Several theories have been proposed recently on the diachronic study of English syntax. They are the results of the work on diachronic syntax conducted in a generative perspective. In many ways the earliest work by Klima on case markings and wh-movement is the best, at least from the viewpoint of methodological clarity. Traugott`s careful study of English auxiliary is instructive from a similar point of view. Lightfoot has made a very important contribution to the study of diachronic syntax. Lightfoot`s view of what constitutes syntactic change and what causes it is more convincing when compared with other theories of syntactic change. In this paper, I review some of the pre-theoretical difficulties which arise in the study of diachronic syntax, sketch each theory briefly, and point out its problems and defects. Regardless of a few criticisms directed to Lightfoot, which come from both generative and non-generative camps, his grammatical theory-based on the Extended Standard Theory model-seems more plausible and explanative.