Reasoning & Problem SolvingLecture 5b

More Fallacies

By David Kelsey

Ad Hominem

• 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: – Criticizing the person not the claim itself

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

• Inconsistency ad hominem: – to hold that what someone says is

false because it is inconsistent with something else she has said or done.

– Examples

Circumstantial &Positive ad hominem

• 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.

– Einstein example

Poisoning the Well

• To poison the well– an in advance ad hominem.

– For example, • Rumors…

Genetic Fallacy

• 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

– 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:

– Using a false dilemma for the purpose of deception

– Example:• Prayer in public schools

Perfectionist fallacy

• Perfectionist fallacy – Rejecting a policy or claim because it isn’t perfect.

– A kind of false dilemma

– Example:

• Instant replay

Line Drawing Fallacy

• 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

• 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.

– Example:

• Iraq again

– Temporal Priority

Where does the burden lie?

• Placing the burden– Plausibility:

• The burden ought to be placed on whichever side of an issue is less plausible.

• Example:

– Affirmative: • The burden, in general, ought to be placed on the affirmative side of an

issue.• Example:

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: • The defendant is always innocent until proven guilty

Appeal to ignorance

• Appeal to ignorance– claiming that we should believe that some claim is true because no one has

proved it false.

– Example:• Ghosts exist

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