SEC. 4. III. We speak of seeing the same material thing at different times. Suppose a man passing along a country road to look across a field at a distant tree. What he actually sees is a small bluish patch of color, which, interpreting in terms furnished by his previous experience, he supplements with material drawn from memory and imagination. On the following day he looks at the tree again from a nearer point and sees a larger green patch of color with distinct differences of shading and with a clear outline. This he interprets in a similar manner. Now, without being a philosopher at all, and without conscious reference to anything beyond what he has experienced or can experience, he affirms that he has on two successive days seen the same tree. I ask, just what is the significance of the word same as used in this connection? What peculiar experience has it been employed to mark? What is perceived on the one occasion is not the same as what is perceived on the other in the sense of the word first given (by "perceived" I mean existing in consciousness as a complex of mental elements. With the supposed external correlates of our percepts I am not now concerned). And it is equally clear that two such percepts need not be the same in the second sense of the word, for they may be quite unlike. In this case they are unlike, so far at least as what is actually in sensation is concerned. What peculiar experience then does the word mark when the observer declares that he has seen the same tree twice? We are now in the sphere of material objects (_i. e._, as experienced; I refer to the mental content and nothing more), and are not concerned with our experiences as isolated elements, but as grouped and arranged in series. Our total possible experience of any one object is a collection of partly simultaneous and partly successive actual and possible sensations which condition each other, and which we regard as a unit. The Idealist believes that this is all there is of the object, and all we mean when we commonly employ the word. The Realist assumes that there is something beyond and corresponding to this experience, and which is to be regarded as the real thing. He, however, must admit that all we can know of any object, in whatever sense we choose to employ that word, all our evidence for maintaining its existence and determining its qualities, must be drawn from this group of sensations. It is this that we immediately know, and anything inferred must be inferred from this.