 Finally, let us consider how Aristotle fares according to the criteria of substance with which we ended the introduction. Aristotelian substance, whether construed as individualised form or composite of form and matter meets (i), the criterion of ontological basicness. It also meets (ii), relative durability, although in a rather modest manner. Individual substances are more durable than instances of the properties in the other categories, for it is substances that can take on and lose those other properties. Individuals are not, however, very long-lived and on this criterion Aristotle makes what could be regarded as a concession to Plato, for it is form as universal, which Aristotle does not consider properly substance, that is most durable. There are at least two senses in which substantial forms are eternal. First, Aristotle believes the world to be eternal and all the same species to exist eternally. So that, even though particular objects are subject to degeneration and decay, the species as such are eternal. Second, generation and decay depend on the material component in composites. Any form that does not require matter for its activity will be eternal by nature. This applies to the active intellect, which is an essential feature of all human intellects, and to the immaterial movers of the cosmos described in Metaphysics, Book Lambda. (Further consideration of these topics would take us into Aristotle’s philosophy of mind and his theology.)