Review Part 2
Critical Thinking
Is there any evidence to support the claim?
Is the evidence reliable and trustworthy? How
reliable is it? Should you accept it?
Does the evidence actually support the claim?
Is there other evidence you should consider?
Popularity, Tradition, Ignorance
Fallacies:
• Appeal to popularity: arguing that something
is true because it’s popular.
• Appeal to tradition: arguing that something is
true because it’s traditional.
• Argument from ignorance: arguing that
something is true because it hasn’t been
proven false.
Not Fallacies
The following things are not fallacies:
• Having traditions
• Being popular
• Lacking evidence
Appeal to Popularity
After Fukushima, many
people in China and
California rushed out to
buy salt.
Why? Some people may
have had some dumb
scientific idea, but for
most it was because that’s
what everyone else was
doing.
Antonin Scalia
• Longest serving justice
on US Supreme Court.
• Taught at the University
of Chicago.
• First Italian-American SC
justice.
• Extremely powerful and
influential
Interview with Scalia
Q: Isn’t it terribly frightening to believe in the
Devil?
Scalia: You’re looking at me as though I’m weird.
My God!... Most of mankind has believed in the
Devil, for all of history. Many more intelligent
people than you or me have believed in the
Devil.
Appeal to Tradition
“With a history of more
than 2000 years,
Traditional Chinese
Medicine (TCM) has
formed a unique system
to diagnose and cure
illness.” – eastday.com
Argument from Ignorance
“Absence of evidence is not evidence of
absence.” – Carl Sagan
Just because there is no evidence that
something is true, does not mean that it is false.
Just because there is no evidence that
something is false, does not mean that it is true.
Shifting the Burden of Proof
A similar fallacy is “shifting the burden of proof”.
It goes:
“God exists. If you think otherwise, prove that
he doesn’t!”
Here, you make a claim (“God exists”) but
instead of giving evidence for it, you require that
your opponent give evidence for the opposite.
Appeal to Authority
It’s OK to find out what to believe from experts
in many cases. However, this is not true when:
• The expert is not an expert about what you
want to know.
• Experts in general disagree about the
question.
• The expert has a history of lying or misleading
about the question.
Irrelevant Evidence
There are many ways that evidence can seem to
support a conclusion, without actually doing so:
•
•
•
•
No connection with the claim.
Circular reasoning.
Better alternative explanations.
Special circumstances.
No Connection with the Claim
• Clustering illusion: it looked like there was a
pattern there, but there wasn’t.
• Regression fallacy: going back to normal
seemed to be for a reason, when it wasn’t.
• Base rate neglect fallacy: a reliable test said
the claim was true, but since the base rate of
the condition is very low, it is still unlikely that
the claim is true.
Circular Reasoning
Circular reasoning involves trying to show that a
claim is true by assuming that it is true in the
premises. It has the form:
X is true. Why? Because X.
Carbon Dating
The Earth’s atmosphere contains a mix of
carbon, including regular carbon (C-12) and also
radioactive carbon, C-14.
Plants take in carbon for photosynthesis,
trapping both types of carbon. Animals eat the
plants and trap the carbon too.
Carbon Dating
Once an organism dies, it stops trapping carbon.
C-14 decays at a constant rate into nitrogen-14.
So the ratio of carbon-12 to carbon-14 slowly
goes up over time in a dead organism.
We can use this ratio to determine how old
something is!
Circular?
Some young-Earth creationists argue that
carbon dating is circular.
Scientists say this bone is 50,000 years old
because carbon dating says so. But how do we
know that carbon dating is correct? Because this
bone is 50,000 years old, and you can see that
carbon dating gets the right answer!
Straw Man Fallacy
A straw man argument is where you
mischaracterize your opponent’s claims or
reasons for those claims. You show that the
mischaracterization is false or misleading, and
then claim that your opponent believes false
claims or has bad reasons for her claims.
Straw Man Fallacy
Many in Hong Kong think
that President Benigno
Aquino of the Philippines
should apologize for the
Manila bus crisis.
People feel so strongly
they have been heartless
after the recent tragedy.
Straw Man
Aquino argues:
1. No one should apologize for something that
they did not do.
2. Rolando Mendoza acted alone in taking
hostages and in killing hostages. The
Philippine government didn’t do it and the
Philippine people didn’t do it.
3. Therefore, the government/ people of the
Philippines should not apologize.
Straw Man Fallacy
Aquino is suggesting that people want him to
apologize for Mendoza’s actions.
BUT that is not what people want. They want
him to apologize for the Philippine government’s
actions: specifically, the way the crisis was
mishandled by the police.
False Dilemma
An argument commits the false dilemma fallacy
when it presents two options as the only
options, even though there are actually more
options.
National Education
1. We can either have
national education
with the materials we
now have, or not have
national education.
2. The materials now
falsely portray China
and ignore historical
events like Tiananmen
Square.
National Education
3. Therefore, there should
be no national education
in Hong Kong.
Fallacy of the Mean
The fallacy of the mean is the assumption that a
“middle point” between two views is the right
one.
Distribution Fallacy
The distribution fallacy is when you assume that
the parts have the same properties as the whole
they comprise:
1. Lingnan has a great philosophy department.
2. Therefore, Michael is a great philosopher.
1. For the “whole” of Hong Kong kindergartens,
there is enough space for all children to go to
school.
2. Demand is for 168,000 spaces, but there are
a total of 241,000 spaces.
3. Therefore, there is no shortage of space in
kindergartens.
Distribution Fallacy
Just because there is enough space in the whole
system does not mean there is enough space in
the high-demand districts.
Mainlanders want to go to kindergarten in the
northern districts, because that’s closer to
China. These kindergarten seats have much
lower availability.
Ecological Fallacy
The ecological fallacy is a form of the
distribution fallacy– a particularly tricky one!
As we saw before, just because Catholic
countries have fewer suicides than protestant
countries, doesn’t mean that Catholics commit
less suicide!
Blue = Democrat
Green = $$$
Ecological Fallacy
States with the highest average incomes have a
higher percentage of democratic voters.
So does this mean that people who are wealthy
are more likely to vote democrat?
No! The opposite is true.
Appeal to Nature
The appeal to nature fallacy is when someone
argues that something is true/ good because it’s
natural or when they argue that something is
false/ bad because it’s unnatural.
Harmful “Natural” Ingredients
Pure sugar pills (or saltwater injections) can’t
harm you any more than your beliefs can (which
can be significantly).
But invasive treatments or treatments with
pharmacologically active ingredients can harm
you, even if they are only as good as a placebo
at helping you.
Cancer in Taiwan
Taiwan has the highest per-capita incidence of
UUC (upper urinary tract cancer) of anywhere in
the world.
Plants of the genera Ephedra and Asarum
produce the toxic chemical aristolochic acid
which causes UUC.
TCM herbal remedies contain lots of these
plants, and tests have shown they contain
aristolochic acid as well.
Kidney Failure in Belgium
In a case report in “Nature” in 2011, a “slimming
clinic” in Belgium where women were taking
Chinese herbal remedies led to more than 100
women suffering kidney failure and many of
them later developing cancer…
From aristolochic acid, the same thing making
Taiwan #1 in UUC!
Other Harmful Side-Effects
Here’s a bottle of Saiga
Antelope Horn Powder.
The Saiga Antelope is
critically endangered, so
the fact that people take
these pills is currently
harming endangered
species.
Is there other evidence we should
consider?
This is what we talked about in the first week:
context. But it’s not always true that when we
should consider more evidence, something has
been taken out of context.
Out of Context
Words are taken out of context when:
• You present some, but not all, of what
someone said.
• What you present makes it seem as if they
believe or support some claim.
• If we look at all of what they said, it is clear
that they do not support or believe that claim.
Out of Context: 1998-present
Broader Context: 1850-present
Are there lots more Americans on
Welfare?
…Not really.
The Fallacy Fallacy
This is a bad argument:
1. You have presented argument A for your
claim C.
2. A is a fallacious argument.
3. Therefore, C is false.
CORRELATION AND CAUSATION
Causation
Much of science is concerned with discovering
the causal structure of the world.
We want to understand what causes what so we
can predict, explain, and control the events
around us.
Causation ≠ Correlation
http://www.critthink2.org/2011/05/23/lisasimpson-demonstrates-causal-reasoning/
Homer: Not a bear in sight. The Bear Patrol must
be working like a charm.
Lisa: That’s specious reasoning, Dad.
Homer: Thank you, dear.
Lisa: By your logic I could claim that this rock
keeps tigers away.
Homer: Oh, how does it work?
Lisa: It doesn’t work.
Homer: Uh-huh.
Lisa: It’s just a stupid rock.
Homer: Uh-huh.
Lisa: But I don’t see any tigers around, do you?
Homer: Lisa, I want to buy your rock.
Causation ≠ Correlation
But causation does not imply correlation. If A
and B are correlated there are several
possibilities:
•
•
•
•
A causes B
B causes A
C causes A and C causes B
A and B are only accidentally correlated
B causes A
B causes A
B causes A
B causes A
B causes A
C causes A and B
Much more common than “B causes A”
explanations are explanations where the causal
relationship between A and B is due to a third
variable.
Common Cause!
From the Daily Mail
Lede: “[new] findings, published in the latest
online edition of the journal Appetite, show the
way we perceive tasty treats like chocolate cake
is just as important as the calorie count when it
comes to expanding waistlines.”
From the Daily Mail
“They recruited almost 300 volunteers, aged from
18 to 86, and quizzed them on their eating habits
and whether they were trying to lose weight. They
also asked them if eating chocolate cake made
them feel happy or guilty.
The results showed 27 per cent associated it with
guilt and 73 per cent with celebration. When the
researchers looked at weight control 18 months
later, they found those riddled with guilt had gained
significantly more.”
Probably Common Cause
Maybe people who eat unhealthily feel more
guilty about eating chocolate. After all, they can
see the harm they’re doing to themselves.
And maybe people who eat very well don’t feel
guilty having chocolate.
Coincidence
In 1979, two researchers,
Nancy Wertheimer and Ed
Leeper, published an
article alleging that the
incidence of childhood
leukemia was higher in
Denver neighborhoods
that were near electric
power lines.
The “Texas Sharp Shooter”
Suppose I stand in front of a barn. I have a
machine gun with me, and I am blindfolded. I
shoot wildly at the barn for several minutes.
Afterward, I walk up to the barn. I find a spot
where three bullets are very close together, and
I paint a target around them. “Look!” I say, “at
what an excellent marksman I am!”
Power Lines and Cancer
The power lines study is just like this.
The researchers found places near power lines
and looked at all the health problems anyone
had in the area.
Of all the health problems what’s the chance
that one is accidentally correlated with power
lines?
Coincidence
High enough!
Later studies showed there was no relationship.