Friday, April 11, 2008

Logical Fallacies

Since thinking is passe, logical fallacies are rife and unseen. Truth used to be a concern. Now no one cares. It's all made up anyway. Right?

If, you do get concerned about thinking and using it as your tool of survival which is its purpose, then it may be worth while to notice some of the pitfalls of thinking. I found this list of fallacies in The Art of Reasoning, a logic textbook by David Kelley and published by Norton in 1988. I like this book because it is based on Objectivist epistemology. (See Favorite Books on the sidebar.)


Subjectivist Fallacies

Subjectivism: I believe/want p to be true therefore p is true.

Appeal to Majority: Using the fact that large numbers of people believe a proposition to be true as evidence of its truth.

Appeal to Emotion: Trying to get someone to accept a proposition on the basis of an emotion one induces.

Appeal to Force (Argumentum ad Baculum): Trying to gain the acceptance of argument on the basis of a threat.

Credibility Fallacies

Since we rely on other people for much of what we know, we engage in the argument: X says p therefore p is true. This depends on two conditions: X must know the truth and X must tell the truth. Fallacies misuse the standards for credibility.

Appeal to Authority (Argumentum ad Verecundiam): Using testimonial evidence for a proposition when the conditions for credibility are not satisfied, or the use of such evidence is inappropriate.

Ad Hominem: (X says p) + (X is a bad person) therefore p is false. Variations: Tu quoque: trying to refute an accusation by showing that the speaker is guilty of it. Poisoning the well: trying to refute a statement or argument by showing that the speaker has a nonrational motive for adopting it.

Fallacies of Logical Structure

Begging the Question (Circular argument): Trying to support a proposition with an argument in which that proposition is a premise. Variation: Complex question: trying to get someone to accept a proposition by posing a question that presupposes it.

Post Hoc (post hoc ergo propter hoc): A occurred before B therefore A caused B.

False Alternative: Excluding relevant possibilities without justification.

Appeal to Ignorance (Argumentum ad ignorantiam): Using the absence of proof for a proposition as evidence for the truth of the opposing proposition.

Non Sequitur: Trying to support a proposition on the basis of irrelevant premises. Variations: Diversion: trying to support one proposition by arguing for another proposition. Straw man: trying to refute one proposition by arguing against another proposition.

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