Set theory for poets / Poetry for set theorists
One modern incarnation of the debate between nominalism and realism is to be found in philosophical arguments about sets.  There are two ways of characterizing a set: intensionally, through description (e.g. the set of all inhabitants of London, to use an example of Russell's), and extensionally, which is just a list of the members of the set.
Judging God
Teaching Milton this semester, I think I made a couple of connections that must be obvious, but that I'd never quite seen before (or maybe I had: these days I'm finding the obvious striking again, which I don't know whether that's a good or a bad thing).