1

Fallacies of Weak Induction

2

IntroductionThe key characteristic of these fallacies is

that the connection between the premises and conclusion is not strong enough to support the conclusion

3

Appeal to Unqualified

Authority: DefinitionThis fallacy occurs when the appeal is

made to an authority or witness that is not trustworthy or is not qualified in that particular area.

4

Appeal to Unqualified Authority:

Example We should all accept the claim that the

moon is made of green cheese. After all, Professor McNellis says it is, and he’s a recognized authority in ethics.

Comment: McNellis is not qualified in the area of astronomy!

5

Appeal to Unqualified

Authority:Key Question Does the arguer appeal to an authority

who is actually not qualified in that area for support of his/her conclusion ?

6

Appeal to Ignorance

Occurs when the premises of an argument state that nothing has been proved one way or the other about something, and the conclusion then makes a definite assertion about that thing

7

Appeal to Ignorance:

Example Example: People have been trying for centuries to disprove the claims of astrology, and no one has ever succeeded. Therefore, we must conclude that the claims of astrology are true.

Comment: The only justified conclusion is that we don’t know.

8

Appeal to Ignorance:

Key Question Does the arguer claim something is true

because no one has disproved it or that something is false because no one has proved it to be true?

9

Hasty Generalization

DefinitionThis fallacy occurs in inductive

generalizations where there is a reasonable likelihood that the sample is not representative of the group

10

Hasty Generalization:

Example Four Arab fundamentalists were convicted of bombing the World Trade Center in New York City. The message is clear: Arabs are nothing but a pack of religious fanatics prone to violence.

Comment: This draws a conclusion about a whole group on the basis of one incident.

11

Hasty Generalization:

Key Question Does the speaker/author draw an inductive conclusion based on a sample that is too small or too unrepresentative?

12

False Cause: Definition

Occurs whenever the link between premises and conclusion depends on some imagined causal connection that probably does not exist

13

False Cause: Example During the past two months, every time that

the cheerleaders have worn blue ribbons in their hair, the basketball team has been defeated. Therefore, to prevent future defeats, the cheerleaders should get rid of those blue ribbons.

Comment: There’s no reason to believe wearing the ribbons caused the defeats.

14

False Cause: Key Question

Does the conclusion maintain that one thing caused another when it probably did not?

15

Slippery Slope:Definition

This fallacy occurs when the conclusion rests on an alleged chain reaction and there is not sufficient evidence to believe that the chair reaction will actually occur.

16

Slippery Slope:Example

“Immediate steps should be taken to outlaw pornography once and for all. The continued manufacture and sale of pornographic material will almost certainly lead to an increase in sex-related crimes such as rape and incest. This in turn will gradually erode the moral fabric of society and result in an increase in crimes of all sorts. Eventually a complete disintegration of law and order will occur, leading the the total collapse of civilization”

Comment: It’s not proved that legal pornography leads to these consequences.

17

Slippery Slope:Key Question

Does the speaker/author claim that a single step will eventually lead to disastrous consequences when there is little evidence that this will actually occur?

18

Weak Analogy:Definition

This fallacy occurs in some arguments from analogy in cases where the arguer ignores important differences between the type types of cases

19

Weak AnalogyExample

“Political dissent is like a cancer in the body politic. And we all know what the best treatment for cancer is: radical surgery. So when we see dissidents, we should cut them out of society as fast as possible before they spread!”

Comment: This ignores important differences between cancer and political dissent, especially:people have rights, cancer cells don’t.

20

Weak Analogy:Key Question

Does the arguer introduce an analogy but ignore important differences between the two classes of things being compared?