What we recognise as modern art has one outstanding characteristic: it is not mimetic. That is, it does not seek to create an illusionistic representation of the visible world but rather to establish its own reality as an independent object - its autonomy, in the jargon. With this goes a corresponding emphasis on the purely formal or aesthetic aspect of the work - its character as an autonomous structure of line, form, colour, texture. In modern art, everyday reality may be referred to, or evoked, in ways ranging from more or less distorted or stylised representations to the direct incorporation in the work of "real" objects or materials. Or it may be excluded altogether in …