The document discusses how 20th century art challenged traditional definitions and purposes of art through several influences and movements. Photography changed art by providing exact depictions, decreasing the need for some types of art and shifting reasons for creating art. Post-Impressionism influenced abstraction and composition. Artists began exploring personal experiences and expression through art. Movements like Cubism, Surrealism, De Stijl and works by artists like Picasso, Dali, Mondrian and Giacometti further pushed boundaries of what art could be and its role in personal expression and social commentary.