Modernism as Purification of Medium

Ok. Isn't there some art history/aesthetics consensus around the idea that (at least at one time) progress was thought to mean (1) differentiation of the various arts and (2) purification of the medium. So, for example, abstract painting was the medium of "the picture"(or what?) minus the inessential attribute of representation. 

Does that sound right? Before moving on to the critique of that view, I have two questions. First, can we say that the extraneous aspect of the various arts was thought to be, in each case, representation? Second, can we app

ly this to the modern novel, and say that the attempt to do away with plot was a similar attempt to purify the medium of the written text of its extraneous need for representation?