Defining grammatical types

It seems that a reflection on the nature of grammatical type is necessary. The categories of common noun, qualifying adjective, verb, personal pronoun, etc. are well known. But what is a grammatical type? What is the criterion for distinguishing them? For the purposes of machine translation, the notion of grammatical type must be defined rigorously and precisely. Categories have an important role to play in the translation process, especially in the crucial process of disambiguation. The appropriate criterion here seems to be the place of one grammatical category in relation to another. For example, the definite article determinant precedes the common noun.