The dualist believes that he would dissolve away the whole world into a mere abstract. scheme of concepts, did he not insist on real connections between the objects besides the conceptual ones. In other words, the ideal principles which thinking discovers seem too airy for the dualist, and he seeks, in addition, real principles with which to support them.
 Let us examine these real principles a little more closely. The naïve man (naïve realist) regards the objects of external experience as realities. The fact that his hands can grasp these objects, and his eyes see them, is for him sufficient proof of their reality. "Nothing exists that cannot be perceived" is, in fact, the first axiom of the naïve man; and it is held to be equally valid in its converse: "Everything which can be perceived exists." The best evidence for this assertion is the naïve man's belief in immortality and ghosts. He thinks of the soul as refined material substance which may, in special circumstances, become visible even to the ordinary man (naïve belief in ghosts).
 In contrast with this real world of his, the naïve realist regards everything else, especially the world of ideas, as unreal or "merely ideal". What we add to objects by thinking is nothing more than thoughts about the things. Thought adds nothing real to the percept.
 But it is not only with reference to the existence of things that the naïve man regards sense perception as the sole proof of reality, but also with reference to events. A thing, according to him, can act on another only when a force actually present to sense perception issues from the one and seizes upon the other. In the older physics it was thought that very fine substances emanate from the objects and penetrate through the sense organs into the soul. The actual seeing of these substances is impossible only because of the coarseness of our sense organs relative to the fineness of these substances. In principle, the reason for attributing reality to these substances was the same as for attributing it to the objects of the sense-perceptible world, namely because of their mode of existence, which was thought to be analogous to that of sense-perceptible reality.