Logic and
Critical Thinking
Philosophy 4
Gale Justin
The objectives of today’s class are:
uTo
review how to evaluate the strength of an argument.
uTo
learn how to recognize some common fallacies in argument.
To criticize an argument, you must:
uIdentify
the conclusion of the argument.
uIdentify
the reasons given for the conclusion (i.e. the premisses of the argument).
uState
a reason (or reasons) why the reason supporting the conclusion is not a strong
reason.
When you evaluate an argument, you can make two kinds of
criticisms of the argument.
uThe
content of the premisses of the argument can be criticized. This kind of evaluation is called a content
criticism.
uThe
relationship between the premisses and the conclusion can be criticized. This kind of criticism is called a formal
criticism.
To make a content criticism:
uYou
give some reason for thinking that one or more of the premisses of the argument
is false.
uFor
example, “The oldest rule in my rule book, which is rule number 41, states that
anyone over 5 feet tall should leave the courtroom immediately. You Alice, are over 5 feet tall. Therefore, the oldest rule in my rule book
implies that you (Alice) should leave the courtroom immediately.” What reason is there for thinking that one of
the premisses of this argument is false?
To make a formal criticism:
uYou
give some reason for thinking that the relationship between the premisses and
the conclusion does not show that the conclusion is true.
uThe
premiss-conclusion relationship can be criticized for the following reasons.
Reasons for making a formal criticism:
uThe
cases mentioned in the premisses are relevantly different from the case
mentioned in the conclusion.
uAn
inference about the future based on the past where background information makes
the inference unlikely.
uThe
case mentioned in the premiss is a single case (or an unusual case) the
conclusion is about the majority (or all) cases (or usual cases).
Examples:
uWe
do not allow the sale of drugs on campus.
So we should not allow the sale of soft drinks on campus.
uWe
have never had a female president. So it
is unlikely that we will ever have a female president.
uGrant was an alcoholic and a great general. So any general who is an alcoholic is a great
general.
Chapter 2: Fallacies
Focuses on common mistakes that people make when they
give or criticize arguments.
Our text defines a fallacy as:
A defective argument.
These defects are so common that they have been given names.
The Fallacies that our text stresses include:
See list of Fallacies.
Fallacies occur:
generally under the following circumstances:
a. When
a person does not fully understand his/her conversational partners point of
view.
b. When
a person wants to gain some advantage by using inaccurate language.
Here are in my opinion some more interesting kinds of
fallacies, which fall into two categories:
Constructive fallacies/mistakes occur when people give an
argument.
Critical fallacies/mistakes occur when people criticize
an argument.
Here are some constructive fallacies, which occur when
people give an argument.
Loaded Descriptions:
Descriptions of key elements of the support are not
impartially stated. The descriptions are
“loaded” in favor of one side such that accepting the description is tantamount
to accepting the conclusion.
For example, a politician might characterize opponents of
the Republican plan to privatize social security as special interest
groups. The term “special interest
groups” is not objective or accurate. It
is emotionally colored, since there are lots of ordinary, non-union, members of
the
.
Other examples of loaded descriptions include:
“Girlie men,” “war monger,” “flip-flopper,” “tree-hugger.”
When you disagree with someone about an issue, you should (rationally speaking)
give a neutral and objective description, not a biased, over-simplified,
emotionally colored description.
Politicians commonly use loaded descriptions to gain a
political advantage. But the average
citizen may also uses them when they don’t take the time to understand the
other person’s point of view. So we hear
about “animal lovers,” “family wreckers,” “pot heads,” “easy women,” “dumb
blonds,” “hard hats,” “nit pickers,” “bean counters,” etc.
Another Example:
“Those nurses who are lobbying for a lower patient-nurse
ratio are making a fuss over nothing.”
When you disagree with someone about an issue, you should
(rationally speaking) give a neutral and objective description, not a biased,
over-simplified, emotionally colored description.
Revision of the previous example:
“Those nurses who are lobbying for a lower patient-nurse
ratio are caring for 10 patients a day.
This is only a little over twice what a parent of four children has to
deal with 24 hours a day.”
False Dilemma:
In this form of reasoning the reasoner presents only two
alternatives when there are in fact other choices.
Examples of False Dilemma:
1. Would you prefer to be operated on by the
best-qualified doctor or by an incompetent one?
2. Do you want a fire-fighter who can’t carry you out of
a building or one that is the strongest available?
3. Either you
subscribe to Bush’s moral convictions or you have no moral convictions at all.
In each of these cases, the reaasoner is presenting false
alternatives. The only options are not
either the best or the worst or being a born again Christian and being without
any morals at all. Most qualified people
and most moral people fall somewhere in between the proposed options.
Begging the Question:
A person uses as support for a conclusion something that
no one would accept unless they already accepted the conclusion.
Example of Begging the Question:
Abortion is murder, so it should be outlawed.
But no one who supports abortion would accept the claim
that it is murder. To characterize
abortion as murder is to assume what you are trying to prove.
The same point can made about characterizing abortion as
the killing of innocent children. This way of characterizing the fetus is
itself controversial.
Revision of the previous example:
Life is sacred.
The practice of abortion has a tendency to lower the value of life. So
it should be outlawed.
Another example of Begging the Question:
Lies are always immoral.
Even in extreme circumstances a lie is still a lie. And to lie is to act contrary to ethical
principles.
Slippery Slope:
A person claims that a first step will ultimately lead to
a state which most people would regard as big trouble. If the likelihood of the trouble occurring is
exaggerated, the slippery slope fallacy is committed.
EXAMPLES:
If one person gets up during class to go to the bathroom,
eventually everyone will get up to use the restroom and no one will be in
class.
Another example of Slippery Slope:
All Americans should be against laws permitting gay marriage. If that kind of thing is allowed, then before
you know it anything goes: bestiality,
prostitution, illegal drug use, violence, and ultimately the destruction of our
society.
Appeal to Ignorance:
When the issue is controversial, rather than familiar,
and you are not an objective authority, you cannot offer as a reason for your position either the fact that there is
nothing wrong with it or the fact that there is no evidence for the opposed
position. You must try to find a
positive reason for your position, a reason that works for the other person,
since from the other person’s point of view your judgment is not entirely objective.
For example:
It is not correct to argue:
To a friend: “There
is no reason why I cannot smoke anything that I want to. So I should be able to
smoke marijuana.”
To support your position, you could argue:
An adult should have the right to choose how to behave so
long as his/her behavior does not interfere with the behavior of other
people. Hence, an adult should have the
right to smoke marijuana in the privacy of his/her home.
Another example:
Of course the war in
The problem here is that there is a lack of
evidence. The lack of evidence proves
nothing. It simply reveals our ignorance
about something. So if there is no
evidence to support one side of an issue, you cannot infer that the opposing
side is correct.
Another example:
There’s no evidence that any of the kitchen workers at
Wendy’s lost a finger. So the woman must
have planted it.
Exercise:
People should only buy small cars because large gas
guzzlers, like SUV’s, irresponsibly squander natural resources.
(a) Identify the loaded terms. (b) Rewrite the argument
in a way that does not favor the freight side of the issue.
Exercise:
Either you get a college degree or you will find yourself
with no marketable skills.
(a) Explain why the above quotation offers a false
dilemma. (b) Rephrase it as an argument that does not depend on a false
dilemma.
Now here are some Critical Fallacies:
Recall that these are fallacies that arise when you
criticize an argument rather than give one.
Straw Man:
Instead of making an argument as strong as possible
before criticizing it, you make it weak and easy to criticize it by giving it
by stating it in an oversimplified or an uncharitable form..
Example of Straw Man:
Me: Society will benefit
from having a broader spectrum of people in the positions to which more
advantages attach. Preferential
treatment programs enhance the likelihood of
such diversity in higher level positions. Therefore, we should adopt programs of
preferential treatment.
Example of Straw Man:
Rephrased:
Professor Justin is advocating giving preference to unqualfied people in
order to have more minorities in positions of power in our society.
Another example of Straw Man:
Senator Kennedy is opposed to the military spending bill,
saying that it’s too costly. Why does he
always want to slash everything to the bone?
He wants a pint-sized military that couldn’t fight off a crazed band of
terrorists, let along a rogue nation.
Hasty Generalization:
My debating partner draws an unqualified conclusion from
my premiss that is qualified. I argue
that we should on some occasions give preference to a minority person who meets
the normal qualifications for the job. My partner draws the inference that we
would be hiring unqualified people for every position and, therefore, the
practice would cause the business to fail.
Another example of Hasty Generalization:
The French are really snobby and rude. Remember those two high-and-mighty guys with
really bad manners? They’re French. I rest my case.
Homework:
On pp. 63 – 64 of your text identify the fallacy
committed by each of the following passages. (Note each passage commits only 1
fallacy. Moreover, each fallacy commits
one of the fallacies on your list of fallacies.
Do #s 1, 2, 3, 5, 8;
and, on pg. 87 do #’s 1, 3, 4, and 9.
Do also the fallacy exercise sheet and the evaluating
argument excise sheet. No class on March
19th.