1. a metaphysical position propounded by William James in 1904 holding that reality consists not of subject and object (mind and matter) but of pure experience. The position is therefore one of neutral monism.

2. the associated position, also propounded by William James, that the whole of human experience is the legitimate domain for psychological investigation. This is in contrast to the tendency of certain schools of psychology, such as structuralism, to define the subject much more narrowly. The methodological implication of radical empiricism is that psychology should not be restricted to a single method, but that it should employ methods appropriate to the study of any phenomenon that forms part of human experience.

3. the general position that (a) empirical methods provide the only reliable sources of knowledge and (b) only propositions that can be tested by such methods have real meaning. See empiricism; logical positivism; positivism.