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Fallacies of Presumption,

Ambiguity, and Grammatical Analogy

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Fallacies of Presumption

Overview Key characteristic: Premises presume

what they claim to prove.

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Begging the Question:Definition

Occurs when an arguer uses some form of phraseology to conceal a key premise that may be unsupported by argument

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Begging the Question:Examples

Murder is morally wrong. This being the case, it follows that abortion is morally wrong.

Comment: Ignores the fact that the argument doesn’t prove that abortion is murder, which is the real point of controversy.

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Complex Question:Definition

Occurs when a single question that is really two (or more) question is asked and a single answer is then applied to both questions

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Complex Question:Examples

Do you still beat your wife?– Comment: However you answer this

question, it commits you to saying that you engaged in this behavior in the past.

Have you stopped cheating on exams?– Comment: Supposes that you have

cheated in the past.

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False Dichotomy:

Definition Occurs when the arguer assumes there are only two alternatives when in fact there are more than two.

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False Dichotomy:

Example Either you buy only American-made products or you don’t deserve to be called a loyal America. Yesterday you bought a new Toyota. It’s clear you don’t deserve to be called a loyal American!– Comment: The person may still be a very

loyal citizen.

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Suppressed Evidence:Definition Ignores some important piece of

evidence that:1) outweighs the presented evidence 2) entails a very different conclusion.

Difficult to detect because you must know about the details of the case.

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Suppressed Evidence:Example

Used car salesman: “This car is a great value. It’s clean and has low mileage.”– Comment: The salesman may not be

telling you that the car had been in a serious crash.

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Equivocation:Definition

Occurs when the conclusion of an argument depends on a word or phrase that is used (explicitly or implicitly) in two different senses.

Such arguments are either invalid or have a false premise.

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Equivocation:Example

Some triangles are obtuse. Whatever is obtuse is ignorant. So some triangles are ignorant.– Comment: “Obtuse” is used in two ways:

• Greater than 90 degrees• Not smart

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Amphiboly:Definition

Occurs when the arguer misinterprets a statement that is syntactically or grammatically ambiguous

and then proceeds to draw a conclusion based on this faulty interpretation.

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Amphiboly:Example

Professor Johnson said that he will give a lecture about heart failure in the biology lecture hall. It must be the case that a number of heart failures have occurred there recently.– Comment: The phrase “in the biology

lecture hall” should be placed immediately after “lecture” instead of “heart failure.”

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Composition:Definition

This fallacy occurs when the conclusion of an argument depends on the erroneous transference of an attribute from the part of something to the whole.

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Composition:Example

Each sentence in this composition is well-written. Therefore the whole essay is well-written.– Comment: It doesn’t follow from the fact

that each individual sentence is well written that the whole essay is well written.

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Division: Definition

Occurs when the conclusion of an argument depends on the erroneous transference of an attribute form a whole (or a class) onto its parts (or members).

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Division: Example

America is a wealthy country. Bill Smith is an American, therefore he is wealthy.– Comment: Even though it is true that the

country as a whole is wealthy, it doesn’t follow that each individual in the country is a wealthy individual.