Letter 58 — On Being (§14)

“I therefore distribute “that which exists” into these two species,—things with, and things without, substance. There is no third class. And how do I distribute “substance”? By saying that it is either animate or inanimate. And how do I distribute the “animate”? By saying: “Certain things have mind, while others have only life.” Or the idea may be expressed as follows: “Certain things have the power of movement, of progress, of change of position, while others are rooted in the ground; they are fed and they grow only through their roots.” Again, into what species do I divide “animals”? They are either perishable or imperishable.”