Anyway. In the midst of marking I had a flashback to Standard Four with Mr Cooper and "that" and "which" and restrictive and nonrestrictive clauses, and me not really believing it. And I still don't really believe it.
Microsoft Word Grammar Checker I'm looking at you.
Consider this should-be-straightforward example of a nonrestrictive clause:
Jo Walton, who wrote Among Others, is a brilliant writer.... taking this inkling any further would involve exploring how "narrowing down a set" is maybe a clunky and misleading model for both the phenomenology and the metaphysics of reference. I'd probably have to remind myself what intensionality is again. Thank God for marking.