logical fallacies
DESCRIPTION
Logical fallacies lectureTRANSCRIPT
logical fallacieslogical fallacieslogical fallacieslogical fallacies
THE ART OF DEBATETHE ART OF DEBATE
From OWL English PurdueFrom OWL English PurdueTHE ART OF DEBATETHE ART OF DEBATE
From OWL English PurdueFrom OWL English Purdue
What is a logical What is a logical fallacy?fallacy?
What is a logical What is a logical fallacy?fallacy?
Fallacies are common errors in reasoning that Fallacies are common errors in reasoning that
will undermine the logic of your argument. will undermine the logic of your argument.
Fallacies can be either illegitimate arguments Fallacies can be either illegitimate arguments
or irrelevant pointsor irrelevant points
They are often identified because they lack They are often identified because they lack
evidence that supports their claim. evidence that supports their claim.
Avoid these fallaciesAvoid these fallacies
Types of Logical Types of Logical FallaciesFallacies
Types of Logical Types of Logical FallaciesFallacies
SLIPPERY SLOPE SLIPPERY SLOPE
HASTY GENERALIZATIONHASTY GENERALIZATION
POST HOC ERGO PROPTER HOCPOST HOC ERGO PROPTER HOC
GENERIC FALLACYGENERIC FALLACY
BEGGING THE CLAIMBEGGING THE CLAIM
CIRCULAR ARGUMENTCIRCULAR ARGUMENT
EITHER/ OREITHER/ OR
AD HOMINEMAD HOMINEM
AD POPULUMAD POPULUM
RED HERRINGRED HERRING
STRAW MANSTRAW MAN
MORAL EQUIVALENCEMORAL EQUIVALENCE
Slippery SlopeSlippery SlopeSlippery SlopeSlippery Slope
This is a conclusion based on the premise This is a conclusion based on the premise
that is that is AA happens, then eventually happens, then eventually
through a series of small steps, through through a series of small steps, through BB, ,
CC, ...., ....XX, , YY, , ZZ will happen, too, basically will happen, too, basically
equating equating AA and and ZZ. So , if we don’t want . So , if we don’t want ZZ
to occur, to occur, AA must not be allowed to occur must not be allowed to occur
either. either.
Slippery SlopeSlippery SlopeSlippery SlopeSlippery SlopeThis is a conclusion based on the premise that is This is a conclusion based on the premise that is AA happens, then eventually happens, then eventually
through a series of small steps, through through a series of small steps, through BB, , CC, ...., ....XX, , YY, , ZZ will happen, too, will happen, too,
basically equating basically equating AA and and ZZ. So , if we don’t want . So , if we don’t want ZZ to occur, to occur, AA must not be must not be
allowed to occur either. allowed to occur either.
Example:Example: If we ban Hummers because they are bad If we ban Hummers because they are bad
for the environment, eventually the government will for the environment, eventually the government will
ban all cars, so we should not ban Hummers.ban all cars, so we should not ban Hummers.
In this example the author is equating banning In this example the author is equating banning
Hummers with banning all cars, which is not the Hummers with banning all cars, which is not the
same thing.same thing.
Hasty Hasty GeneralizationGeneralization
Hasty Hasty GeneralizationGeneralization
This is conclusion based on insufficient or This is conclusion based on insufficient or
biased evidence. biased evidence.
In other words, you are rushing to a In other words, you are rushing to a
conclusion before you have all the conclusion before you have all the
relevant facts.relevant facts.
Hasty Hasty GeneralizationGeneralization
Hasty Hasty GeneralizationGeneralization
This is conclusion based on insufficient or This is conclusion based on insufficient or
biased evidence. biased evidence.
In other words, you are rushing to a conclusion In other words, you are rushing to a conclusion
before you have all the relevant facts.before you have all the relevant facts.
Example: Example: Even though it’s only the first day, I Even though it’s only the first day, I
can tell this is going to be a boring course.can tell this is going to be a boring course.
Write your own fallacy.Write your own fallacy.
post hoc ergo post hoc ergo propter hocpropter hoc
post hoc ergo post hoc ergo propter hocpropter hoc
This is the conclusion that assumes that if This is the conclusion that assumes that if
AA occurred after occurred after BB then then BB must have must have
caused caused AA
post hoc ergo post hoc ergo propter hocpropter hoc
post hoc ergo post hoc ergo propter hocpropter hoc
This is the conclusion that assumes that if This is the conclusion that assumes that if AA
occurred after occurred after BB then then BB must have caused must have caused AA
ExampleExample: I drank bottled water and now I am : I drank bottled water and now I am
sick, so the water must have made me sick.sick, so the water must have made me sick.
In this example the author assumes that if one In this example the author assumes that if one
event chronologically follows another the first event chronologically follows another the first
event must have caused the second. event must have caused the second.
Write your own fallacy.Write your own fallacy.
generic fallacygeneric fallacygeneric fallacygeneric fallacy
A conclusion is based on an argument that A conclusion is based on an argument that
the origins of a person, idea, institution, or the origins of a person, idea, institution, or
theory determine its character, nature or theory determine its character, nature or
worth.worth.
generic fallacygeneric fallacygeneric fallacygeneric fallacy
A conclusion is based on an argument that A conclusion is based on an argument that
the origins of a person, idea, institution, or the origins of a person, idea, institution, or
theory determine its character, nature or theory determine its character, nature or
worth.worth.
Example: Example: The Volkswagen Beetle is an evil The Volkswagen Beetle is an evil
car because it was originally designed by car because it was originally designed by
Hitler’s army.Hitler’s army.
Write your own fallacy.Write your own fallacy.
Begging the claimBegging the claimBegging the claimBegging the claim
The conclusion that the writer should The conclusion that the writer should
prove is validated within the claimprove is validated within the claim
Begging the claimBegging the claimBegging the claimBegging the claim
The conclusion that the writer’s proof is The conclusion that the writer’s proof is
validated within the claimvalidated within the claim
Example:Example: Filthy and polluting coal should Filthy and polluting coal should
be banned.be banned.
Write your own fallacy.Write your own fallacy.
Circular argumentCircular argumentCircular argumentCircular argument
This restates the argument rather than This restates the argument rather than
actually proving it.actually proving it.
Circular argumentCircular argumentCircular argumentCircular argument
This restates the argument rather than This restates the argument rather than
actually proving it.actually proving it.
Example: Example: George Bush is a good George Bush is a good
communicator because he speaks communicator because he speaks
effectively.effectively.
Write your own fallacy.Write your own fallacy.
Either/orEither/orEither/orEither/or
This is a conclusion that oversimplifies the This is a conclusion that oversimplifies the
argument by reducing it to only two sides argument by reducing it to only two sides
or choices.or choices.
Either/orEither/orEither/orEither/or
This is a conclusion that oversimplifies the This is a conclusion that oversimplifies the
argument by reducing it to only two sides argument by reducing it to only two sides
or choices.or choices.
Example:Example: We can either stop using cars We can either stop using cars
or destroy the earth.or destroy the earth.
Write your own fallacy.Write your own fallacy.
Ad HominemAd HominemAd HominemAd Hominem
This is an attack on the character of a This is an attack on the character of a
person rather than their opinions or person rather than their opinions or
argumentsarguments
Ad HominemAd HominemAd HominemAd Hominem
This is an attack on the character of a This is an attack on the character of a
person rather than their opinions or person rather than their opinions or
argumentsarguments
Example: Example: Green Peace’s strategies aren’t Green Peace’s strategies aren’t
effective because they are all dirty, lazy effective because they are all dirty, lazy
hippies.hippies.
Write your own fallacy.Write your own fallacy.
Ad PopulumAd PopulumAd PopulumAd Populum
This is an emotional appeal that speaks to This is an emotional appeal that speaks to
positive (such as patriotism, religion, positive (such as patriotism, religion,
democracy) or negative (such as terrorism democracy) or negative (such as terrorism
or fascism) concepts rather than the real or fascism) concepts rather than the real
issue at handissue at hand
Ad PopulumAd PopulumAd PopulumAd Populum
This is an emotional appeal that speaks to This is an emotional appeal that speaks to
positive (such as patriotism, religion, positive (such as patriotism, religion,
democracy) or negative (such as terrorism or democracy) or negative (such as terrorism or
fascism) concepts rather than the real issue at fascism) concepts rather than the real issue at
handhand
Example:Example: If you were a true American you If you were a true American you
would support the rights of people to choose would support the rights of people to choose
whatever vehicle they want.whatever vehicle they want.
Write your own fallacy.Write your own fallacy.
Red HerringRed HerringRed HerringRed Herring
This is a diversionary tactic that avoids This is a diversionary tactic that avoids
the key issues, often by avoiding opposing the key issues, often by avoiding opposing
arguments rather than addressing them.arguments rather than addressing them.
Red HerringRed HerringRed HerringRed Herring
This is a diversionary tactic that avoids This is a diversionary tactic that avoids
the key issues, often by avoiding opposing the key issues, often by avoiding opposing
arguments rather than addressing them.arguments rather than addressing them.
Example:Example: The level of mercury in seafood The level of mercury in seafood
may be unsafe, but what will fishers do to may be unsafe, but what will fishers do to
support their families?support their families?
Write your own fallacy.Write your own fallacy.
Straw manStraw manStraw manStraw man
This move oversimplifies an opponent’s This move oversimplifies an opponent’s
viewpoint and then attacks that hollow viewpoint and then attacks that hollow
argument.argument.
Straw manStraw manStraw manStraw man
This move oversimplifies an opponent’s This move oversimplifies an opponent’s
viewpoint and then attacks that hollow viewpoint and then attacks that hollow
argument.argument.
People who don’t support the proposed state People who don’t support the proposed state
minimum wage increase hate the poor.minimum wage increase hate the poor.
Write your own fallacy.Write your own fallacy.
Moral EquivalenceMoral EquivalenceMoral EquivalenceMoral Equivalence
This fallacy compares minor misdeeds This fallacy compares minor misdeeds
with major atrocities.with major atrocities.
Moral EquivalenceMoral EquivalenceMoral EquivalenceMoral Equivalence
This fallacy compares minor misdeeds This fallacy compares minor misdeeds
with major atrocities.with major atrocities.
Example:Example: That parking attendant who That parking attendant who
gave me a ticket is as bad as Hitler.gave me a ticket is as bad as Hitler.
Moral EquivalenceMoral EquivalenceMoral EquivalenceMoral Equivalence
This fallacy compares minor misdeeds This fallacy compares minor misdeeds
with major atrocities.with major atrocities.
Example:Example: That parking attendant who That parking attendant who
gave me a ticket is as bad as Hitler.gave me a ticket is as bad as Hitler.
Write your own fallacy.Write your own fallacy.