“There's intelligent life on other planets.”

Would you accept this claim?

Accept the claim as TRUE

Reject the claim as FALSE

SUSPEND JUDGMENT

CredibilityCredibility

Who can we believe? Who can we believe? SOURCESSOURCESWhat can we believe? What can we believe? CLAIMSCLAIMSAnd how confident can we be in what we believe?

Assessing CredibilityAssessing Credibility

There is no simple rule for assessing credibility.

Assessing credibility requires judgment.

Judgment depends on background knowledge.

This sort of judgment is basically induction.

Assessing content of a Assessing content of a claimclaim

Role of personal observationRole of personal observation

• Focus of attention

• Preparation to distinguish features

• Conditions of observation

• Expectations, beliefs, biases

Assessing content of a Assessing content of a claimclaim

Role of personal observationRole of personal observation Role of background informationRole of background information

• Initial plausibility

• Novelty and conflict

• Extent of background information

Credibility of a sourceCredibility of a source

KnowledgeKnowledge

AbilityAbility

MotivationMotivation

Education and experience both matter

Physical and mental factors may both be relevant

Desires and beliefs, including prejudices may work in various ways

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards

Arguing backwards is to reason that Arguing backwards is to reason that because we have an argument because we have an argument with a true conclusion, in premises with a true conclusion, in premises must be true. An argument is must be true. An argument is supposed to convince us that its supposed to convince us that its conclusion is true, not that its conclusion is true, not that its premises are true.premises are true.

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing BackwardsExample :Example : Your friend says, “All CEOs of computer Your friend says, “All CEOs of computer

software companies are rich. Bill Gates is a CEO software companies are rich. Bill Gates is a CEO of a computer software company. So Bill Gates of a computer software company. So Bill Gates is rich.” Since you know that Bill Gates is rich, is rich.” Since you know that Bill Gates is rich, you decide the argument is good and that all you decide the argument is good and that all CEOs of computer software companies are rich.CEOs of computer software companies are rich.

Analysis: Analysis: This is arguing backwards. There are This is arguing backwards. There are lots of CEOs of computer software companies lots of CEOs of computer software companies that are struggling to make a living. An that are struggling to make a living. An argument is supposed to convince us that its argument is supposed to convince us that its conclusion is true, not that its premises are true.conclusion is true, not that its premises are true.

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authority Appeal to authority

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authority Appeal to authority

We saw above that we can often accept a We saw above that we can often accept a claim based on authority. But it is a bad claim based on authority. But it is a bad appeal to authority to say that we appeal to authority to say that we should accept a claim because a should accept a claim because a particular person said it when that particular person said it when that person is not really an authority on the person is not really an authority on the subject or has motive to mislead.subject or has motive to mislead.

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authority Appeal to authority

Example : Example : What do you think of the new What do you think of the new tax plan the President announced?tax plan the President announced?

It must be good, ‘ cause Dan Rather It must be good, ‘ cause Dan Rather said so.said so.

AnalysisAnalysis : : Not everything that Dan Not everything that Dan Rather says is true.Rather says is true.

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authority Appeal to authority Mistaking the Person for the ClaimMistaking the Person for the Claim

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authority Appeal to authority Mistaking the Person for the ClaimMistaking the Person for the ClaimMistaking the person for the claim. You’re Mistaking the person for the claim. You’re

mistaking the person (or group) for the claim if mistaking the person (or group) for the claim if you believe that the claim is false because of you believe that the claim is false because of who said it. It’s often right to suspend who said it. It’s often right to suspend judgment on a claim if you don’t consider the judgment on a claim if you don’t consider the person who’s making the claim to be a person who’s making the claim to be a reputable authority on the subject. But saying reputable authority on the subject. But saying that the claim is actually false because of who that the claim is actually false because of who said it is a mistake in reasoning. said it is a mistake in reasoning.

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authority Appeal to authority Mistaking the person for the claim Mistaking the person for the claim Example : Example : I don’t believe the tax cut will I don’t believe the tax cut will

benefit the poorest in our society. That’s benefit the poorest in our society. That’s just another lie our senator said.just another lie our senator said.

Analysis : Analysis : This is mistaking the person for This is mistaking the person for the claim. Politicians don’t lie the claim. Politicians don’t lie allall the the time. There’s no shortcut for reading time. There’s no shortcut for reading and reasoning about a claim in and reasoning about a claim in evaluating whether to accept it.evaluating whether to accept it.

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authorityAppeal to authority Mistaking the person for the claim Mistaking the person for the claim Appeal to common belief Appeal to common belief

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authorityAppeal to authority Mistaking the person for the claim Mistaking the person for the claim Appeal to common belief Appeal to common belief An appeal to common belief is to An appeal to common belief is to

accept a claim as true because a lot accept a claim as true because a lot of other people believe it. Typically, of other people believe it. Typically, such reasoning is a bad appeal to such reasoning is a bad appeal to authority.authority.

Common Mistakes in Common Mistakes in Evaluating unsupported Evaluating unsupported claims.claims.

Arguing BackwardsArguing Backwards Appeal to authority Appeal to authority Mistaking the person for the claim Mistaking the person for the claim Appeal to common belief Appeal to common belief Example : Example : You go to England and find that You go to England and find that

everyone there is driving on the left-everyone there is driving on the left-hand side of the road. You conclude that hand side of the road. You conclude that you should, too.you should, too.

AnalysisAnalysis : : This is a good reasoning, since This is a good reasoning, since you also know that every country allows you also know that every country allows driving on just one side.driving on just one side.