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  1. Chapter 3: MAKING SENSE OFARGUMENTS • Exploring in more depth the nature of arguments • Evaluating them • Diagramming them

  2. ARGUMENT BASICS • Arguments allow us to support claims and to evaluate claims • 2 Forms: Deductive and Inductive • Deductive: to deduce means to draw out or distill • Intended to provide CONCLUSIVE support

  3. ARGUMENTS • Inductive: to broaden out. • Intended to provide PROBABLE support

  4. More on Deductive Arguments • Validity: if premises are true, then conclusion must be true. • Guaranteed conclusion (All or nothing) • Necessity • Truth Preserving: The conclusion cannot be false if the premises are true.

  5. Examples: Deductive • Socrates is a man. All men are mortal. Therefore, Socrates is mortal • Example in invalid argument with same form: • All dogs are mammals. All cows are mammals. Therefore, all dogs are cows

  6. Examples: Deductive • If Socrates is a man, then he is mortal. Socrates is a man. Therefore, Socrates is mortal Invalid form: • If Socrates has horns, he is mortal. He is mortal. Therefore he has horns.

  7. INDUCTIVE ARGUMENTS • probable logical support • Strong and Weak • Structure of Inductive Arguments cannot guarantee that if the premises are true the conclusion must also be true. • Implies: premises can be true, and conclusion still questionable.

  8. Slippage/free play: • Conclusion always goes a bit beyond what is contained in premises. • The idea of Gap: • It is always possible to go to another conclusion, sometimes even an opposite one with weak arguments.

  9. Degrees of Strength • varying from weak, to modestly weak, to modestly strong and to strong • eg. Most dogs have fleas My dog Bowser, therefore, probably has fleas. What about the premise here?

  10. SOUNDNESS: • Applied to deductive arguments. When arguments have true premises and true conclusions (to be sure). • It is possible to have valid deductive arguments while having false premises and false conclusions. • Page 69-70 in text

  11. COGENCY • applies to inductive arguments • When inductive arguments have true premises • Good inductive arguments are both strong and cogent

  12. JUDGING AND EVALUATING ARGUMENTS • Skills to start • 1. identifying form: inductive or deductive • Mixed Arguments • 2. Determining or judging whether it is cogent or sound

  13. A STRATEGY: 4 Steps • 1. Identify conclusion and premises. Even number them. • 2. Test of deduction: Do the premises seem to make the conclusion necessary? LOOK TO FORM! • 3. Test of Induction: What degree of probability do the premises confer on the conclusion?

  14. STRATEGY Cont. • Are the premises true (cogency)? If no, go to 4. • 4. Test of Invalidity and weakness: Only 2 options left. • Does the argument intend to offer conclusive or probable support but fail to do so?

  15. Form and Indicator words • Some examples from text pp. 74-75 and Exercise 3.2

  16. FINDING MISSING OR IMPLIES PREMISES • What are they? Premises essential to the argument that are left unstated or unspoken • i.e. Socrates in the deductive argument • Assumes there was someone named Socrates, etc.

  17. Implied Premises, con. • Text: P. 79 • “Handguns are rare in Canada, but the availability of shotguns and rifles poses a risk of death and injury. Shotguns and rifles should be banned, too!” • Implied premise: Anything or most anything that poses a risk of death or injury should be banned.

  18. IMPLIED PREMISES cont. • The Point: We need to evaluate also this implied premise. • Other examples. Page 80.

  19. SOME IMPORTANT HINTS • 1. It is best always to identify missing premises. We cannot take them for granted. • 2. Formulate the implied premise with as much charity as possible. • 3. Premise should be plausible (or, as strong as possible)

  20. IMPLIED PREMISES, cont. • 4. Premise fits author’s intent • 5. Principle of connecting unconnected terms

  21. FULL EVALUATION: • Degree of controversy of both given premises and implied premises. • What further support do they require? • P. 81-82 example • Exercise 3.4 (I: 1, 3, 6, 9)

  22. ARGUMENT PATTERNS • Hypothetical syllogism • E.g. If the job is worth doing, then it’s worth doing well. The job is worth doing. Therefore, it is worth doing well.

  23. ARGUMENT PATTERNS • 2 Patterns to start: • 1. Hypothetical • 2. Disjunctive • 3. Categorical • Hypothetical has two parts • Antecedent: the job is worth doing • Consequent: the job is worth doing well. • Antecedent: p • Consequent: q

  24. FORMS • Form: Modus Ponens and valid: • Affirming the antecedent. if p, then q p. therefore , q

  25. FORMS Another valid Form: Modus Tollens E.G: If Austin is happy, then Barb is happy Barb is not happy. Therefore, Austin is not happy. Denying the consequent!

  26. Pure Hypothetical Syllogism if p, then q if q, then r if p, then r

  27. Pure Hypothetical Syllogism: If polar bears thrive, then they eat more seals. If they eat more seals, they will gain more weight. Therefore, If polar bears thrive, they will gain more weight.

  28. INVALID FORMS • eg. If Dogbert commits one more fallacy, I will eat my hat. Dogbert did not commit one more fallacy. Therefore, I did not eat my hat. p. 89 in Review Notes

  29. DISJUNCTIVE SYLLOGISMS • eg. Either O.J. will go to jail, or his lawyer will do a good job to get him off. O.J. did not go to jail. Therefore, his lawyer did a good job to get him off. • FORM: • either p or q not p q

  30. DISJUNCTIVE SYLLOGISMS • Disjuncts: • P= O.J. will go to jail • Q= His lawyer will do a good job ….

  31. DIAGRAMMING ARGUMENTS • 1. Underline indicator words, if present • 2. Number all statements (or propositions) in sequential order. • 3. Break down compound statements (statements using connectives ‘and,’ ‘but,’ ‘or’) into single statements.

  32. DIAGRAMMING ARGUMENTS • Caution sometimes ‘or’ should not be broken down. • 4. Cross out extraneous or irrelevant statements. None-premises or conclusions. Preludes, redundant statements, or background information.

  33. DIAGRAMMING, cont. • Page 93 and on.

  34. Pulling it all together • 1. Diagram argument • Implies identifying premises, conclusions, etc. • 2. Determine type based on form • 3. Evaluate: • For deductive determine whether valid or not, sound or not • For non-deductive, determine degree of strength and cogency • Borderline cases: mixed forms

  35. Pulling it all together, cont. • Full Evaluation of Non-deductive • Measure gap between premises and conclusion • Identify implied premises and judge truth • Ask whether other premises need to be added to support implied and explicit premises • Determine whether we can get from given premises to other or opposite conclusions