Are generalizations about art possible? As soon as one school of thought isolates principles and rules about what makes art good, instances of good art that break the rules flood in to negate them. Instances of bad art that obey all the rules are not far behind. However, even without any stable set of criteria to make aesthetic judgments, we still seem to know what good art is, just as we seem to know that something is funny without being able to explain why. Explanations of why a piece of art is good are more astutely made after we've already agreed that it is good!
