The following is a list of book-length resources and studies relevant to the argument of this book. No claims of fullness are made here; this list simply represents some works the present author has found useful. All books mentioned contain their own suggestions for further reading, including discussions of earlier controversies. Full bibliographical details appear in the list of References. Those suitable for beginners are marked *; those of special importance or usefulness are marked +. A major limitation is that this list of suggestions for further reading is restricted to works written in or translated into English; thus, for instance, K. Luick's extremely important (although incomplete) Historische Grammatik der englischen Sprache (1964) has not been included.