Theosophy, by Rudolf Steiner, , at sacred-texts.com
The soul being of man is not determined by the body alone. Man does not wander aimlessly and without a goal from one sensation to another; neither does he act under the influence of every casual incitement directed on 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 also that he will fulfill his duty as a human being only when he lets himself be guided by correct thinking in knowledge as well as in acts. The soul of man, therefore, faces a twofold necessity. The laws of the body govern it in accordance with the necessities of nature, but it allows itself to be governed by
the laws which guide it to exact thinking because it voluntarily acknowledges their necessity. Nature subjects man to the laws of the change of matter, but he subjects himself to the laws of thought. By this means he makes himself a member of a higher order than that to which he belongs through his body. And this order is the spiritual. The soul is as different from the body as the body is different from the soul. So long as one speaks only of the particles of carbon, hydrogen, nitrogen, and oxygen which stir in the body, one has not the soul in view. The soul life begins only when within the motion of these particles sensation arises, and one can say: "I taste sweetness" or "I feel pleasure." Just as little has one the spiritual in view when one considers merely the soul experiences which course through a man who gives himself over entirely to the outer world and his bodily life. Rather is this soul life merely the basis for the spiritual, just as the body is the basis of the soul life. The naturalist, or investigator of nature, has to do with the body, the investigator of the soul (the psychologist) with the soul, and the investigator of the spirit with the spirit. To
realize what one is in oneself, and thus become clear as to the difference between body, soul, and spirit, is a requirement which must be demanded from those who wish by thinking to enlighten themselves regarding the constitution of man.