In 1956, Morris Weitz wrote a famous article still much discussed in aesthetics classes called “The Role of Theory in Aesthetics” Journal of Aesthetics and Art Criticism, 15: 27–35.) I say it is much discussed today, although interestingly, the main point of the article is hardly ever mentioned. Most readers of the essay just focus on its first part. Weitz is then seen as advocating skepticism with regard to defining art or as holding the view that art can never be defined. A typical comment about Weitz is that of Thomas Adajian in his article on "The Definition of Art" in the Stanford Encyclopedia of Philosophy, in which he describes Weitz's view in this way: "any concept is open if a case can be imagined which would call for some sort of decision on our part to extend the use of the concept to cover it, or to close the concept and invent a new one to deal with the new case; all open concepts are indefinable; and there are cases calling for a decision about whether to extend or close the concept of art. Hence art is indefinable..."
This is part of the truth about Weitz's article, but in being partly true, it is also a distortion. Weitz in fact held that art is definable and that the definitions that have been offered in the past are immensely valuable. His point was that art could not be given a "real" definition. This means that, unlike "triangle" or "water," art could not be defined in terms of necessary and sufficient properties. "Art" is a different kind of concept. "Art" as Adajian correctly observes, is, for Weitz, an "open concept." However, this does not mean that it cannot be defined. It has been defined every time a definition has been put forward. There is just no final definition. Weitz's point is that all of the great definitions of art in the past are what he calls "honorific definitions." He sees previous theories as theories of the evaluative use of "Art" and not "true and real definitions of the necessary and sufficient properties of art." They are "definitions...in which 'Art' has been redefined in terms of chosen criteria." He also thinks that these definitions are "supremely valuable" because of the "debates over the reasons for changing the criteria of the concept of art which are built into the definitions." In part, Weitz sees the history of debates over the nature of art as something like one long Socratic dialogue in which each character successively provides us with a definition of the concept under consideration, in this case 'art,' which is in turn debated. But there is something else going on: this debate is also sequenced in a historical way. At each time in history there is a dominant theory of "Art," and the debate is over changing the criteria to be found in that dominant theory, thus replacing it, presumably, with a new dominant theory. Philosophers coming after, and responding to, Weitz have typically thought that the moral of his story was that one cannot define art. The moral, rather, is that we need to see previous definitions of art in a larger historical context, one in which the activities of artists, frankly, are either as important or more important than the activities of philosophers. Hegel has a nice way of looking at this: it is his concept of the "spirit of the culture" as something that is manifested not only in one area of the culture but in others as well, a zeitgeist. So the spirit of the culture might be manifest both in philosophy, art, religion and so forth. So the moral of Weitz's story is that each new definition of art stresses new things to focus on. This, by the way, is true for theories of art after Weitz as much as it is for those that came before Weitz, even for those theories that claim to have no evaluative component at all. This is a subtle point but it is noteworthy that the theories of George Dickie and Arthur Danto focused on examples of art that were "hot" during their own time. Danto especially stresses the impact of seeing Andy Warhol's Brillo Boxes in an art gallery. Although Danto believed that his theory of art was universal (he was something of a Platonist in this regard) he also continuously throughout his career went back to that moment he walked into a gallery and saw Warhol's work. Clearly the dynamic of the interaction of Warhol and Danto can be described in Weitzian terms as creation of a new honorific definition of art (Danto's and Warhol's) in which certain new elements are stressed and certain older elements essential to older definitions of art are disregarded, downplayed, ignored, refuted, despised, etc.
Now, although I think Weitz is right about all of this, the view needs amendment. The reason is that what is considered to be the dominant theory at any one time in history is also open to debate. Nonetheless, there is usually consensus that there are some top contenders at any one time in history, for example expressionism vs. formalism in 1914, and that certain writings, as well as other cultural phenomena, including most importantly, events in the artworld itself, tended to put certain theories "in the front." Note that Weitz's view is by not means that art is an open concept in the sense that "anything goes."
Weitz writes that "the value of each of the theories resides in its attempt to state and to justify certain criteria which are either neglected or distorted by previous theories." so that, for example, the Bell/Fry formalist theory states that "Art is significant form" which is to say that art should be redefined "in terms of the chosen condition of significant form." Weitz interprets this to mean: "In an age in which literary and representational elements have been paramount in painting, return to the plastic ones since they are indigenous to painting." (177) The claim that art is significant form is really a request or demand that we behave in a different way, that for example, we admire Giotto and Cezanne's use of lines and colors to give us a special aesthetic experience over Frith and other academic painters who were fascinated instead with the stories that could be told when looking at their paintings. This is essentially right...but it is not to say that one can just replace the theory with a request or demand for certain behavior or a certain kind of valuing since the term "indigenous" indicates that something is being said about the essence of art: it is just not the kind of thing that can be said by giving a real definition in terms of necessary and sufficient conditions. The way that Weitz puts it is that the "definitional form" is used to "turn our attention" to "the plastic elements in painting." I think this does not tell the whole story of what happens in the definitional debate, but it does capture an aspect often neglected, and it is consistent with my main point, which is that Weitz was right that so-called real definitions are really honorific definitions in disguise....how "honorific definition" is to be defined is still open to debate.
I mentioned that some modifications are needed. I think that the point being made by various definers of art cannot always be made in terms of "emphasizing or centering upon some particular feature of art that has been neglected or perverted." Sometimes it is more a matter of bringing out completely new features, and sometimes the debate has more to do with debates over the nature of humanity, freedom, justice, spirituality, wisdom or some other big philosophical question, than with neglected features. Weitz did not spread his net widely enough, and it is here that a Hegelian approach might be more appropriate.