Chapter 3: MAKING SENSE OFARGUMENTS

Exploring in more depth the nature of arguments

Evaluating themDiagramming them

ARGUMENT BASICS

Arguments allow us to support claims and to evaluate claims

2 Forms: Deductive and InductiveDeductive: to deduce means to draw

out or distillIntended 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)

NecessityTruth Preserving: The conclusion

cannot be false if the premises are true.

Examples: Deductive

Socrates is a man. All men are mortal. Therefore, Socrates is mortalExample 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 supportStrong and WeakStructure of Inductive Argumentscannot guarantee that if the premisesare true the conclusion must also betrue.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 argumentsWhen inductive arguments have true

premisesGood inductive arguments are both

strong and cogent

JUDGING AND EVALUATING ARGUMENTS

Skills to start

1. identifying form: inductive or deductive

Mixed Arguments2. 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

unspokeni.e. Socrates in the deductive

argumentAssumes 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 exampleExercise 3.4 (I: 1, 3, 6, 9)

ARGUMENT PATTERNS

Hypothetical syllogismE.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 hislawyer will do a good job to get himoff.O.J. did not go to jail.Therefore, his lawyer did a good job toget him off. FORM: either p or qnot pq

DISJUNCTIVE SYLLOGISMS

Disjuncts:P= O.J. will go to jailQ= 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-deductiveMeasure gap between premises and

conclusion Identify implied premises and judge truthAsk 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