Modernism is a school of thought that took place on the late 1800s and early 1900s. It advocated rational thinking and the use of science and reason for the advancement of man. It aimed at creating a clear and rational view of the world; believing that through science and reason mankind can advance and grow. Modernist artists experimented with form, technique and processes rather than focusing on subjects, believing they could find a way of purely reflecting the modern world.
Postmodernism is a movement that took place after Second World War and gained popularity around 1960s. It was a reaction against modernism. In a chaotic era it advocated that there is no universal truth. Unlike modernism it used an unscientific approach to life and believed that all things are irrational. In art, postmodernism was specifically a reaction against modernism which had dominated art theory and practice since the beginning of the twentieth century.
While modernism was based on idealism and reason, postmodernism was born of skepticism and a suspicion of reason. The modernists embraced clarity and simplicity; postmodernism was all about complex and often contradictory layers of meaning.
Postmodernism refused to recognize the authority of any single style or definition of what art should be and because postmodernism broke the established rules about style, it introduced a new era of freedom and a sense that ‘anything goes’.
I myself have been working on a series of self-portraits that have this kind of postmodern surrealist feel to them. See a few examples below.