1. Chapter 3: MAKING SENSE OF ARGUMENTS
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.
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 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
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 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: Hypothetical has two parts
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