Tree Composition and Generalized Transformations

A major goal of research in generative grammar is to correctly characterize the principle constraining the locality of movement. While various proposed principles e.g., subjacency, shortest move, minimal link condition, phase impenetrability condition(PIC) have their differences, they also all have the disturbing property that they are stipulations imposed upon the computational system. For example, one could have a version of minimalism without a shortest move constraint, or the PIC, etc., and such a system would allow all sorts of undesirable locality violations. An alternative line of research, starting with Kroch and Joshi (1985) and given its most recent and rigorous exposition in Frank (to appear), has pursued a more radical course. This work, based on the framework of Tree Adjoining Grammar (TAG), has argued that given an appropriately defined formal system, there is no need for a constraint such as shortest move, since the effects of such a constraint follow from the nature of the formal system. The basic idea is that instead of combining trees and then doing movement, all movement is localized to independently constructed trees, where each tree represents one clause. These trees are then put together using a certain generalized transformation the operation of adjoining, hence Tree Adjoining Grammar (TAG). There are no singulary transformations in a TAG derivation. Instead, the basic elements of the system are pieces of phrase structure, called elementary trees, and movement is captured by using the adjoining operation to insert one tree within another, thus allowing components of a tree to be “stretched” apart. This stretching gives the effect of inter-clausal movement. TAG is related to the derivational system of the