COMMON LOGICAL FALLACIES
Flawed Arguments
LOGICAL FALLACIES…
 Flaws
in an argument
 Often
subtle
 Learning
to recognize these will:
 Strengthen your own arguments
 Help you critique other’s arguments
HASTY GENERALIZATION

A generalization based on insufficient or
unrepresented evidence

Deaths from drug overdoses in Metropolis have
doubled over the last three years. Therefore,
more Americans than ever are dying from drug
abuse.

An environmental group illegally blocked
loggers and workers at a nuclear plant.
Therefore, environmentalists are radicals who
take the law into their own hands.
NON SEQUITUR (DOES NOT FOLLOW)

A conclusion that does not follow logically from
preceding statements. Or the train of thought jumps
the tracks at some point.

"Warming was caused by sunspots, or fluctuations in the
Earth's orbit, or volcanic eruptions. Therefore it cannot be
caused by mankind.

“If you loved me you’d buy me this car.”

“I can’t believe you don’t like The Lake House; you loved
Matrix and Keanu Reaves is in The Lake House.”
Fallacy: it does not follow that all Matrix lovers love The
Lake House; the error is that one may love Matrix in spite
of the fact that Keanu was in it (this is an Affirming The
Consequent fallacy).
FALSE ANALOGY

The assumption that because two things are alike in
some respects, they are alike in others.

Ted Stevens famously said, the Internet is a series
of tubes. You put too much in, and it overflows.
Now, this is actually a pretty good analogy: Each
network connection allows a certain number of bits
per second, like a tube allows a certain rate of fluid
flow. There's a reason network engineers refer to
their connections as pipes.
However, it's not accurate that stuff just spills out
of the Internet. It's more accurate to say that the
flow turns into a trickle, as we continue the
analogy, but real-life tubes don't act this way.
“EITHER… OR” FALLACY
 The
suggestion that only two alternatives
exist when in fact there are more.

“You're either with us or against us.”

“I’m not a doctor, but your runny nose
and cough tell me that you either have a
cold or the flu.”
FALSE CAUSE (POST HOC,
COINCIDENCE VS. CAUSALITY)

The assumption that because one event follows
another, the first is the cause of the second.

Drinkers are more likely than non-drinkers to get
lung cancer, suggesting drinking causes lung cancer.
(It turns out there is a strong correlation between
consuming alcohol and developing lung cancer. The
post hoc fallacy would be asserting that alcohol
consumption causes lung cancer; the actual reason is
that people who drink more also tend to smoke, or
smoke more, than non drinkers.)
FALSE CAUSE CONTINUED

The assumption that because one event follows
another, the first is the cause of the second.

Many claim that marijuana is a “gateway drug”
because those who have smoked marijuana are more
likely than those who haven’t to go on to try other
drugs. The post hoc fallacy would be asserting that
marijuana use leads to increased use of other drugs;
the more logical explanation is that those who are
willing to try one drug are obviously also willing to
try other drugs: the cause – willingness to try or use
drugs – must necessarily exist before one tries pot;
otherwise, you wouldn’t try it in the first place.
CIRCULAR REASONING/ BEGGING
THE QUESTION

An argument in which the writer, instead of applying evidence
simply restates the point in other language.

A confused student argues: “You can’t give me a C. I’m an A
student!”
To clarify, no one is an “A student” by definition. Grades are earned
in every class and are derived from a variety of different methods.
The requirements in one class are set by the school and the
instructor, so the same class taught by a different teacher or in a
different location should yield two very different results (final
grades). Merely claiming to be an A student does not make the claim
valid.
CIRCULAR REASONING/ BEGGING
THE QUESTION

An argument in which the writer, instead of applying
evidence simply restates the point in other language.

A satisfied citizen says: “Richardson is the most
successful mayor the town has ever had because he's
the best mayor of our history.”
The second part of this sentence offers no evidence — it
simply repeats the claim that was already presented.
Don’t be fooled into believing that using the word
“because” in an argument automatically provides a valid
reason. Be sure to provide clear evidence to support your
claims, not a version of the premise (the initial statement
in an argument).
FALSE AUTHORITY
o
The person presenting the argument is an authority,
but not on the subject at hand.

Three types:
Self Proof—”Because I said so”
Spokes Person—”Because famous person says so”
Too much Credit—”Because they are good at one
thing, they know all things”

Britney Spears says that George W. Bush has got a
great plan for the economy, and so therefore I am
supporting him because I trust what she has to say.
ARGUMENT TO THE PERSON (AD
HOMINEM)

An attack on the person proposing an argument
rather than on the argument itself.

Senator Jones was a conscientious objector during the
Vietnam War, so his proposal to limit military
spending has no merit.
RED HERRING

An argument that focuses on an irrelevant issue
to detract attention from the real issue.

We start debating the evidence supporting global
warming, but you bring up the fact that believing this
theory is depressing...or that Al Gore has a big house
and flies on jets a lot.
PITY (AD MISERICORDIAM)
 Ad
Misericordiam is an appeal to accept
the truth of a conclusion out of pity for the
arguer or some third party. Either the
arguer (or someone else) is already an
object of pity, or they will become one if
the conclusion is not accepted.

If I don’t get at least a B in this course
my GPA will drop below 2.0. If that
happens I’ll lose my scholarship and
have to quit school, so I ought to get a B
in this course.
NON-DISPROOF
 One
sometimes encounters arguments
that some claim should be accepted
because they have never been disproved.
The move from ‘not disproved’ to ‘proved’
is invalid.

No one has ever proved that
Big Foot doesn’t exist, so
thus he does!
SLIPPERY SLOPE
 Claiming
that one choice or action will lead a
series of unrelated events
“The inevitable result of handgun control is
the government seizure of all guns.”
 “Why stop at $7.25 an hour? Why not raise
the minimum wage to $15 or $20 an hour?
For that matter, why not mandate the price
of housing? ... If we believe Congress has the
power to raise minimum wages, where do we
go next?”

STRAW MAN

The person attacks an argument which is
different from, and usually weaker than, the
opposition's best argument.

Setting up a fake version of something or someone
that is easy for others to not like.

Characterizing evolution, for example, as “all random
chance” is a straw man argument; it misrepresents a
complex theory that only partly rests on the
randomness of mutations that may lead to better
chances of survival.
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