Unification and efficient computation in the minimalist program

This talk explores issues in the construction of computationally simple grammars. In particular, we investigate the trade-off between simplicity of implementation and expressive power. We begin by developing what appears to be the simplest possible definite clause grammar implementation for a sub-theory in the minimalist program: that of probe-goal case agreement (Chomsky, Lectures in Government and Binding. Dordrecht: Foris; 2001). In computational modeling, there is a simple trade-off between simplicity of mechanism and expressive power, e.g., the Chomsky hierarchy. However, simplicity of implementation need not correlate with limited expressive power. Unification is a simple but powerful mechanism that can be used to implement uninterpretable/interpretable feature matching. We show, using examples from Chomsky (Lectures in Government and Binding. Dordrecht: Foris; 2001), as in (1)-(3), that unification-based derivations result in agree relations with fewer probe-goal steps than predicted. This economy of derivation results because once unified, unvalued features from different heads can be instantiated or valued simultaneously at a parse global level. Therefore, unification trades off fewer probe-goal steps for possibly unbounded agree relations.