The soul nature of man is not determined by the body alone. Man does not wander aimlessly and without purpose from one sensation to another, nor does he act under the influence of every casual incitement that plays upon him either from without or through the processes of his body. He thinks about his perceptions and his acts. By thinking about his perceptions he gains knowledge of things. By thinking about his acts he introduces a reasonable coherence into his life. He knows that he will worthily fulfill his duty as a man only when he lets himself be guided by correct thoughts in knowing as well as in acting. The soul of man, therefore, is confronted by a twofold necessity. By the laws of the body it is governed by natural necessity. It allows itself also to be governed by the laws that guide it to exact thinking because it voluntarily acknowledges their necessity. Nature subjects man to the laws of changing matter, but he subjects himself to the laws of thought. By this means he makes himself a member of a higher order than the one to which he belongs through his body. This order is the spiritual. The spiritual is as different from the soul as the soul is from the body. As long as only the particles of carbon, hydrogen, nitrogen and oxygen that are in motion in the body are spoken of, we do not have the soul in view. Soul life begins only when within the motion of these particles the feeling arises, I taste sweetness, or, I feel pleasure. Likewise, we do not have the spirit in view as long as merely those soul experiences are considered that course through anyone who gives himself over entirely to the outer world and his bodily life. This soul life is rather the basis of the spiritual just as the body is the basis of the soul life. The biologist is concerned with the body, the investigator of the soul the psychologist with the soul, and the investigator of the spirit with the spirit. It is incumbent on those who would understand the nature of man by means of thinking, first to make clear to themselves through self-reflection the difference between body, soul and spirit.