Substance, Form and Matter: Aristotle Rethinks Plato

Aristotle respected Plato but rejected the idea that Forms exist separately in another realm. For Aristotle, the most real things are individual substances, such as this horse or that man. Each substance is a combination of matter, what it is made of, and form, the structure that makes it the kind of thing it is. The form of a horse does not float apart from horses; it exists in each one.

Aristotle also explained change with the ideas of potentiality and actuality: an acorn is potentially an oak and becomes actually one as it grows. This solved the old Parmenidean puzzle, since change is not something coming from nothing but potential becoming actual. Aristotle's approach brought the objects of knowledge down into the world we observe, encouraging empirical study. Later thinkers debated whether he really escaped Plato, since forms remain central to his system.