phenomenalism the view that propositions asserting the existence of physical objects are equivalent in meaning to propositions asserting that subjects would have certain sequences of sensations were they to have certain others. The basic idea behind phenomenalism is compatible with a number of different analyses of the self or conscious subject. A phenomenalist might understand the self as a substance, a particular, or a construct out of actual and possible experience. The view also is compatible with any number of different analyses of the visual, tactile, auditory, olfactory, gustatory, and kinesthetic sensations described in the antecedents and consequents of the subjunctive conditionals that the phenomenalist uses to analyze physical object propositions (as illustrated in the last paragraph). Probably the most common analysis of sensations adopted by traditional phenomenalists is a sense-datum theory, with the sense-data construed as mind-dependent entities. But there is nothing to prevent a phenomenalist from accepting an adverbial theory or theory of appearing instead. The origins of phenomenalism are difficult to trace, in part because early statements of the view were usually not careful. In his Dialogues, Berkeley hinted at phenomenalism when he had Philonous explain how he could reconcile an ontology containing only minds and ideas with the story of a creation that took place before the existence of people. Philonous imagines that if he had been present at the creation he should have seen things, i.e., had sensations, in the order described in the Bible. It can also be argued, however, that J. S. Mill in An Examination of Sir William Hamilton’s Philosophy was the first to put forth a clearly phenomenalistic analysis when he identified matter with the ‘permanent possibility of sensation.’ When Mill explained what these permanent possibilities are, he typically used conditionals that describe the sensations one would have if one were placed in certain conditions. The attraction of classical phenomenalism grew with the rise of logical positivism and its acceptance of the verifiability criterion of meaning. Phenomenalists were usually foundationalists who were convinced that justified belief in the physical world rested ultimately on our noninferentially justified beliefs about our sensations. Implicitly committed to the view that only deductive and inductive inferences are legitimate, and further assuming that to be justified in believing one proposition P on the basis of another E, one must be justified in believing both E and that E makes P probable, the phenomenalist saw an insuperable difficulty in justifying belief in ordinary statements about the physical world given prevalent conceptions of physical objects. If all we ultimately have as our evidence for believing in physical objects is what we know about the occurrence of sensation, how can we establish sensation as evidence for the existence of physical objects? We obviously cannot deduce the existence of physical objects from any finite sequence of sensations. The sensations could, e.g., be hallucinatory. Nor, it seems, can we observe a correlation between sensation and something else in order to generate the premises of an inductive argument for the conclusion that sensations are reliable indicators of physical objects. The key to solving this problem, the phenomenalist argues, is to reduce assertions about the physical world to complicated assertions about the sequences of sensations a subject would have were he to have certain others. The truth of such conditionals, e.g., that if I have the clear visual impression of a cat, then there is one before me, might be mind-independent in the way in which one wants the truth of assertions about the physical world to be mind-independent. And to the phenomenalist’s great relief, it would seem that we could justify our belief in such conditional statements without having to correlate anything but sensations.
Many philosophers today reject some of the epistemological, ontological, and metaphilosophical presuppositions with which phenomenalists approached the problem of understanding our relation to the physical world through sensation. But the argument that was historically most decisive in convincing many philosophers to abandon phenomenalism was the argument from perceptual relativity first advanced by Chisholm in ‘The Problem of Perception.’ Chisholm offers a strategy for attacking any phenomenalistic analysis. The first move is to force the phenomenalist to state a conditional describing only sensations that is an alleged consequence of a physical object proposition. C. I. Lewis, e.g., in An Analysis of Knowledge and Valuation, claims that the assertion (P) that there is a doorknob before me and to the left entails (C) that if I were to seem to see a doorknob and seem to reach out and touch it then I would seem to feel it. Chisholm argues that if P really did entail C then there could be no assertion R that when conjoined with P did not entail C. There is, however, such an assertion: I am unable to move my limbs and my hands but am subject to delusions such that I think I am moving them; I often seem to be initiating a grasping motion but with no feeling of contacting anything. Chisholm argues, in effect, that what sensations one would have if one were to have certain others always depends in part on the internal and external physical conditions of perception and that this fact dooms any attempt to find necessary and sufficient conditions for the truth of a physical object proposition couched in terms that describe only connections between sensations. See also BERKELEY ; LEWIS, C. I.; LOGICAL POSITIVISM ; PERCEPTIO. R.A.F.