Fallacies
The quickest ways to lose arguments
Introduction to Logic
O Argument: The assertion of a conclusion
based on logical premises
O Premise: Proposition used as evidence in an
argument
O Conclusion: Logical result of the relationship
between the premises. Conclusions serve as
the thesis of the argument.
O Syllogism: The simplest sequence of logical
premises and conclusions. Developed by
Aristotle.
Syllogism
O Premise 1: All men are mortal.
O Premise 2: Socrates is a man.
O Conclusion: Therefore, Socrates is mortal.
O Reaching logical conclusions depends on the
proper analysis of premises.
O The goal of a syllogism is to arrange premises so
that only one true conclusion is possible.
O Logic allows specific conclusions to be drawn
from general premises.
Syllogism
O Logic requires decisive statements in order
to work.
O For example, the premise that “SOME men
are mortal” does not contain enough
information to allow a verifiable conclusion.
O Logic cannot be based on premises which the
audience does not accept.
Let’s Practice!
O Complete the syllogism:
O Premise 1:
O Premise 2:
O Conclusion: Therefore, the California
minimum wage should be increased.
Possible Answer
O Premise 1: Minimum wage should match the
cost of living in society.
O Premise 2: The current California minimum
wage does not match the cost of living in
society.
O Conclusion: Therefore, the California
minimum wage should be increased.
What is a fallacy?
O A fallacy is a flaw or an error in an argument
Hasty Generalization
O Making assumptions about an entire range
of people or a range of cases based on an
inadequately small sample or one
experience
O Stereotypes are a common example
Missing the Point
O The premise supports a conclusion other
than the one it’s meant to support
O Example: Premise 1: There has been an
increase in burglaries in the area. Premise
2: More people are moving into the area.
Conclusion: Therefore, the burglaries are
caused by and increased number of people
moving to the area.
False Cause
O In Latin, this fallacy is called post hoc. It comes
from the phrase post hoc, ergo propter hoc,
which means after this because of this
O This fallacy presumes that because X preceded
Y, X caused Y.
O Example: Premise 1: Cell phone usage has
increased in the last 20 years. Premise 2:
Researchers discovered that incidences of brain
cancer have increased in the last 20 years.
Conclusion: Therefore, cell phone usage must
cause brain cancer.
Slippery Slope
O Falsely assuming that one thing will
inevitably lead to another, and another, and
another until we have reached some
unavoidable, dire consequence.
Weak Analogy
O When you compare two things that aren’t
really similar
Appeal to Authority
O When an arguer tries to get people to agree
with them by appealing to a supposed
authority figure who is not really an expert
Appeal to Pity
O Attempting to convince someone to do
something or agree with them by making
them feel sorry
O Students are great at using this fallacy!
Appeal to Ignorance
O This fallacy states that because there is no
conclusive evidence, the arguer’s
conclusions on the subject should just be
accepted.
O The lack of evidence is used to support the
conclusion
O Example: Premise: Not a single report of a
UFO has been authenticated. Conclusion:
Therefore, UFOs do not exist.
Bandwagon
O When the arguer tries to convince someone
to do something because everyone else
(supposedly) does
O Example: Premise: An increasing number of
people are turning to CrossFit to get in tough
with their center. Conclusion: Therefore,
CrossFit helps everyone get in touch with
their center.
Ad Hominem
O Attacking the other side instead of their
argument.
Tu quoque
O The arguer points out that the opponent has
actually done the thing they are arguing
against, concluding that we do not have to
listen to the argument
Straw Man
O The arguer sets up a weaker version of the
opponent’s position and seeks to prove that
version rather than the position the arguer
actually holds
O Through misrepresentation, the arguer
concludes that the real position has been
refuted.
O Example: Those who seek to abolish the death
penalty are seeking to allow murderers and
others who commit heinous crimes to simply get
off scot-free with no consequence for their
actions
Red Herring
O The arguer goes off on a tangent midway
through the argument, raising a side issue
that distracts the audience from the main or
original argument
False Dichotomy
O The arguer sets up the situation so that it looks
as though there are only two choices. When the
arguer then eliminates one of the choices, it
appears as if there’s only one option left—the
arguer’s assertion.
O Usually a situation is oversimplified and other
options are eliminated.
O Example: Premise 1: I can’t find my book! Either
someone stole it or I never had it. Premise 2: I
know I had it. Conclusion: Therefore, someone
stole it.
Begging the Question
O The arguer asks the audience to simply accept the
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conclusion without providing any real evidence, either
through the use of circular reasoning or by ignoring
an important (but questionable) assumption that the
argument rests on.
Circular reasoning occurs when the premise states
the same thing as the conclusion.
This is a harder fallacy to detect/avoid.
Example: Paranormal activity is real because I have
experienced what can only be described as
paranormal activity.
Example: If such acts weren’t illegal, then they would
not be prohibited by the law.
Information adapted from
O Lecture by Andrea Hernandez—Summer
2015.
O Various slideshare presentations on
fallacies.