A number of people have asked about the value of addressing aesthetics, the philosophy of art, or the definition of art. The reasoning is that if it is so difficult to define, it must therefor be ultimately subjective, and each person should just determine for herself what it is.
Perhaps we all do determine for ourselves the meaning of anything. Because, as in the "tree falling in the forest" example, the meaning does not exist if it does not exist for me personally. I am allowed to define "table" or "chair" any way I wish for myself, but if I hope to communicate with others about tables and chairs, the meaning or definition must be shared. And that shared meaning derives from a combination of (a) acquired meanings from those whom we give credibility and (b) connotations developed from our experiences with tables and chairs.
If there were really no way to define art, there would be no way to determine what is art, and art could be anything. Fortunately, art can be defined, although not succinctly in verbal form, as we might define "table" or "chair." We learn the definition indirectly through understanding why works have been labeled art by critics and artists in the past, and directly by understanding the perspectives of those critics and artists.
From the standpoint of complete subjectivity, if art can be anything, it is meaningless as a term == art is everything and nothing. There is nothing that is not art, so everything is art. The term "art" has no shared meaning and has no value in communication, and yet we use it all the time.
By what criteria do you determine what is art for yourself? Because it pleases you? Because it pleases your friends, or someone you respect, or most people around you? What criteria constitute pleasing? What does it do to please?
From another perspective, other than pragmatic needs, by what criteria do we select a season? Or what material we place in museums? By what criteria do we judge quality? How do we determine "good" from "not good?" Whatever criteria we use become our criteria for our aesthetic, which then become, in fact, our definition of our art.
It is useful and valid for us to question what those criteria are, to challenge the validity of those criteria, and to constantly explore new criteria to define the art experience.
In order to comprehend the options of criteria, the kinds of questions to ask of our criteria, the possible limits of our personal vision, it is worthwhile to explore the explorations of others. Understand that the definition of art and the determination of quality are linked and mutually affected. Alter one and the other is changed.
One additional concern is the value in trying to understand how art works have meaning. Once we begin to explore this as artists, our work instantly changes dimension. It moves from the surface to the soul and allows us to refocus on the meaningful.