Exocentric - Representing Endo- and Exocentric Structures

Representing Endo- and Exocentric Structures

Theories of syntax (and morphology) represent endocentric and exocentric structures using tree diagrams and specific labeling conventions. The distinction is illustrated here using the following trees. The first three trees show the distinction in a constituency-based grammar, and the second two trees show the same structures in a dependency-based grammar:

The upper two trees on the left are endocentric since each time, one of the parts, i.e. the head, projects its category status up to the mother node. The upper tree on the right, in contrast, is exocentric, because neither of the parts projects its category status up to the mother node; Z is a category distinct from X or Y. The two dependency trees show the manner in which dependency-based structures are inherently endocentric. Since the number of nodes in the tree structure is necessarily equal to the number of elements (e.g. words) in the string, there is no way to assign the whole (i.e. XY) a category status that is distinct from both X and Y.

Traditional phrase structure trees are mostly endocentric, although the initial binary division of the clause is exocentric (S → NP VP), as mentioned above, e.g.

This tree structure contains four divisions, whereby only one of these division is exocentric (the highest one). The other three divisions are endocentric because the mother node has the same basic category status of one of its daughters. The one exocentric division disappears in the corresponding dependency tree:

Dependency positions the finite verb is the root of the entire tree, which means the initial exocentric division is impossible. This tree is entirely endocentric.