Supposedly Shakespeare used verse for upperclass ch’s and prose for lower-class ch’s. He does but not exclusively, he switches btwn them for effect. Hamlet speaks verse until he goes mad when he switches to prose, Prince Hal speaks verse with his father but prose with his tavern-mates, Lady Macbeth speaks verse until she sleepwalks during which she speaks only prose.
Taken from The Great Courses’ Shakespeare: The Word and the Action