The primary motivation for the DP Hypothesis has been a claimed parallel with the clausal domain, where functional projections (at least IP and CP) dominate the lexical projection of the verb. However, the claimed parallels are not real. Verbs that select for clausal complements only select things that are high in the clause, plausibly on C (questions vs. declaratives, finite vs. non-finite, etc.); they never select V. In contrast, verbs that select for nominal arguments only select for N, and never for the functional elements like D. In form selection, each head in the clausal domain determines the form of the head of its complement. In contrast, within nominals, it is N that determines the form of everything else. These asymmetries indicate that the head of the clause is C, but the head of the nominal is not D, it is N. A review of other arguments that have been given for the DP Hypothesis indicates that none of them are compelling.
"Selectional Asymmetries between CP and DP Suggest that the DP Hypothesis is Wrong,"
University of Pennsylvania Working Papers in Linguistics:
1, Article 5.
Available at: http://repository.upenn.edu/pwpl/vol15/iss1/5