Toronto Metropolitan University
Faculty of Arts
SSH 105: Critical Thinking
Professor David Hunter
Chapter 4
Acceptable Reasons
Chapter 4: acceptable reasons
Critical thinking is reasonable thinking (in part) because it
requires us to have good reasons for our conclusions.
Reasons are good only when (i) they support our conclusions
and (ii) they are acceptable.
In this chapter, we will consider when our reasons for believing
are acceptable.
Evidence is acceptable when (i) it comes from a reliable source
and (ii) it is neither undermined nor overridden by other
evidence that we have.
A source of evidence is reliable when it provides accurate
information most of the time.
–Reliability is a matter of degree.
–Reliability depends on optimal conditions.
–Reliability is topic-relative.
When Evidence Conflicts
Two bits of evidence are in direct conflict when one indicates
that something is true and the other indicates that it is
false.
If one piece is stronger than the other, then the first
overrides the second.
Over-ridden evidence is not acceptable.
Evidence is overridden when
– It conflicts with evidence from a known reliable source;
– It directly conflicts with expert consensus;
– It directly conflicts with what we already have good reason
to believe.
When Evidence Conflicts
Two bits of evidence are in indirect conflict when one indicates
that the other is not acceptable.
If the first is stronger than the other, then the first
undermines the second.
Undermined evidence is not acceptable.
Critical Thinking Mistake: Appeal to ignorance
It is a mistake to believe something just because you do not
have evidence that it is false.
We have a duty as critical thinkers to make sure
– that our sources are reliable
– that there is no conflicting evidence
Observation and memory
Observation is a source of evidence and memory is a kind of
store-house for evidence.
But before we trust either one we need to ask:
–
–
–
Is it reliable for this topic?
Is it reliable enough?
Are the conditions optimal?
•
List three topics on which direct visual observation is not
reliable?
•
Describe a situation where direct visual observation is
reliable on a topic but the conditions are not optimal.
Testimony
Testimonial evidence is acceptable only if:
–
–
–
–
It is on an appropriate topic
The witness is properly trained
The witness is properly informed
The witness is unbiased.
The evidence must be on an appropriate topic.
On some topics there are no experts.
• Matters of personal taste or preference.
– E.g., whether Springsteen is better than Eminem.
• Where the facts are too complex.
– E.g., why stock market goes up or down within a few hours
• Where there is no settled expert opinion.
– E.g., the leading edge of scientific investigation.
The witness must be properly trained.
The witness must be properly informed.
The witness must be unbiased.
Testimony
Note 1: These four conditions are independent.
– So you have to check each one.
Note 2: If you think that some testimony is not acceptable, then
have to say which of the conditions it fails to meet.
Note 3: Testimony that is not acceptable might still be true!
– Even biased fools can speak the truth.
you
Sometimes the proper thing for a critical thinker to do is to
withhold belief.
Advertising and the Media
Advertising and news reports are just special cases of testimony.
Advertising
Celebrities are often used to help sell products, even though
they are not trained, informed or unbiased.
Should they
be trusted?
News Media
•
Some reporters are not trained experts on the issues.
•
Reporters are informed by sources, and some sources are
anonymous.
•
Sometimes, reporters simply repeat what their sources say
without thinking critically about it (passive reporting).
News is prone to several kinds of bias
–
Reporter Bias
–
Corporate Bias
–
Cultural Bias
Academic Journals
Even Academic results need to treated with caution.
–
Overstating results
–
Funding bias
The case of dark chocolate.
–
Publishing Bias
Don’t publish negative inconclusive results.
Don’t publish failures to reproduce studies
Surveys
Opinion polls are a familiar source of evidence.
We use questionnaires to find out what people believe about
some topic or other.
We can use what we learned about testimony to figure out
when survey results are acceptable.
Evidence from a survey is acceptable just in case
(i) the survey questions are not bad
(ii) the survey subjects are properly trained
informed
(iii) there is no researcher or subject bias
and
If a question is ‘bad’ then asking it is not a reliable way to find
out what the answerer believes.
--ambiguous/vague, ‘Are you happy?’
--charged/slanted. ‘Do you think that students should be
forced to pay more tuition?’
--loaded, ‘Have you stopped cheating on exams?’
--badly ordered, ‘Is it OK to smoke while you pray?’
The survey subjects must be properly trained and informed
Public opinion polls often ask people about topics on which they lack training or
information.
Forcing them to take a position may disguise the fact that they really are agnostic or
undecided.
Survey results are acceptable only if there is no bias.
Subject bias: the subjects might be motivated to lie or exaggerate.
Researcher bias: those asking the questions might bias the results by the way
they ask the questions.
A double blind survey is one with questions on many different topics where
neither the subject nor the questioner knows which is the target one.
A recent poll in the US found that