In a proposition, one component may be singled out as the one which matters, while the rest of the proposition is taken for granted. The proposition of the reply in a and b takes it for granted that someone broke the window and only focuses on the identity of the agent.

The component of a proposition that currently matters is its focus, while the rest of the proposition is presupposed. The material coding the presupposed portion is extrafocal.

At the level of discourse structure and the speaker's communicative intentions, focusing on one particular component of a proposition may serve different purposes. Two general functions may be distinguished which are regularly reflected in linguistic structure:

• The speaker may insist that a certain functional position in the proposition is occupied by the particular entity under focus, to the exclusion of any conceivable alternatives which may be in the context. This is insistence or insistent focus. Its structural manifestation is clause-initial position of the focal component.
• The speaker may be connecting up with the preceding context, state that portion of the proposition which is not contentious between interlocutors and then reveal the entity occupying the position in the proposition left open so far. This is suspension or suspensive focus. Its structural manifestation is clause-final position of the focal component.

The replies in illustrate insistent focus. Their alternatives in illustrate suspensive focus.

and illustrate the most explicit variety of focus constructions, which is clefting. Some languages like English require such a high-level syntactic operation to place the focal component in the initial or final position of a clause. In other languages with freer word order, it suffices to place the focal component in either of these two clause positions (f).

In any case, the focal component bears emphatic stress.