 The first reason is that this exemplar, since it is abstracted from changeable things, has to share in the nature of changeability. Therefore, since physical things are more changeable than mathematical objects, this is why the Philosopher claimed that we have a greater certainty of knowledge about mathematical objects than about physical things by means of their universal species. And this is why Augustine, discussing this cause of the uncertainty of the knowledge of natural things in q. 9 of his Eighty-Three Different Questions, says that from the bodily senses one should not expect the pure truth [syncera veritas]