 This codified form is still used in the pedagogy of the sonata form.In the 20th century, emphasis moved from the study of themes and keys to how harmony changed through the course of a work and the importance of cadences and transitions in establishing a sense of "closeness" and "distance" in a sonata.The work of Heinrich Schenker and his ideas about "foreground", "middleground", and "background" became enormously influential in the teaching of composition and interpretation.