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Reliance on experience as the source of ideas and knowledge. More specifically, empiricism is the epistemological theory that genuine information about the world must be acquired by a posteriori means, so that nothing can be thought without first being sensed.

Prominent modern empiricists include Bacon, Locke, Berkeley, Hume, and Mill. In the twentieth century, empiricism principles were extended and applied by the pragmatists and the logical positivists.

(Via Philosophical Dictionary)