Recursion in Grammar and Performance

The deeper, more recursive structures posited by linguists reflect important insights into similarities among linguistic constituents and operations, which would seem to be lost in computational models that posit simpler, flatter structures. We show how this apparent conflict can be resolved with a substantive theory of how linguistic computations are implemented. We begin with a review of standard notions of recursive depth and some basic ideas about how computations can be implemented. We then articulate a consensus position about linguistic structure, which disentangles what is computed from how it is computed. This leads to a unifying perspective on what it is to represent and manipulate structure, within some large classes of parsing models that compute exactly the consensus structures in such a way that the depth of the linguistic analysis does not correspond to processing depth. From this unifying perspective, we argue that adequate performance models must, unsurprisingly, be more superficial than adequate linguistic models, and that the two perspectives are reconciled by a substantial theory of how linguistic computations are implemented. In a sense that will be made precise, the recursive depth of a structural analysis does not correspond in any simple way to depth of the calculation of that structure in linguistic performance.