Logic

Front 1

I’m willing to discuss this in depth, but if you don’t come around soon, there may be dire consequences.

Back 1

Argumentum ad baculum (fallacy of the stick)

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Argumentum ad baculum (fallacy of the stick)

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Argumentum ad baculum: appeal to force in order to either silence or threaten the opponent.

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My opponent suggests that lowering taxes will be a good idea – this is coming from a woman who eats a pint of Ben and Jerry’s every night!

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Argumentum ad hominem - direct attack: abusive

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You may argue that God doesn’t exist, but you are just following a fad.

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Argumentum ad hominem - direct attack: abusive

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Argumentum ad hominem - direct attack: abusive

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Argumentum ad hominem - direct attack: Character or other irrelevant personal qualities of the opponent are given as evidence against her position, often coupled with insults. An abusive and extreme way to distract the audience from the topic of the debate.

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We should disregard Share B.C.’s argument because they are being funded by the logging industry.

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Argumentum ad hominem - indirect attack: circumstantial

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We should discount what Premier Klein says about taxation because he won’t be hurt by the increase.

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Argumentum ad hominem - indirect attack: circumstantial

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Argumentum ad hominem - indirect attack: circumstantial

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Argumentum ad hominem: circumstantial. The position of the opponent is not criticised, rather (irrelevant) personal facts of the opponent are brought in in order to undermine his credibility and distract attention of the audience from the topic of the debate. Alternatively, doubt is cast on the opponent’s motives for arguing the way she does.

Front 9

I wish it were possible for men to get really emotionally involved in this question [abortion]. It is really impossible for the man, for whom it is impossible to be in this situation, to really see it from the woman’s point of view. That is why I am concerned that there are not more women in this House available to speak about this from the woman’s point of view.Source: House of Commons Debates of Canada, Volume 2, November 30, 1979, p. 1920

Back 9

Argumentum ad hominem - indirect attack: poisoning the well

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Argumentum ad hominem - indirect attack: poisoning the well

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Poisoning the well: committing a pre-emptive ad hominem attack on the opponent, based on personal qualities irrelevant to the debate, before the opponent has been able to make her case. This may stall the debate, and leave the position of the attacker as the apparent winner.[fallacies list]

Front 11

You accuse me of abusing my position, but you’re the one whose company car is seen propping up the rails at the local race-course!

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Argumentum ad hominem: tu quoque

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Argumentum ad hominem: tu quoque

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Tu quoque: The attempt to counter an attack from the opponent by retorting the attack on the opponent herself, thus distracting the audience from the original issue.

Front 13

Augusto Pinochet is an old, dying man. It is wrong to make him stand trial for alleged oenses.

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Argumentum ad misericordiam (or appeal to pity)

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Argumentum ad misericordiam (or appeal to pity)

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Argumentum ad misericordiam: Appeal to emotions of pity rather than rationality in order to support a proposition.

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- I think that we should invest more money in expanding the interstate system.- I think that would be a bad idea, considering the state of the treasury. - How can anyone be against highway improvements?

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Straw man

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Straw man

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Straw man: oversimplifying or pushing to the extreme the opponent’s thesis.

Front 17

God must exist: so many people nd happiness in religion.

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Ignoratio elenchi

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How could my client have ordered the murder? I have proven beyond a shadow of doubt that he was not even in the country at the time.

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Ignoratio elenchi

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Ignoratio elenchi

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Ignoratio elenchi: fallacy of irrelevance. Putting forward an argument which might in itself be valid, but of which the conclusion does not have any relation with the matter at hand.

Front 20

I read the other day that most people really like the new gun control laws. I was sort of suspicious of them, but I guess if most people like them, then they must be okay.

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Argumentum ad verecundiam (or abuse of authority)

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Argumentum ad verecundiam (or abuse of authority)

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Argumentum ad verecundiam: appeal to authority rather than rational arguments for the support or dismissal of a proposition.Not all appeals to authority are instances of bad reasoning. For instance, appealing to authority in order to provide support for a proposition during a debate is acceptable if it is clear that the person appealed to is really an authority in the eld.However, evidence for or against a proposition usually has to be evaluated on its own merits, as also authorities might be subject to committing mistakes.

Front 22

How often have you beaten your wife?

Back 22

Plurium interrogationum (or many questions fallacy)

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Plurium interrogationum (or many questions fallacy)

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Many questions: a question Q is posed to the opponent, which implicitely assumes an armative or negative answer to one or more questions P1,...,Pn on which the validity of question Q depends.

Front 24

- We should implement budget cuts.- Give me a reason why we should.- Give me a reason why we shouldn’t.

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Shifting the burden of proof

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Shifting the burden of proof

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Shifting the burden of proof: Instead of justifying ones thesis, forcing the other person to prove her wrong or justify her own thesis.

Front 26

If such actions were not illegal, then they would not be prohibited by the law.

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Petitio principii (or begging the question, or circular reasoning)

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Petitio principii (or begging the question, or circular reasoning)

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Petitio principii: assuming as a premise of the argument its conclusion. The more premises the argument has, and the more convoluted it is, the more dicult to spot the circularity.

Front 28

In the 20th century, India was justied in ghting for independence from the British. Today the National Football Alliance is ghting for its independence. So its cause is justied too.

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False analogy

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False analogy

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False analogy: a fallacy which introduces a weak analogy between A and B in order to claim that since A has property P, then also B has property P.

Front 30

Of course your columnist Michele Slatalla was joking when she wrote about needing to talk with her 58-year-old mother about going into a nursing home. While I admire Slatalla’s concern for her parents, and agree that as one approaches 60 it is wise to make some long-term plans, I hardly think that 58 is the right age at which to talk about a retirement home unless there are some serious health concerns. In this era, when people are living to a healthy and ripe old age, Slatalla is jumping the gun. My 85-year-old mother power-walks two miles each day, drives her car (safely), climbs stairs, does crosswords, reads the daily paper and could probably beat Slatalla at almost anything.

Back 30

Hasty generalization

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Hasty generalization

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Hasty generalization: supporting the truth of a proposition by means of a generalization from a few cases which are either not representative of the variability of the whole population, or whose representativity has not been suciently argued for.A hasty generalization occurs whenever conclusions are made based on a sample which is too small to represent the whole population.

Front 32

- A cat ran across my path. Ten minutes later I was hit by a truck.- I bet it was a black cat.

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Post hoc ergo propter hoc

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Post hoc ergo propter hoc

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Post hoc ergo propter hoc: a fallacy committed whenever one infers the conclusion that A must be the cause of B exclusively from the observation that A and B are in temporal succession.Temporal succession of events A and B is a necessary condition for A to be a cause of B, but it is not a sucient condition.(Roosters crow just before the sun rises but do not, therefore, cause the sun to rise.)[fallacies list]

Front 34

Then the ecologist superimposed the two curves atop a similar graph representing the concurrent sunspot activity: voil`a! The three cycles approximately coincided over a good portion of their range. The ecologist leaped to the conclusion that the annual uctuations of the lynx and rabbit populations were controlled by the eleven-year sunspot cycle

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Cum hoc ergo propter hoc

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Cum hoc ergo propter hoc

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Cum hoc ergo propter hoc: a fallacy committed whenever one infers the conclusion that A must be the cause of B exclusively from the observation that A and B vary simultaneously.“Near-perfect correlations exist between the death rate in Hyderabad, India, from 1911 to 1919, and variations in the membership of the International Association of Machinists during the same period. Nobody seriously believes that there is anything more than a coincidence in that odd and insignificant fact.”There may be an additional variable which causes both variations. Or it may just be chance.

Front 36

We’ve got to stop them from banning pornography. Once they start banning one form of literature, they will never stop. Next thing you know, they will be burning all the books!

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Slippery slope

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Slippery slope

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Slippery slope: arguing that there exists a causal chain of events C1,...,Cn leading from an event A to another event B which is usually considered bad in some way (morally or otherwise).This type of reasoning is not always a fallacy. The strength of the argument depends on the strength of the causal links C1,...,Cn. In general, the more causal links there are, the harder it is to justify the argument.

Front 38

Bob Murch, spirit board collector: “There’s been thousands of years of accounts of ghosts and hauntings, and if those are true, you know, surely a spirit board can work.”Penn Jillette:“So, if those aren’t true, a spirit board can’t work? Cool!”Source: Penn & Teller, “Ouija Boards/Near Death Experiences”, B.S.!A clearer example:If the sprinkler is on, the street is wet. But the sprinkler isn’t on. Therefore, the street is not wet.

Back 38

Denying the antecedent

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Denying the antecedent

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Denying the antecedent: a conditional statement of the form “if P is the case, then Q must be the case” establishes P as a sucient condition for Q to occur.Assuming that the conditional statement holds, claiming that P is false is, however, not sucient to conclude that Q is also false; for instance, there might be other sucient conditions enforcing the truth of Q, as in the sprinkler example before.

Front 40

If I have the u, then I have a sore throat.I have a sore throat.Therefore, I have the u.

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Arming the consequent

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Arming the consequent

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Armation of the consequent: a fallacy committed whenever one concludes, from the observation that the truth of A logically implies the truth of B (so: A is a sucient condition for B) and that B occurs, that A must also occur.

Front 42

The food is denitely going to be delicious, since all its ingredients are delicious too.

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Fallacy of composition

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Fallacy of composition

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Fallacy of composition: to deduce, from the fact that all of the component parts of a whole possess the property P, that the whole possesses P.Again, this is not always fallacious: it depends on the type of property considered. For example: “all the molecules composing my body are extended. Therefore, my body is extended.”

Front 44

- The community of Pacic Palisades is extremely wealthy.- Adam lives there.- He must be extremely wealthy.

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Fallacy of division

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Fallacy of division

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Fallacy of division: the converse of the fallacy of composition.

Front 46

No one knows it is true. Therefore it is false.

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Argumentum ad ignorantiam

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Argumentum ad ignorantiam

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Ad ignorantiam: absence of evidence for a proposition does not constitute evidence for its contrary.

Front 48

One day late in December[Charles] Dickens announced that he couldn’t travel by train anymore that year, “on the grounds that the average annual quota of railroad accidents in Britain had not been lled and therefore further disasters were obviously imminent.”

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The gambler’s fallacyThe gambler’s fallacy

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The gambler’s fallacy

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The gambler’s fallacy: inferring that a certain outcome of a random trial is more likely, given that a specic history of outcomes of previous, statistically independent random trials has been observed. Suppose a coin has been tossed 10 times producing the outcomes HHHHHHHHHH. What is the probability that the eleventh toss of the coin turns up T?1

Front 50

Gerda Reith is convinced that superstition can be a positive force. “It gives you a sense of control by making you think you can work out what’s going to happen next,” she says. “And it also makes you feel lucky. And to take a risk or to enter into a chancy situation, you really have to believe in your own luck. In that sense, it’s a very useful way of thinking, because the alternative is fatalism, which is to say, ’Oh, there’s nothing I can do.’ At least superstition makes people do things.” Source: David Newnham, “Hostages to Fortune”

Back 50

False dilemma (or bifurcation fallacy)

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False dilemma (or bifurcation fallacy)

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False dilemma: arguing for a proposition P by assuming without support that either P or Q must be the case, and that Q must be rejected.The fallacy resides in the premise that either P or Q must be the case, neglecting other possible alternatives.

Front 52

1 ad hominem: ad baculum2 ad hominem: abusive3 ad hominem: circumstantial4 ad hominem: poisoning the well5 ad hominem: tu quoque6 ad misericordiam7 straw man8 ignoratio elenchi9 ad verecundiam10 plurium interrogationum11 shifting the burden of proof12 petitio principii13 false analogy14 hasty generalization15 post (/cum) hoc ergo propter hoc16 slippery slope17 denying the antecedent18 arming the consequent19 fallacy of composition/division20 ad ignorantiam21 gambler’s fallacy22 false dilemma

Back 52

1 ad hominem: ad baculum2 ad hominem: abusive3 ad hominem: circumstantial4 ad hominem: poisoning the well5 ad hominem: tu quoque6 ad misericordiam7 straw man8 ignoratio elenchi9 ad verecundiam10 plurium interrogationum11 shifting the burden of proof12 petitio principii13 false analogy14 hasty generalization15 post (/cum) hoc ergo propter hoc16 slippery slope17 denying the antecedent18 arming the consequent19 fallacy of composition/division20 ad ignorantiam21 gambler’s fallacy22 false dilemma