Dependency Grammar - Linear Order and Discontinuities

Linear Order and Discontinuities

Traditionally, DGs have had a different approach to linear order (word order) than constituency grammars. Dependency-based structures are minimal compared to their constituency-based counterparts, and these minimal structures allow one to focus intently on the two ordering dimensions. Separating the vertical dimension (hierarchical order) from the horizontal dimension (linear order) is easily accomplished. This aspect of dependency-based structures has allowed DGs, starting with Tesnière (1959), to focus on hierarchical order in a manner that is hardly possible for constituency grammars. For Tesnière, linear order was secondary to hierarchical order insofar as hierarchical order preceded linear order in the mind of a speaker. The stemmas (trees) that Tesnière produced reflected this view; they abstracted away from linear order to focus almost entirely on hierarchical order. Many DGs that followed Tesnière adopted this practice, that is, they produced tree structures that reflect hierarchical order alone, e.g.

The traditional focus on hierarchical order generated the impression that DGs have little to say about linear order, and it has contributed to the view that DGs are particularly well-suited to examine languages with free word order. A negative result of this focus on hierarchical order, however, is that there is a dearth of dependency-based explorations of particular word order phenomena, such as of standard discontinuities. Comprehensive dependency grammar accounts of topicalization, wh-fronting, scrambling, and extraposition are mostly absent from many established dependency-based frameworks. This situation can be contrasted with constituency grammars, which have devoted tremendous effort to exploring these phenomena.

The nature of the dependency relation does not, however, prevent one from focusing on linear order. Dependency-based structures are as capable of exploring word order phenomena as constituency-based structures. The following trees illustrate this point; they represent one way of exploring discontinuities using dependency-based structures. The trees suggest the manner in which common discontinuities can be addressed. An example from German is used to illustrate a scrambling discontinuity:

The a-trees on the left show projectivity violations (= crossing lines), and the b-trees on the right demonstrate one means of addressing these violations. The displaced constituent takes on a word as its head that is not its governor. The words in red mark the catena (=chain) of words that extends from the root of the displaced constituent to the governor of that constituent. Discontinuities are then explored in terms of these catenae. The limitations on topicalization, wh-fronting, scrambling, and extraposition can be explored and identified by examining the nature of the catenae involved.