Western Logic Informal Fallacies of Presumptions & Fallacies of Ambiguity

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Western Logic Informal Fallacy: Fallacy of Ambiguity & Presumption (Philosophy)

Fallacies of Presumption

  • Fallacies of presumption occur when too much is assumed in the premises of an argument.

  • As a result, the conclusion to the premises results primarily on the pre-assumed or unwarranted assumptions or presumptions.

  • There are three kinds of such fallacies;

    • Fallacy of Accident

    • Fallacy of Complex Question

    • Fallacy of Begging the Question

Fallacy of Accident

  • Accident is a type of fallacies of Presumption, these fallacies occur when we presume too much in the premises.

  • Accident as a fallacy can be explained as when we apply the generalisation to particular instances. We think what is true for the whole, is also true for the parts.

  • For example, people of North-East India like momos. Therefore, my friend from North-East must definitely like momos.

  • Hence, in this fallacy, we move from generalisations to a particular instance.

  • Similar example would be, killing is wrong. Mercy killing is a type of killing. Therefore. Mercy killing is wrong. In other words, the general rule is misapplied to the specific or particular individual case.

  • This fallacy is an opposite of Hasty Generalisation, where we move from particulars to generalisation. As a result, hasty generalisation is also called fallacy of converse accident.

Fallacy of Complex Question

  • Complex question is a fallacy where a question is asked in such a way as it pre-supposes the truth of some proposition buried in the question.

  • For example, have you stopped beating your children? And have you stopped cheating in tests? Or have you stopped shoplifting now? Or Have you stop cheating on your wife?

Fallacy of Begging the Question

  • The circular argument fallacy is called the fallacy of begging the question.

  • It is also known as Petitio Principi.

  • It occurs when the conclusion is already stated or present in one of the premises.

  • In other words, it occurs when we argue in circles.

  • For example, “Men are better drivers than women because men have better controls of cars than women on road.”

  • Here, the conclusion, men have better controls of cars on roads than women is already given in the premise- men are better drivers than women.

  • A better driver is one who obviously will have better control of the car on the roads.

  • Hence, this argument in circular in nature.

  • This fallacy is technically valid but always worthless, nothing new comes out of it.

  • Similar example would be, the soul is immortal, the soul never dies. Therefore, the soul goes on to live for ever.

Fallacies of Ambiguity

  • Fallacies of ambiguity occur due to equivocal (more than one interpretation) use of words or phrases in the argument.

  • In other words, they occur when there are different meanings possible of the words or the phases used in the argument.

  • They are primarily categorised under five heads;

    • Fallacy of Equivocation

    • Fallacy Amphiboly

    • Fallacy of Accent

    • Fallacy of Composition

    • Fallacy of Division

Fallacy of Equivocation

  • Equivocation is one of the five fallacies of ambiguity.

  • It is a fallacy where two or more than two meaning of the same words are used in an argument.

  • Or when there is a change in the meaning of the same word which happens to be used in both the premise and the conclusion.

  • For example,

A: Who did you meet on the road? B: Nobody. A: okay, so did nobody say hi to you?

  • Here, the word nobody has two meanings.

  • Nobody as in any body and nobody as in a name.

  • Similar example would be, all trees have bark, and dogs also have bark. Therefore, all dogs are trees.

Fallacy of Amphiboly

  • Amphiboly is also a fallacy of ambiguity where words are used in a manner which leads to alternative possible meanings of the statement.

  • For example, if you take the motor out from the car, I’ll sell it to you very cheap.

  • Here, “it” could be motor or could be car.

  • Similar example would be, she watched the monkey eating a banana.

  • Here, who is eating the banana, the monkey or the girl ?

  • Hence, under the fallacy of amphiboly, the words are combined in an awkward, loose manner which leads to alternative possible meanings of a statement.

The Fallacy of Accent

  • Accent is an informal fallacy of ambiguity where a word has one meaning in the conclusion and a different meaning in the premise.

  • The difference arises dues to a change in emphasis given to the words used.

  • For example, we should not speak ill of our friends.

  • Here, when we put emphasis on word friends, it appears as such that we should not speak ill of our friends

The Fallacy of Composition

  • Composition is an informal fallacy of ambiguity where we think that, because something holds true of a group of things taken individually, it must hold true of the same things taken collectively or as a group.

  • For example, Ram, Shyam and Mohan are the best singers in my society. Therefore, it holds true that all these three together would make a great band.

  • Similar example would be A is a part of B, B has property X, Therefore, A has property X

The Fallacy of Division

  • The opposite of Composition fallacy is division.

  • In division, we think that because something holds true of a thing taken as a group or taken collectively. Therefore, it must also hold true when things are taken individually.

  • For example, Stars is the name of the best band in my society. The singers of the band are Ram, Shyam and Mohan. Therefore, all these three boys taken individually are the best singers.

  • Similar example would be, each brick in the building weighs less than a pound. Therefore, the building weighs less than a pound.


1. Fallacy of Accident, Fallacy of Complex Question and Fallacy of Begging the Question belong to

A. Fallacies of Defective Induction

B. Fallacies of Presumption

C. Fallacies of Ambiguity

D. None of these

Answer: B

2. Fallacy of Equivocation, Fallacy Amphiboly, Fallacy of Accent, Fallacy of Composition and Fallacy of Division belong to

A. Fallacies of Defective Induction

B. Fallacies of Presumption

C. Fallacies of Ambiguity

D. None of these

Answer: C

3. Have you stopped shoplifting now? Is an example of?

A. Fallacy of Complex Question

B. Fallacy of Amphiboly

C. Fallacy of Equivocation

D. None of these

Answer: A

4. A is a part of B, B has property X, Therefore, A has property X is an example of

A. Fallacy of Composition

B. Fallacy of Division

C. Fallacy of Amphiboly

D. None of these

Answer: A

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