Introduction to Philosophy/Logic

Before we are ready to ask any questions, we must first understand how to go about reasoning about them. The branch of philosophy that covers the study of reasoning is called logic. It stands at the foundation of all philosophical and scientific thinking processes.

Logic is very important. After all, if we want good answers to our questions, we need some way to verify that we didn't make a mistake in our reasoning.

The field of logic has matured to give rise to a very structured way of approaching the art of reasoning, turning it into a science. Even so, of course, interesting questions and problems still remain to be researched. However, for this introductory book, we will cover the basics of correct reasoning, and slowly introduce you to the most structured form of all: formal logic.

This book will only provide an introduction. To read more about formal logic specifically, we recommend advanced readers to check out the related wikibook Formal Logic.

Table of Contents

1. Introductory Material
   1. Older Pages
      1. Preface
      2. Logic and Reason
      3. Truth and Validity
      4. Paradoxes
      5. Classical Logic
         1. Modes
2. Sentential Logic
   1. Older Pages
      1. The Sentential Language (heavily modified) (moved to Formal Logic)
      2. |Truth Tables (completely rewritten) (moved to Formal Logic)
      3. Building More Complicated Formulas
      4. Tautologies and Contradictions
      5. Fault Diagnosis
      6. Some Properties of the Logical Connectives
      7. Nand and Nor
      8. A More Formal Approach to Sentential Logic
      9. Soundness, consistency, completeness
      10. Syntax and semantics
      11. Propositional calculus and probability theory
      12. Summary for propositional calculus
      13. Tableau proofs
3. Predicate Logic
4. Other Material
   1. Older Pages
      1. Modal Logic
      2. Names - Frege, Sinn and Bedeutung
      3. Equality - Leibniz's law
      4. Definite descriptions - Russell
      5. Intensionality, Belief, Scope
      6. Truth, Tarski
      7. Vagueness
      8. Bibliography
   2. Newer Pages