The ʻmost markedʼ type of Theme in a declarative clause is thus a Complement: for example 'nature' in 'nature I loved', 'this responsibility' in 'this responsibility we accept wholly'. This is a nominal element which, being nominal, has the potentiality of being Subject; which has not been selected as Subject; and which nevertheless has been made thematic. Since it could have been Subject, and therefore 'unmarked' Theme, there must be very good reason for making it a thematic Complement – it is being explicitly foregrounded as the Theme of the clause.
- Halliday (1985), a pag.45