For many, art is a product: the painting to be observed and contemplated, the concert to be heard and enjoyed. There is, however, another conception of art – art as activity – and it is in this context that Howard Becker (1984) develops his concept of art worlds. Art worlds, Becker argues, include more than the artists who create the work which the public commonly defines as art. Any given art world will consist of the network of people whose co-operative activity produces that art world's certain type of artistic product (Becker 1984, p. x). Organised according to their knowledge of the art world's goals and conventions for achieving those goals, the art world includes five basic categories of people: the artists who actually create and produce the art; the producers who provide the funds and support for the production of the art; the distributors who bring the art to the audience; the audience who purchases and collects the art; and finally, the critics, aestheticians and philosophers who create and maintain the rationales according to which all these other activities make sense and have value. These rationales, however, are not merely descriptive but prescriptive. For despite the efforts of those who would keep an art world static in its products and function, art worlds are dynamic. Changes in the art world are often made in response to changes in the rationales - i.e., the philosophical justifications for an art world's art - which identify the art world's product as ‘good’ art and explain how that art fills a particular need for people and society (Becker 1984, p. 4).