 In the history of Western aesthetics, the subject matters that received attention ranged from natural objects and phenomena, built structures, utilitarian objects, and human actions, to what is today regarded as the fine arts. However, beginning with the nineteenth century, the discourse has become increasingly focused on the fine arts. This narrowing attention occurred despite the prominence of the aesthetic attitude theory in modern aesthetics, according to which there is virtually no limit to what can become a source of aesthetic experience. The tendency to equate aesthetics with the philosophy of art became widespread in twentieth century aesthetics, particularly within the Anglo-American tradition.