Important 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 development Picasso, Braque, Léger, and Gris. The terms "analytical" and "synthetic" which subsequently emerged have been widely accepted since the mid-1930s.
