sentences:  Proper nouns and pronouns cannot grammatically have a determiner attached to them, though they still are part of the DP phrase.In this case, one needs to include a null category to stand as the D of the phrase as its head.Since a DP phrase has a determiner as its head, but one can end up with NPs that are not preceded by an overt determiner, a null symbol (e or Ø) is used to represent the null determiner at the beginning of the DP.