Even concerning the hierarchical structure of coordinated strings, there is much disagreement. Whether or not coordinate structures should be analyzed in terms of the basic tree conventions employed for subordination is an issue that divides experts. Broadly speaking, there are two options: either a flat or a layered analysis. There are two possibilities for the flat option, both of which are shown here. The a-trees represent the analyses in a constituency-based system, and the b-trees in a dependency-based system:
