Letter 58 — On Being (§10)

“But there are certain things which have life (anima) and yet are not “animals.” For it is agreed that plants and trees possess life, and that is why we speak of them as living and dying. Therefore the term “living things” will occupy a still higher place, because both animals and plants are included in this category. Certain objects, however, lack life,—such as rocks. There will therefore be another term to take precedence over “living things,” and that is “substance.” I shall classify “substance” by saying that all substances are either animate or inanimate.”