of everyday life, the general method of verifying the laws of the
sentential calculus, the necessity of a sharp distinction between
words and their names, the concepts of the universal class and
the null class, the fundamental notions of the calculus of relations,
and finally the conception of methodology as a general science of
sciences. In the present edition all these topics are discussed
(although not all in an equally thorough manner), since it seemed
to me that to avoid them would constitute an essential gap in any
textbook of modern logic. Consequently, the chapters of the
first, general part of the book have been more or less extended;
in particular, Chapter II, which is devoted to the sentential
calculus, contains much new material. I have also added many
new exercises to these chapters, and have increased the number
of historical indications.

While in previous editions the use of special symbols was re-
duced to a minimum, I considered it necessary in the present
edition to familiarize the reader with the elements of logical
symbolism. Nevertheless, the use of this symbolism in practice
remains very restricted, and is limited mostly to exercises.

In previous editions the principal domain from which examples
were drawn for illustrating general and abstract considerations
was high-school mathematics; for it was, and still is, my opinion
that elementary mathematics, and especially algebra, because of
the simplicity of its concepts and the uniformity of its methods of
inference, is peculiarly appropriate for exemplifying various funda-
mental phenomena of a logical and methodological nature. Never-
theless, in the present edition, particularly in the newly added
passages, I draw examples more frequently from other domains,
especially from everyday life.

Independent of these additions, I have rewritten certain sections
whose mastery by students had been found somewhat difficult.

The essential features of the book remain unchanged. The pref-
ace to the original edition, the major part of which is reprinted
in the next few pages, will give the reader an idea of the general
character of the book. Perhaps, however, it is desirable to point
out explicitly at this place what he should not expect to find in it.

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