Thales first pronounced that the soul is that being which is in a perpetual motion, or that whose motion proceeds from itself. Pythagoras, that it is a number moving itself; he takes a number to be the same thing with a mind. Plato, that it is an intellectual substance moving itself, and that motion is in a numerical harmony. Aristotle, that it is the first actuality [Greek ommitted] of a natural organical body which has life potentially; and this actuality must be understood to be the same thing with energy or operation. Dicaearchus, that it is the harmony of the four elements. Asclepiades the physician, that it is the concurrent exercitation of the senses.
CHAPTER III. WHETHER THE SOUL BE A BODY, AND WHAT IS THE NATURE AND ESSENCE OF IT.
All those named by me do affirm that the soul itself is incorporeal, and by its own nature is in a motion, and in its own self is an intelligent substance, and the living actuality of a natural organical body. The followers of Anaxagoras, that it is airy and a body. The Stoics, that it is a hot exhalation. Democritus, that it is a fiery composition of things which are perceptible by reason alone, the same having their forms spherical and without an inflaming faculty; and it is a body. Epicurus, that it is constituted of four qualities, of a fiery quality, of an aerial quality, a pneumatical, and of a fourth quality which hath no name, but it contains the virtue of the sense. Heraclitus, that the soul of the world is the exhalation which proceeds from the moist parts of it; but the soul of animals, arising from exhalations that are exterior and from those that are within them, is homogeneous to it.
CHAPTER IV. OF THE PARTS OF THE SOUL.
Plato and Pythagoras, according to their first account, distribute the soul into two parts, the rational and irrational. By a more accurate and strict account the soul is branched into three parts; they divide the unreasonable part into the concupiscible and the irascible. The Stoics say the soul is constituted of eight parts; five of which are the senses, hearing, seeing, tasting, touching, smelling, the sixth is the faculty of speaking, the seventh of generating, the eighth of commanding; this is the principal of all, by which all the other are guided and ordered in their proper organs, as we see the eight arms of a polypus aptly disposed. Democritus and Epicurus divide the soul into two parts, the one rational, which bath its residence in the breast, and the irrational, which is diffused through the whole structure of the body. Democritus, that the quality of the soul is communicated to everything, yea, to the dead corpses; for they are partakers of heat and some sense, when the most of both is expired out of them.
CHAPTER V. WHAT IS THE PRINCIPAL PART OF THE SOUL, AND IN WHAT PART OF THE BODY IT RESIDES.
Plato and Democritus place its residence in the whole head. Strato, in that part of the forehead where the eyebrows are separated. Erasiatratus, in the Epikranis, or membrane which involves the brain. Herophilus, in that sinus of the brain which is the basis of it. Parmenides, in the breast; which opinion is embraced by Epicurus. The Stoics are generally of this opinion, that the seat of the soul is throughout the heart, or in the spirit about it. Diogenes, in the arterial ventricle of the heart, which is also full of vital spirit. Empedocles, in the mass of the blood. There are that say it is in the neck of the heart, others in the pericardium, others in the midriff. Certain of the Neoterics, that the seat of the soul is extended from the head to the diaphragm. Pythagoras, that the animal part of the soul resides in the heart, the intellectual in the head.