SAGE Flex for Public Speaking

Logical

Brief: When a logical in included as part of a persuasive speech , there’s a risk of compromising the validity of the argument and undermining credibility with the audience.

Learning Objective: Identify different types of logical fallacies.

Key Terms: • : A fallacy of attacking the person making the argument or claim, rather than by addressing the substance of the argument or producing against the claim. • Ad Populum: A fallacy that concludes a must be true because many or most people believe it. • Either/Or fallacy: A fallacy in which the listener is forced to make a choice between two things that are not really related or relevant. • Hasty generalization: A fallacy of examining just one or very few examples and generalizing that to be representative of the whole class of objects or phenomena. • Loaded questions: A fallacy in which more than one question is grouped in the form of a single question, hiding the speaker’s true motivation and setting up a bad outcome for the respondent. • Non sequitur: A fallacy in which there’s an invalid argument whose conclusion does not flow from its . • Post hoc ergo propter hoc: A fallacy in which there is a false that experiencing one thing after another implies a causal relation. • : A fallacy in which the speaker intentionally or unintentionally misleads or distracts the audience from the actual issue. • : A fallacy that creates the illusion of having refuted a proposition by replacing it with a superficially similar proposition (the “straw man”) and refuting it without ever actually refuting the original proposition.

What is a Logical Fallacy?

A fallacy is a clearly identifiable error in logical reasoning used to support or refute an argument. When you include a logical fallacy as part of your persuasive speech argument, you risk compromising the validity of your argument and undermining your credibility with your audience. Your best protection against unintentionally including a logical fallacy is to be able to identify — and avoid — commonly used fallacies.

Types of Logical Fallacies

Hasty Generalization

When a speaker makes a hasty generalization, they examine just one or very few examples, generalizing that to be representative of the whole class of objects or phenomena.

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Argument: “Every person I’ve met has ten fingers, therefore, all people have ten fingers.”

Problem: Just because the speaker has only met people with ten fingers doesn’t mean all people have ten fingers.

Ad Hominem

When a speaker uses this strategy, they discredit the person making the claim, rather than by addressing the substance of the argument or producing evidence against the claim.

Argument: “What do you know about the United States? You aren’t even a citizen.”

Problem: The speaker unfairly attacks their opponent instead of focusing on their opponent’s argument.

Ad Populum

Also known as a band wagon appeal, this is an appeal to the majority or an , or a combination of the two. It occurs when a speaker concludes that something must be true because many or most people believe it.

Argument: “Everyone’s doing it.”

Problem: The speaker suggests that something that is popular is acceptable, even though that might not be the case.

Red Herring

This is an appeal that intentionally or unintentionally misleads or distracts from the actual issue.

Argument: “I think that we should make the academic requirements stricter for students. I recommend that you support this measure because we are in a budget crisis and we don’t want our salaries affected.”

Problem: Here the second sentence does not address the topic of the first sentence, instead switching the focus to a different topic.

Non Sequitur

When a speaker uses a non sequitur, they make an invalid argument whose conclusion is not supported by its premises. Non sequitur is Latin for “it does not follow.”

Argument: I hear the rain falling outside my window; therefore, the sun is not shining.

Problem: The conclusion is false because the sun can shine while it is raining.

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Post Hoc Ergo Propter Hoc

Latin for “because of this, therefore that,” this is a false inference that experiencing one thing after another implies a causal relation.

Argument: It rained just before the car died. The rain caused the car to break down.

Problem: There may be no connection between the two events.

Loaded Questions

In a , more than one question is grouped in the form of a single question, hiding the speaker’s true motivation and setting up a bad outcome for the respondent.

Argument: Have you broken your bad habits?

Problem: Either a yes or no answer is an admission of guilt.

Straw Man

A straw man creates the illusion of having refuted a proposition by replacing it with a superficially similar proposition (the “straw man”), and refuting it, without ever actually refuting the original.

Argument: Person A: “Sunny days are good.” Person B: “If all days were sunny, we’d never have rain, and without rain, we’d have famine and death. Therefore, you are wrong.”

Problem: Person B has misrepresented A’s claim by falsely suggesting that A claimed that only sunny days are good, and then B refuted the misrepresented version of the claim, rather than refuting A’s original assertion.

Either/Or Fallacy

In this case, the listener is forced to make a choice between two things that are not really related or relevant.

Argument: If you are not with us, you are against us.

Problem: The presentation of a false choice often reflects a deliberate attempt to eliminate any middle ground.

From Concept to Action

After you’ve identified your proposition, chosen your line of reasoning, and selected and organized your main and sub-points, conduct a review of your evidence for logical fallacies. Using the list above, compare your to each of the logical fallacies. Did you unintentionally use one or more of these fallacies? If so, how can you change your reasoning to eliminate the fallacies? Specifically, are you able to remove the fallacies and still make the point you’re trying to make? Perhaps you need more or different sources of evidence? Or, maybe your best choice is to start over and develop an entirely new line of reasoning with fresh support?

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OER TEXT SOURCES:

“ad hominem.” Wiktionary. https://en.wiktionary.org/wiki/ad_hominem. Accessed 17 June 2019. [CC BY-SA 3.0]

“.” Wikipedia. https://en.wikipedia.org/wiki/Faulty_generalization. Accessed 17 June 2019. [CC BY-SA 3.0]

“.” Wikipedia. https://en.wikipedia.org/wiki/Formal_fallacy. Accessed 16 June 2019. [CC BY-SA 3.0]

“Logical fallacy.” Wiktionary. https://en.wiktionary.org/wiki/logical_fallacy Accessed 7 June 2019. [CC BY-SA 3.0]

“Logical Fallacies.” Lumen Learning. https://lumen.instructure.com/courses/218897/pages/linkedtext54322. Accessed 7 June 2019. [CC BY-SA 3.0]

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