Transcript Fallacies - Michael Johnson's Homepage | All things

Fallacies
(Really)
Remember that a fallacy is just an invalid
argument. An invalid argument is one where
even if the premises are true, the conclusion can
still be false. So there are lots of fallacies.
However, there are certain tricky patterns that
often fool people. These patterns come to have
names.
Straw Man Fallacy
Straw Man Fallacy
The Straw Man Fallacy (sometimes in the UK
called “Aunt Sally Fallacy”) is when you
misrepresent your opponent, and argue against
the misrepresentation, rather than against your
opponents claim.
http://www.youtube.com/watch?v=xO
n7DInBWK4&feature=related
Assuming the Original Conclusion
Assuming the original conclusion* 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.
*This is Aristotle’s name for the fallacy.
Example:
“It says in the Bible that God exists. Since the
Bible is God's word, and God never speaks
falsely, then everything in the Bible must be
true. So, God must exist.”
Example
Premise 1: The bible is God’s word.
Premise 2: God never speaks falsely.
Conclusion: Everything in the bible is true.
Premise 1: Everything in the bible is true.
Premise 2: The bible says that God exists.
Conclusion: God exists.
Note
The most common name of the fallacy of
assuming the original conclusion is “begging the
question”. There’s a long story about why that is.
Sometimes people misuse “begging the
question” to mean “inviting or raising the
question”. You should know that some people
look down at you if you do this.
Mark Liberman of Language Log found:
http://languagelog.ldc.upenn.edu/nll/?p=2290
‘if we search the NYT index for recent uses of
"beg the question", we find that out of the first
20 hits, 15 use "beg the question" to mean
"raise the question" — and of the five that
don't, four are usage articles berating people for
misusing the phrase!’
False Equivocation
Equivocation (or “false equivocation”) is when
one word is used with two meanings in the
same argument, rendering it invalid.
Silly Example
God is love.
Love is blind.
Ray Charles is blind.
So, Ray Charles is God.
False Equivocation
If evolution is true, then we should expect that
creatures act selfishly.
If evolution is true, then creatures ought to act
selfishly.
But we know that it’s morally wrong to act
selfishly.
Creatures ought not to act selfishly.
So evolution is false.
Begging the Question + Equivocation
“To allow every man unbounded freedom of
speech must always be, on the whole,
advantageous to the state; for it is highly
conducive to the interests of the community
that each individual should enjoy a liberty,
perfectly unlimited, of expressing his
sentiments” Richard Whately's Elements of Logic
(1826)
Loaded Question Fallacy
Sometimes certain forms of words presuppose
certain things. For example:
1. John’s son won the race.
2. John’s son did not win the race.
Both sentences presuppose that John has a son.
So if I ask you “Did John’s son win the race?”
whether you answer ‘yes’ or ‘no’ you are
agreeing that John has a son.
Suppose instead that I ask you:
“At what age did you first use drugs?”
Any answer to this question is an admission that
you used drugs at some point.
Or consider:
“Have you stopped beating your wife?”
‘I stopped beating my wife’ and ‘I didn’t stop
beating my wife’ both presuppose that at some
point in the past, you beat your wife. You can’t
answer this question without admitting guilt.
Masked Man Fallacy
Inderscernability of Identicals
Normally, if you have two things X and Y, but X
and Y are really one thing, because X = Y, then if
something is true of X, it’s true of Y. For
example:
Confucius was the greatest Chinese philosopher.
Confucius = Kongzi.__________________
Therefore, Kongzi was the greatest Chinese
philosopher.
Indiscernibility of Identicals
This also means that if something is true of X,
and it’s not true of Y, then X and Y are different
things:
This gas is deadly to humans.
Oxygen is not deadly to humans.
Therefore this gas ≠ not oxygen.
Masked Man Fallacy
Sometimes, however, this argument doesn’t
work:
I know who Bruce Wayne is.
I don’t know who Batman is.
Therefore, Bruce Wayne ≠ Batman.
More serious example…
I know that I have a mind.
I don’t know that I have a
brain._____________
Therefore, the mind ≠
brain.
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.
False Dilemma
Premise 1: We can either raise taxes on
everyone, or cut social programs.
Premise 2: Raising taxes on the poor would be
terrible, they can’t afford it.
Conclusion: We should cut social programs.
Fallacy of the Mean
The fallacy of the mean is the assumption that a
“middle point” between two views is the right
one.
Fallacy of the Mean
Candidate 1: “We should raise taxes on
everyone”
Candidate 2: “We should cut social programs”
Therefore,
Compromise: We should raise taxes on everyone
a little and cut social programs a little.
Distribution Fallacy
The distribution fallacy is committed when one
assumes that individuals have the properties of
groups to which they belong.
Lingnan has an excellent philosophy
department.
I am a philosopher at Lingnan._________
Therefore, I am an excellent philosopher.
Distribution Fallacy
Kooks and quacks will often try to make their
theories sound better “by association”:
• Having a PhD.
• Making one’s work sound “science-y”.
• Debating serious scholars.
• Associating oneself with respectable
institutions (Stanford, Smithsonian, etc.)
Composition Fallacy
The converse of the distribution fallacy is the
composition fallacy, assuming that groups have
the properties of the individuals that compose
them.
For example: “A point doesn’t have any length;
lines are made out of points; therefore, a line
doesn’t have any length.”
Condorcet Paradox
One example of the composition fallacy is the
Condorcet Paradox, where every voter can have
rational preferences (doesn’t prefer A to B, B to
C, and prefer C to A), but the preferences of all
the voters taken together are irrational.
Condorcet Paradox
First Choice
Second Choice
Third Choice
Voter #1
George
Bill
Barry
Voter #2
Barry
George
Bill
Voter #3
Bill
Barry
George
Condorcet Paradox
Here, the preferences of the group are
irrational:
A majority like George better than Bill.
A majority like Bill better than Barry.
A majority like Barry better than George.
Ecological Fallacy
Here’s an “ecological inference”.
Countries where, on average, people consume
more fat have higher rates of breast cancer.
Therefore, consuming more fat leads to a higher
risk of breast cancer.
There’s a potential problem here with
“confounding variables”.
Maybe countries that consume more fat, on
average, are also countries that have more
pollution, on average (perhaps because
pollution and fat consumption both correlate
with poverty). So maybe it’s the pollution and
not the fat that causes breast cancer.
Ecological Fallacy
But let’s assume we know there aren’t any
confounding variables. Does the premise
support the conclusion:
Premise: Countries that on average consume
more fat on average have higher rates of breast
cancer.
Conclusion: Consuming fat leads to a higher risk
for breast cancer.
Ecological Fallacy
But the conclusion doesn’t follow.
Suppose that in Country A (10 people):
5 people eat 4 pounds of fat a day.
5 people eat 0 pounds of fat a day.
Average fat consumption: 2 pounds/ day.
Ecological Fallacy
In Country B (also 10 people):
5 people eat 2 pounds of fat/ day
5 people eat 1 pound of fat/ day
Average fat consumption 1.5 pounds fat/ day.
Country B on average consumes less fat.
Ecological Fallacy
Now assume that in Country A, all 5 people who
consume no fat get breast cancer. And in
Country B, no one gets breast cancer.
So on average, Country B consumes less fat and
has a lower rate of breast cancer. Country B
consumes more fat and has a higher rate of
breast cancer.
Ecological Fallacy
But still, this doesn’t mean people who consume
more fat are more likely to get breast cancer.
It’s the people who consume no fat that get
cancer!
Ecological Fallacy
A famous (purported) instance of the ecological
fallacy was Durkheim’s argument that since
suicide rates in Catholic countries were lower
than in Protestant countries, Catholics were less
likely to commit suicide than Protestants.
Prosecutor’s Fallacy
Suppose you are arrested on the basis of some
evidence– you have very large feet, just like the
footprints we found at the scene of the crime.
If someone is the killer, there’s a 100% chance
that they have very large feet.
If someone is not the killer, there’s a 95% chance
they don’t have very large feet.
Prosecutor’s Fallacy
The Prosecutor’s Fallacy is to assume that
therefore you must be guilty.
Why does this not follow?
What other fallacy (already discussed) is
identical to the Prosecutor’s Fallacy?
Argument from Ignorance
The argument from ignorance goes like this:
“You can’t prove that God doesn’t exist.
Therefore God exists.”
It assumes that because there is no argument
against a position, that that position must be
correct.
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.
Genetic Fallacy
The genetic fallacy seeks to evaluate a claim on
the basis of its origin.
So, for example, someone might say, “Eugenics
is wrong, because the Nazis began it and did
horrible things for its sake.”
Eugenics may be wrong, but the fact that the
Nazis began it is irrelevant to this claim.
Genetic Fallacy
The genetic fallacy seeks to evaluate a claim on
the basis of its origin.
So, for example, someone might say “Clearly
God does not exist. The reason I know this is
that your argument for his existence is
fallacious. Since you provided a fallacious
argument that God exists, it follows that God
does not exist.”
Appeal to Motive
Sometimes people argue that a certain claim
must be false, or an argument invalid, because
of the motives of the person making the claim/
argument.
Appeal to Motive
For example:
“My opponent claims that the government
should give free cookies to everyone. But he
stands to benefit most, because he likes cookies
so much!”
Tu Quoque
“Tu quoque” is Latin for “you too”. It’s a defense
of an invalid argument that goes:
“You’ve made a similar argument. So you cannot
criticize the flaws in this argument.”
Just because other people are doing it doesn’t
make it right!