1. • When Claims Conflict
 Contradictions - If a claim conflicts with
other claims we have good reason to
accept, we have good grounds for doubting
it.
 If a claim conflicts with our background
information, we have good reason to doubt
it.
Chapter 4: Reasons for Belief and Doubt

2. Fact and Opinions
• Two meanings of “fact”
– State of affairs
– Claims that is true
• “That’s a matter of opinion”
– There are many different opinions about this issue
– There is no objective fact of the matter as the
grounds for deciding are entirely subjective

3. • Belief and Evidence
 We should proportion our belief to the
evidence.
 It’s not reasonable to believe a claim
when there is no good reason for doing
so.

4. • Experts and Evidence
 If a claim conflicts with expert opinion,
we have good reason to doubt it.
 Who is an expert?
 Access to more information on the subject
than we do
 They are better at judging that
information than we are.

5. When to rely on experts
• When they are experts in the relevant field
• When the are speaking or writing on their
subject of expertise
• When there is not some reason to doubt their
motivation
• When experts agree

6. • When the experts disagree about a claim, we
have good reason to doubt it.

7. Appeal to authority
• When any of the previous conditions is
violated the fallacy of appeal to authority is
committed.
• The reliance on expert opinion is undermined.

8. Some hints that the authority is dubious
• The expert is guilty of simple factual or formal errors.
• The expert’s claims conflict with what we have good
reason to believe.
• The expert does not adequately support his or her
assertions.
• The expert’s writing contains logical contradictions or
inconsistent statements
• The expert is strongly biased, emotional, or dismissive.
• The expert relies on information you know is out of date.
• The other experts in the same field disagree.

9. •Personal Experience
•It’s reasonable to accept the evidence
provided by personal experience only if
there’s no good reason to doubt it.
• Factors that can give us good reason to
doubt the reliability of personal experience:
 Impairment
 Expectation
 Innumeracy

10. Impairment
• Memory
– We construct our memories
• Perception
– We sometimes see what we want to see – the
constructive nature of perception

11. Expectation
• Experiments showing that if we are told that
something is going to happen we will
experience it
• Pareidolia
• Stereotypes and perceptions:
racism/sexism/prejudice

12. Innumeracy
• We (humans) are bad at making judgments
about probabilities.
• We frequently make misjudgments about
coincidences.
• Gambler’s fallacy
So what conclusion should we draw from this?
Don’t rely solely on our intuitions.

14. Fooling ourselves
• Resisting contrary evidence
• Looking for confirming evidence
• Preferring available evidence

15. Resisting contrary evidence
• We may deny, ignore, or reinterpret evidence
that contradicts cherished beliefs.

16. Looking only for confirming evidence
• Confirmation bias
• Popper’s point about confirmation – what
makes a theory scientific

17. Preferring available evidence
• Availability error
– Not just what is readily available in the sense of
easy to find, but also what is psychologically
available.
– Weighting what you have seen or experienced
more heavily than it should be weighted
– Hasty generalization

18. • How to evaluate the reliability of
the news:
 Consider whether the report conflicts
with what you have good reason to
believe.
 Look for reporter slanting.
 Consider the source.
 Check for missing information.
 Look for false emphasis.
 Check alternative news sources.

19. Advertising and persuasion
• We generally have good reason to doubt
advertising claims and to be wary of
advertising’s persuasive powers.
– The purpose of advertising is to sell or promote
something.
– History of misleading messages

20. Identification
• Snob appeal
– Ads asking you to identify with particular groups
of people
– Insinuating that you will be identified with such
people if you….

21. Slogans
• Catch phrases get our attention

22. Misleading comparisons
• Vagueness of comparisons
• What’s the baseline with which we are
comparing?
• Emptiness of claims
• Comparing “apples and oranges”

24. Weasel words
• Words which appear to make a strong claim
but are really close to lying
• Taking back what was said with modifiers that
undermine the claim