*©2022 The MIT Press. Reproduction by any means strictly prohibited.*
## About the Third Edition

In the third edition, we have reorganized the material in response
to feedback from instructors and students. The goal has been to
produce a more modular text, so that, for example, instructors who
wish to proceed to truth tables before proofs no longer have to
break in the middle of chapter 1, but can jump past chapter 2 (where
the material on sentential proofs is now confined) and proceed
directly to the new chapter 3 before returning to teach the material
in the second chapter. In the second part of the book we have
similarly divided the material from the two original chapters into
three new chapters 4–6, maintaining the same three-part division
between the language, the rules of proof, and the semantic treatment
of predicate logic via models.

We have also extracted all the material on identity into a seventh
chapter. This material was originally added in the second edition
where it was distributed through the third and fourth chapters of
that edition, but many instructors who did not wish to cover the
toqpic found it distracting to have to work around that material
when teaching basic predicate logic. We have maintained the
tripartite language/proof/semantics structure within the three
sections of the new chapter, again allowing some flexibility in the
way the material is approached. We hope that these changes allow
instructors to choose a path through the material that will maximize
their students’ success.

Lastly, we have made some changes in the Exercises to try to support
students moving from easier to harder problems as they work through
an exercise. We heard from both instructors and students that
encountering a very hard problem at the beginning of an exercise
often proved discouraging, and that this was often compounded when a
student turned to the appendix for the answer, only to find a proof
spanning more than a page. We don’t promise to have made the
sequencing perfect, but we do hope that it is better, and that after
nearly three decades in print, this book continues to fulfill our
original intent of a concise, rigorous, yet accessible introduction
to symbolic logic.