Within generative syntax, there is a debate on the role of the Spec,Head Configuration (Chomsky 1995) vs. Long-Distance Agreement, LDA (Chomsky 2000, etc.). Traditionally, an argument for the Spec,Head approach is found in the fact that in a number of languages in situ elements do not trigger agreement as opposed to elements that have moved into a Spec,Head configuration overtly. In this context, it is argued that the above facts follow from computational dynamics of the interfaces, in particular, from the incremental nature of the production system (c.f., Bock et al. 1992, Phillips 1996 and Ferreira 1996). The crosslinguistic variation regarding agreement (and lack of thereof) with in situ elements comes from the fact that the strategies of the parser/production system are defeasible: e.g., central embedding in English is disfavored due to its costly nature, but it is not banned by the parser.