The Role of Reasoning and Persuasion in Legal Argumentation (URL links in Endnotes are web-enabled in electronic versions of this article: http://www.orsinger.com/PDFFiles/constructing-a-persuasive-argument3.pdf) Richard R. Orsinger [email protected] http://www.orsinger.com McCurley, Orsinger, McCurley, Nelson & Downing, L.L.P. San Antonio Office: 1717 Tower Life Building San Antonio, Texas 78205 (210) 225-5567 http://www.orsinger.com and Dallas Office: 5950 Sherry Lane, Suite 800 Dallas, Texas 75225 (214) 273-2400 State Bar of Texas Exceptional Legal Writing April 26, 2013 Texas Law Center Austin, Texas © 2013 Richard R. Orsinger All Rights Reserved Table of Contents I. INTRODUCTION..................................................................... -1- II. USEFULNESS OF THE TOPIC.......................................................... -1- III. THE IMPORTANCE OF INTUITION..................................................... -2- IV. THE COMMON LAW.. ............................................................... -2- V. LEGAL REASONING (OVERVIEW)..................................................... -5- A. FORMAL LOGIC............................................................... -6- 1.Deductive Logic......................................................... -7- 2.Inductive Logic.......................................................... -7- 3.Reasoning With Probabilities............................................... -7- 4.Reasoning by Analogy. ................................................... -8- B. INFORMAL LOGIC............................................................. -8- C. A RULE-ORIENTED APPROACH................................................. -8- D. MODERN ARGUMENT THEORIES............................................... -9- VI. FORMAL LOGIC..................................................................... -9- A. ARISTOTLE................................................................... -9- B. STATEMENTS, PROPOSITIONS, AND ARGUMENTS.. -10- C. TRUTH, VALIDITY, AND SOUNDNESS.......................................... -10- 1. True and False.......................................................... -10- 2. Valid and Invalid........................................................ -10- 3. Sound and Unsound...................................................... -11- 4. Application to Statements, Propositions, and Arguments.. -11- VII. DEDUCTIVE LOGIC................................................................. -12- A. DEFINING CONCEPTS ESSENTIAL TO ARISTOTLE’S DEDUCTIVE LOGIC... -12- 1. Statements............................................................. -12- 2. Affirmation, Denial, and Contradiction... -12- 3. All; None; and Some..................................................... -12- 4. Principles, Rules, and Symbols............................................. -13- 5. Three Fundamental Principles of Logic.. -13- B. THE SYLLOGISM............................................................. -13- 1. The Simple Syllogism.................................................... -13- 2. Polysyllogism........................................................... -16- 3. Enthymeme.. .......................................................... -16- 4. Sorites.. .............................................................. -16- 5. When Premises are Inconsistent.. .......................................... -17- 6. The Hypothetical Syllogism.. ............................................. -17- a. The Conditional Syllogism.....................................-18- b. The Conjunctive Syllogism.....................................-18- c. The Disjunctive Syllogism.....................................-18- 7. Quantifiers and Distribution.. ............................................. -18- 8. The Rules of Opposition.................................................. -19- 9. Rules for Syllogisms..................................................... -19- 10. Fallacies of Syllogistic Logic.. ............................................ -20- a. The Fallacy of Four Terms.....................................-20- b. The Fallacy of the Undistributed Middle Term.. -21- c. The Fallacy of Illicit Process of the Major or Illicit Minor Term.. -21- d. The Fallacy of Negative Premises... -21- e. The Fallacy of Drawing Affirmative Conclusions From a Negative Premise. ..........................................................-21- f. The Existential Fallacy........................................-21- -i- g. Belief Bias..................................................-21- 11. Translating Natural Language Arguments Into Syllogisms... -21- 12. Viewing Legal Disputes as Syllogisms....................................... -22- C. IMPLICATION................................................................ -22- 1. The Validity and Soundness of Implications... -23- 2. The Five Forms of Conditional Propositions. -23- 3. The Material Implication.................................................. -23- 4. Modus Ponens (Affirming the Antecedent)... -23- 5. Modus Tollens (Denying the Consequent).. -23- 6. “Not-P or Q.”. ......................................................... -24- 7. Fallacy of Denying the Antecedent.......................................... -24- 8. Fallacy of Affirming the Consequent.. ...................................... -24- 9. Conditional Propositions Can Be Sorites.. -24- 10. Attacking a Conditional Proposition......................................... -25- 11. Disproving a Material Implication........................................... -25- 12. Biconditional........................................................... -25- 13. Conjunctive Conditional Propositions... -25- 14. Disjunctive Conditional Propositions.. -25- 15. Other Conditionals....................................................... -26- a. Indicative Conditionals........................................-26- b. Subjunctive Conditionals......................................-26- c. Counterfactual Conditionals....................................-27- 16. The Dilemma. ......................................................... -27- 17. Degrees of Conditionals.. ................................................ -28- 18. Disproving Other Conditionals............................................. -28- 19. Legal Presumptions...................................................... -28- D. EULER CIRCLES.. ........................................................... -28- E. TRUTH TABLES.............................................................. -29- F. LOGIC CONNECTORS......................................................... -30- 1. Logical Negation........................................................ -30- 2. Logical Conjunction.. ................................................... -31- 3. Logical Disjunction...................................................... -31- 4. Material Implication.. ................................................... -33- 5. Material Equivalence..................................................... -34- 6. Material Nonequivalence.................................................. -34- 7. Alternative Denial....................................................... -35- 8. Joint Denial............................................................ -35- G. SYMBOLIC LOGIC.................................................................. -35- H. TAUTOLOGIES AND SELF-CONTRADICTIONS... -35- I. AXIOMS..................................................................... -36- J. CONSTRUCTING DEDUCTIVE ARGUMENTS IN PROPOSITIONAL LOGIC.. -36- 1. Direct Deductive Arguments. ............................................ -36- a. Rules of Inference............................................-37- b. Rules of Replacement. .......................................-38- c. Logic Arguments............................................-39- 2. Conditional Proof........................................................ -39- 3. Indirect Proof. ......................................................... -39- K. FALLACIES OF DEDUCTION................................................... -39- 1. The Fallacy of Affirming the Consequent... -39- 2. False Dichotomy........................................................ -40- 3. Inconsistency........................................................... -40- -ii- 4. Non Sequitur........................................................... -40- 5. Slippery Slope.......................................................... -40- 6. Begging the Question..................................................... -41- 7. Circular Reasoning...................................................... -41- 8. Changing the Premises.................................................... -41- L. PARADOXES................................................................. -42- 1. The Sorites Paradox...................................................... -42- 2. The Liar Paradox........................................................ -42- 3. Eubulides’s Paradox.. ................................................... -43- 4. Socrates’ Paradox.. ..................................................... -43- 5. Smasandache Paradox.................................................... -43- 6. The Catalog Paradox..................................................... -43- 7. The Omnipotent God Paradox.............................................. -43- 8. The Surprise Test Paradox................................................. -43- 9. The Grandfather Paradox.................................................. -43- 10. The Envelope Paradox.................................................... -44- 11. Orsinger’s Paradox.