384. Since all the elements of the mind have to do with volition and discernment and all the elements of the body with the heart and lungs, there are two brains in our heads, as distinct from each other as volition and discernment. The cerebellum serves volition primarily, and the cerebrum serves discernment primarily. In the same way, heart and lungs are distinct from everything else in the body. They are marked off by the diaphragm and enclosed in their own membrane, the pleura, forming the region of the body known as the chest.

These two aspects are found united in other parts of the body, the ones called members, organs, and viscera; so they too occur in pairs--arms and hands, legs and feet, eyes, and nostrils, for example. Within the body there are the kidneys, the ureters, and the reproductive glands; and the viscera that are not paired are still divided between right and left. Further, the brain itself is divided into two hemispheres, the heart into two ventricles, and the lungs into two lobes. The right side has to do with the good that results from truth and the left to the truth that results from good; or in other words, the right refers to the good that love can do, which leads to the truth of wisdom, while the left refers to the truth of wisdom that results from the good that love can do. Since the union of what is good and what is true is reciprocal, and since they become a virtual single whole by virtue of that union, these pairs within us act together as a unit in our deeds, motions, and sensations.