One of my favourite art historians, Robert Rosenblum is credited with challenging accepted norms of modern art and its history. He believed that Modernism had a much longer history than people assumed. Instead of examining and judging works of art within time-specific frameworks, Rosenblum tended to critique art regardless of its associated movement or place in history.
Rosenblum believed that Modern art can trace its roots back to the French, German and Danish painters (who worked mostly in the Neo-Classical style) of the late 18th-century. Rosenblum constantly confronted formal ideas of Modernism and even art history itself, and challenged those in the art world to view Modern art as a vast well of ideas rather than being a product of particular timelines.
Of Impressionism, Rosenblum wrote that it rejuvenated Western painting and forced us to rediscover what children had always known, that the most immediate spectacle of light, colour and movement, perceived before the brain can sort out other kinds of order, is a tonic, joyous experience.
Of contemporary art he said (rather sadly, I suspect) "We're in what might be called, in the phrase of the day, a Postmodernist situation, and the feeling that Modern art can be heroic, that it makes a difference to the world, all this seems sort of quaint and nostalgic rather than a part of living reality."