Soul Many Presocratics talked of human soul as a kind of stuff like other things in the cosmos. Anaxagoras thought of soul as an intelligent substance. Pythagoras conceived of the soul more spiritually and mystically, as the ground of human perception of and harmony with the mathematical-musical order of the cosmos. Plato, owing something to the Pythagoreans, thought of human soul as an invisible, non-material reality that is embodied in human life. Aristotle denied that soul was an invisible substance, and thought of it as the principle of unity of a thing, a part of its form.
Observation working with reason can detect a number of kinds of soul in primary beings.
Aristotle also argued that human soul has rational and irrational parts, corresponding to the organizing and organized aspects of human beings. He urged that the rational part must rule the irrational, accordingly, and used this to justify slavery and the denigration of women. Slaves, according to Aristotle, have no rational part, and the rational part of the souls of women is inactive, so they need to be ruled by men, whose rational part is active. For Plotinus, Soul is the third primal process, and includes everything that emanates into temporal being from the One via eternal Mind. The lower part of Soul is material.