Aesthetics Subjectivism
One theory in aesthetics is called subjectivism. Subjectivism says that each person has their own sense of beauty. So, the only way of judging something's beauty is if people say it is beautiful. Subjectivism also says, for the same reason, that something is art simply because someone says it is art. This is backed up by the experience that, even though people feel they find something beautiful, they may not be able to explain why.