concept further than Cézanne. They represented all the surfaces of depicted objects in a single picture plane, as if the objects had all their faces visible at the same time. This new kind of depiction revolutionized the way objects could be visualized in painting and art. The historical study of Cubism began in the late 1920s, drawing at first from sources of limited data, namely the opinions of Guillaume Apollinaire. It came to rely heavily on Daniel-Henry Kahnweiler's book Der Weg zum Kubismus (published in 1920), which centered on the developments of Picasso, Braque, Léger, and Gris. The terms "analytical" and "synthetic" which subsequently emerged have been widely accepted since the mid-1930s. Both terms are historical impositions that occurred after the facts they identify. Neither phase was designated as such at the time corresponding works were created. "If Kahnweiler considers Cubism as Picasso and Braque," wrote Daniel Robbins, "our only fault is in subjecting other Cubists' works to the rigors of that limited definition." The traditional interpretation of "Cubism", formulated post facto as a means of understanding the works of Braque and Picasso, has affected our appreciation of other twentieth-century artists. It is difficult to apply to painters such as Jean Metzinger, Albert Gleizes, Robert Delaunay and Henri Le Fauconnier, whose fundamental differences from traditional Cubism compelled Kahnweiler to question whether to call them Cubists at all. According to Daniel Robbins, "To suggest that merely because these artists developed differently or varied from the traditional pattern they deserved to be relegated to a secondary or satellite role in Cubism is a profound mistake." The history of the term "Cubism" usually stresses the fact that Matisse referred to "cubes" in connection with a painting by Braque in 1908, and that the term was published twice by the critic Louis Vauxcelles in a similar context. However, the word "cube" was used in 1906 by another critic, Louis Chassevent, with reference not to Picasso or Braque but rather to Metzinger and Delaunay: "M. Metzinger is a mosaicist like M. Signac but he brings more precision to the cutting of his cubes of color which appear to have been made mechanically [...]". The critical use of the word "cube" goes back at least to May 1901 when Jean Béral, reviewing the work of Henri-Edmond Cross at the Indépendants in Art et Littérature, commented that he "uses a large and square pointillism, giving the impression