30 ROBERT D. VAN VALIN, JR.
2.5 Formal representation of focus structure
It is necessary to integrate focus structure into the projection grammar rep
resentation of clause structure. Focus structure will be a separate projection
from both the constituent and operator projections, but it is related to both.
With respect to the constituent projection, predicates, arguments and
peripheral PPs form the basic information units in focus structure; that is,
the minimal focus domain is the nucleus, a core argument or a peripheral
PP. With respect to the operator projection, the IF operator specifies the
type of speech act that the sentence is in, and the PFD must fall within the
scope of this operator. It may be coextensive with it in simple clauses, as in
English, or it may be a subset of it, as in Italian and Setswana. Within each
focus structure projection both the PFD and the Actual Focus Domain [AFD]
will be represented. This is illustrated in Figure 12. The IF operator anchors
the focus structure projection, and the potential and actual focus domains
are represented within its scope. Figure 12 is an example of predicate focus
in English; the PFD is the whole clause, and the AFD is the nucleus plus
the post-nuclear arguments. In Figure 13 two examples of narrow focus in
English are given. Italian differs from English with respect to the PFD in
simple sentences, as noted above; in Figure 14, the structure of (lib) (pred-