Transcript LOGIC 101: Introduction to Persuasive Methods

LOGIC 101: Introduction to
Persuasive Methods
What is a PREMISE and
how does it relate to a
CONCLUSION?
How could a FALSE
PREMISE lead to an
INVALID CONCLUSION?
Errors in LOGIC (Logical
Fallacies)
Red Herring
 The name of this fallacy comes from the
sport of fox hunting in which a dried,
smoked herring, which is red in color, is
dragged across the trail of the fox to
throw the hounds off the scent.
Thus, a "red herring"
argument is one which
distracts the audience from
the issue by introducing
something that is irrelevant.
introduces an irrelevant
point into an argument. He
may think (or he may want
us to think) it proves his side,
but it really doesn’t.
Here’s how it works:
Topic A is under discussion.
Topic B is introduced under the guise of
being relevant to topic A (when topic B is
actually not relevant to topic A).
Topic A is abandoned.
Examples of Red Herring:
Grizzly bears can’t be dangerous – they look
so cute.
You shouldn’t give us homework - it’s
raining and its supposed to be a bad storm!
"I think there is great merit in making the
requirements stricter for the graduate
students. I recommend that you support it,
too. After all, we are in a budget crisis and
we do not want our salaries affected."
Slippery Slope
 Argues that A will cause B, then C, D,
E….. all the way downhill to Z!
 Much of it is based on assumption.
Examples of slippery slope
arguments:
 Kids start out using the internet to do their
schoolwork, but it isn’t long before they start surfing
the net and chatting with perverts wearing leather
and using fake names in chat rooms. Next thing you
know, they start meeting pedophiles in malls and
end up dead. So, I don’t let my kids use the internet.
 Today its gay marriage, and tomorrow they’ll be
asking to legalize polygamy. Then marriage
between family members. What about to pets? After
all, animals have rights too, don’t they?
One more slippery slope…
 “If you give us homework, then I’m going to
have to stay up late. If I do that, I’m probably
going to get sick just like my little sister who
has a fever of 106 and is throwing up
everything. Then , I’m going to do horrible at
baseball tryouts, and I’ll never make Varsity.
So, I’ll have to forget the major leagues,
abandon my childhood dreams, and resign
myself to collecting cans for a living. But, if
you want to go ahead and give us homework, I
can’t stop you; you’re the teacher.”
Oversimplification
 Arguer claims that A causes B to occur,
when in fact several causes may be
responsible for event B to occur.
Examples of
oversimplification:
Only 72% of high school kids graduate from
college in our town. The teachers are just
not doing their jobs!
Over the past ten years, the crime rate has
been rising, and so has the number of illegal
immigrants crossing the border. As soon as
they come over, that’s when the problems
start.
Signal of oversimplification:
The arguer makes a complex problem sound
simple and easy to fix
Either/or reasoning
 The arguer illegitimately claims that there are only 2
alternatives in a situation when there are actually more
Examples of either/or
reasoning:
“Eat your vegetables. You don’t want to die
of malnourishment, do you?”
“Are you going to stay in college, or are you
going to scrape around forever looking for a
good job?” (It is possible to get a good job
and not go to college)
 “We either fight back and invade Iraq, or
we let the terrorists have their way.”
Circular logic
The argument claims to prove a conclusion
BUT
The conclusion has already been assumed as
a premise
Examples of circular logic:
McDonald’s is the best place to eat because
so many people eat there and so many people
don’t eat at a restaurant if its not the best
place to eat.
Bush on unity of the Republican party: “I
am confident there will be (unity). I’m
confident people are coming together. And
the reason I believe this is because our party
is united.”
More Examples of circular
logic
 Senator Flummox on gay marriage: “I oppose gay
marriage because two people of the same sex should
not be entitled to the same privileges that married
couples are entitled to.”
 Bush on whether he will run for president: “There is
a lot of speculation and I guess there is going to
continue to be a lot of speculation until the
speculation ends.” (Austin American-Statesman,
October 18, 1998).
Signals of circular logic:
 An arguer keeps repeating a claim as if he has
given evidence to support a conclusion.
 This is actually a ploy to avoid giving any
justification
Begging the question:
Called “begging the question” because at the
end of an argument the careful listener still
has questions such as , “but how do you
know…?”
This kind of logic is false because the arguer
assumes part of the conclusion in one of the
premises.
Examples of begging the
question:
God exists because the Bible says so. The
Bible was written by God.
That restaurant has the best food in town,
because it has the best chef. It attracted the
best chef in town because it had the best
reputation. It got the best reputation by
serving the best food.
I am not a liar
The Bare Assertion
 Definition: to close a debate with a
simple declaration that it's over simply
because you say so.
 Example:




Son: Dad, can I have the car tonight?
Father: Nope.
Son: Why not?
Father: Because I said so.
These phrases are bare
assertions




Because I said so.
That's just the way it is.
That's all there is to it.
Trust me.
Other Examples of Bare
Assertion
 Literature. The bare assertion is common in
literature (The play Twelve Angry Men is loaded
with fallacies. Juror #3 offers the bare assertion to
another juror, number 4, when he says, "Now listen
to this man (Juror #4), he knows what he's talking
about.")
 Expository writing. Often bare assertions are given
instead of evidence or support for a point. A student
essay might read: "Though some people don't agree
that smoking causes cancer, they are wrong and
that's all there is to it."
BIAS and Persuasive
techniques
What is Bias?
Some ways evidence may
be misused in order to
persuade…
Bandwagon Appeal
(Impressing with large
numbers)
Assumes that “if everybody’s
doing it, it must be good/ right/
okay”
Examples of bandwagon
appeal:
“McDonald’s Hamburgers, billions sold”
Have you seen Spiderman III? The lines at
the theatre are a block long! It must be really
good!
Remember, everybody does
it is the opposite of thinking
for yourself.
Critical thinkers think for
themselves!
Appeal to tradition
Argues “this is how it
has been done in the
past” as a reason for
why something should
continue to be done
Irrelevant Appeals to
authority
An arguer claims he/ she is
knowledgeable enough in a subject
to make a judgment, but actually is
not.
Often used in advertising
Examples of irrelevant appeals
to authority:
Actresses selling cosmetics
An Olympic athlete selling an over-
the-counter or prescription drug
Bob Dole as spokesperson for Viagra
Appeal to Ignorance
Arguer claims something has
been proven based on a lack of
evidence disproving it.
Examples of appeals to
ignorance:
You can’t prove that other forms of life don’t
exist in the universe. Therefore, other forms
of life must exist in the universe.
And here’s a sensitive issue….
Nobody has proven that Clarence has not
been stealing churros from the concession
stand. Therefore, Clarence must be stealing
churros.