Free relatives with null head

Spanish has a type of free relatives (that is, relative clauses without antecedent) that clearly shows that these structures should be analyzed as containing a null head:

(1) Compró el _ que le recomendaste
(2) Trajo la _ que le pediste

In these cases, the relative particle (que ‘that’) has a determiner. Notice that the head can be reconstructed:

(3) Compró el auto que le recomendaste
(4) Trajo la carta que le pediste

In addition, it is possible to have other nominal constructions with a null head. In these cases, the determiner also must be present:

(5) El _ invisible

Even the ‘neutral’ determiner lo can be used in free relatives:

(6) Dile lo _ que quieras

This is the same determiner that we use in the so called “nominal adjectives” (which are used to express an abstract concept):

(7) Lo _ invisible

This suggests that, contrary to some proposals that conceive free relatives as bare CPs, in these constructions we have a structure like (8), that is, with a null head:

(8) [DP DET [NP __ [CP que…. ] ] ]