Argument/reasoning/logic??

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• an argument is a claim or series of claims supported by evidence through reasoning
• reasoning is drawing of a conclusion based on evidence and steps in thinking
• logic is a formal structure for reasoning

Types of Reasoning

• deduction (general to specific)
• induction (specific to general)
• abduction (inference to the best explanation, often by elimination)
• analogical (similarity)

Structure of Reasoning

Deductive

• Reasoning from the general premises to specific conclusion.
• For example: the syllogism, “Penguins are flightless birds; Bob is a penguin; thus, Bob is a bird that cannot fly.”
• If premises are true and reasoning is valid, the conclusion is sound and definitely true.

Many everyday arguments leave premises unsaid (enthymeme)

Syllogism: formal deduction

an argument that consists of a major premise, a minor premise, and a conclusion drawn from those premises (Gunn 2017, loc. 467)

Induction

• Reasoning from the specific to the general.
• For example: Both Canada and Denmark have socialized medicine. They both also have high taxes. Therefore, if the US adopts socialized medicine our taxes will be increased. (Gunn 2017, loc. 466)
• If premises are true and reasoning is strong, the conclusion is coherent and probably true.

Abduction

• Reasoning by elimination.
• For example: If parents have brown eyes and their three children have hazel eyes and we eliminate infidelity, it’s likely the parents are recessive hazel.
• If eliminations are valid, the inference is plausible.

Induction & abduction

Analogical

• Reasoning from similarity (can have elements of induction and abduction)
• For example: learning a musical instrument is like learning a new language, requiring practice and immersion.
• If the similarity is relevant and strong, the analogy is plausible.

Quiz

deductive, inductive, abductive, analogical?

Bad vegetables?

Ad Hominem

a fallacy that attacks the person rather than dealing with the real issue in dispute (Tucker 2018, p. 314)

example?

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“Climate change is not true. It is supported by Congressman Jones, who was convicted of fraud last year.”

False cause

A correlation is used to imply causation.

example?

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“Dinosaurs ate vegetables and went extinct; eating vegetables will kill us.”

Bandwagon / Ad Populum (“To the People”)

a fallacy that assumes that because something is popular, it is therefore good, correct, or desirable (Tucker 2018, p. 313)

example?

. . .

“Four out of five dentists would recommend chewing Cheesit gum!”

(also an “appeal to authority” fallacy)

Either-Or Fallacy / False dichotomy

a fallacy that forces listeners to choose between two alternatives when more than two alternatives exist (Tucker 2018, p. 313)

example?

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“You can either have a successful career or be a good parent.”

Non Sequitur

the conclusion does not follow from its premise (Tucker 2018, p. 312)

example?

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“All people are mortal; Socrates is a person; therefore, Socrates cannot dance.”

Begging the question

Circular reasoning wherein an argument’s premises assume the truth of the conclusion instead of supporting it. (Also known as “assuming the conclusion.”)

example?

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“Marijuana should remain illegal because it’s a dangerous illegal drug.”

Red-Herring

creating a diversion or introducing an irrelevant point to distract someone or get someone off the subject of the argument (Tucker 2018, p. 314)

example?

. . .

(also false dichotomy)

Slippery Slope

something bad or undesirable will inevitably happen under a debated proposal

example?

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“If we legalize marijuana, people will start using harder drugs, leading to widespread addiction and the collapse of society.”

Straw-man

a fallacy that shows only the weaker side of an opponent’s argument in order to more easily tear it down (Tucker 2018, p. 311)

example?

. . .

We need stronger regulations on industrial emissions.

That will shut down all factories and destroy the economy!

Wrap up

Find a “live” example of a fallacy on the web.

Which fallacy?

Google “Recognizing Fallacies Exercises”, review their fallacy, and complete quiz.

• Hasty generalization
• False cause
• False analogy
• Ad hominem
• Either-or
• Bandwagon

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