REALISM, as understood here, is a philosophical position developed in opposition to idealism in its various forms, from mentalism, or subjective idealism, to the objective, or speculative idealism associated with the name of Hegel. It is also to be noted that it takes a stronger stand in its affirmations than does phenomenalism, which hesitates to go beyond sensations and appearances in its analyses. As for logical positivism, this turned out to be largely a programmatic movement with a shifting base. Its center of gravity has oscillated between phenomenalism, pragmatism and realism. It has been very effective, nonetheless, largely in the way of exploration.
To bring out this modern setting of realism, I have preferred to call it physical realism. Thus, it has nothing in common with Platonic realism, which reifies universals or forms. Of course, any systematic philosophy must work out its theory of the status of concepts and universals and the part they play in human knowing and the nature of things. On this topic, we must here content ourselves with saying that physical realism belongs to the empirical tradition, when this is taken broadly.
Modern philosophy was led to emphasize epistemology, partly because of the impact of physics. Because the full conditions of perceiving were not understood, the implication was drawn that the human mind is shut into its ideas. This approach is usually called the causal theory of perceiving. It was Berkeley who developed the idealistic possibilities of this gambit.
To put it sharply, the physical realist rejects Berkeley's attempt to reduce material things to percepts, or presentations, as well as Kant's identification of them with phenomena or mental constructs. In so doing, he goes back to a reconsideration of perceiving, holding it likely that the assumptions of the seventeenth century with its stress upon a mind-body (or soul-body) dualism, a mechanistic physical science, and a purely causal theory of the direction and import of perceiving have been outgrown in this more biological age with its recognition of responsive activity. Is