Abstract This article examines how and why auxiliaries combine into complex verb constructions in Old West Germanic. It integrates findings from prior corpus studies on Old Dutch and Old English with original corpus research on Old Saxon, Old High German, and Early Middle High German up to 1150. The combined results indicate that all Old West Germanic varieties combine only two auxiliaries, with the finite auxiliary always being a modal. These finite modals could have scope over a wide range of potential auxiliaries, including passive, perfect, modal, aspectual, and causative auxiliaries, as well as perception verbs. The range of auxiliary combinations is shown to expand progressively over time and across regions. The article reveals that the combinatorial potential of auxiliaries relates to their degree of grammaticalization and the availability of a nonfinite verb form. This relationship is argued to be bidirectional: (a) the ongoing grammaticalization of auxiliaries creates and expands their combinatorial potential, while (b) the combination of auxiliaries into complex verb constructions in turn stimulates the emergence of auxiliaries as a category of their own. This implies that the combination of auxiliaries is not only a symptom of their grammaticalization but also a catalyst for further change.*
Evie Coussé (Mon,) studied this question.