth of the proposition that S knows that P. The same
argument will
show that (b) and (c) fail if 'has adequate evidence for' or 'has the right
to be sure that'
is substituted for 'is justified in believing that' throughout.
I shall begin by noting two points. First, in that sense of 'justified'
in which S's
being justified
in believing P is a necessary condition of S's knowing that P, it is
possible for
a person to be justified in believing a proposition that is in fact false
Secondly, for
any proposition P, if S is justified in believing P, and P entails Q, and
S
deduces Q from
P and accepts Q as a result of this deduction, then S is justified in
believing Q.
Keeping these two points in mind, I shall now present two cases in which
the conditions
stated in (a) are true for some proposition, though it is at the same time
false that the
person in question knows that proposition.
Case
I
Suppose that Smith and Jones have applied for a certain job. And suppose
that
Smith has strong
evidence for the following conjunctive proposition:
d. Jones is the man who will get the job, and Jones has ten coins in his pocket.
Smith's evidence
for (d) might be that the president of the company assured him that
Jones would
in the end be selected, and that he, Smith, had counted the coins in
Jones's pocket
ten minutes ago. Proposition (d) entails:
e. The man who will get the job has ten coins in his pocket.
Let us suppose
that Smith sees the entailment from (d) to (e), and accepts (e) on the
grounds of (d),
for which he has strong evidence. In this case, Smith is clearly justified
in believing
that (e) is true.
But imagine, further, that unknown to Smith, he himself, not Jones, will
get the
job. And, also,
unknown to Smith, he himself has ten coins in his pocket. Proposition (e)
is then true,
though proposition (d), from which Smith inferred (e), is false. In our
example, then,
all of the following are true: (i) (e) is true, (ii) Smith believes that
(e) is
true, and (iii)
Smith is justified in believing that (e) is true. But it is equally clear
that
Smith does not
know that (e) is true; for (e) is true in virtue of the number of coins
in
Smith's pocket,
while Smith does not know how many coins are in Smith's pocket, and
bases his belief
in (e) on a count of the coins in Jones's pocket, whom he falsely
believes to
be the man who will get the job.
Case II
Let us suppose that Smith has strong evidence for the following proposition:
f. Jones owns a Ford.
Smith's evidence
might be that Jones has at all times in the past within Smitb's
memory owned
a car, and always a Ford, and that Jones has just offered Smith a ride
while driving
a Ford. Let us imagine, now, that Smith has another friend, Brown, of
whose whereabouts
he is totally ignorant. Smith selects three place names quite at
random and constructs
the following three propositions:
g. Either Jones owns a Ford, or Brown is in Boston.
h. Either Jones owns a Ford, or Brown is in Barcelona.
i. Either Jones owns a Ford, or Brown is in Brest-Litovsk.
Each of these
propositions is entailed by (f). Imagine that Smith realizes the entailment
of each of these
propositions he has constructed by (f), and proceeds to accept (g), (h),
and (i) on the
basis of (f). Smith has correctly inferred (g), (h), and (i) from a
proposition
for which be has strong evidence. Smith is therefore completely justified
in
believing each
of these three propositions, Smith, of course, has no idea where Brown
is.
But imagine now that two further conditions hold. First Jones does not
own a
Ford, but is
at present driving a rented car. And secondly, by the sheerest coincidence,
and entirely
unknown to Smith, the place mentioned in proposition (h) happens really
to be the place
where Brown is. If these two conditions hold, then Smith does not know
that (h) is
true, even though (i) (h) is true, (ii) Smith does believe that (h) is
true, and
(iii) Smith
is justified in believing that (h) is true.
These two examples show that definition (a) does not state a sufficient
condition
for someone's
knowing a given proposition. The same cases, with appropriate changes,
will suffice
to show that neither definition (b) nor definition (c) do so either.
Notes
1. Plato seems
to be considering some such definition at Theaetetus 201, and perhaps
accepting one,
at Meno 98.
2. Roderick M.
Chisholm, Perceiving: A Philosophical Study (Ithaca, New York:
Cornell University
Press, 1957), p. 16.
3. A. J. Ayer, The Problem of Knowledge (London: Macmillan, 1956), p. 34.
This article was first transcribed into hypertext by Andrew Chrucky, Sept. 13, 1997.
[It has been edited by HH for us, 2002.]
Editor's notes: DO NOT RELY ON THE
FORMAT OF THIS DOCUMENT AS A MODEL.
Things between [ ... ] are this editor's.
The above article was found at http://www.ditext.com/
Epistemology student Ted Bowen's essay about Mark Kaplan's response to the Gettier problem: http://www.personal.kent.edu/~ebowen/Gettier.html
Please visit: Ric Carter's [Beliefs
are "Games People Play"] http://www.sonic.net/~ric/go/knowbel.htm
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