COMMON LOGICAL FALLACIESFlawed Arguments

LOGICAL FALLACIES…

Flaws in an argument

Often subtle

Learning to recognize these will:Strengthen your own argumentsHelp 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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