Preface.

However, that cannot change the fact that it was she who gave the impetus for the investigations set down here and who spared no effort in providing suggestions and encouragement throughout their course. And if, as I have good reason to believe, large and important areas of facts have indeed been opened up to scientific research by this work, then it must not be forgotten to whom this gain is ultimately owed.

As far as the present expositions themselves are concerned, it hardly needs to be said explicitly that the attempt to work on an area of facts hitherto ignored in theory can only offer a first beginning, not a completed theory. This is already clearly evident in the arrangement of the material, which was not brought into the subject from a "principle" but was forced upon me by the facts. I must report that this, like much else in this work, turned out very differently from my initial expectations. At the time when I took the first steps in the new field of facts, I had no idea that I would encounter so many problems that were well known to everyone or at least to myself, and that I would catch sight of them from a side that promises to be particularly favorable to their solution. If this, as cannot be doubted, has been detrimental to the formal cohesion of these statements, I may nevertheless draw from it a welcome confirmation of my confidence that empiricism was not reshaped here in the sense of a predetermined theory, but rather that a theorem taken from empiricism itself was developed in the sense of the facts crowding in from all sides in the greatest diversity.

The diversity of these facts corresponds to some extent to the variety of preliminary studies in several chapters of this work that lead to the assumptions, whose justification for existence, however, I hope is not only to be found in their...