Optimality and diachronic adaptation

In this programmatic paper, I argue that the universal constraints of Optimality Theory (OT) need to be complemented by a theory of diachronic adaptation. OT constraints are traditionally stipulated as part of Universal Grammar, but this misses the generalization that the grammatical constraints normally correspond to constraints on language use. As in biology, observed adaptive patterns in language can be explained through diachronic evolutionary processes, as the unintended cumulative outcome of numerous individual intentional actions. The theory of diachronic adaptation also provides a solution to the teleology problem, which has often been used as an argument against usage-based functional explanations. Finally, I argue against the view that the grammatical constraints could be due to accident. Thus, an adaptive explanation must eventually be found, whether at the level of language use and diachronic change (as proposed in this paper), or at the level of biological evolutionary change.