Logical Fallacies - Riverdale High School

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What is a fallacy?
 A fallacy
 May
 In
is an error in reason
be accidental or intentional
arguments or propaganda, they are
often used to persuade
There are various types of fallacies:
Appeal to fear
 Personal attack (Ad hominem)
 False dilemma
 False analogy
 Slippery Slope
 Non sequitur (should sound familiar)
 False authority
 Red Herring
Appeal to fear (Scare tactics)
Creates fear in people as evidence to
support a claim
 Examples:
 "If you continue to drink, you will die
early as your father did."
 "If you cannot graduate from high
school, you will live in poverty for the
rest of your life."
Personal attack (Ad hominem)
Involves insulting or
belittling one's opponent
in order to attack his
claim or invalidate his
attacks the person and
not the issue
Personal attack (Ad hominem)
"You can't believe John when he says the
proposed policy would help the economy. He
doesn't even have a job."
"Candidate Jane's proposal about zoning is
ridiculous. She was caught cheating on her taxes
in 2003."
False dilemma
A reasoner who unfairly presents too few choices
and then implies that a choice must be made
among this short menu of choices commits the
false dilemma fallacy, as does the person who
accepts this faulty reasoning.
In other words…. limits the possible choices to
avoid consideration of another choice
False dilemma
Either the eyewitness saw an alien spacecraft or
he's a liar. Perhaps he's simply mistaken.
"It wasn't medicine that cured Ms. X, so it must
have been a miracle."
False analogy
When reasoning by analogy, the fallacy occurs
when the analogy is irrelevant or very weak or
when there is a more relevant disanalogy
A school is not so different from a business. It
needs a clear competitive strategy that will lead to
profitable growth.
 People are like dogs. They respond best to clear
Slippery Slope
Someone claims that a first step
(in a chain of causes and
effects, or a chain of reasoning)
will probably lead to a second
step that in turn will probably
lead to another step and so on
until a final step ends in trouble
If the likelihood of the trouble
occurring is exaggerated, the
slippery slope fallacy is
Slippery Slope
If we pass laws against fully-automatic weapons, then
it won't be long before we pass laws on all weapons,
and then we will begin to restrict other rights, and
finally we will end up living in a communist state.
Thus, we should not ban fully-automatic weapons.
You should never gamble. Once you start gambling
you find it hard to stop. Soon you are spending all
your money on gambling, and eventually you will turn
to crime to support your earnings.
Non sequitur (should sound familiar)
When a conclusion is supported only
by extremely weak reasons or by
irrelevant reasons
Example: Nuclear disarmament is a
risk, but everything in life involves a
risk. Every time you drive in a car you
are taking a risk. If you’re willing to
drive in a car, you should be willing to
have disarmament.
False authority
Fallacious whenever the
authority appealed to is not
really an authority on subject
“Name dropping”
Example: "We should
abolish the death penalty.
Many respected people,
such as Snooki, have
publicly stated their
opposition to it."
Red Herring
A red herring is a smelly fish
that would distract even a
 It is also a digression that
leads the reasoner off the
track of considering only
relevant information.
 Basically a distracter
Red Herring Examples
I know your car isn't working right. But,
if you had gone to the store one day
earlier, you'd not be having problems.
I know I forgot to deposit the check into
the bank yesterday. But, nothing I do
pleases you.