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Introduction to Logic
Lecture 5b
More Fallacies
By David Kelsey
Ad Hominem
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To commit this fallacy is to think that some consideration about a person refutes
the claims that he or she makes.
•
Confusing the person and the claim:
Ad Hominem again
•
A personal attack ad hominem:
–
claiming that because someone has
certain negative features it follows
that a claim she makes is false.
–
Examples
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Inconsistency ad hominem:
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to hold that what someone says is
false because it is inconsistent with
something else she has said or
done.
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Examples
Circumstantial &
Positive ad hominem
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Circumstantial ad hominem:
–
holding that because a person’s
circumstances are a certain way it
follows that some claim she makes
is false.
–
Priest example
•
Positive ad hominem:
–
holding that the claim a person
makes follows from some positive
consideration about the person.
Poisoning the Well
• To poison the well
– an in advance ad hominem.
– For example,
Genetic Fallacy
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When one tries to refute a claim based on its origin or history she has
committed the genetic fallacy.
– Belief in God’s existence
– Genetic fallacy vs. Circumstantial ad Hominem
Straw Man
•
Straw man fallacy:
– trying to refute a claim or argument by distorting it or oversimplifying it or
misrepresenting it in such a way that it can be easily refuted.
– Reconfiguring a claim
– Knocking down a straw man is easy business but knocking down a good
argument is not.
False Dilemma
•
False dilemma
–
–
limits considerations to a choice between only two alternatives although other
reasonable alternatives are available.
The form of a false dilemma:
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Using a false dilemma for the purpose of deception
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Example:
Perfectionist fallacy
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Perfectionist fallacy
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Rejecting a policy or claim because it isn’t perfect.
–
A kind of false dilemma
–
Example:
Line Drawing Fallacy
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The Line-Drawing fallacy
–
insisting that a conceptual line must be drawn at a particular point when drawing such
a line isn’t necessary.
–
Examples:
•
•
•
–
Rich
Bald
Excessive force
Line drawing and Vagueness
Slippery Slope
•
Slippery Slope:
–
Claiming that if we let some thing X occur it follows that something else Y will occur,
yet there is no reason to think that if X occurs so must Y.
–
Causation and slippery slope arguments
–
Example:
• Hand gun laws
Misplacing the Burden of Proof
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Misplacing the burden of proof:
– Misplacing the burden of proof on the wrong side of an issue.
– The 2 sides of an issue
– Example:
• Should we go to war with Iraq?
The burden of proof
•
To say the burden of proof rests on a claim:
–
This just means that if one is to hold this position, then she must support it with
argumentation.
–
Temporal Priority
–
Example:
Where does the burden lie?
• Placing the burden
– Plausibility:
– Affirmative:
The burden of proof #3
•
Special Circumstances:
– Under special circumstances the burden of proof is placed on a particular
side of an issue.
– The court:
Appeal to ignorance
•
Appeal to ignorance
– claiming that we should believe that some claim is true because no one has
proved it false.
– A type of burden of proof fallacy
– Example:
Begging the Question
•
One begs the question when one of the premises of her argument
assumes the truth of the conclusion.
•
Examples:
– Abortion
– An argument for God’s existence
•
Circular reasoning