In contrast, the present theory follows Steedman (2000aSteedman ( , 2000b in assuming that restrictive and nonrestrictive rhemes are semantically and grammatically indistinguishable, and only differ in the nature of the context in which they are uttered.
we draw the following distinctions: the theme is a predication over the existing context or common ground, and the rheme seeks to effect an update on the context or common ground.