rather than as being first person subjective pronouncements. Bertrand Russell took issue with Neurath's account of protocol statements in his book An Inquiry Into Meaning and Truth (p. 139ff), on the grounds that it severed the connection to experience that is essential to an empiricist account of truth, facts and knowledge.

One of Neurath's later works, Physicalism, completely transformed the nature of the logical positivist discussion of the program of unifying the sciences. Neurath delineates