| There is a certain dependency that seems to inhere in the form of a PS-rule. The fact that an item is obligatory seems to imply that optional elements, when present, depend on it. Some grammarians (Hudson, 1984) take this relationship to be of primary importance, rejecting the PS-rule per se and establishing each dependency by fiat. Dependencies between the words of a sentence are then diagramed with graphs: the words become nodes and the arcs, dependencies, of which thirteen kinds have so far been identified. |
| Our position is that while dependencies are very important, we can derive them from the form of the PS-rule as already indicated. Proponents of this model deny PS-rules out of hand, but they define elements that beg for description by this device. Figure 2 illustrates the form that the phrase structure rule must take to describe the network elements that dependency grammarians create. Then there is an important transformation that introduces a binary linkage between two selected wordforms. For a particular language, some parts of speech stand in the left-to-right relationship and others in the right-to-left. The linguists using the dependency model must state these constraints on the i and j in the transformation on the individual lexical items. The left-to-right link is created by the transformation illustrated in the figure. The feature on Wi in the first base specifies its context: that Wj come after it. The various predilections of particular words to govern others (“valency”) is stated by means of such selectional restraints being features on the respective lexical items. The presence of such a feature becomes a condition on the lexical insertion transformation that establishes each linkage. In this formulation each linkage begins as nothing more than a set of word identifiers. |
| To the table in figure 3 one might add such valency features as is characteristic of each wordform. The transformation would presumably provide additional features on the linkages indicating what sorts of items are being linked. It is then these features that are subclassified by such features as are listed on the right. |
