LOGICAL REASONING Study Unit 5 – eLearning RPK 214

1. LOGICAL REASONING Study Unit 5 – eLearning RPK 214

2. Cannot engage in logical reasoning? Base arguments on emotion / feeling? • Poor legal arguments • Loss of cases • And if you cannot win cases... • You MUST learn logical reasoning…

3. Why? Convine your audience of your case, including your interpretation of the law Solve legal problems Test the acceptability of conclusions How? Initial assumption (premise) Interim conclusions (inferences) Final conclusion Rules of logic

4. PREMISE / STARTING ASSUMPTION MUST BE TRUE / ACCEPTABLE VALID INFERENCE / INTERIM CONCLUSION MUST BE VALID FINAL CONCLUSION MUST FOLLOW LOGICALLY FROM THE ABOVE If DOES follow: argument SOUND! If NOT follow logically: INVALID reasoning / non sequitur

5. PREMISE / STARTING ASSUMPTION MUST BE TRUE / ACCEPTABLE All men are liars Thapelo is a man VALID INFERENCE / INTERIM CONCLUSION MUST BE VALID Thapelo is a liar FINAL CONCLUSION MUST FOLLOW LOGICALLY FROM THE ABOVE • Premises = Untrue / unacceptable • BUT: Conclusion = Valid – follows logically from premises • Argument is unsound

6. PREMISE / STARTING ASSUMPTION MUST BE TRUE / ACCEPTABLE 1: Fingerprints were found on the gun 2: The fingerprints belong to Jimmy VALID INFERENCE / INTERIM CONCLUSION MUST BE VALID Jimmy’s finger touched the gun FINAL CONCLUSION MUST FOLLOW LOGICALLY FROM THE ABOVE • Premises = True / acceptable • Conclusion = Valid – follows logically from premises • Argument is sound

7. PREMISE / STARTING ASSUMPTION MUST BE TRUE / ACCEPTABLE 1: Fingerprints were found on the gun 2: The fingerprints belong to Jimmy VALID INFERENCE / INTERIM CONCLUSION MUST BE VALID Jimmy shot the victim FINAL CONCLUSION MUST FOLLOW LOGICALLY FROM THE ABOVE ?

8. PREMISE / STARTING ASSUMPTION MUST BE TRUE / ACCEPTABLE 1: Fingerprints were found on the gun 2: The fingerprints belong to Jimmy VALID INFERENCE / INTERIM CONCLUSION MUST BE VALID Jimmy may have shot the victim FINAL CONCLUSION MUST FOLLOW LOGICALLY FROM THE ABOVE • Premises = True / acceptable • Conclusion = Valid – follows logically from premises • Argument is sound

9. CONCLUSIVE INFERENCE Jimmy touched the weapon PROBABILITY INFERENCE Jimmy shot the victim vs DEDUCTIVE REASONING INDUCTIVE REASONING

10. DEDUCTIVE INDUCTIVE • PROBABLE INFERENCES • The higher the PROBABILITY, the more persuasive the argument • CONCLUSIVE INFERENCES • Premise = TRUE • Inference = ALSO TRUE • Argument = VALID (an argument is valid if conclusions follows premises) Syllogism

11. DEDUCTIVE LOGIC: THE SYLLOGISM PREMISE REASONING CONCLUSION PREMISE 1: JOHN COMMITTED FRAUD PREMISE 2: PEOPLE WHO COMMIT FRAUD ARE INTELLIGENT CONCLUSION: JOHN IS INTELLIGENT PROCESS OF REASONING / INFERENCE

12. DEDUCTIVE LOGIC (cont.) IF... PREMISES = True / acceptable PROCESS OF REASONING = Valid • Final conclusions MUST BE ACCEPTED • Argument is 100% concusive

13. BUT... Practice of law... Premises & inferences cannot always be proven to be 100% conclusive

14. INDUCTIVE LOGIC Argument made using inductive reasoning Prove argument by relying on different starting premises to prove argument = PROBABLY true  Proven on balance of probabilities < persuasive than deductive reasoning > persuasive than nothing!  degree of probability,  persuasive effect

15. INDUCTIVE LOGIC (cont.) PREMISE 1: A group of 30 armed men is gathered outside the courtroom PREMISE 2: Many members of the group are threatening to kill Bill Conclusion: It is, therefore, PROBABLEthat Bill’s life will be in danger if he is released on bail

16. ATTACKING REASONING PREMISE  False / unacceptable PROCESS OF REASONING / inferences drawn…flawed (Logical fallacy – causative / preconceptions / Tautologous) Final conclusion does not follow series of inferences (non sequitur)

17. ATTACKING REASONING (cont.) If you argue deductively & your opponent refuses to accept your premises... Switch to inductive reasoning... If fail: opponent must prove his assertions

18. ATTACKING REASONING (cont.) When is premises true / accepted? EVIDENCE! Logical fallacies– When the evidence fails us Causal fallacy Preconceived ideas Appealing to authority Tautologous arguments

19. ATTACKING REASONING (cont.) DISTORTION OF EVIDENCE When receiving info always search for distortions in evidence Omitting, understating, overemphasising facts ‘Surely’, ‘clearly’, ‘obviously’  substitute real evidence Improper juxtaposition  creates unfair impressions Different interpretations of same evidence

20. ATTACKING REASONING (cont.) IMORTANCE OF DEFINITIONS Not understanding the correct meaning of words / concepts  fuzzy thinking & fuzzy writing Using words without understanding meaning properly  opportunity for the opposition to attack reasoning on premise Understanding words & concepts will allow YOU to attack opposition’s premises

21. Remember to complete class exercise 8…