Gettier: Is Justified True Belief Knowledge?

Transcription

1 Review Preliminaries Case 1 Case 2 General remarks Replies Gettier: Is Justified True Belief Knowledge? Gettier: Is Justified True Belief Knowledge? March 7, 2014

2 Overview I Review Preliminaries Case 1 Case 2 General remarks Replies

3 Knowledge as Justified True Belief The JTB Account of Knowledge S knows that p is true if and only if: 1 p is true (false propositions cannot be known) 2 S believes that p (if S doesn t even believe that p, then obviously S cannot know that p) 3 S s belief in p is justified (it is not merely a result of luck) Gettier s thesis: This is not su cient (= we can have (1) (3) while still not having knowledge).

4 Preliminaries Fallibility: we can justifiably believe something that is in fact false. Example: I am justified in believing that my brother is in Switzerland at the moment, although it very well might be that he is not. Transitivity of justification: If S is justifiably believes P, and P entails Q, ands knows that P entails Q, thens justifiably believes Q. Example: If I am justified in believing that my brother is in Switzerland at the moment, and I also know that Switzerland is in Europe, then I am justified in believing that my brother is in Europe.

5 Gettier Case 1: Jones, Smith, and the Job Interview

6 Gettier Case 1: Jones, Smith, and the Job Interview Smith has justified belief in the following: 1 Jones is the one who will get the job (Justification: overhearing the boss) 2 Jones has ten coins in his pocket (Justification: S has seen it) Therefore, Smith has also justified belief in: The guy who will get the job has ten coins in his pocket (from (1) and (2), by transitivity of justification). As it turns out: 1 Smith gets the job 2 Smith happens to have 10 coins in his pocket

7 Gettier Case 1: Jones, Smith, and the Job Interview In this case, S: 1 had a belief 2 S s belief was true 3 S s belief was justified However, S still did not have knowledge! This means that we have a case where S satisfied the JTB definition of knowledge, and still did not have knowledge Therefore, the JTB definition is too broad.

8 Gettier Case 2: Smith, Jones, Brown, and the Ford Smith has justified belief in the following: 1 Jones owns a Ford. (Justification: he has always owned one, and S saw him driving a Ford yesterday) Therefore, Smith has also justified belief in: Either Jones owns a Ford, or Brown is in Boston (from (1), by transitivity of justification, and since whenever Jones owns a Ford is true, Either Jones owns a Ford, or Brown is in Boston is also true). As it turns out: 1 Jones does NOT own a Ford 2 Brown happens to be in Boston indeed.

9 Gettier Case 2: Smith, Jones, Brown, and the Ford In this case, S: 1 had a belief 2 S s belief was true 3 S s belief was justified However, S still did not have knowledge! This means that we have another case where S satisfied the JTB definition of knowledge, and still did not have knowledge. Therefore, the JTB definition is too broad.

10 Some General Remarks A definition is supposed to give a necessary and su condition for the thing defined. cient One counter-example is enough to refute a definition Common in the Gettier-cases: we have justified belief in something the belief is in fact true but it is not true by the reasons we thought it was true we were gettierized!

11 Some Possible Replies to Gettier: Supplement the JTB account with some extra condition Give up the justification condition and replace it with something else that works Give up one or both of the initial assumptions (fallibility, transitivity of justification)