from concrete objects of sense. They then imagined that what exists in the mind subsists in external reality, just as their predecessors, such as Plato’s followers, imagined that universals subsist eternally outside the mind—these being the Platonic Forms. They also imagined the existence of prime matter coexisting with form, and of a duration beyond the motion of bodies. Others, such as the followers of Pythagoras, imagined the existence of numbers apart from the things counted. Aristotle, the author of the instructional works, and his followers imagined that bodies are composed of matter and form, and that matter