The more the form and material of a work are disregarded in favor of its subject matter the more we seem to lose a work of art. So, suppose we are listening to a folk musician with a compelling political message. We are dwelling on the message and thinking about it. But we suddenly find that, despite the fact that the musician is still playing, we are not paying attention to the song. In fact, we have turned away from it to the message. It is no longer the message as embodied in the organized material. It is now disembodied from the work. Perhaps, if we reflected on the situation, we would discern that we turned away because there was very little imagination employed: we were listening to the same old three chords in the same old sequence. Or perhaps the vocals were off-key and not pleasing to listen to. Whatever the case may be, we are no longer attending to a subject matter as presented in that song by that artist.
Consider Andy Warhol’s Brillo Box (1964). Perhaps, once divested of its everyday supermarket associations, we can come to see its formal features as interesting. But for many people it is only interesting because we wonder why it is in a museum and, perhaps more philosophically, what makes something art. That is, many look beyond the work to some perceived subject matter and quickly disregard the form and material. Of course, we could argue that Warhol’s work is not the box but the box in the museum that makes us think about how it is different from one in the supermarket. Perhaps then our thoughts don’t really move from the subject matter since the subject matter is the box in the museum. We dwell on that box in that context and, in doing so, have our perceptions and thoughts challenged. So if we neither exclude institutional context nor conceptual thought from aesthetics then perhaps we have a work of art on our hands. But this approach to Warhol’s boxes has always seemed a bit forced to me: I am inclined to see the work as a mere means to a meaning outside it.
In any case, Roger Scruton has articulated a test to see if there is what he refers to as an “aesthetic perception” of a subject matter. He says we take an aesthetic interest in x, or an interest in x for its own sake, if and only if the answer to the question “Why are you interested in x?” consists in a further description of x. In the case of the folk song experience, we would probably find that our answer to Scruton’s question would not entail describing the song further. Rather, we would discuss the message divorced from its material and formal organization. This test can be used to evaluate a work to see to what extent it holds our attention and is not just a means to having an interesting perception, thought, or feeling (see his Art and Imagination, p. 143).
Now if we think art should be inherently valuable – taken to be interesting for its own sake – then any work which serves as a mere means to the end of conveying a subject matter would not be a work of art. A necessary condition for a work of art would be perceiving the subject matter in the work, in other words, aesthetic perception.
Go here for a post on Kant’s conception of beauty (which emphasizes the above notion of being interesting for its own sake) and its relation to freedom.