Halliday & Matthiessen (1999: 530):
It may be a general principle [across languages] that thematic status is more closely tied to the clause (as the locus of experiential and interpersonal choices) than is the listener-oriented pattern of given and new; in English the “quantum” of information that is defined by this latter construction is not, in fact, identical with the clause and may be smaller or larger. But all discourse is organised around these two motifs, which between them “add value” to the clause, enabling it to ‘mean’ effectively in the context in which it occurs.