Modernism-a definition

http://www.tate.org.uk/collections/glossary/definition.jsp?entryId=174

In the field of art the broad movement in Western art, architecture and design which self-consciously rejected the past as a model for the art of the present. Hence the term modernist or modern art. Modernism gathered pace from about 1850. Modernism proposes new forms of art on the grounds that these are more appropriate to the present time. It is thus characterised by constant innovation. But modern art has often been driven too by various social and political agendas. These were often utopian, and modernism was in general associated with ideal visions of human life and society and a belief in progress. The terms modernism and modern art are generally used to describe the succession of art movements that critics and historians have identified since the Realism of Courbet, culminating in abstract art and its developments up to the 1960s. By that time modernism had become a dominant idea of art, and a particularly narrow theory of modernist painting had been formulated by the highly influential American critic Clement Greenberg. A reaction then took place which was quickly identified as Postmodernism.

From Tate glossary.