Morphological Effects On Word Order And Subject Omission: A Diachronic Study

The purpose of this dissertation is to study the morphological effects on word order change and subject omission through a systematic analysis of morphological evolution. Morphological change concerns two respects, morphological case on nouns and agreement inflection on verbs. We propose that both are the major factors determining word order change and subject omission.In the analyses of word order, we propose that in agreement-rich languages affixation takes place in syntax, and that in agreement-impoverished languages affixation takes place in the phonological component via affix lowering. Agreement-rich languages can be divided into two subtypes: C-Agr languages which have complementizer agreement, and T-Agr languages which have no complementizer agreement. In C-Agr languages, verb movement for affixation is up till C, whereas in T-Agr languages, verb movement for affixation is up to T.During morphological development, the referential power of agreeing verbs gradually gets lost. The loss of the referential power causes the disability of covering the content of a null subject and thus causes the loss of empty topics, i.e. the loss of VSO sentence pattern. Moreover, along with the gradual loss of morphological cases, the OV order is replaced by the VO order and the nominative phrase is fixed to the typical subject position, [Spec, TP]. The combination of the three syntactic changes results in SVO to become the predominant sentence pattern in a language.In addition to the influence of word order variation, change of verbal agreement morphology also has effects on null subject permission: Licensing of null subjects is determined by the strength of the referential power of agreeing verbs. During the fusional process of agreement markers, the referential power of agreeing verbs gradually gets lost from full-referential to quasi-referential and then to non-referential. Correspondingly, subject omission gradually becomes more restricted: some languages allow three types of null subjects; some allow only null expletives; and some other languages allow only null non-referential subjects. As for languages with...