Revolutionary Art

Yesterday we had a discussion on what some of our favorite revolutionary art is. I couldn't really come up with anything. I'd mentioned Salman Rushdie's Satanic Verses because it was the first thing that came to mind, and because in my mind it is a work that is hard hitting and has gall. I was rightfully critiqued, however. It seems that art that critiques culture, creates change, goes against the social norm, etc. or awakens is not enough. There is a piece of the definition I am missing, obviously. I suppose revolutionary art must have a certain aim, must be good, must hit a spot in the watcher and then evoke change (hopefully as some sort of action). Can you help me with this? What is your definition and what are some very hard hitting examples? I am eager to get this clear in my mind.