Hortatory Address to the Greeks

And that these very wise sages of yours do not even agree in other ways, can be easily learned from this. For while Plato says that there are three first principles of all things—God, matter, and form—God is the maker of everything; matter is the subject of the first production of all that is created and gives God the chance for His work; and form is the type of each of the things produced. Aristotle, however, makes no mention of form as a first principle, but says that there are two: God and matter.

And again, while Plato says that the highest God and the ideas exist in the prime place of the highest heavens, in a fixed sphere, Aristotle says that, next to the most high God, there are not ideas, but certain gods who can be perceived by the mind. So, they differ on heavenly matters. It is clear that they not only fail to understand earthly matters, but also, being in disagreement among themselves regarding these things, they appear untrustworthy when they talk about heavenly matters.

That even their doctrine about the human soul as it currently exists does not align is evident from what each has said about it. For Plato says that it has three parts, with the faculties of reason, affection, and appetite.

But Aristotle says that the soul is not so comprehensive as to include corruptible parts, but only reason. And Plato strongly asserts that "the whole soul is immortal." However, Aristotle, calling it "the actuality," believes it to be mortal, not immortal.

Furthermore, Plato says it is always in motion, but Aristotle claims that it is immovable since it must itself precede all motion.