Logical Fallacies

What is a Fallacy?

Fallacy (n.)

•a mistaken belief, especially one based on an unsound

argument

•a failure in reasoning that makes an argument invalid

•faulty reasoning; misleading or unsound argument

The word fallacy comes from the Latin word “fallere”,

meaning “to deceive”.

Related words:

Fallacious (adj.), fallaciously (adv.)

False, falsely, falsehood

Fail, failure

Fallible (adj.) – capable of making mistakes or being erroneous

Hasty Generalization

drawing conclusions from too little evidence and often

relying on stereotypes.

All lawyers are verbose and unethical.

I have known several politicians who were corrupt. So all

politicians are untrustworthy; whenever they speak, you

can be sure they are blowing hot air.

Sweeping Generalization

committed by applying a fair generalization, usually true,

to an exceptional case by ignoring the peculiarities of the

case.

If he can lose weight, then you can too.

That particular diet works for him, so you should be successful

with it too.

Post Hoc Ergo Propter Hoc (Coincidental Correlation)

Just because two events follow each other chronologically

does not necessarily mean that a cause and effect

relationship exists.

I forgot to read the assigned chapter last night, and we had a

pop quiz in class today!

I washed my car, so it just had to rain.

Begging the Question

Premises are passed on as being valid without supporting

evidence.

Premises are restated in the conclusion rather than proving

or disproving them.

When combined, History Majors and unmotivated English

Majors make up 30% of the student population.

President Obama is an excellent speech giver because he

delivers exceptional speeches.

False Analogy

An ambiguous comparison with more dissimilarities than

similarities that are not acknowledged or even clearly

explained.

Government is like business, so just as business must be

sensitive primarily to the bottom line, so also must

government.

Either – Or Fallacy (False Dilemma)

An oversimplification that reduces several alternatives to

merely two choices.

If the agency does not approve my proposal, they can say

goodbye forever to affordable transportation.

It’s better to be single wishing you were married, than married

wishing you were single.

Non Sequitur (in Latin, “it does not follow”)

A conclusion does not necessarily follow from the premises

upon which it is based.

If these politicians were patriotic, they would not question the

President.

All the students have high grades in their classes, so they must

be excellent writers.

Red Herring

Avoiding the main argument by diversionary tactics such

as following tangents.

I forgot to go grocery shopping for you, but I did buy you a

dozen roses because I love you.

Yes, my grades are low; however, I volunteer a lot of time to

worthy causes.

Slippery Slope (Bad Precedent)

Assuming that a proposed step will set off an

uncontrollable chain of undesirable events.

We have to stop the tuition increase! The next thing you know,

they'll be charging $40,000 per semester!

You can never give anyone a break. If you do, they'll walk all

over you.