Logical FallaciesBy J. Clark with reference to D. Pogreba’s notesWikipedia, LogicallyFallacious.com, web.cn.edu

A note before we begin

• There are MANY logical fallacies.

• What follows is a small selection of the most common

• There are several sites online that list others—if you think

you’ve spotted a fallacy, you can always look these up to check what it is!

•Don’t be limited by this presentation: consider

it a basic introduction to a much broader topic.

What are logical fallacies?

According to Purdue OWL,

“Fallacies are common errors in reasoning that will undermine the logic of your argument.

Fallacies can be either illegitimate arguments or irrelevant points, and are

often identified because they lack evidence that supports their claim.”

Fallacies of Relevance

• Appeal to Ignorance is an argument that relies on the audience’s lack of knowledge about a subject. “Absence of evidence is not evidence of absence” (logicallyfallacious.com).

• Appeal to Fear is an argument that relies on frightening the audience into an emotional response.

• Appeal to Authority can be a fallacy in several ways:• the authority is not an expert in the field being

discussed

• the authority is being misrepresented

• analysis of the authority’s claim is misleading

You can’t prove that sasquatch doesn’t exist, so it must exist.

"The streets of our country are in turmoil. The universities are filled with students rebelling and rioting. Communists are seeking to destroy our country. Russia is threatening us with her might, and the Republic is in danger. Yes - danger from within and without. We need law and order! Without it our nation cannot survive."

Adolf Hitler, 1932http://www.critical-thinking.org.uk/critical-thinking/fallacies/appeal-to-fear.php

“a small masterpiece.” (Ad copy for … Se7en : Owen Gleiberman, a critic for Entertainment Weekly)

Gleiberman’s actual statement:

“The [opening] credit sequence, with its jumpy frames and near-subliminal flashes of psychoparaphernalia, is a small masterpiece of dementia.”

Fallacies of Relevance

• Appeal to Pity is a logical fallacy that relies on the speaker appealing to the sympathy of his/her audience.

• Gambler’s Fallacy is the mistaken belief that if something happens more frequently than normal during some period, then it will happen less frequently in the future.

"You must have graded my exam incorrectly. I studied very hard for weeks specifically because I knew my career depended on getting a good grade. If you give me a failing grade I'm ruined!” (Wikipedia).

Fallacies of Relevance

• Argumentam Ad Populum: There are three ways to appeal to the people:• Bandwagon: “Everybody is doing

it!”

• Patriotism: “A true American would never take that approach because their rugged individualism wouldn’t allow it.”• Emotionally charged language

• Snob: “All the best people are doing it!”

Fallacies of Inadequate Evidence

• Post Hoc Ergo Propter Hoc is a logical fallacy which states, “Since that event followed this one, that event must have been caused by this one.” Post hoc is a particularly tempting error because temporal sequence appears to be integral to causality.

• “Correlation does not imply causation.”

Fallacies of Inadequate Evidence• Hasty Generalization is an

argument in which someone makes a broad claim based on too small a sample size.

• Unrepresentative Sample

• sample is not only too small, but also biased or unrepresentative

• Fallacy of Exclusion

• evidence which would change the outcome of an inductive argument is excluded from consideration

• The service at that restaurant is great: I went there

once and my waiter was fantastic.

• “Based on a survey of 1000 American homeowners, 99% of those surveyed have two

or more automobiles worth on average $100,000 each. Therefore, Americans are very wealthy.” (logicallyfallacious.com)

• My political candidate gives 10% of his income to the

needy, goes to church every Sunday, and

volunteers one day a week at a homeless shelter. Therefore, he is honest and morally straight.• Explanation: …this same candidate gives 10% of

his income to needy prostitutes in exchange for services, goes to the bar every Sunday after church (and sometimes before), and only works at the homeless shelter to get clients for his drug dealing business.

Fallacies of Inadequate Evidence • Circular reasoning: The conclusion is

simply the premise reworded.

• Slippery Slope: Once we take the first step, the worst case scenario is sure to play out.

• Either/Or (False Dichotomy): Gives only two options, when really there are more.

• Straw person: Creates a weakened or distorted interpretation of opposing claims, then argues against those interpretations instead of the actual claims.

Fallacies of Criticism

• Genetic Fallacy is claiming that an argument is invalid because it originated from a tainted or suspect source (racial, geographic, or ethnic origins) rather than attacking the quality of the argument. Linked to ad hominem.

“Why should I listen to her argument? She comes from California, and we all know those people are flakes.” (https://web.cn.edu/kwheeler/fallacies_list.html)

Fallacies of Criticism• Ad Hominem refers to attacking

the person rather than his/her argument.

• Pooh Pooh : Dismisses an argument as unworthy of serious consideration

• Loaded Words: words that appeal to the audience’s emotions or have a highly emotional connotation.• Terrorist, Torture, Freedom, Tax Relief, No

Child Left Behind, Fascist, Investment in Public Services vs. Public Spending, Democracy