my friend's bodily structure. Now, the difference between the materialist and the positivist lies just in this, that the former is embarrassed at the decided effects which he sees produced by impalpable things, while the latter escapes such embarrassment entirely, simply by not having set up any arbitrary standard of what constitutes reality. The materialist does not want to recognize anything as real that does not more or less resemble his piece of granite, that does not affect the tactual sense; while the positivist is content to recognize all things as real that reveal their existence to the mind by affecting it in a definite manner. He cordially admits that the piece of granite does this, but he says also that a thousand things that have no analogy with it whatever do it as well.
Some people, chiefly materialists, will heedlessly say that this is idealism. But they are totally mistaken. Idealism consists in affirming reality of the mind and denying it to objective existences, or in affirming that the apparent distinction between subject and object is unreal and illusive. The positivist does neither the one nor the other. He simply abstains from setting up an arbitrary standard of reality. He talks neither of mind-stuff nor of world-stuff; such talk, indeed, he can not help regarding as all stuff. He knows that he knows and that he feels, and that there are certain definite sources of knowledge and feeling. He perceives that he has an environment upon which he can act, and which reacts upon him. That environment is a very complex one, answering to the complexity of his own nature. There is nothing within him, indeed, that has not some answering element without. Regarding him first as an animal, he has a nutritive system, which has its answering external realities; he has a nervous and muscular system, to which the outward frame of things in like manner responds. Taking a higher point of view, he has intellectual faculties which lay hold of the relations of things in the outer world; he has an emotional nature, with moods that vary according to the nature of the stimulus they receive; he has social faculties and propensities that find exercise in the domain of society; he has powers of moral judgment that recognize, apart altogether from the verdict of society, the essential moral qualities of actions. To each range or level of function in the individual man there are corresponding realities in the outer world; and it is to be observed that what are realities to one set of functions are not realities in the same sense to any other. The nutritive quality of an apple is not a reality to the muscular sense, nor is the weight of the apple which is cognized by the muscular sense a reality to the nutritive function. The test of reality is, we thus see, the existence or non-existence of definite relationship. To illustrate the same form further, we may observe that the physical properties of bodies are not realities to the intellectual faculty that investigates their spatial or numerical relations. The weight of a statue, or the chemical composition of the marble or bronze of which it is made, is