Most philosophers have been led by the argument from illusion, by the causal argument, or by the introspective analysis advocated in the sense-datum theory to conclude that our immediate awareness in perception is not, as direct, or commonsense, realism claims, of material objects (of distinct, external physical entities perceptible by different persons at once) but of sensa (private, transitory, probably mental existents that may also be called sensations, sense data, ideas, representations, or impressions). Once this position is adopted, a serious difficulty arises concerning the nature and status of material objects. Representative realism claims that they exist external to us and cause the sensa or representations that correspond to them. The notorious difficulty of this view is that if all our direct awareness is concerned with the alleged effects, or sensa, how do we ever find out that material objects exist as their causes or what characteristics they...