On Gettier Problems

by Tim Harding

Gettier problems or cases are named in honor of the American philosopher Edmund Gettier, who discovered them in 1963. They function as challenges to the philosophical tradition of defining knowledge as justified true belief . The problems are actual or possible situations in which someone has a belief that is both true and well supported by evidence, yet which fails to be knowledge (Hetherington 2017:1).

The traditional ‘justified true belief’ (JTB) account of knowledge is comprised of three conditions as follows: S knows P if and only if (i) P is true, (ii) S believes that P is true, and (iii) S is justified in believing that P is true. In his discussion of this account of knowledge, Gettier (1963:192) begins by noting two points.  His first point is that it is possible for a person to be justified in believing a proposition which is in fact false (for which he later gives examples).  His second point is that if a person is justified in believing any proposition P, and that proposition P entails another proposition Q, and that if the person accepts that Q is deduced from P, then the person is justified in believing Q.

Gettier (1963: 192-193) provides two counterexamples to show that it is possible meet these three JTB conditions and yet not know P.  I think that his second counterexample demonstrates both of his two opening points better than his first counterexample.  The proposition (f) ‘Jones owns a Ford’ entails the disjunctive proposition (h) ‘Either Jones owns a Ford or Brown is in Barcelona’.  In accordance with Gettier’s first opening point, Smith is justified in believing (f) even if it is false, because Smith did not know that Jones was lying about his ownership of the Ford. Thus in accordance with Gettier’s second opening point, if Smith is justified in believing (f), he is justified in believing (h).  So if (f) is false, (h) could still be true by chance, if unbeknown to Smith Brown just happens to be in Barcelona.  So Smith was justified in believing (h) yet he did not know (h).  Yet proposition (h) meets each of the three JTB conditions.  So I think that this counterexample shows that Gettier’s two opening points are both plausible.

Zagzebski (1994: 207) notes that Gettier problems arise ‘when it is only by chance that a justified true belief is true’, as in the case of Brown happening to be in Barcelona in the Gettier counterexample discussed above. She argues that ‘since justification does not guarantee truth, it is possible for there to be a break in the connection between justification and truth, but for that connection to be regained by chance’ (Zagzebski 1994: 207).  Gettier’s counterexample created a problem for ‘justified true belief’ because an accident of bad luck (Jones lying about owning a Ford) was cancelled out by an accident of good luck (Brown happening to be in Barcelona), thus preserving both the truth of the disjunction (h) ‘Either Jones owns a Ford or Brown is in Barcelona’ and Smith’s justification for believing the truth of (h).

I think this break in the connection between justification and truth is what Zagzebski (1994: 209) means when she later refers to the concept of knowledge closely connecting the justification and the truth component of a given belief, but permitting some degree of independence between them.  In a later essay (1999: 101), Zagzebski explains that ‘Gettier problems arise for any definition in which knowledge is true belief plus something else that is closely connected with the truth but does not entail it’.  She argues that all that is necessary is that there be a small gap or independence the between truth and justification components of knowledge (Zagzebski (1999: 101), as shown in Gettier’s abovementioned counterexample.  It follows that Gettier problems can be avoided if there is no degree of independence at all between the truth and the justification of a belief (Zagzebski (1994: 211).

Zagzebski (1994: 209-210) describes a general rule for generating Gettier cases. As long as there is a small degree of independence referred to in (ii) above, we can construct Gettier cases by the following procedure.  We start with a case of justified false belief, where the falsity of the belief is due to some element of luck (such as Jones lying about owning a Ford).  Now amend the case by adding another element of luck (such as Brown happening to be in Barcelona) which makes the belief (in this case a disjunction) true after all.  So the ‘belief’ that Zagzebski is referring to here is any justified false belief where the falsity is by chance.


Gettier, E., (1963) ‘Is Justified True Belief Knowledge’ in Sosa, E., Kim, J., Fantl, J., and McGrath. M. Epistemology : An Anthology 2nd edition. Carlton, Blackwell. 192-193.

Hetherington, S., ‘Gettier Problems’, The Internet Encyclopedia of Philosophy, ISSN 2161-0002, http://www.iep.utm.edu/gettier/, 29 October 2017.

Zagzebski, L., (1994) ‘The Inescapability of Gettier Problems’ in Sosa, E., Kim, J., Fantl, J., and McGrath. M. Epistemology : An Anthology 2nd edition. Carlton, Blackwell. 207-212.

Zagzebski, L., (1999) ‘What is Knowledge?’ in Greco, J. and Sosa, E., The Blackwell Guide to Epistemology. Carlton, Blackwell. 92-116.


If you find the information on this blog useful, you might like to consider supporting us.

Make a Donation Button

Leave a comment

Filed under Reblogs

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s