A general category of Being, particular categories of Becoming: this is a suggested philosophical guide for sorting the two original kinds of toposes and what they have become. The unity and cohesiveness of Being provides the basis for Becoming, and the historicity and controlled variability of Becoming produces new Being from old.
– F. William Lawvere: Some thoughts on the future of category theory. In: Category Theory. Springer, Berlin, Heidelberg, 1991.