Chapter 3: MAKING SENSE OFARGUMENTS • Exploring in more depth the nature of arguments • Evaluating them • Diagramming them
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
ARGUMENTS • Inductive: to broaden out. • Intended to provide PROBABLE support
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.
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
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.
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.
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.
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?
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
COGENCY • applies to inductive arguments • When inductive arguments have true premises • Good inductive arguments are both strong and cogent
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
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?
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?
Form and Indicator words • Some examples from text pp. 74-75 and Exercise 3.2
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.
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.
IMPLIED PREMISES cont. • The Point: We need to evaluate also this implied premise. • Other examples. Page 80.
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)
IMPLIED PREMISES, cont. • 4. Premise fits author’s intent • 5. Principle of connecting unconnected terms
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)
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.
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
FORMS • Form: Modus Ponens and valid: • Affirming the antecedent. if p, then q p. therefore , q
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!
Pure Hypothetical Syllogism if p, then q if q, then r if p, then r
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.
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
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
DISJUNCTIVE SYLLOGISMS • Disjuncts: • P= O.J. will go to jail • Q= His lawyer will do a good job ….
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.
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.
DIAGRAMMING, cont. • Page 93 and on.
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
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