Logical Fallacies

What are logical fallacies?
When trying to make a case or argument
where logic is missing or something in the
case is not clear
 Is not necessarily a false statement
 Can be useful in debates
Why learn logical fallacies?
Point them out when an opponent uses one or
offer reasoning if you use them
Make you look smart
Impresses judges
Can remove an argument from the table not just
weaken it
You can know when you are using them and
prepare for your opponents argument rather
than being taken off guard and unprepared
How do you point them out?
State the name of fallacy in Latin and English
making sure to use the phrase “logical fallacy”
Tell everyone what the fallacy means and why it is
wrong but do it without sounding pedantic (smarter
than everyone else)
Give a really obvious example of why the fallacy is
incorrect, preferably the example should also be an
unfavorable analogy for your opponents case
Point out why the fallacy matters to the debate
Argumentun ad antiquitatem
The argument to antiquity or tradition
Argument that a policy, behavior or practice is right or
acceptable because “its always been done that way”
Example: “every great civilization in history has provided
states subsidies for art and culture”
Try to avoid it but if you do use it, try to give a reason
why it should be considered
Argumentum ad hominem
Argument directed at the person
 Attacking the character or motives of a person
who has stated and idea rather than the idea
itself; can also be an attack on the source of
 “my opponents are fascists” or “Richard Nixon was
liar and a cheat”
 Can also be used when the person talking has
something to gain from the policy (example: Bill
Gates talking against anti-trust legislation)
Argumentum ad ignorantiam
Argument to ignorance
Assuming something is true simple because it hasn’t
been proven false (example: global warming is true
because nobody has demonstrated conclusively it is
Which ever team/person has “burden of proof”
(usually affirmative) has to be more careful in using
this fallacy
Example: Prosecution who says that no alibi means
guilty vs.. Defense saying prosecution didn’t prove
case so defendant is not guilty
Argument ad logicam
Argument to logic
 Assuming that something is false simply because
proof or argument that someone has offered for it is
 Also known as Straw Man argument
 Burden of proof determines whether it is fallacy or
not (if affirmative team fails to provide sufficient
support for its case, the burden of proof dictates
they should lose the debate even if there exist other
arguments not presented that could have supported
the case)
Argumentum ad misericordian
Argument or appeal to pity
 Example: “Think of all the poor, starving people
in Ethiopia. How can we not help them?”
 This doesn’t mean you can’t argue for something
like aid to Ethiopia, what it does mean is that
you can’t just use emotional pleas
 Do not use it unless the opposition has ONLY
offered emotional pleas
Argumentum ad nauseam
Argument to the point of disgust (repetition)
 Trying to prove something by saying it again
and again
 Stating a main point over and over again instead
of real arguments
 Make sure you SUPPORT your main points
Argumentum ad numerum
Argument or appeal to numbers
 Attempt to prove something by showing
how many people think that it’s true
 Example: 70% of all Americans support
restrictions on access to abortions
 Don’t confuse this with argumentum ad
Argumentum ad populum
Appeal to people or to popularity
 Trying to prove something by showing
that the public agrees with you
 Narrowly designates an appeal to the
opinions of people in the immediate
vicinity like your judges
Argumentum ad verecundiam
Argument or appeal to authority
 Someone tries to demonstrate the truth of a
proposition by citing some person who agrees,
even though that person may have no expertise
in the given area
 Example: Quoting Einstein on politics
 Only use this when they don’t use qualified
quotes to support the same point and/or imply
some policy is right because so-and-so thought
Circulus in demonstrando
Circular argument
 Someone uses what they are trying to
prove as part of the proof of that thing
 Always illegitimate but hard to spot
Complex Question
Question that implicitly assumes something to
be true by its construction
 Example: Have you stopped beating your wife”
or “Inasmuch as the majority of black Americans
live in poverty, do you really think that self-help
within the black community is sufficient to
address their problems?”
 Only a fallacy when used for something that
hasn’t been proved
Cum hoc ergo propter hoc
With this, therefore because of this
 Mistaking correlation for causation (because two
things occur simultaneously, one must be a
cause of the other)
 Example: President Clinton has great economic
policies, just look at how great the economy is
 Usually called post hoc
Dicto simpliciter
Sweeping generalization
 Making a sweeping statement and expecting it
to be true of every specific case; aka
 Example: Women on average are not as strong
as mean and less able to carry a gun. Therefore
women can’t pull their weight in a military unit.
 When pointing it out in a round, try not to use
the Latin and just attack the generalization
Nature, appeal to
Assuming that whatever is natural or
consistent with nature is good or that
whatever conflicts with nature is bad
 Fairly rare, but usually seen in
environmentalist argument
Naturalistic Fallacy
Trying to derive conclusions about what is right
or good (about values) from statements of fact
 Any inference of fact is another fact NOT a value
 “The medicine will prevent you from dying” does
not lead to ‘you should take this medicine”
 Examples include argumentum ad antiquities or
appeal to nature
Non Sequitur
It does not follow
 Stating as a conclusion, something that does not
strictly follow from the premises
 Example: Racism is wrong, therefore, we need
affirmative action”
 Try to to use this for every argument but use it
when the opposition is trying to construct A lead
to B leads to C without justifying each step in
the chain
Petitio Principii
Begging the question
Assuming, when trying to prove something, what it is
that your are trying to prove
Very similar to circular argument
Occurs when a question has been asked before in the
discussion then a conclusion is reached on a related
matter without the question having been answered
Example: “The fact that we believe pornography should
be legal means that it is valid form of free expression.
And since it’s free expression, it shouldn’t be banned”
Post hoc ergo propter hoc
After this, therefore because of this
 Assuming that A caused B simply because A
happened prior to B
 Example: most rapists read pornography when
they were teenagers; obviously, pornography
causes violence toward women.
 Similar to cum hoc ergo prompter hoc
Red herring
Introducing irrelevant facts or arguments to
distract from the question at hand
 Example: The opposition claims that welfare
dependency leads to higher crime rates - but
how are poor people supposed to keep a roof
over their heads without our help?
 It is not fallacious to argue that benefits of one
kind may justify incurring costs of another kind
Slippery slope
Not always a fallacy
 Argument that says adopting one policy or
taking one action will lead to a series of other
policies or actions also being taken without
showing a causal connection between the
advocated policy and the consequent policies
Example: If we legalize marijuana, the next
thing you know we’ll legalize heroin, LSD and
crack cocaine.
Straw man
Refuting a caricatured or extreme version
of somebody’s argument rather than the
actual argument they’ve made
 Putting words into someone else’s mouth
or misinterpreting something said
Tu quoque
You too
 Defending an error in one’s reasoning by
pointing out that one’s opponent has made the
same error
 Example: They accuse us of making unjustified
assertions. But they asserted a lot of things,
 Can be helpful if both sides have done a bad job
of debating and you want to point that out to
the judges
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