FALLACIES OF LOGIC

REASONING the process of drawing a conclusion

on the basis of evidence.

DEDUCTIVE VS. INDUCTIVE DEDUCTIVE: Reasoning from the general

to the specific (cause to effect) INDUCTIVE: Reasoning from detailed

facts to general principles.

http://www.sjsu.edu/depts/itl/graphics/induc/ind-ded.html

http://www.philosophypages.com/lg/e13.htm

Four Types of Reasoning

Reasoning from specific instances

Reasoning from principle

Causal reasoning

Analogical reasoning

FALLACIES-FAULTY REASONING

Red Herring

Ad Hominem

Either-Or

False Cause

Invalid Analogy

Bandwagon

Slippery Slope

Hasty/Sweeping

Generalizations

RED HERRING A fallacy that introduces an

irrelevant issue to divert attention from the subject under discussion.

AD HOMINEM A fallacy that attacks the person

rather than dealing with the real issue in dispute.

EITHER-OR A fallacy that forces listeners to

choose between two alternatives when more than two alternatives exist.

False Cause One event precedes the next so it

must be the cause.

Invalid Analogy Using an analogy in which the

concepts being compared in reality are not similar or do not have important enough similarities to justify the analogy as support.

SLIPPERY SLOPE A fallacy which assumes that

taking a first step will lead to subsequent steps that cannot be prevented.

BANDWAGON Everyone’s doing it!

HASTY/SWEEPING GENERALIZATIONS

Drawing conclusion on too few examples

OMITTED FACTS

Leaving out important facts because those facts might hurt your argument.

STACKED DECK

Presenting only information that supports your position

FALSE ASSUMPTIONS

Applying what is true in general to all.

EXAMPLEIn his essay on animal training, Roberto said

that food rewards are the only way to get animals to learn.

He was basing his conclusion on his experience with only two dogs. Audience members who had success training with other methods knew that Roberto had not considered enough animals before forming his opinion.

EXAMPLE

In an essay on wolves it might be tempting to assume that because wolves are like dogs in some ways, they are like them in all ways. Also, that since wolves are social, the idea of the lone wolf must be a myth.

However, while most wolves are social, a few do fall away from the pack.

Rather than using faulty reasoning, good writers recognize that their readers know that every position has some drawbacks. Instead of denying the drawbacks in your position, address them honestly. Show how they fail to outweigh the benefits of your position.