On George Santayana's The Sense of Beauty (1896).
What are we saying when we call something "beautiful?" Are we pointing out an objective quality that other people (anyone?) can ferret out, or just essentially saying "yay!" without any logic necessarily behind our exclamation? The poet and philosopher Santayana thought that while aesthetic appreciation is an immediate experience--we don't "infer" the beauty of something by recognizing some natural qualities that it has--we can nonetheless analyze the experience after the fact to uncover a number of grounds on which we might appreciate something. He divides these into areas of matter (e.g. the pretty color or texture), form (the relations between perceived parts), and expression (what external to the work itself does it bring to mind?) and ends up being able to distinguish high art (form-centric) from more savage forms (centered on matter or expression) while distinguishing real appreciation (which can include any of the three elements) from mere pretension (when you don't really have an immediate experience at all but merely recognize that you're supposed to think that this is good).
The regular foursome talk through Santayana's theory with regard to expressionist painting, rock 'n roll, beautiful landscapes, abstract expressionism, and more. Read more about the topic and get the book.