The Argument from Hallucination

Abstract

In this chapter I want to consider a final argument for the introduction of sense-data, the Argument from Hallucination. I shall begin by discussing a formulation of the argument given by D. M. Armstrong in his book, Perception and the Physical World. Armstrong’s formulation is an instructive one for two reasons. First, it does not confuse hallucinations with other phenomena such as illusions and perceptual relativity, as do some other, looser presentations of the argument.¹ Second (and more significantly, from the point of view being developed here), Armstrong is careful to point out that the purpose of the argument is to show that the immediate object of perception is always a sense-datum. Unlike many other writers, Armstrong recognizes that the sense-datum theory need not deny that physical things are perceived, but only that they are immediately perceived. He correctly insists that unless this point is kept clearly in mind, philosophers who accept the sense-datum theory will seem to be defending the absurd view that we never perceive physical objects, while those who reject the theory will seem to be defending the platitude that we do perceive physical objects.