In metaphysics, Chisholm maintained that certain things are genuinely persisting “substances”. Such things literally last through time and survive changes in their properties. Each person is such a being, retaining his or her strict identity over time. On the other hand, ordinary physical objects can be said to persist only in an extended sense. Since it has undergone changes of parts, today’s chair is only “loosely identical” with yesterday’s chair. Chisholm thought that a complex thing could strictly persist only if it retained all of its parts. Thus, he endorsed mereological essentialism. He thought that persons would have to be ontologically simple in such a way as to permit strict identity over time. Thus, we are not to be identified with our bodies.