If the initial element in the clause does not function as Subject or Complement or CIRCUMSTANTIAL Adjunct [...] then the Subject, Complement or Adjunct next following is still part of the Theme. This introduces the notion of a MULTIPLE THEME – where the part of the clause functioning as Theme has a further, internal structure of its own. The internal structure of a multiple Theme is based on the functional principle that was presented in chapter 2: the principle that a clause is the product of three simultaneous semantic processes. It is at one and the same time a representation of experience, an interactive exchange, and a message.
- Halliday (1985), Pag. 53