Phenomenalism

Phenomenalism is the metaphysical and epistemological position that physical objects are not independently existing substances but logical constructions out of actual and possible sense-data or elementary experiences. On this view, statements about tables, electrons, or galaxies are ultimately translatable into — or at least grounded in — statements about what observers would perceive under specified conditions. Phenomenalism is not idealism in the Berkeleyan sense; it does not claim that matter depends on being perceived in order to exist. Rather, it claims that the meaning and warrant of physical-object statements derive from their connection to experiential content, however complex and conditional that connection may be.

The most systematic attempt to execute phenomenalism as a formal program was Rudolf Carnap's Der logische Aufbau der Welt (1928), which sought to construct all scientific concepts from a primitive basis of elementary experiences linked by a relation of recollection of similarity. The project collapsed under the weight of its own formal demands — the transitivity and individuation assumptions required to make the construction work could not themselves be derived from the phenomenal primitive. Carnap's subsequent shift to a physical-thing language as the preferred protocol basis marked the decline of phenomenalism as a research program in analytic philosophy, though it persists in perceptual psychology and in arguments for the primacy of perception in epistemology.