By looking at human nature. There are aspects of art (symmetry, rotational/translatioanl patterns, imitation of nature, etc) that are present in every culture where art has been found. This tells us that there is something “hardwired” in the brain that is responsible for these artistic preoccupations. You can read more on my views of aesthetics here (though I would want to slightly modify some of the things I wrote then, especially in my arguments with I.Ryan. If I could draw it down to one sentence: the enjoyment of art is subjective but not arbitrary.
Clayton -