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Logic: informal fallaciesWhat is an informal fallacy?

Fallacy - any flaw in reasoning

Informal fallacy - a flaw in reasoningbecause of content rather than form

Note 1: The notion of an informalfallacy is more inclusive than invalidity

and weakness. It can occur in bothdeductive & inductive arguments.

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Logic: informal fallacies Note 2: The number of informal

fallacies is in principle indefinite. Wewill examine twelve.

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Logic: informal fallacies (1) Case for analysis:

If we dont increase our military

spending dramatically, our militarypower will be greatly diminished. Evensmall countries with little more thansmall arms and mines will be a threat

to our sovereignty. Identification: False dilemma (6)

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Logic: informal fallacies (2) Cases for analysis:

(a) I asked my doctor why my mouth

is so dry and he said because mysalivary glands are not producingenough saliva.

(b) Have you given up that annoying

habit of answering every questionwith a question?

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Logic: informal fallacies (c) Jamie: We ought to have national

health insurance? Brendt: But that issocialism.

Identification: Begging the question(petitio principii)

(a) circular form (8)

The conclusion says approximatelythe same thing as the premises.

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Logic: informal fallacies (b) Begging the question - loaded or

leading question (8)

Framing a question in such a waythat it requires a specific answer.

(c) Begging the question - use ofquestion begging words or phrases

Arguing by labeling, as if this is asufficient reason. Packing tacitassumptions into a label.

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Logic: informal fallacies (3) Case for analysis:

Defendants attorney at a sentencinghearing. My client caused serious

bodily harm to another innocentperson. But his mother died last yearand his father is seriously ill. [Assumeno other reasons are given for a lightsentence.]

Identification: Appeal to emotion orpity (1)

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Logic: informal fallacies (4) Case for analysis:

News conference with Mayor Guliani:Shouldnt you resign because you no longer

enjoy the support of the people of NewYork? Response: We have made tremendousprogress toward our goal of lower taxes anda balanced budget. Just last week the City

Council passed a bill cutting spending forwelfare by $500 million dollars. No longerwill these millions of dollars go down arapacious endless sinkhole.

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Logic: informal fallacies Identification: Red herring (12)

Distracting attention from the main

issue under debate by dwelling onanother issue.

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Logic: informal fallacies (5) Case for analysis:

Whenever I feel a cold coming on, I

drink Mrs. Wizners herbal tea. Mycolds are always mild and do not lastlong.

Identification: Post hoc, ergo

propter hoc, or false cause (9)

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Logic: informal fallacies (6) Case for analysis:

John P. Roche, in his political column

(Oct. 1970): Every society is, ofcourse, repressive to some extent--asSigmund Freud pointed out, repressionis the price we pay for civilization.

Identification: Equivocation (10)

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Logic: informal fallacies (7) Case for analysis:

How can I take your campaign against

drunk driving seriously? You yourselfwere convicted of drunk driving (DWI)in 1980.

Identification: Ad hominem (4)

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Logic: informal fallacies (8) Case for analysis:

The construction of the new F-18s has

run way over projected costs. But theNavy argues that there are goodreasons for this--the radar is acompletely new system, the missals

are experimental, . . . We ought tolisten to the experts from the Navy.The understand these problems.

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Logic: informal fallacies Einstein said that God is the geometer

of the universe, but not a personalGod. We ought to accept this becauseEinstein was a brilliant scientist.

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Logic: informal fallacies Identification: Improper appeal toauthority (2)

Two versions: (a) Exaggerated authority (1stcase above)

(b) Misplaced authority (2nd case

above)

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Logic: informal fallacies (9) Case for analysis:

Haly Barbour (former Chair of

Republican National Committee):The Democratic position on taxeshas consistently been that themore the better. The Democrats

have never seen a social programwhich they do not like.

Identification: Straw man (11)

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Logic: informal fallacies (10) Case for analysis:

The Social Security Advisory Council

has backed away from a proposal toincrease the maximum pay subject toSoc-Sec taxation from $14,000 to$24,000 to keep the plan on a pay-

as-you-go basis. Instead, it hasrecommended shifting the cost ofMedicare to the general fund. (more)

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Logic: informal fallacies (contd) The proposal, if adopted,

would begin the process oftransforming Soc. Sec. into an out-and-out welfare program. Once westart in that direction, were do westop? (N.Y. Daily News, Jan. 21,

1975) Identification: Slippery slope (7)

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Logic: informal fallacies Comments:

Not all slopes are slippery.

Guidelines for determining Is there empirical support for

the slipperiness of the slope?

Is there an alternative ofsharpening civil or moral normsin order to avoid going downthe slope?

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Logic: informal fallacies (11) Case for analysis:

Tom Wolfes new novel, A Man in Full,

must be a great work of literaturesince it has been on the best-sellerlist for several months.

Identification: Appeal to popular

belief (3)

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Logic: informal fallacies (12) Case for analysis:

In 1950, Joseph McCarthy responded to adoubting question about the 40th name on alist of 81 case histories he claimed were ofcommunists working for the United StatesState Dept. by saying: I do not have muchinformation on this except the general

statement of the agency that there isnothing in the files to disprove hisCommunist connections.

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Logic: informal fallacies Darwins theory should be rejected

because no missing links have beenfound and the dating techniques usedto determine the age of the earthare suspect.

Identification: Appeal to ignorance

(5)

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Logic: informal fallacies Two versions:

(a) Arguing that a position is

true because it has not beenproven false. The most commonversion. (1st case above)

(b) Arguing that a position isfalse because it has not beenproven true. Less commonversion. (2nd case above)