Introduction

Abstract

Among the large variety of possible conditions and situations which can prevail when a book on a particular topic is being prepared, two extreme conditions can be imagined. First, the topic is completely new, and nothing has been written about it; second, the topic is not new at all; many people have been working on it for years, and numerous books and publications are available and still appearing. At each of these extremes, some kind of explanation for working and publishing on that particular topic seems to be demanded by the potential recipients. In the first case, therefore, the explanation will refer to reasons for dealing with that particular topic at all, reasons why these questions are raised and thought about. In the second case, explanations will refer to reasons for once again presenting a publication after so many have already appeared — justifications for the author’s opinion that particularly this publication should be useful in addition to so many others, and which make it different from others and therefore necessary.