Skill 12: Detecting Flaws in an Argument

Assuming Casual Links

An argument has several components: an author’s position, aline of reasoning that uses reasons to support a conclusion and the intentionto persuade. But an argument can be weakened by poor structure, logicalinconsistency and hidden assumptions.

Assuming acausal link can be a type of flaw that may occur in an argument. Flawedreasoning is to assume that because two things are found together, or occur atthe same time, there must be a link between them. One example of this isassuming a link to be one of cause and effect: that one thing must be the“cause” of another, or, in effect, jumping to a particular kind of conclusion.

Example 1:

Whereverdinosaur imprints are found in rocks, there are geologists around. Therefore,geologists must make the imprints.

Example 2:

Theentire family was ill last night. They all ate fish at the restaurantyesterday. Therefore the fish must have been contaminated.

Example 3:

Lifeexpectancy is much higher in Western countries than in the past. Obesity isalso much higher. Therefore, obesity must increase ourlife expectancy.

Example 4:

Aprisoner who protested his innocence by sitting on the prison roof has beenreleased. This is the second time that a prisoner who has protested in this wayhas been released. Roof-top protests must be a good way of securing releasefrom the prison.

Activity : For each of the passages below,identify whether:

1. A.   The reasons support the conclusion throughcausal links.

2. B.   The conclusion only works if there is anassumption or assumptions that are not covered by the reasons.

3. C.  There is no link between the reasons and theconclusion.

Passage 1:

Reason1: Sugar destroys teeth.

Reason2: Children eat a lot of sugar.

Reason3: Children’s teeth decay quickly.

Conclusion:Children’s teeth decay quickly because of the sugar they eat.

Passage 2:

Reason1: The man’s body was found in the kitchen.

Reason2: A bloody knife was found nearby. The lock on the door had been broken.

Conclusion:Somebody must have broken in and killed the man.

Passage 3:

Reason1: The price of football tickets has risen.

Reason2: Football players receive higher wages than ever before.

Conclusion:Spectators are paying more to watch matches in order to pay footballers’ high wages.

Passage4:

Reason 1: Dubai’spopulation doubled every ten years between 1940 and 2000 and is continuing torise.

Reason2: The port created in 1979 at Jebel Ali provided a prosperous free trade zonethat brought in people from all over the world.

Reason3: Many projects for improving the economic infrastructure, from sportingevents and theme parks to world-class technology parks and internationalfinance centers, have encouraged people to settle in Dubai.

Reason4: Large-scale property development is underway, offering better opportunitiesfor foreign nationals to own property in Dubai.

Conclusion:Dubai’s population is increasing because of the opportunities it provides toforeign nationals.

Passage 5:

MarieCurie, Einstein, and Darwin had long hair. They were all great scientists. Therefore,to be a great scientist you need long hair.

Not meeting thenecessary / sufficient conditions

Necessary conditions

In order to prove an argument, certain supportingreasons or evidence will be

essential to it. These are called necessaryconditions. A necessary condition is

just as it sounds: It is an essential requirement. Ifit is not present, there is a

gap in the argument, and the outcome could bedifferent, Then the argument

isn’t proved. It is important to bear in mind that theremay be many necessary

conditions or requirements for proving the case.

Example 1

If you don’t make advance arrangements for a taxi tocome to the house to

take you to the station, then a taxi won’t arrive intime for you to catch your

train.

( A necessary condition or requirement for the taxiarriving in time in this case

is that arrangements are made in advance. This isthe sound argument.)

Sufficient conditions: Necessary is not enough proof.

Necessary and sufficient conditions are different.If a necessary condition is

met, this might not be sufficient to prove a case. Thereare many other

conditions that must be met. You need to considerwhether the conditions are

sufficient to support the conclusion. If not, thenthe argument is not yet proved.

Example 2

 One way ofmaking a lot of money is by winning the lottery. In order to win the

lottery, you have to have a lottery ticket for thedraw. John has a lottery ticket

for the draw so he will make a lot of money.

( One necessary condition or requirement for makingmoney through the

lottery is to have a relevant lottery ticket. Johnhas met this necessary

condition by having such a ticket. However, simplyhaving a ticket for the

lottery draw is not the sufficient condition formaking money: the ticket might

not win. This illustrates the difference betweennecessary and sufficient

conditions.)

Example 3

 Birds havewings. The item has wings. The item is a bird.

(To check whether wings are a necessary condition ofthe item being a bird,

we can Ask questions like this:

      --- Ifit doesn’t have wings, then it can’t be a bird. True or false?

This is true. If an item did not have wings, itwould be hard to argue that it was

a bird. However, it is important to take the contextinto consideration: If a bird

had lost its wings in an accident, or had been bornwithout wings. It would be

flawed to argue that this prevented it from being abird. In this case, we can

ask another question:

---If wings are present, then that proves this is a bird. True or false?

The answer is false. Its having wings is notsufficient proof that this is a bird. Other necessary conditions would be thatit was, or had been, a living creature,  withfeathers, and that it had the DNA of a bird. A winged item could simply be an Aeroplan.)

Activity:  Foreach argument below, decide whether the reasons given meet the necessaryconditions to support conclusion，and whether the reasons given meetthe sufficient conclusions.  如果无法直接判断，可通过必要条件和充分条件结构句进行检验判断，每题必须选两个答案，即判断是否分别满足必要条件和充分条件。

1. 1.    The report makes reference to branches. It must be about a tree.

2. A.    Meet the necessary condition   B.do not meet the necessary condition

3. C. Meet thesufficient condition     D. do not meet the sufficient condition

1. 2.     The boxer doesn’t eat meat orfish, he does eat dairy products and vegetables. The boxer is a vegetarian.

2. A.    Meet the necessary condition   B.do not meet the necessary condition

3. C. Meet the sufficient condition    D. do not meet the sufficientcondition

1. 3.    Amir is under the age of 20. Teenagers are less than 20 years old. Amirmust be a teenager.

2. A. Meet the necessary condition   B. do not meet the necessary condition

3. C. Meet the sufficient condition   D. do not meet the sufficient condition

1. 4.    The bishop arrived on a vehicle with two wheels, one in front of theother. The bishop must have been on a bicycle

2. A.    Meet the necessary condition   B.do not meet the necessary condition

3. C. Meet the sufficient condition    D. do not meet the sufficientcondition

1. 5.    A television usually costs more than a radio. This one costs less thanthe radio, so it must be a bargain.

2. A.    Meet the necessary condition   B.do not meet the necessary condition

3. C. Meet the sufficient condition    D. do not meet the sufficientcondition

1. 6.    Diana had the benefit of an exceptionally happy childhood. She must be avery happy adult.

2. A.    Meet the necessary condition   B.do not meet the necessary condition

3. C. Meet the sufficient condition    D. do not meet the sufficientcondition

False analogies

An analogy is the comparison made to draw outsimilarities between two

things. Comparisons draw attention to those aspectswhich are similar. As two

things are never identical, it takes criticalevaluation and judgment to

decide whether a comparison is valid for the context.If the comparison helps

to give a more accurate understanding, then it islikely to be valid.

Example:

The heart works as a pump, moving blood through the bodyby opening and

constricting.

For most purposes, the comparison with a pump helpsus to understand the

action of the heart, so this is valid.

Activity: For each of the passages below, identify what the analogy is and whetherthe comparisons are valid.

Passage 1

The earth atmosphere is like a blanket of gasesaround the earth. It is only a

thin layer but it helps to maintain the temperatureof the earth, keeping us

warm. It also offers a layer of protection from intensityof the sun.

Passage 2

As the basis of an argument, the premises are likethe foundations of a

building. If the premises are not well founded, theargument is likely to

collapse.

Passage 3

There was no way the defendant was able to help himself.He had been under

excessive strain for some time and his emotions hadbeen building up like

steam under pressure. The witness had been goadingthe defendant, knowing

he was likely to get angry. The defendant was like apressure cooker, just

waiting to explode. Eventually, he just reachedboiling point and an explosion

became inevitable.

Other types of flawedargument

There aremany ways an argument may be flawed. As you become used to critical analysis,you will become more attuned to spotting the weak parts of an argument. It isuseful to develop an increased sensitivity to potential flaws so that you canrecognize them in different kinds of circumstance.

Unwarranted leaps

Where there are unwarranted leaps, the authorappears to add two and two to make five. The argument races ahead, leaving gapsin the reasoning, and relying on unsubstantiated assumptions.

Example

More people should travel by public transport, asthis would improve traffic flows in the city. If there were tolls for usingroads, people would use public transport. Polls indicate that most people wantthe traffic flow to be improved. This shows that people would be willing tosupport the introduction of tolls. Therefore, the council should introduceheavy tolls.

Here there is an unwarranted leapto the conclusion that, because a poll shows

people want the traffic flow tobe improved, they would also support tolls. We

are not told whether the pollasked questions about tolls, so we do not know that a toll would be welcomed.The public might preferred a different solution, such as shuttles orcar-sharing.

Tautology

Theline of reasoning should take an argument forward. Tautological arguments, onthe other hand, merely repeat the same point in different words, withoutadvancing the argument. Tautology means using different words to repeat thesame concept.

Example:

Thepublic’s knowledgeof health is poor and more money is needed for education in this area. Increasedsums of money should be spent on courses to make people aware of personalhealth issues. People don’t alwaysknow what they can do to take care of their health so further investmentsneeded in training health matters.

Two wrongs don’t make aright

Anotherform of flawed argument is to argue that an action is acceptable simply becausesomeone else acted in a similar way. Similarly, It is usually considered to beflawed reasoning to argue for consistent treatment when this would mean that aninjustice or an illogical outcome was perpetuated by doing so. For example. Ifone person cheats in an exam, then it is not reasonable to argue that otherpeople should be able to cheat too. If one person lies. It doesn’t make itright for others to tell lies.

Example

Theopposition party is wrong to condemn the leader of the council for selling ofpublic assets at a low price to its own supporters. When the opposition had amajority in the council, they sold off cemeteries and houses below the commercialprice, benefiting their own supporters. If they can do it, then the currentcouncil can do it too.

Flaws facilitated bylanguage

Languagecan be used skillfully to construct a powerful argument. However, it can alsobe used in ways that are unfair and which produce flaws in the line ofreasoning. Language can be used to lull the audience into a false sense ofsecurity about whether an argument is valid, or can divert the audience fromthe line of reasoning.

Activity: Identifydifferent types of flaw in the following arguments and describe them.

Passage1:

Morepeople should be informed of the value of studying maths to a higher level atschool or university. A mathematical education can be very advantageous.Therefore, the guidance given to young people should emphasize the benefits ofchoosing maths.

Passage 2:

Personalidentity cards don’t presentany real dangers to human rights. They add to our security, by making it easierfor the police to tract and catch criminals. Opponents of identity cards arewishy-washy liberals who live in leafy areas and haven’t a clue what it is like to live in run-downareas where crime is rife.

Passage 3:

Juvenilecrime has risen sharply in cities. Young people are out of control. There areonly two options in a situation like this. Either we agree to put up withsavage assaults on our persons and property, or we place a curfew on all youngpeople after 10 o’clock.

Passage 4: Sellingassets

Mr.Malcolm’s employerspay their stylists much lower wages and expect them to work much longer hoursthan owners of other salons. Mr. Malcolm supplemented his income by takingequipment and styling products from the workplace and selling these in his ownarea. He was justified in stealing from his employer because his employer wasexploiting him.

Passage 5: Internet Copying

Althoughit is possible to devise software to catch people who copy on the internet itis unlikely that everyone who does this could be charged. If you can’t enforcea law, then there isn’t any point in passing it. If there isn’t a law, thenthere isn’t a crime. If there isn’t a crime, then nobody has done anythingwrong.

Passage 6 : Nature or nurture

Thosewho argue that intelligence is not in-born do a disservice to the truly brightindividual and hinder attempts to discover excellence. Many of us had intensivetraining on an instrument such as the piano when we were children, but weobviously did not all turn out to be a Beethoven or Mozart. We are all able torecognize brilliance when we see it. Proponents of the view that intelligencecan be nurtured are too ready to blame society or the education system for notturning out more geniuses. They want us to believe that any of our childrencould be a genius, which is unfair on parents and teachers alike.