ABSTRACT
One way of casting doubt on the doctrine that private impressions alone are the direct and immediate objects of perception is to consider the unappetising consequences that it has for our knowledge of the external world. The relevance of the conception of certainty as logical necessity can be eliminated right away since the knowledge perception gives material things and appearances is empirical. The perception of material things is an intelligent activity; that is a reason for its fallibility. According to direct realism, perception supplies with a mass of uninferred beliefs about the external world. The first scientific argument against direct realism is the weakest and, perhaps on that account, is seldom formulated very explicitly. It starts from the fact that perception, as an act of the mind, is the last element in a causal process which originates in the ostensible object of the perception.
