I'm a student doing some basic research into LFG and I've read some of Falk 2001 Lexical Functional-Grammar: an Introduction to Parallel Constraint-Based Syntax and there's an exercise in the chapter on c-structure that's been giving me a headache.
Unlike GB, LFG has a nonprojective (non X'-category) S. Consider a sentence with no auxillary, such as Joan wrote a book. Should it be analyzed as an IP (as in (i)) or an S (as in (ii))
Falk also states a principle of "Economy of Expression" earlier in the chapter:
All syntactic phrase structure nodes are optional and are not used unless required to license elements required to create a well-formed f-structure or to add semantic content
So now my confusion: On one hand, the I' node does not help us create f-structure or (to my mind) add semantic content. On the other hand, it seems fishy that we should need to fall back to a S node. I feel like there's some loss of information?
Can someone help me understand what's going on?
I think my intuition about what it means to "license" f-structure is off, so something even about that might help.