Cubism and Gleizes. Cubism as a publicly debated movement became relatively unified and open to definition. Its theoretical purity made it a gauge against which such diverse tendencies as Realism or Naturalism, Dada, Surrealism and abstraction could be compared. The Cubism of Picasso, Braque and Gris had more than a technical or formal significance, and the distinct attitudes and intentions of the Salon Cubists produced different kinds of Cubism, rather than a derivative of their work. "It is by no means clear, in any case," wrote Christopher Green, "to what extent these other Cubists depended on Picasso and Braque for their
20th-century Western painting for that spiritual knowledge. Other major pioneers of early abstraction include Swedish painter Hilma af Klint, Russian painter Kazimir Malevich, and Swiss painter Paul Klee. Robert Delaunay was a French artist who is associated with Orphism, (reminiscent of a link between pure abstraction and cubism). His later works were more abstract, reminiscent of Paul Klee. His key contributions to abstract painting refer to his bold use of color, and a clear love of experimentation of both depth and tone. At the invitation of Kandinsky, Delaunay and his wife the artist Sonia Delaunay, joined The Blue Rider (Der Blaue Reiter), a