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Nutters.org The Nutter Log
Justified True Belief Entry id: jtb
By The Famous Brett Watson
On Sat, 10 Apr 2004 16:07:00 +1000

The traditional formulation of propositional knowledge (in Western philosophy) involves three key components: justification, truth, and belief (JTB). Propositional knowledge is, in this tradition, a justified belief held about a truth. To elaborate, the formulation holds that three conditions are necessary, and jointly sufficient for "knowledge". First, belief: you do not know something unless you also hold it as true in your mind; if you do not believe it, then you do not know it. Second, truth: there can be no knowledge of false propositions; belief in a falsehood is delusion or misapprehension, not knowledge. Third, justification: the belief must be appropriately supported; there must be sufficient evidence for the belief.

Thus, knowledge is like a three-legged stool which cannot stand when any one leg is removed. Consider lack of belief: it may be true that Alice's twin sister has just been killed in a car accident, and the police officer reporting the fact may be sufficient evidence to warrant belief, but Alice may find herself unable to accept it, and will thus fail to know it. Lack of truth also disqualifies knowledge: the pre-Copernican belief (amply justified at the time) that heavenly bodies moved around a stationary Earth is false, and is thus not knowledge, even if educated persons of the day operated under the misapprehension that it was. Lastly, lack of justification precludes knowledge: if a charlatan fortune-teller informs Alice that she will meet the man of her dreams within a month, then this proposition isn't knowledge for Alice even if she believes it and it actually happens. Knowledge must be properly grounded, and the charlatan's claim had no grounds whatsoever.

This traditional formulation is not without its problems. One could argue, for example, that "knowledge", so defined, is not a very interesting concept: the individual questions of whether a proposition is true, whether a subject believes it, and whether the subject is justified in doing so do not become more interesting when the answers happen to be uniformly affirmative. Or one could argue the pragmatic case that "knowledge" is not a useful concept: it's all very well to ponder whether subject S knows proposition P given a hypothetical situation with specified truths, but what of knowledge in the real world, where determining the truth of P is part of the problem?

More significantly, perhaps, one could argue that JTB is not actually an entirely sufficient account of knowledge; that situations arise in which a justified true belief is not knowledge. Edmund Gettier makes a famously disruptive case for this view in a short paper entitled, "Is Justified True Belief Knowledge?" (originally published in Analysis, 1963, pp. 121-3). Consider the following scenario from that paper. Smith and Jones are candidates for a job, and Smith believes that (a) Jones will get the job, and (b) Jones has ten coins in his pocket. Smith's belief in both these propositions is justified: a company executive has informed him that Jones will be hired, and he's seen the coins in question. Based on these justified beliefs, Smith also believes (quite justifiably) their logical implication: (c) the person who will get the job has ten coins in his pocket.

Events transpire in such a way that Jones does not get the job, despite assurances to the contrary, and the job is offered to Smith instead. As chance would have it, proposition (c) turns out to be true anyway, because Smith also had ten coins in his pocket, although he didn't realise it at the time. Thus, Smith justifiably believed proposition (c), and it turned out to be true, but did he know it? The traditional account says so, but does this still match our intuitive grasp of what knowledge entails? It seems not.

One possible way of saving the JTB account from Gettier is to argue that Smith's justification for (c) was undermined, and thus he did not know (c) because his belief was not appropriately justified. Proposition (c) follows logically from (a) and (b) only if they are both true, and it turns out that (a) is false. Proposition (c) can still be true independently of both (a) and (b), as actually transpired, but Smith's grounds for belief in (c) was the truth of (a) and (b). If there is a shortfall in JTB, it is merely that we ought to have mentioned that justification must not be undermined by subsequent events.

This embellishment of JTB salvages it from the given counterexample by denying the presence of justification, but other Gettier-style counterexamples may still prove problematic. More than anything else, this saving measure serves to demonstrate how much wriggle-room exists in the "justification" component, and that makes it a more intrinsically interesting concept (to my mind) than its possible by-product, "knowledge".

Public Domain: the author waives copyright on this log entry. Other sources (if any) are quoted with permission or on the principle of "fair dealing" and retain their original copyrights.