Daniel Amneus argued that Macbeth as it survives is a revision of an earlier play, in which Duncan granted Macbeth not only the title of Thane of Cawdor, but the "greater honor" of Prince of Cumberland (i.e. heir to the throne of Scotland).
Daniel Amneus proposed that the current version of Macbeth is a modified version of an earlier play, where Duncan granted Macbeth both the title of Thane of Cawdor and the "greater honor" of Prince of Cumberland (which signifies the position of heir to the Scottish throne).