See Kenneth Lansing, who argues against Morris Weitz in particular, that we can and must define art. A brief excerpt:
"If art educators teach anything at all, they teach composition, artistic procedures or techniques, and skill building. But how can they justify the teaching of composition or design if there is no specific compositional characteristic that a work of art must possess? How can they justify efforts to develop skill in the handling of the tools and materials of art if such skill does not need to be reflected in works of art? Who is to say what students must know and be able to do in art if the production of art objects doesn't require any particular knowledge or ability?
Consequently, I am compelled to ask why someone doesn't entertain the idea that we may have assigned the term "work of art" unjustifiably to certain things in the past. Or is it "okay" to have thrown that term around carelessly only to discover, years later, that we can't define the nature of its referents because they don't have anything in common?I am also compelled to ask how evaluation in art can be carried out in any logical fashion if we don't know what the subject is or what it requires. To get an idea of how important such a problem is, try applying it to a different discipline. Consider, for example, the fix that teachers of aeronautical engineering would be in if they didn't know what an airplane was."