[4] Because of his background in music, Walton expected that he would have an interest in aesthetics and philosophy of art, but was unmoved by his contacts with these fields at Berkeley.
After having been invited to teach a course on aesthetics that he was not fully prepared for (having only had the one seminar with Sibley), he stayed up nearly all night brainstorming topics,[4] which led to his paper 'Categories of Art'.
Walton has been working on this philosophical theory since 1973,[7] and it is expounded in his 1990 magnum opus Mimesis as Make -Believe: On the Foundations of the Representational Arts.
[12] Props are divided into two forms: sensory depictions (such as paintings, sculpture and certain kinds of music), and verbal representations (such as novels and the spoken component of theater).
[20] In later papers, Walton has expanded his theory to recognize a distinction between content oriented make-believe, which describes a participant's relationship to the fictional worlds of novels, films, paintings etc.
[22] Stephen Yablo has developed Walton's concept of prop oriented make-believe in connection with numbers and concluded that our understanding of cardinality is essentially based upon fiction.
[23][24] The make-believe theory has been described by Jerrold Levinson as “the most significant event in Anglo-American aesthetics in many a year”, and compares it to Nelson Goodman's Languages of Art (1968), Richard Wollheim's Art and Its Objects and Arthur Danto's Transfiguration of the Commonplace by suggesting that it “joins a small pantheon of landmark books”.
[25] Simo Säätelä compared Walton's approach with the make-believe theory to that of Gilbert Ryle in The Concept of Mind (1949), albeit far wider in scope.
We see the world through them.”[33] Walton recognizes that this use of 'see' may differ from its conventional usage, but considers it parallel to the way we talk about 'seeing' through a telescope or other such tool.