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.