The Role of Reasoning and Persuasion in the Legal Process
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The Role of Reasoning and Persuasion in the Legal Process 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 24th Annual Advanced Civil Appellate Practice Course September 2-3, 2010 Four Seasons Hotel Austin, Texas © 2010 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.................................................. -3- V. LEGAL REASONING (OVERVIEW). .................................... -7- A. FORMAL LOGIC................................................ -8- 1. Deductive Logic ........................................... -8- 2. Inductive Logic ........................................... -9- 3. Reasoning With Probabilities ................................ -9- 4. Reasoning by Analogy ..................................... -10- B. INFORMAL LOGIC. ........................................... -10- C. A RULE-ORIENTED APPROACH................................. -11- D. MODERN ARGUMENT THEORIES............................... -11- VI. FORMAL LOGIC..................................................... -12- A. ARISTOTLE. .................................................. -12- B. STATEMENTS, PROPOSITIONS, AND ARGUMENTS. .............. -13- C. TRUTH, VALIDITY, AND SOUNDNESS. .......................... -13- 1. True and False............................................ -13- 2. Valid and Invalid. ........................................ -14- 3. Sound and Unsound. ...................................... -14- 4. Application to Statements, Propositions, and Arguments. ......... -14- VII. DEDUCTIVE LOGIC. ................................................ -15- A. DEFINING CONCEPTS ESSENTIAL TO ARISTOTLE’S DEDUCTIVE LOGIC. ...................................................... -16- 1. Statements............................................... -16- 2. Affirmation, Denial, and Contradiction. ....................... -16- 3. All; None; and Some. ...................................... -16- 4. Principles, Rules, and Symbols............................... -16- 5. Three Fundamental Principles of Logic. ....................... -17- B. THE SYLLOGISM.............................................. -17- 1. The Simple Syllogism...................................... -17- 2. Polysyllogism............................................ -20- 3. Enthymeme.............................................. -20- 4. Sorites.................................................. -21- 5. When Premises are Inconsistent.............................. -22- 6. The Hypothetical Syllogism. ................................ -23- a. The Conditional Syllogism............................ -23- b. The Conjunctive Syllogism. .......................... -23- c. The Disjunctive Syllogism............................ -23- 7. Quantifiers and Distribution................................. -23- 8. The Rules of Opposition ................................... -24- 9. Rules for Syllogisms....................................... -25- 10. Fallacies of Syllogistic Logic................................ -26- a. The Fallacy of Four Terms............................ -26- b. The Fallacy of the Undistributed Middle Term. ........... -26- -i- c. The Fallacy of Illicit Process of the Major or Illicit Minor Term. ................................................. -27- d. The Fallacy of Negative Premises. ..................... -27- e. The Fallacy of Drawing Affirmative Conclusions From a Negative Premise........................................... -27- f. The Existential Fallacy............................... -27- g. Belief Bias......................................... -27- 11. Translating Natural Language Arguments to Syllogisms. .......... -28- 12. Viewing Legal Disputes as Syllogisms. ....................... -28- C. IMPLICATION................................................. -28- 1. The Validity and Soundness of Implications. ................... -29- 2. The Five Forms of Conditional Propositions .................... -29- 3. The Material Implication. .................................. -29- 4. Modus Ponens (Affirming the Antecedent). .................... -30- 5. Modus Tollens (Denying the Consequent). ..................... -30- 6. “Not-P or Q.”............................................ -31- 7. Affirming the Consequent................................... -31- 8. Conditional Propositions Can Be Sorites. ...................... -31- 9. Attacking a Conditional Proposition. .......................... -32- 10. Disproving a Material Implication............................ -32- 11. Biconditional............................................ -32- 12. Conjunctive Conditional Propositions. ........................ -32- 13. Disjunctive Conditional Propositions. ......................... -32- 14. Other Conditionals. ....................................... -33- a. Indicative Conditionals............................... -33- b. Subjunctive Conditionals. ............................ -33- c. Counterfactual Conditionals. .......................... -34- 15. The Dilemma............................................ -35- 16. Degrees of Conditionals.................................... -35- 17. Disproving Other Conditionals............................... -36- 18. Legal Presumptions........................................ -36- D. EULER CIRCLES. ............................................. -36- E. TRUTH TABLES............................................... -37- F. LOGICAL CONNECTORS. ...................................... -39- 1. Logical Negation.......................................... -39- 2. Logical Conjunction....................................... -39- 3. Logical Disjunction........................................ -40- 4. Material Implication....................................... -42- 5. Material Equivalence. ..................................... -43- 6. Material Nonequivalence. .................................. -44- 7. Alternative Denial......................................... -44- 8. Joint Denial.............................................. -44- G. SYMBOLIC LOGIC............................................. -45- H. TAUTOLOGIES AND SELF-CONTRADICTIONS. .................. -45- I. AXIOMS...................................................... -46- J. CONSTRUCTING DEDUCTIVE ARGUMENTS IN PROPOSITIONAL LOGIC. .................................................................. -46- -ii- 1. Direct Deductive Arguments. ............................... -46- a. Rules of Inference................................... -46- b. Rules of Replacement ............................... -48- c. Logic Arguments................................... -49- 2. Conditional Proof......................................... -49- 3. Indirect Proof. ........................................... -49- K. FALLACIES OF DEDUCTION.................................... -49- 1. The Fallacy of Affirming the Consequent. ..................... -50- 2. False Dichotomy.......................................... -51- 3. Inconsistency. ........................................... -51- 4. Non Sequitur ............................................ -51- 5. Slippery Slope............................................ -51- 6. Begging the Question...................................... -52- 7. Circular Reasoning ....................................... -52- 8. Changing the Premises..................................... -52- L. PARADOXES. ................................................. -53- 1. The Sorites Paradox. ...................................... -53- 2. The Liar Paradox. ........................................ -53- 3. Eubulides’s Paradox. ...................................... -54- 4. Socrates’ Paradox. ........................................ -54- 5. Smasandache Paradox. ..................................... -54- 6. The Catalog Paradox...................................... -54- 7. The Omnipotent God Paradox. .............................. -54- 8. The Surprise Test Paradox. ................................. -54- 9. The Grandfather Paradox. .................................. -55- 10. The Envelope Paradox. .................................... -55- 11. Orsinger’s Paradox. ....................................... -56- 12. A Famous Scientific Paradox. ............................... -56- 13. A Famous Political Paradox. ................................ -56- 14. Avoiding “All” or “None.” ................................. -58- M. THE IMPORTANCE OF RELEVANCE. ............................ -58- N. THE PROBLEMS OF CONDITIONALS. ........................... -59- 1. Problems with the Material Conditional........................ -59- 2. Problems With the Indicative Conditional...................... -60- 3. Problems With Subjunctive Conditionals....................... -60- 4. Problems With Counterfactual Conditionals. ................... -61- O. “SOME” and “ALL.”............................................ -61- P. PROBABILITIES............................................... -61- Q. TRANSLATING ENGLISH TO DEDUCTIVE LOGIC................. -62- 1. Negation. ............................................... -62- 2. Logical Conjunction....................................... -62- 3. Logical Disjunction.......................................