Evaluation: Logical Fallacies (Insufficient Evidence)

What, again, is an ARGUMENT?

Criteria for Cogency

1. Premises are true

2. Premises are relevant to the conclusion

3. Premises provide good reason to believe conclusion is true

What is a FALLACY?

An argument which contains a mistake in reasoning

Fallacies

• Fallacies of Insufficient Evidence – premises do not bring enough evidence to bear on the conclusion

• Fallacies of Relevance – premises are irrelevant to the conclusion!

Fallacies of Insufficient Evidence

#1 Fallacy of Unqualified Authority

How do you evaluate a doctor’s

expertise?

The kung-fu expert’s choice?

How do you DISCREDIT someone in authority?

• How much training does the person have? What are his credentials and qualifications?

• Is the person an authority on the issue at hand?

• Could the person be biased?

Does USING something make you an authority on that item?

Is Tiger Woods an expert in the making of golf clubs?

Persuasiveness is NOT the same as cogency

When the LACK of evidence is used to support your

conclusion…!

#2 Fallacy of

Appeal to Ignorance

• God exists. No one has proven that He doesn’t.

• God doesn’t exist. No one has proven that He does.

“If Anwar thinks he is innocent of the charges then he should prove it.” Dr. Mahathir Mohamad

The Problem: You can then argue for

ANYTHING!

#3 Fallacy of False Alternatives

• Either you support Pakatan OR you condemn Malaysia to injustice and oppression!

• Why don’t you, as a Chinese, celebrate Chinese New Year? Are you anti-Chinese?

• “It’s us. Or rust” (Advertisement)

• Najib’s approval rating has gone up. Either the rating is false or the people are stupid!

#4 Fallacy of Loaded Question

Examples

• When are you going to stop acting so immature?

• Do you still steal from your boss?

• Is the assignment deadline always to rigid?

#5 Fallacy of False Cause

• I don’t believe I failed. I should’ve used my lucky pen.

• The SPM results have fallen steeply over the years. Obviously, the influence of the Internet is detrimental to studying.

• Air-Asia passengers have dropped a little; it must be because people are st

CAUSE vs. CORRELATION

#6 Fallacy of Generalization

• All girls like flowers.

• “Anyone can make a million dollars! I did it by age 35.”

For sampling

• Was the sample taken at random?

• What kinds of questions were asked? And how were the questions asked?

#7 Fallacy of Slippery Slope

• Don’t fire the rocket in these snowy mountains. The rocket could cause an avalanche, and the avalanche could destroy the ski-hotel and the village below. Hundreds could die.

• If we don’t raise our army spending, soon Chinese will surpass us as a military power. Who knows when we’ll all be speaking Chinese and eating chop suey?

#8 Fallacy of Weak Analogy

• There’s nothing wrong with separating bathrooms based on race. After all, don’t we separate bathrooms based on men and women?

• Coke is like family. You can never have enough. Coca-Cola. Always.

#9 Fallacy of Inconsistency

• “Smoking is a sin because if you smoke that means you don’t care about your health”, said Brian whilst eating his chow kuey teow…

• Police: Did you get a good look at the bank robber?

• Witness: Yes, I saw his face clearly. It was William, the security guard.

• Police: And were you able to recognise his voice?

• Witness: No, I couldn’t hear what he said because of the ski mask he was wearing.

Quick Test• Skeptics have tried for centuries to prove

that reincarnation is a myth and no one has ever succeeded. Therefore, we should conclude that reincarnation is a fact.

• Ford cars are so troublesome. I own two, and they give me nothing but headaches.

• Either you support preferential treatment for the Indians or you’re anti-Indian.

• Sunway is a better college than Taylor’s; I know this is true because Dr. Lee (the Dean of Business at Sunway) told me so)

A fallacy does NOT imply that the conclusion is false!