The first possibility is that there is a cause both for the things that become, and those that are; the cause of the former being their becoming, and that of the latter, their existence. Again, neither of them may have a cause. Or, in both cases, some may have a cause, and some not. Further, those that become might have a cause, while, of these that exist, some might partly have a cause. Contrariwise, all things that exist may have a cause, while of those that become, parts may have a caus...