As a message, the clause comprises two parts: the Theme, which “serves as the point of departure of the message” (IFG, p64) and the Rheme. In an unmarked clause the Theme (in bold) matches the subject with the rest of the clause being the Rheme:
- I usually play tennis on Wednesdays.
It is also possible to highlight different parts of the message by placing them in the position of Theme:
- Usually, I play tennis on Wednesdays.
- On Wednesdays, I usually play tennis.
One point for EFL classes, however, is that the Theme that is chosen is one part of a network system. This means that the Theme simultaneously highlights what the clause is about and also delimits the scope of the clause. By saying “On Wednesdays, I usually play tennis” the speaker is implicitly excluding the other days of the week (this could be made grammatically explicit through it-clefting – “It is on Wednesdays that I usually play tennis”). Similarly, by saying “Usually, I play tennis on Wednesdays” the speaker is opposing that habituality with some unusual event. The message thus feels, in a sense, incomplete and we would expect some additional information, such as “but today it’s raining”. Also often overlooked for EFL is that by saying “I usually play tennis” the speaker is implicitly excluding the other participants in the exchange. The Rheme is then adding information within the limits placed by the Theme.