Full Idea
Fire, earth, water and air, and other simple bodies are agreed to be substances, as are plants, plant parts, animals, animal parts, and the heavens and their parts. Forms and mathematicals are more controversial.
Gist of Idea
Elements and physical objects are substances, but ideas and mathematics are not so clear
Source
Aristotle (Metaphysics [c.324 BCE], 1042a07)
Book Reference
Aristotle: 'Metaphysics', ed/tr. Lawson-Tancred,Hugh [Penguin 1998], p.233