That distinction is very familiar to me. Forgeries are pastiches. Leaving behind the business of painting, a lot of art these days -- performance, conceptual --

That distinction is very familiar to me. Forgeries are pastiches. Leaving behind the business of painting, a lot of art these days -- performance, conceptual --would be equally difficult (or easy) to forge because it communicates a particular attitude or state of affairs, truthful or phony. Graphic designers ("commercial artists") or advertising art directors know that their business is communicating a particular desired state of affairs, regardless of whether it actually "obtains" as they say in philosophy. If you accept that all the things we call art are very broadly and fundamentally concerned with that (making a convincing statement, not necessarily a likeness of reality) then it's really clear how a class of skilled imitators can exist who can't come up with the "opinions" themselves. Why anyone should care whether a particular work is a product of original thought or not is the big, dangerous issue that forgery raises.