The only words that can occur in the open slot in (12a) are words like the, a, this, that, and so
forth, which are determiner (Det). (12b) provides a frame for conjunctions (Conj) such as and,
but, so, for, or, yet.
9
In (12c), we can have the category we call ‘complementizer’, here the word
that – we return to these in (16) below.