Sunday, September 28, 2008


For all CAT 2008 aspirants who love to argue among their friends, here is a potent weapon to hone their reasoning skills. A knowledge of errors that we commit while making arguments will prevent us from committing them. A fallacy is an error in reasoning where the argument fails to establish the truth because it relies on premisses that do not imply the conclusion. In a fallacious argument, the conclusion could be false even if all its premisses were true. Therefore, a fallacy is an argument which may seem to be correct but is not so. Aristotle, in his Sophistical Refutations (Sophistici Elenchi), identified thirteen fallacies. Today, a list of more than 100 has been developed.

Fallacy of the Consequent or the If-then fallacy:

Fallacy of the consequent draws a conclusion from premises that do not support that conclusion. The fallacy is based on the following argument:


Only two valid reasoning can be made out of this argument:

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If it rains, peacock will dance.

There will be hypothetical deductions from this statement:

  1. It rains
  2. It does not rain
  3. Peacock dances
  4. Peacock does not dance

1) It rains- If this statement is true, then peacock will dance.
If it does not rain- From this statement, we can deduce nothing because it is not necessary that peacock dances only when it rains. There can be other reasons why a peacock may dance.
If peacock dances- From this statement also we can deduce nothing because peacock can dance even when it does not rain.
If peacock does not dance- From this statement it can be deduced that it has not rained for sure. Because, had it rained, peacock would have danced for sure.

From the following example, we are sure of 2 things-

1) What will happen if A occurs.
What happened if B did not occur.

Embedded if-then statements:

The pattern

A only if B ⇒ If A then B.

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Ram and Shyam both cannot dance.

From the above statement, two conclusions can be drawn.

1) If Ram dances, then Shyam cannot dance.
If Shyam dances, then Ram cannot dance.

I will go to Goa only if I have enough money.

Correct Interpretation:

If I go to Goa, then for sure I have enough money.

Incorrect Interpretation:

If I have enough money, then I will go to Goa.

The only surety that we get from the main statement is that if I went to Goa then I had enough money.

Fallacy of accident/Hasty Generalization:

This fallacy is committed when assumptions are made based on a sample, which is either inadequate or incomplete. The Fallacy of Accident is committed when a general rule is applied to a particular case.

My friend said her mother is strict.
My mother is also strict.
All mothers must be strict.

This is a faulty generalization because I am making a biased conclusion based on a small sample. Many mothers may not be strict at all.

I have tasted 3 ice-creams from Wality Qualls.
I didn’t like the taste of all three.
Therefore, the ice-creams from Wality Qualls are bad.

The conclusion is fallacious because the three ice-creams that I didn’t like may be liked by someone else. But the generalization that the ice-creams from Wallity Qualls are bad is wrong.

Tu Quoque Fallacy:

Tu Quoque means ‘you too’. This type of argument is focused on the personal character of the opponent. Here the arguer points out that the opponent’s opinion are not be trusted because the opponent has actually done something he/she is arguing against. This fallacy attempts to show that a criticism or objection applies equally to the person stating it.

The pattern

A makes criticism B.
A is also guilty of B.

Therefore, B is false.

Mom: Rohan, don’t smoke. It is harmful for your health.
Rohan: I will smoke because you too smoked when you were of my age.

Here Rohan’s response is fallacious because the fact that Rohan’s mom has done something that she is comdemning Rohan to do has no bearing on the premise that she puts forward in her argument. (i.e. Smoking is harmful for health)

Q: Now, the United States government says that you are still funding military training camps here in Afghanistan for militant, Islamic fighters and that you're a sponsor of international terrorism.… Are these accusations true? …

Osama Bin Laden: …At the time that they condemn any Muslim who calls for his right, they receive the highest top official of the Irish Republican Army at the White House as a political leader, while woe, all woe is the Muslims if they cry out for their rights. Wherever we look, we find the US as the leader of terrorism and crime in the world. The US does not consider it a terrorist act to throw atomic bombs at nations thousands of miles away, when it would not be possible for those bombs to hit military troops only. These bombs were rather thrown at entire nations, including women, children and elderly people and up to this day the traces of those bombs remain in Japan. The US does not consider it terrorism when hundreds of thousands of our sons and brothers in Iraq died for lack of food or medicine. So, there is no base for what the US says and this saying does not affect us.…

Ad Hominen Fallacy:

Ad Hominen means ‘against the person’. This fallacy is committed based on the person’s personal character rather than on evidence or conclusion. In this kind of argument, the opponent is attacked rather than his statements. Participants in heated conversation sometimes disparage the character of their opponent and question their integrity. But the character of an individual is logically irrelevant to the truth or falsity of his argument or reasoning.

The pattern

1. Person A makes claim X.
Person B makes an attack on person A.
Therefore A's claim is false.

Jane has written many books on feminism and female infanticide. But I do not trust her writings because she was convicted for felony drug addiction when she was young.

Circular Reasoning/ Begging the question / petitio principii:

Petitio principii is a Latin phrase meaning begging or taking for granted of the beginning or of a principle. This fallacy is committed when one assumes the claim to be true what one is proving. It is essentially repeating the statement in different or stronger terms. This logical fallacy attempts to undermine a speaker's argument by attacking the speaker instead of addressing the argument.

"Dear Friend, a man who has studied law to its highest degree is a brilliant lawyer, for a brilliant lawyer has studied law to its highest degree." Oscar Wilde, De Profundis.

In the above example the conclusion has been assumed in the premise itself that Cricket has the biggest fan following in the world without even proving or putting forward the essential facts. The statement by Rob is actually the restatement of what Richard has claimed.

The pattern:

  • A implies B

  • suppose A

  • Therefore, B. OR A is B, therefore A is B.

"You know that God is a just and loving God because God is God and cannot be unjust or unloving."

The second claim does not offer any evidence; it is essentially repeating the premise.

Weak or Faulty Analogy/ Ceteris Paribus Assumption/ Questionable Analogy / Faulty Analogy / Vague Similarities /Extended Analogy/ Faulty Comparison/ False Metaphor:

Ceteris Paribus means with other things being the same. In faulty/weak analogy, an argument takes place between two or more things, situations or ideas. The argument is taken for granted that since a few things are same, the rest of things would also be the same.

The pattern :

A and B are similar.
B has property X.
Therefore, A has property X.

Eg. Railways are like airlines.
Both are modes of transportation.
Since railways have lower fares, airlines should also have lower fares.

The conclusion is fallacious because the arguer is not considering many other factors into consideration for airlines charging higher fares.

Eg. Giraffes have fur, eat plants, and have names that start with G.
Guinea pigs also have a name that starts with a G, have fur, and eat plants.
Guinea pigs are also probably very large.

Ad Populam:

This Latin phrase means ‘to the people’. This fallacy is committed when the arguer tries to convince the audience by putting the desires or likes of most of the people and ultimately convincing the audience to believe something because ‘everyone else does.’ The basis of the ad populum appeal is the assumption that large numbers of audience is more likely to be right than you are likely to be right.

The Pattern

Most, many, or all persons approve of statement A.
Statement A is true.

Eg: 70% of Indians agree that they become lazy during the winters. So, winters are a season of laziness.

The conclusion is fallacious because the arguer is trying to convince that because 70% Indians agree to a common cause, it must be taken true for all. Always remember that it is good to keep a popular opinion but it may not be right always.

This fallacy is also commonly used for marketing and advertising purposes:

Sony. Ask anyone.
Fifty million Elvis fans can't be wrong.

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False cause/ Post Hoc:

Post hoc is taken form a Latin phrase ‘ Post hoc ergo propter hoc. It means ‘after this, therefore, because of this. The fallacy takes place because of mere proximity of time. Assuming that B comes after A, A caused it.

The Pattern:

  1. A occured just before B.

  2. Therefore A caused B.

The only policy that effectively reduces public shootings is right-to-carry laws. Allowing citizens to carry concealed handguns reduces violent crime. In the 31 states that have passed right-to-carry laws since the mid-1980s, the number of multiple-victim public shootings and other violent crimes has dropped dramatically. Murders fell by 7.65%, rapes by 5.2%, aggravated assaults by 7%, and robberies by 3%.

The statement is fallacious because crimes may have dropped because of some other reasons but the arguer has overlooked them and assumed that B comes after A so, A caused it.

Straw Man:

In this fallacy, the arguer attributes an argument to the opponent that does not represent opponent’s true position. The arguer sets up an untrue version of the opponent’s position. To "set up a straw man" or "set up a straw man argument" is to describe a position that superficially resembles an opponent's actual view but is easier to refute, then attribute that position to the opponent (for example, deliberately overstating the opponent's position).

The pattern:-

  1. Person A has position X.

  2. Person B presents position Y (which is actually the distorted version of X).

  3. Person B attacks position Y.

  4. Therefore X is false/incorrect/flawed.

Animal lovers want ban on using leather items.

This argument is fallacious because many animal lovers may themselves be using leather items and their love for animals may be restricted to stray animals.

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‘All things are equal’ Fallacy:

This fallacy is committed when it is assumed that the background conditions have remained same irrespective of place, situation, or time.

Eg. Rashi stood first in class last year.
She will stand first this year as well.

The argument is fallacious because the arguer has overlooked that factors that may go against Rashi standing first in the class this year as well. The factors may range from Rashi not have worked hard enough this year or she might have fallen ill because of which she couldn’t prepare much etc.

Fallacy of Equivocation:

The term equivocation comes from the Latin terms equi (equal) and vox (voice) - and means "with equal voice .This fallacy is committed when a phrase/ word has more than one meaning but the word/ phrase slides between the different meanings that are important according to the context of the argument.

The Pattern:

a. Premise: Statement(s) using term A in sense 1
Premise: Statement using term A in sense 2
AND/OR Conclusion: Statement using term X in sense 2

Eg. Jam is better than nothing
Nothing is better than butter
Therefore jam is better than butter

This equivocation exploits two different meanings of the word "nothing" to come to an apparent conclusion about the relative merits of two different things without actually making reference to any of their respective merits. In the first statement, "nothing" really means "dry bread" (such that the sentence means "it is preferable to have jam [on bread] than nothing at all"), whereas in the second, it means, literally, "no thing" (so the sentence means "there exists no thing that is better than butter").

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Non Sequitor:

Non Sequitor means ‘does not follow’. This fallacy is committed when the conclusion does not strictly follow from the premises. The premises have no direct relationship to the conclusion.

Eg. Abhinav is tall, he must be fat.

The statement is fallacious because Abhinav’s being tall does not qualify that he is fat.
Rhea will stand first in class because she has put in lot of efforts.

The argument does not consider that someone else might be better than Rhea or Rhea must have put in lot of efforts but have not written her answers well in her exams etc.

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