Art of Pure Cinema

In a now-famous interview with François Truffaut in 1962, Alfred Hitchcock described his masterpiece Rear Window (1954) as "the purest expression of a cinematic idea." But what, precisely, did Hitchcock mean by pure cinema? Was pure cinema a function of mise en scène, or composition within the frame? Was it a function of montage, "of pieces of film assembled"? This notion of pure cinema has intrig...