Reason & Argument
Lecture 5
Coursework Assignment
Will be released automatically on MOLE, first thing on
Monday the 12th of November.
Consists of two sections - you must do BOTH.
One section requires you to identify a particular
type of argument in a real-world source (e.g. a
newspaper or web-site)
The other section requires you to construct
arguments of your own to meet various criteria.
Lecture Synopsis
•
POP QUIZ!
•
How much do you really know about what we’ve
learned so far?
•
This quiz should help you to consolidate your
knowledge & help you identify any gaps or
weaknesses.
What You’ve Learned
In theory you can all now do the following:
Identify an argument, identify its premises & conclusion.
Reconstruct an argument, even when it is not fully explicit.
Determine whether an argument is valid and/or sound.
Identify common syllogisms & fallacies.
Argue effectively (and validly) for a ‘should’ conclusion.
Identify indexicals, predicates, vagueness, 3 types of
ambiguity, and equivocation.
Pop Quiz
Can you do it in practice?
Identifying valid arguments
Identifying tacit/implicit premises
Identifying common syllogisms/fallacies
Constructing ‘should’ arguments
Identifying & Resolving ambiguities
Real-world Scenario
Imagine you are the CEO of a large company.
You are presented with a report by your Human
Resources/Personnel division about the company’s
employees, consultants and information about the
Trade Union.
You must approve the report as containing accurate
information & valid/sound arguments.
The information in the report will be vital for various
decisions: raising/lowering pay, hiring/firing staff, etc.
Identifying valid arguments
•
“All employees have degrees, and all consultants have
degrees. So at least some employees must be
consultants.”
Argument?
Yes.
Conclusion?
‘at least some employees must be consultants.’
Valid?
No.
Identifying valid arguments
•
“All new employees have degrees, but all consultants
have degrees. Also, since 1990, none of our employees
has been a consultant.”
Argument?
No. (N.B. no premise or conclusion indicators)
Identifying valid arguments
•
“Since all our employees have degrees, and anyone who
has a degree has attended school, all our employees
must have attended school.”
Argument?
Yes.
Conclusion
‘ [So] all our employees must have attended school.’
Valid?
Yes.
Identifying valid arguments
•
“Every employee is a member of the Union. Every member
of the Union has a right to strike. So every employee must
have a right to strike.”
Argument?
Yes.
Conclusion?
‘every employee must have a right to strike.’
Valid?
Yes.
Identifying valid
arguments
•
“Not all employees work overtime. Some consultants are
part-time. But every employee who works overtime is
part-time.”
Argument?
No.
Identifying valid
arguments
•
“If employees stage a strike, then company profits
will decrease. Company profits have decreased. So
employees must be staging a strike.”
Argument?
Yes.
Conclusion?
‘employees must be staging a strike’
Valid?
No.
Tacit/Implicit Premises
What is a tacit premise?
A premise that is unstated, but which is
needed to make the argument valid.
Can you identify the tacit premises in the
following arguments from our fictional HR
report?
Tacit Premises
•
“Part-time employees have higher rates of sick
leave than full-time employees. So part-time
employees are not as dedicated to their jobs
as full-time employees.”
Tacit premise?
Employees with higher rates of sick leave
are not as dedicated to their jobs as
those with normal rates of sick leave.
Tacit Premises
•
“Employees hired on fixed term contracts
cannot join the pension scheme. So the last 8
employees hired cannot join the pension
scheme.”
Tacit premise?
The last 8 employees hired are on fixed
term contracts.
Tacit Premises
•
“If company profits increase, then our employees
must be working hard. Company profits have
increased. So our employees deserve pay rises.”
Tacit sub-conclusion?
So our employees must be working hard.
Tacit premise?
Employees who work hard deserve pay rises.
Syllogisms/Fallacies
Remember this argument?
•
“If employees stage a strike [If X], then company profits will decrease
[then Y]. Company profits have decreased [Y]. So employees must be
staging a strike. [So X]”
This argument is an example of a fallacy.
What is a fallacy?
A pattern of reasoning that is always invalid.
But which fallacy?
Affirming the consequent (If X, then Y; Y; So X)
Syllogisms/Fallacies
•“If
Union members object to the pay cut, then the
Union will lodge a complaint. The Union has not
lodged a complaint. So Union members do not object
to the pay cut.”
This is an example of a syllogism:
What is a syllogism?
A pattern of reasoning that is always valid (at
least, according to Aristotle).
Which syllogism?
Modus Tollens (If X, then Y; Not-Y; So not-X)
Syllogisms/Fallacies
•“If
all employees join the Union, then the Union will grow
stronger. If the Union grows stronger, cutting pay will be
more difficult. So if all employees join the Union, cutting pay
will be more difficult.”
Valid?
Yes.
Is it a syllogism?
Yes!
Which one?
Hypothetical Syllogism (If X, then Y; If Y, then Z; So
if X, then Z)
Syllogisms/Fallacies
“If the Union agrees to the pension deal, then we can raise
salaries. The Union does not agree to the pension deal. So
we cannot raise salaries.”
Valid?
No!
Is it a fallacy?
Yes.
Which one?
Denying the antecedent (If X, then Y; Not-X; So not-Y)
Syllogisms/Fallacies
•
“If the Union agrees, then we can raise salaries. The
Union agrees. So we can raise salaries.”
Valid?
Yes!
Which syllogism?
Modus Ponens (If X, then Y; X; So Y)
Syllogisms/Fallacies
“If all our employees join the pension fund, the fund will
collapse. The fund has collapsed. So all our employees
joined the pension fund.”
Valid?
No!
Which fallacy?
Affirming the consequent(again) (If X, then Y; Y; So X)
Constructing Should
Arguments
What are the components of a successful & valid
‘should’ argument?
Success Condition (SC)
P’s doing x will achieve y.
Optimal Means Condition (OMC)
x is the best way of P’s achieving y.
Ends-Justify-Means (EJM)
All things considered, P’s doing x and
achieving y is better than P’s not doing so.
Example
Conclusion: The company should hire more employees.
SC: Hiring more employees will increase company
profits.
OMC: Hiring more employees is the best way to
increase company profits.
EJM: All things considered, hiring more employees and
increasing company profits is better than not doing so.
(If SC, OMC, EJM, then the company should hire more
employees)
Ambiguity
Lexical
A word in the sentence has two or more meanings.
Syntactic
The sentence structure allows for two or more different interpretations of
its meaning.
Contextual
The context allows for different interpretations of the meaning of a
sentence. Examples?
Indexicals (I, he, she, them, yesterday, etc.)
Comparison Classes (healthier, smarter, better, bigger, etc.)
Quantifier Omission (all, most, some, both, one, etc.)
Ambiguities
SAFETY EXPERTS SAY SCHOOL BUS
PASSENGERS SHOULD BE BELTED
Lexical (‘belted’)
STOLEN PAINTING FOUND BY TREE
Syntactic (found beside vs. found by)
Ambiguities
MINERS REFUSE TO WORK AFTER DEATH
Syntactic (work after death)
PROSTITUTES APPEAL TO POPE
Lexical (‘appeal’: entreaty vs. attract)
KIDS MAKE NUTRITIOUS SNACKS
Lexical (‘make’)
Equivocation
What is equivocation?
The use of ambiguous words or syntax to conceal the truth
or avoid committing oneself.
•Hot
dogs are better than nothing
•Nothing
is better than steak.
•Therefore,
hot dogs are better than steak.
Where is the ambiguity?
‘nothing’: (1) no food at all vs. (2) no other food.
Equivocation
A less frivolous example:
•We
are told that discrimination is morally wrong. But we
always praise people for being discriminating in their taste
for good wine, books or friends. So if I discriminate against
women when they apply for jobs in my department, I will be
praised for it.
Lexical - ‘Discrimination’ - (1) being able to detect subtle
differences in the quality of things (2) treating people differently
on the basis of arbitrary characterisitcs (sex/gender, race,
religion, etc.)
Dealing with
Equivocation
Phase 1:
Identify the word or phrase with multiple
meanings.
Phase 2:
Eliminate the word & replace it with a phrase that
clearly expresses *one* of the meanings. Note
how the argument fails. AND/OR
Replace the word with a phrase expressing the
other meaning, and note how it still fails.
Equivocation
We are told that treating people differently on the basis of
their sex, race or religious beliefs is morally wrong. But we
always praise people for treating people like this. So if I
discriminate against women when they apply for jobs in my
department, I will be praised for it.
OR:
We are told that being able to detect subtle differences in the
quality of things is morally wrong. But we always praise
people for being able to detect subtle difference in the quality
of wine, books or friends. So if I am able to detect subtle
differences in the quality of women when they apply for jobs
in my department, I will be praised for it.