Representationalism

Representationalism, or the representational theory of perception, is a philosophical doctrine that in any act of perception, the immediate (direct) object of perception is a sense-datum that represents an external object, which is the mediate (indirect) object of perception.

Two 17th century philosophers, Rene Descartes, and John Locke most prominently advocated this theory. The term they used was not "sense-datum" but "idea." This article does not discuss any differences in meaning that these terms might have. "Idea" as used in the theory of perception is a technical term, meaning roughly the same thing as sense-datum.

Representationalism asserts that sense-data represent external objects -- physical objects, properties, and events. But this immediately raises a question: How well do sense-data represent external objects, properties, and events? At least sometimes, they do not represent them at all well.