empiricism (from empiric, ‘doctor who relies on practical experience’, ultimately from Greek empeiria, ‘experience’), a type of theory in epistemology, the basic idea behind all examples of the type being that experience has primacy in human knowledge and justified belief. Because empiricism is not a single view but a type of view with many different examples, it is appropriate to speak not just of empiricism but of empiricisms. Perhaps the most fundamental distinction to be drawn among the various empiricisms is that between those consisting of some claim about concepts and those consisting of some claim about beliefs – call these, respectively, concept-empiricisms and belief-empiricisms. Concept-empiricisms all begin by singling out those concepts that apply to some experience or other; the concept of dizziness, e.g., applies to the experience of dizziness. And what is then claimed is that all concepts that human beings do and can possess either apply to some experience that someone has had, or have been derived from such concepts by someone’s performing on those concepts one or another such mental operation as combination, distinction, and abstraction. How exactly my concepts are and must be related to my experience and to my performance of those mental operations are matters on which concept-empiricists differ; most if not all would grant we each acquire many concepts by learning language, and it does not seem plausible to hold that each concept thus acquired either applies to some experience that one has oneself had or has been derived from such by oneself. But though concept-empiricists disagree concerning the conditions for linguistic acquisition or transmission of a concept, what unites them, to repeat, is the claim that all human concepts either apply to some experience that someone has actually had or they have been derived from such by someone’s actually performing on those the mental operations of combination, distinction, and abstraction. Most concept-empiricists will also say something more: that the experience must have evoked the concept in the person having the experience, or that the person having the experience must have recognized that the concept applies to his or her experience, or something of that sort. What unites all belief-empiricists is the claim that for one’s beliefs to possess one or another truth-relevant merit, they must be related in one or another way to someone’s experience. Beliefempiricisms differ from each other, for one thing, with respect to the merit concerning which the claim is made. Some belief-empiricists claim that a belief does not have the status of knowledge unless it has the requisite relation to experience; some claim that a belief lacks warrant unless it has that relation; others claim that a belief is not permissibly held unless it stands in that relation; and yet others claim that it is not a properly scientific belief unless it stands in that relation. And not even this list exhausts the possibilities. Belief-empiricisms also differ with respect to the specific relation to experience that is said to be necessary for the merit in question to be present. Some belief-empiricists hold, for example, that a belief is permissibly held only if its propositional content is either a report of the person’s present or remembered experience, or the belief is held on the basis of such beliefs and is probable with respect to the beliefs on the basis of which it is held. Kant, by contrast, held the rather different view that if a belief is to constitute (empirical) knowledge, it must in some way be about experience. Third, belief-empiricisms differ from each other with respect to the person to whose experience a belief must stand in the relation specified if it is to possess the merit specified. It need not always be an experience of the person whose belief is being considered. It might be an experience of someone giving testimony about it. It should be obvious that a philosopher might well accept one kind of empiricism while rejecting others. Thus to ask philosophers whether they are empiricists is a question void for vagueness. It is regularly said of Locke that he was an empiricist; and indeed, he was a concept-empiricist of a certain sort. But he embraced no version whatsoever of belief-empiricism. Up to this point, ‘experience’ has been used without explanation. But anyone acquainted with the history of philosophy will be aware that different philosophers pick out different phenomena with the word; and even when they pick out the same phenomenon, they have different views as to the structure of the phenomenon that they call ‘experience.’ The differences on these matters reflect yet more distinctions among empiricisms than have been delineated above. See also EPISTEMOLOGY , LOGICAL POSI- TIVISM , RATIONALIS. N.P.W.