At the heart of empiricist thought is the belief that all human knowledge starts with perception. We acquire information about the world through our senses—sight, hearing, touch, taste, and smell—which provide the raw data from which we form concepts and beliefs. For empiricists, knowledge is not something we discover internally, but something we gather from external reality. This view stands in contrast to the rationalist emphasis on a priori knowledge, which is independent of experience and accessible only through reason.
Empiricism's roots can be traced back to ancient philosophy, with early proponents like Aristotle, who argued that all knowledge comes from sensory observation. However, the modern development of empiricism is largely credited to three major figures: John Locke, George Berkeley, and David Hume. Locke introduced the idea of the mind as a tabula rasa, arguing that individuals are born without innate ideas and that all knowledge comes from experience. Berkeley took this further by suggesting that even the existence of the external world depends on perception, encapsulating the notion that "to be is to be perceived." Hume, the most radical empiricist of the three, questioned the very basis of causality and inductive reasoning, asserting that our beliefs in cause-and-effect relationships were not rationally justified but arose from habitual experience.