Like Romanticism, Post-Modernism is a poorly defined term that means different things in different contexts. But in academe, pomo can pretty much be equated with relativism. This term also means several different things, but all of them apply to pomo.
The relativism that makes me hostile to pomo is knowledge relativism or epistemological relativism. “All statements of fact are historically and culturally situated and thus meaningless outside a local contemporary sphere”. This stance can be applied to itself and immediately yields absurdity.
The other pomo relativism is aesthetic. “All value judgements of art are historically and culturally situated and thus meaningless outside a local contemporary sphere.” In other words, there are no timeless aesthetic pronouncements. Bach and the Beatles (whose work I love right here, right now) are not timeless greats. There are people now, and there will be people in the future, who don’t like them. No canon deserves any respect. There are no classics outside of marketing lingo and university syllabi. High culture and low culture are contingent constructs. No art critic has more authority than another.
I’m an aesthetic relativist who opposes post-modernism. My aesthetic stance isn’t grounded in the humanities. It’s based on a natural sciences perspective and a love of genre literature that rejects the concept of high culture. Aesthetic opinions are not traits of the artworks themselves. They are traits of people. And all people are are historically and culturally situated.