Cognitive explanations, distributional evidence, and diachrony

Cognitively oriented approaches to the study of language standardly use synchronic distributional evidence to make assumptions both about the psychological mechanisms that lead speakers to create particular constructions, and about the components of a speaker’s mental representation of their language. Yet, as synchronic distributional patterns are a result of specific diachronic processes, any assumption about the psychological mechanisms or types of mental representation underlying particular patterns should take into account the diachronic processes that give rise to these patterns. Based on evidence from different languages and language families, the paper discusses several diachronic processes pertaining to the development of various types of alignment systems and prototype effects in dependent clauses. It is shown that these processes provide no evidence for a number of assumptions about psychological mechanisms and a speaker’s mental representation that have been made on synchronic grounds in order to account for the relevant distributional patterns. It follows that this type of assumptions cannot be inferred directly from synchronic distributional patterns, and should be investigated independently of these patterns.