[williamdix]

I mean something along the lines of if head-first and complement-first are the only possibilites for phrase rules and that they must apply to all phrase rules for a given language, i.e.

  for all X, s.t. X is a grammatic category which can be the head of a phrase ; XP := X _

or

  for all X ; s.t. X is a grammatic category which can be the head of a phrase; XP := _ X 

Then, modulo processes which change a sentence from its underlying form to its surface form, we would only see forms characteristic of head-first or complement-first phrase structure.

In the second case, I intend dependent as the article means dependent. That is co-appearing because of the same underlying feature. To use the genetic analogy, co-appearing because one gene (the head firstness gene) determines them.

[T-R]

Thanks kindly, much appreciated.