Fallacies of Logical Structure

In the previous sections, we examined arguments that are fallacious because they introduce irrelevant considerations into the reasoning process--emotions, threats, personal traits, etc.. In this section, we'll examine fallacies that involve errors within the reasoning process itself. The problem in these arguments is not the premises they use, but the relation between the premises and the conclusion.

We examine the following fallacies:


Comprehension Questions

1 Identify the fallacy committed by the following argument.

Caesar's account of the ancient Germanic tribes has been accepted as valid by historians, who rely upon other writers of the period. These writers we know are correct because they base their histories on eyewitness accounts, as described in Caesar's journals.

a) begging the question
b) post hoc
c) false alternative
d) appeal to ignorance
e) diversion
f) straw man
2 Identify the fallacy committed by the following argument.

John: Semiautomatic weapons should be banned because they have no other purpose than to kill civilians.
Jack: We already have laws against murder.

a) begging the question
b) post hoc
c) false alternative
d) appeal to ignorance
e) diversion
f) straw man
3 Identify the fallacy committed by the following argument.

No one has shown that global warming isn't occurring. Therefore, it must be.

a) begging the question
b) post hoc
c) false alternative
d) appeal to ignorance
e) diversion
f) straw man


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