updated: May 15, 2020

1 I updated : May 15, 2020 Logical Reasoning Bradley H. Dowden Philosophy Department California State University Sacramento Sacramento, CA 95819 USA ii Preface Copyright 2011, 2019 by Bradley H. Dowden This book Logical Reasoning by Bradley H. Dowden is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike CC BY-NC-SA. This license lets others remix, tweak, and build upon your work non-commercially, as long as they credit you and license their new creations under the identical terms. An earlier version of the book was published on paper by Wadsworth Publishing Company, Belmont, California USA in 1993 with ISBN number 0-534-17688-7. When Wadsworth decided no longer to print the book, they returned their publishing rights to the original author, Bradley Dowden.

2 The current version has been significantly revised. The current online version is 508 compliant for people with disabilities. If you would like to suggest changes to the text, the author would appreciate your writing to him at iii Praise Comments on the earlier 1993 paper edition, published by Wadsworth Publishing Company, which is owned by Cengage Learning: "There is a great deal of coherence. The chapters build on one another. The organization is sound and the author does a superior job of presenting the structure of arguments. " David M. Adams, California State Polytechnic University "These examples work quite well. Their diversity, literacy, ethnic sensitivity, and relevancy should attract readers." Stanley Baronett. Jr., University of Nevada Las Vegas Far too many authors of contemporary texts in informal logic keeping an eye on the sorts of arguments found in books on formal logic forget, or underplay, how much of our daily reasoning is concerned not with arguments leading to truth-valued conclusions but with making choices, assessing reasons, seeking advice, etc.

3 Dowden gets the balance and the emphasis right. Norman Swartz, Simon Fraser University iv Acknowledgments The following friends and colleagues deserve thanks for their help and encouragement with this project: Clifford Anderson, Hellan Roth Dowden, Louise Dowden, Robert Foreman, Richard Gould, Kenneth King, Marjorie Lee, Elizabeth Perry, Heidi Wackerli, Perry Weddle, Tiffany Whetstone, and the following reviewers: David Adams, California State Polytechnic University; Stanley Baronett, Jr., University of Nevada-Las Vegas; Shirley J. Bell, University of Arkansas at Monticello; Phyllis Berger, Diablo Valley College; Kevin Galvin, East Los Angeles College; Jacquelyn Ann Kegley, California State University-Bakersfield; Darryl Mehring, University of Colorado at Denver; Dean J.

4 Nelson, Dutchess Community College; James E. Parejko, Chicago State University; Robert Sessions, Kirkwood Community College; and Stephanie Tucker, California State University Sacramento. Thinking and writing about logical reasoning has been enjoyable for me, but special thanks go to my children, Joshua, 8, and Justine, 3, for comic relief during the months of writing. This book is dedicated to them. This book is dedicated to my wife Hellan whose good advice has improved the book in many Table of Contents Preface .. ii Copyright .. ii Praise ..iii Acknowledgments .. iv Table of Contents .. v C H A P T E R1 How to Reason Logically .. 1 Facing a Decision as a Critical Thinker .. 2 Advice for Logical Reasoners .. 5 Examples of Good 15 Review of Major Points.

5 18 Glossary .. 19 Exercises .. 20 C H A P T E R2 Claims, Issues, and Arguments .. 24 What is a Statement? .. 24 What is an Argument? .. 26 What is the Issue? .. 29 What is a Proof? .. 31 Indicators .. 32 Premise Indicators .. 35 Conclusion Indicators .. 35 Discount Indicators .. 39 Rewriting Arguments in Standard Form .. 40 Conditionals and the Word If .. 41 Deductively Valid and Inductively 45 Uncovering Implicit Premises .. 47 Locating Unstated Conclusions .. 52 Detecting Obscure Argumentation .. 55 Descriptions and Explanations .. 59 Review of Major Points .. 67 vi Glossary .. 68 Exercises .. 70 C H A P T E R3 Writing with the Appropriate Precision .. 91 Being 92 Context and Background Knowledge .. 93 Disambiguation by Machine .. 98 Semantic Disagreements.

6 99 Equivocation .. 100 Being Too Vague .. 101 Being Too General .. 105 Being Pseudoprecise .. 109 Improper Operationalization .. 111 Creating Helpful Definitions .. 114 Different Definitions for Different Purposes .. 114 How to Avoid Errors when Creating Definitions .. 119 Review of Major Points .. 122 Glossary .. 123 Exercises .. 126 C H A P T E R4 How to Evaluate Information and Judge 143 The Principles of Charity and Fidelity .. 143 When Should You Accept Unusual Statements? .. 146 Assessing a Source's Credibility .. 149 Seeking a Second Opinion .. 153 Trust Me, I Know It on Good Authority .. 156 Suspending Belief .. 156 Getting Solid Information about Whom to Vote For .. 158 Fake News and Misinformation .. 163 Review of Major Points .. 172 Glossary.

7 173 Exercises .. 173 C H A P T E R5 Obstacles to Better Communication .. 181 vii Not Realizing What You Are Saying .. 181 Abusing Rules of Grammar .. 183 Over-Using Euphemisms .. 185 Unintended Innuendo .. 188 Disobeying Rules of 190 Not Sticking to the Issue and Not Treating It Fairly .. 191 Not Accepting the Burden of Proof .. 191 Diverting Attention from the Issue .. 192 Giving Too Many Details .. 199 Re-defining the Issue .. 199 Covering Up the Reasons That Favor Your Opponent .. 201 Review of Major Points .. 203 Glossary .. 203 Exercises .. 204 C H A P T E R6 Writing to Convince Others .. 215 Writing with Precision and to Your Audience .. 217 The 218 The Middle .. 220 The Ending .. 221 Digressions .. 222 Improving Your Writing Style.

8 223 Proving Your 225 Creating Counterarguments .. 228 Review of Major Points .. 237 Glossary .. 238 Exercises .. 238 C H A P T E R7 Defending Against Deception .. 244 Deception Is All Around Us .. 245 Exaggeration and Lying .. 246 Telling Only Half the Truth .. 249 Telling the Truth, While Still Misleading .. 256 viii Saying Little with Lots of Words .. 257 Persuading Without Using Reasons .. 257 Deceiving with Loaded Language .. 259 Using Rhetorical Devices .. 261 Review of Major Points .. 263 Glossary .. 264 Exercises .. 265 C H A P T E R8 Detecting Fallacies .. 269 Ad Hominem Fallacy .. 269 Fallacy of Circular Reasoning .. 271 Straw Man Fallacy .. 272 False Dilemma Fallacy .. 274 Fallacy of Faulty Comparison .. 277 Fallacious Appeal to Authority.

9 278 More about Assessing Credibility .. 279 Spotting an Authority's Bias .. 283 Slippery Slope Fallacy .. 286 Genetic 286 Non Sequitur .. 287 Review of Major Points .. 289 Glossary .. 290 Exercises .. 291 C H A P T E R9 Consistency and Inconsistency .. 299 Recognizing Inconsistency and Contradiction .. 300 Identifying Self-Contradictions and Oxymorons .. 307 Inconsistency with Presuppositions .. 309 Refuting General Statements by Finding 312 Resolving Inconsistencies .. 316 Review of Major Points .. 319 Glossary .. 319 Exercises .. 320 ix C H A P T E R10 Deductive Reasoning .. 334 Implying with Certainty vs. with Probability .. 334 Distinguishing Deduction from Induction .. 341 Review of Major Points .. 346 Glossary .. 347 Exercises .. 348 C H A P T E R11 Logical Form and Sentential logic .

10 355 What is logic ? .. 355 Logical Equivalence .. 356 Logical Forms of Statements and Arguments .. 358 The logic of Not .. 361 The logic of And .. 364 The logic of Or .. 365 The logic of If-Then .. 367 The logic of Only, Only-If, and Unless .. 375 Sentential logic .. 379 Truth Tables .. 380 Arguments, Logical Consequences and Counterexamples .. 384 3-Valued logic .. 385 History of Sentential logic .. 390 Review of Major Points .. 392 Glossary .. 392 Exercises .. 393 C H A P T E R12 Aristotelian logic and Venn-Euler Diagrams .. 402 Aristotle's logic of Classes .. 402 Using Venn-Euler Diagrams to Test for Invalidity .. 408 The logic of Only in Class 418 Review of Major Points .. 421 Glossary .. 421 Exercises .. 422 C H A P T E R13 Inductive Reasoning.