People experience various forms of art (music, theater, painting, sculpture, dance, gourmet cooking) for one or more of the following purposes:
1) to be seen looking cultural
2) to entertain themselves
3) to exercise their emotions
4) to exercise their cognitive abilities
5) to explore the limits of their perceptions
Any discourse on art should address one or more of these purposes. If the claim is made that a particular artwork is great, which of these purposes is it great at fulfilling? The first purpose is too cynical to be involved in most discussions of art, though it can provide insight into how peer pressure and patronage have shaped the arts. The second purpose is not satisfying by itself, because it naturally leads to the question, "why is it entertaining?" Why do we find it preferable to stare at a painting instead of a blank wall, or to listen to our iPods instead of silence? Entertainment has to be caused by one of the other purposes, whether it is the stimulation of emotions or the time kill of a good intellectual challenge.
So a good discourse on art should be about the emotional effect, the perceptual effect, or the cognitive effect. Arguments could and should be made that some of these effects directly influence each other. A cognitive awareness of the structure of a symphony can engender an emotional response. The visual illusions in a painting can affect the cognitive interpretations.
My argument does not specify whether the focus should be on universal effects or individual effects. Both approaches have their benefits and problems. Universal effects allow the discourse to approach the artwork as a tangible object with indisputable attributes. Individual effects are more ephemeral, but more accurate when it comes to emotion. I challenge my fellow members of the bløgösphère to address the purpose of the artwork in your discourses.