Auxiliaries (words such as must, shall, is) are central to English grammar. They are also puzzlingly complex in their behaviour. So much so that disagreement about their nature has been radical, and they remain a major area of difficulty. The interest of this area is compounded by the possibility of working out its history in some detail, given the abundant data available for earlier periods of English. It is clear that the area was much less well defined in earlier times; indeed it has even been claimed that modals were not to be distinguished grammatically from straightforward verbs at the earliest periods for which we have substantial records. Thus change has apparently been considerable. This means that the process of change will itself be important and interesting, and that we may achieve some insights into the nature of the modern category from an understanding of its development. So there is a major twofold challenge: to provide an appropriate synchronic account of English auxiliaries, and to show how this area of grammar developed historically. These are the twin challenges taken up in this book.

First, then, I have established a new account of the working of the modern auxiliary system. Its distinctive claim is that although auxiliaries carry apparently verbal categories such as ‘finite’ or ‘infinitive’ these are not inflectional in auxiliaries but are lexically specified, so that forms such as should or been behave in some respects like independent items. This leads to a simple, new and nonabstract account of a range of the properties of auxiliaries in terms of their distinctness from verbs, and to a fundamentally ‘lexical’ account of major properties of this ‘grammatical’ area.