PROPOSITIONAL KNOWLEDGE, DEFINITION OF

The traditional "definition of propositional knowledge," emerging from Plato's Meno and Theaetetus, proposes that such knowledge—knowledge that something is the case—has three essential components. These components are identified by the view that knowledge is justified true belief. Knowledge, according to the traditional definition, is belief of a special kind, belief that satisfies two necessary conditions: (1) the truth of what is believed and (2) the justification of what is believed. While offering various accounts of the belief condition, the truth condition, and the justification condition for knowledge, many philosophers have held that those three conditions are individually necessary and jointly sufficient for propositional knowledge.

The belief condition requires that one accept, in some manner, any proposition one genuinely knows. This condition thus relates one psychologically to what one knows. It precludes that one knows a proposition while failing to accept that proposition. Some contemporary philosophers reject the belief condition for knowledge, contending that it requires a kind of mentalistic representation absent from many cases of genuine knowledge. Some other contemporary philosophers endorse the belief condition but deny that it requires actual assent to a proposition. They propose that, given the belief condition, a knower need only be disposed to assent to a proposition. Still other philosophers hold that the kind of belief essential to propositional knowledge requires assent to a known proposition, even if the assent need not be current or ongoing. The traditional belief condition is neutral on the exact conditions for belief and for the objects of belief.

The truth condition requires that genuine propositional knowledge be factual, that it represent what is actually the case. This condition precludes, for example, that astronomers before Nicolas Copernicus knew that Earth is flat. Those astronomers may have believed—even justifiably believed—that Earth is flat, as neither belief nor justifiable belief requires truth. Given the truth condition, however, propositional knowledge without truth is impossible. Some contemporary philosophers reject the truth condition for knowledge, but they are a small minority. Proponents of the truth condition fail to agree on the exact conditions for the kind of truth essential to knowledge. Competing approaches to truth include correspondence, coherence, semantic, and redundancy theories, where the latter theories individually admit of variations. The truth condition for knowledge, generally formulated, does not aim to offer an exact account of truth.

The justification condition for propositional knowledge guarantees that such knowledge is not simply true belief. A true belief may stem just from lucky guesswork; in that case it will not qualify as knowledge. Propositional knowledge requires that the satisfaction of its belief condition be suitably related to the satisfaction of its truth condition. In other words, a knower must have adequate indication that a belief qualifying as knowledge is actually true. This adequate indication, on a traditional view of justification suggested by Plato and Immanuel Kant, is suitable evidence indicating that a proposition is true. True beliefs qualifying as knowledge, on this traditional view, must be based on justifying evidence.

Contemporary philosophers acknowledge that justified contingent beliefs can be false; this is fallibilism about epistemic justification, the kind of justification appropriate to propositional knowledge. Given fallibilism, the truth condition for knowledge is not supplied by the justification condition; justification does not entail truth. Similarly, truth does not entail justification; one can lack evidence for a proposition that is true.

Proponents of the justification condition for knowledge do not share an account of the exact conditions for epistemic justification. Competing accounts include epistemic coherentism, which implies that the justification of any belief depends on that belief's coherence relations to other beliefs, and epistemic foundationalism, which implies that some beliefs are justified independently of any other beliefs. Recently, some philosophers have proposed that knowledge requires not evidence but reliable (or truth-conducive) belief formation and belief sustenance. This is reliabilism about the justification condition for knowledge. Whatever the exact conditions for epistemic justification are, proponents of the justification condition maintain that knowledge is not merely true belief.

Although philosophers have not agreed widely on what specifically the defining components of propositional knowledge are, there has been considerable agreement that knowledge requires, in general, justified true belief. Traditionally, many philosophers have assumed that justified true belief is sufficient as well as necessary for knowledge. This is a minority position now, owing mainly to Gettier counterexamples to this view. In 1963 Edmund Gettier challenged the view that if one has a justified true belief that p, then one knows that p. Gettier's counterexamples are:

1. Smith and Jones have applied for the same job. Smith is justified in believing that (i) Jones will get the job, and that (ii) Jones has ten coins in his pocket. On the basis of (i) and (ii), Smith infers, and thus is justified in believing, that (iii) the person who will get the job has ten coins in his pocket. As it turns out, Smith himself will actually get the job, and he also happens to have ten coins in his pocket. So, although Smith is justified in believing the true proposition (iii), Smith does not know (iii).
2. Smith is justified in believing the false proposition that (i) Jones owns a Ford. On the basis of (i), Smith infers, and thus is justified in believing, that (ii) either Jones owns a Ford or Brown is in Barcelona. As it turns out, Brown is in Barcelona, and so (ii) is true. So although Smith is justified in believing the true proposition (ii), Smith does not know (ii).

Gettier counterexamples are cases where one has a justified true belief that p but lacks knowledge that p. The Gettier problem is the difficulty of finding a modification of, or an alternative to, the traditional justified-true-belief analysis that avoids difficulties from Gettier counterexamples.

Contemporary philosophers have not reached a widely accepted solution to the Gettier problem. Many philosophers take the main lesson of Gettier counterexamples to be that propositional knowledge requires a fourth condition, beyond the justification, belief, and truth conditions. Some philosophers have claimed, in opposition, that Gettier counterexamples are defective because they rely on the false principle that false evidence can justify one's beliefs. There are, however, examples similar to Gettier's that do not rely on any such principle. Here is one such example inspired by Keith Lehrer and Richard Feldman:

• (III) Suppose that Smith knows the following proposition, m : Jones, whom Smith has always found to be reliable and whom Smith has no reason to distrust now, has told Smith, his officemate, that p : He, Jones, owns a Ford. Suppose also that Jones has told Smith that p only because of a state of hypnosis Jones is in and that p is true only because, unknown to himself, Jones has won a Ford in a lottery since entering the state of hypnosis. Suppose further that Smith deduces from m its existential generalization, o : There is someone, whom Smith has always found to be reliable and whom Smith has no reason to distrust now, who has told Smith, his officemate, that he owns a Ford. Smith, then, knows that o, since he has correctly deduced o from m, which he also knows. Suppose, however, that on the basis of his knowledge that o, Smith believes that r : Someone in the office owns a Ford. Under these conditions, Smith has justified true belief that r, knows his evidence for r, but does not know that r.

Gettier counterexamples of this sort are especially difficult for attempts to analyze the concept of propositional knowledge.

One noteworthy fourth condition consists of a "defeasibility condition" requiring that the justification appropriate to knowledge be "undefeated" in that an appropriate subjunctive conditional concerning defeaters of justification be true of that justification. A simple defeasibility condition requires of our knowing that p that there be no true proposition, o, such that if q became justified for us, p would no longer be justified for us. If Smith genuinely knows that Laura removed books from the office, then Smith's coming to believe with justification that Laura's identical twin removed books from the office would not defeat the justification for Smith's belief regarding Laura herself. A different approach claims that propositional knowledge requires justified true belief sustained by the collective totality of actual truths. This approach requires a precise, rather complex account of when justification is defeated and restored.

The importance of the Gettier problem arises from the importance of a precise understanding of the nature, or the essential components, of propositional knowledge. A precise understanding of the nature of propositional knowledge, according to many philosophers, requires a Gettier-resistant account of knowledge.

See also Coherentism; Epistemology; Kant, Immanuel; Plato; Reliabilism; Truth.

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Bibliography updated by Benjamin Fiedor (2005)