(from Greek episteme, ‘knowledge’, and logos, ‘explanation’), the study of the nature of knowledge and justification; specifically, the study of (a) the defining features, (b) the substantive conditions or sources, and (c) the limits of knowledge and justification. The latter three categories are represented by traditional philosophical controversy over the analysis of knowledge and justification, the sources of knowledge and justification (e.g., rationalism versus empiricism), and the viability of skepticism about knowledge and justification. Kinds of knowledge. Knowledge can be either explicit or tacit. Explicit knowledge is self-conscious in that the knower is aware of the relevant state of knowledge, whereas tacit knowledge is implicit, hidden from self-consciousness. Much of our knowledge is tacit: it is genuine but we are unaware of the relevant states of knowledge, even if we can achieve awareness upon suitable reflection. In this regard, knowledge resembles many of our psychological states. The existence of a psychological state in a person does not require the person’s awareness of that state, although it may require the person’s awareness of an object of that state (such as what is sensed or perceived). Philosophers have identified various species of knowledge: for example, propositional knowledge (that something is so), non-propositional knowledge of something (e.g., knowledge by acquaintance, or by direct awareness), empirical (a posteriori) propositional knowledge, nonempirical (a priori) propositional knowledge, and knowledge of how to do something. Philosophical controversy has arisen over distinctions between such species, for example, over (i) the relations between some of these species (e.g., does knowing-how reduce to knowledge-that?), and (ii) the viability of some of these species (e.g., is there really such a thing as, or even a coherent notion of, a priori knowledge?). A primary concern of classical modern philosophy, in the seventeenth and eighteenth centuries, was the extent of our a priori knowledge relative to the extent of our a posteriori knowledge. Such rationalists as Descartes, Leibniz, and Spinoza contended that all genuine knowledge of the real world is a priori, whereas such empiricists as Locke, Berkeley, and Hume argued that all such knowledge is a posteriori. In his Critique of Pure Reason (1781), Kant sought a grand reconciliation, aiming to preserve the key lessons of both rationalism and empiricism. Since the seventeenth and eighteenth centuries, a posteriori knowledge has been widely regarded as knowledge that depends for its supporting ground on some specific sensory or perceptual experience; and a priori knowledge has been widely regarded as knowledge that does not depend for its supporting ground on such experience. Kant and others have held that the supporting ground for a priori knowledge comes solely from purely intellectual processes called ‘pure reason’ or ‘pure understanding.’ Knowledge of logical and mathematical truths typically serves as a standard case of a priori knowledge, whereas knowledge of the existence or presence of physical objects typically serves as a standard case of a posteriori knowledge. A major task for an account of a priori knowledge is the explanation of what the relevant purely intellectual processes are, and of how they contribute to non-empirical knowledge. An analogous task for an account of a posteriori knowledge is the explanation of what sensory or perceptual experience is and how it contributes to empirical knowledge. More fundamentally, epistemologists have sought an account of propositional knowledge in general, i.e., an account of what is common to a priori and a posteriori knowledge. Ever since Plato’s Meno and Theaetetus (c.400 . .), epistemologists have tried to identify the essential, defining components of knowledge. Identifying these components will yield an analysis of knowledge. A prominent traditional view, suggested by Plato and Kant among others, is that propositional knowledge (that something is so) has three individually necessary and jointly sufficient components: justification, truth, and belief. On this view, propositional knowledge is, by definition, justified true belief. This is the tripartite definition that has come to be called the standard analysis. We can clarify it by attending briefly to each of its three conditions.
The belief condition. This requires that anyone who knows that p (where ‘p’ stands for any proposition or statement) must believe that p. If, therefore, you do not believe that minds are brains (say, because you have not considered the matter at all), then you do not know that minds are brains. A knower must be psychologically related somehow to a proposition that is an object of knowledge for that knower. Proponents of the standard analysis hold that only belief can provide the needed psychological relation. Philosophers do not share a uniform account of belief, but some considerations supply common ground. Beliefs are not actions of assenting to a proposition; they rather are dispositional psychological states that can exist even when unmanifested. (You do not cease believing that 2 ! 2 % 4, for example, whenever your attention leaves arithmetic.) Our believing that p seems to require that we have a tendency to assent to p in certain situations, but it seems also to be more than just such a tendency. What else believing requires remains highly controversial among philosophers. Some philosophers have opposed the belief condition of the standard analysis on the ground that we can accept, or assent to, a known proposition without actually believing it. They contend that we can accept a proposition even if we fail to acquire a tendency, required by believing, to accept that proposition in certain situations. On this view, acceptance is a psychological act that does not entail any dispositional psychological state, and such acceptance is sufficient to relate a knower psychologically to a known proposition. However this view fares, one underlying assumption of the standard analysis seems correct: our concept of knowledge requires that a knower be psychologically related somehow to a known proposition. Barring that requirement, we shall be hard put to explain how knowers psychologically possess their knowledge of known propositions. Even if knowledge requires belief, belief that p does not require knowledge that p, since belief can typically be false. This observation, familiar from Plato’s Theaetetus, assumes that knowledge has a truth condition. On the standard analysis, if you know that p, then it is true that p. If, therefore, it is false that minds are brains, then you do not know that minds are brains. It is thus misleading to say, e.g., that astronomers before Copernicus knew that the earth is flat; at best, they justifiably believed that they knew this. The truth condition. This condition of the standard analysis has not attracted any serious challenge. Controversy over it has focused instead on Pilate’s vexing question: What is truth? This question concerns what truth consists in, not our ways of finding out what is true. Influential answers come from at least three approaches: truth as correspondence (i.e., agreement, of some specified sort, between a proposition and an actual situation); truth as coherence (i.e., interconnectedness of a proposition with a specified system of propositions); and truth as pragmatic cognitive value (i.e., usefulness of a proposition in achieving certain intellectual goals). Without assessing these prominent approaches, we should recognize, in accord with the standard analysis, that our concept of knowledge seems to have a factual requirement: we genuinely know that p only if it is the case that p. The pertinent notion of ‘its being the case’ seems equivalent to the notion of ‘how reality is’ or ‘how things really are.’ The latter notion seems essential to our notion of knowledge, but is open to controversy over its explication.
The justification condition. Knowledge is not simply true belief. Some true beliefs are supported only by lucky guesswork and hence do not qualify as knowledge. Knowledge requires that the satisfaction of its belief condition be ‘appropriately related’ to the satisfaction of its truth condition. This is one broad way of understanding the justification condition of the standard analysis. More specifically, we might say that a knower must have adequate indication that a known proposition is true. If we understand such adequate indication as a sort of evidence indicating that a proposition is true, we have reached the traditional general view of the justification condition: justification as evidence. Questions about justification attract the lion’s share of attention in contemporary epistemology. Controversy focuses on the meaning of ‘justification’ as well as on the substantive conditions for a belief’s being justified in a way appropriate to knowledge.
Current debates about the meaning of ‘justification’ revolve around the question whether, and if so how, the concept of epistemic (knowledge-relevant) justification is normative. Since the 1950s Chisholm has defended the following deontological (obligation-oriented) notion of justification: the claim that a proposition, p, is epistemically justified for you means that it is false that you ought to refrain from accepting p. In other terms, to say that p is epistemically justified is to say that accepting p is epistemically permissible – at least in the sense that accepting p is consistent with a certain set of epistemic rules. This deontological construal enjoys wide representation in contemporary epistemology. A normative construal of justification need not be deontological; it need not use the notions of obligation and permission. Alston, for instance, has introduced a non-deontological normative concept of justification that relies mainly on the notion of what is epistemically good from the viewpoint of maximizing truth and minimizing falsity. Alston links epistemic goodness to a belief’s being based on adequate grounds in the absence of overriding reasons to the contrary. Some epistemologists shun normative construals of justification as superfluous. One noteworthy view is that ‘epistemic justification’ means simply ‘evidential support’ of a certain sort. To say that p is epistemically justifiable to some extent for you is, on this view,