Is Justified True Belief Knowledge?

April 22, 2025 | 402 words | 2min read

Paper Title: Is Justified True Belief Knowledge?
Link to Paper: https://fitelson.org/proseminar/gettier.pdf
Date: June 1963
Paper Type: Philosophy, Epistomology
Short Abstract:
In this paper Gettier Shows that Justified True Belief does not consitute Knowledge.

There have been many attempts to define what knowledge is. One such attempt is called Justified True Belief (JTB), which can be stated as follows:

A subject S knows proposition P if and only if:
(i) P is true;
(ii) S believes that P;
(iii) S is justified in believing that P.

First and foremost, for any proposition P, if S is justified in believing P, and P entails Q, and S can deduce Q from P and accept Q, then S is also justified in believing Q.

With this in mind, let’s look at the following scenario:

Suppose that Smith and Jones have applied for a certain job, and suppose further that Smith has strong evidence for the following proposition:

(a) Jones is the man who will get the job, and Jones has ten coins in his pocket.

Thus, Smith is justified in believing (a). Furthermore, (a) entails:

(b) The man who will get the job has ten coins in his pocket.

Since (a) is justified and (b) logically follows from it, (b) is also justified.

Now, suppose—unknown to Smith—that Jones will not get the job. Instead, Smith will. Also unbeknownst to Smith, he himself has ten coins in his pocket.

Then Smith knows (b), because:
(i) (b) is true — Smith gets the job and has ten coins;
(ii) Smith believes (b);
(iii) Smith is justified in believing (b).

According to the Justified True Belief definition, we would have to say that Smith knows (b). However, intuitively, we would say that Smith does not know it, because his belief was based on false premises. Such examples are called Gettier cases.

Thus, Justified True Belief cannot be a proper definition of knowledge.

reply via email