PHI10003 Critical Thinking Tutorial 3 Standardise and draw argument diagrams for the following arguments. 1. Start by reading the passage and highlight any premise or conclusion indicators 2. Number each statement in the passage, if this has not already been done 3. Identify the main conclusion 4. Identify the premises that support the main conclusion 5. Identify any sub-arguments that are used to support those premises 6. Indicate whether the premises are linked or independent in your diagram

Exercise 1 (no sub-arguments) (1) We have established that whoever the guilty person is, they must be left-handed. Miss Green is not left-handed, so she is not guilty.

(2) The government’s proposal to introduce a national identity card should be rejected for several reasons. Firstly, identity cards are of doubtful effectiveness in tackling identity fraud, crime and terrorism. Secondly, the cost of a national identity card system would be staggering and wasteful. Finally, there is widespread public opposition to ID cards.

(3) Speed cameras may actually cause more accidents than they prevent. Firstly, they can cause sudden braking as drivers slow down to the posted speed limit. Secondly, they distract the driver’s attention as they look out for the next camera rather than at the road ahead. Thirdly, lower speeds demand and promote lower attention levels from drivers.

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(4) If we finish work early, we will go to the beach or see a movie. But if we go to the beach or see a movie, we will be home late. Therefore, if we finish work early, we will be home late.

(5) Too much exposure to the sun is very unhealthy. It has been shown that sunlight can cause premature aging of the skin. And furthermore, ultraviolet rays in the sun might also trigger skin cancer.

In argument (6) the conclusion is unstated. Supply the missing conclusion. (6) If governments do not act soon, carbon emissions will cause a serious increase in global temperatures. A serious increase in global temperatures will lead to a series of planetary catastrophes. Unfortunately, so far governments have shown little inclination to act. Therefore, ……

Exercise 2 (one sub-argument) (1) Censorship is acceptable only if it can be easily enforced. But censorship cannot be easily enforced because it is difficult to decide who will do the censoring. So censorship is not acceptable.

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(2) It was either Mr. Brown or Mr. Orange who committed the crime. But Brown has a solid alibi and so he can be ruled out. So it must have been Mr. Orange who committed the crime.

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(3) Increasing the size of the police force is only a temporary solution to the problem of rising crime rates since it does not get at the root causes of crime. Therefore, the government should not respond to rising crime rates by increasing the size of the police force.

(4) There are two reasons why we should have a smoking ban in pubs and clubs. Firstly, it will benefit the industry itself, since many more people are likely to go to pubs and clubs if they are smoke free. Secondly, it is wrong to subject people who work in pubs and clubs to the dangers of passive smoking.

(5) Radioactive elements disintegrate and eventually turn into lead. Hence, if matter has always existed there should be no radioactive elements left. But there is still plenty of uranium and other radioactive elements around. This is scientific proof that matter has not always existed.

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(6) For a person to be found guilty of murder, it must be shown that their actions caused the death of another person. But although Hallett beat Smith unconscious, he did not cause Smith’s death because Smith was alive when Hallett left and died later of drowning when the tide came in. Therefore, Hallett is not guilty of murder.

(7) People are mistaken when they claim that the battery-powered electric car represents a potential solution to the problem of air pollution. They forget that it takes electricity to recharge batteries and that most of our electricity is generated by burning polluting fossil fuels. So even if all of the petrolpowered cars on the roads today were replaced by electric cars, it would at best be an exchange of one source of fossil-fuel pollution for another.

Exercise 3 (Several sub-arguments) (1) The speed limit on major highways should not be reduced. Professional drivers spend much more time driving, on average, than do other people and hence they are more competent drivers than are other, less experienced drivers. So reducing the speed limit would have the undesirable effect of forcing some people who are now both law abiding and competent drivers to break the law.

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(2) … Sociologically, however, it may be argued that crime is both normal and necessary. Crime is ‘normal’ in the sense that if we look at all societies, past and present, we always find criminal or ‘deviant’ behaviour which meets with some form of punishment or sanction. Crime is ‘necessary’ in the sense that any behaviour we define as punishable also serves to define the boundaries of what is acceptable and unacceptable behaviour, and such boundary definition is fundamental to social order.

(3) Although providing consumers with information about genetically modified (GM) foods is important, labels may not be the best way to do so. The purpose of food labels is to provide ingredient and nutrition information, or warnings about a health risk, such as the presence of a potential allergen. Because genetically modified foods are already scrutinized to ensure that they do not pose new or unique risks, labels are likely to mislead consumers by implying a warning. Moreover, labelling GM foods would not be economically feasible. Thousands of common foods containing small amounts of genetically modified ingredients, such as soybean and corn products would have to be labelled. Costs associated with this would be passed on to producers and consumers. (Adapted from “Genetically Modified Organisms”, published online by the Institute of Food Technologists, 1999).

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Challenge question (4) The kidnapper must have gone either east or west along the road or north or south across country. But we know he did not go east along the road because a policeman was on duty in that direction all night and he says he saw no one. And we know he did not go west because the people at the inn to the west were awake all night, waiting for a doctor to arrive and they also saw no one. So the kidnapper must have gone north or south across country. But he cannot have gone south since he took the bicycle and the country to the south is impossible to cross with a bicycle. Therefore, the kidnapper must have gone north. (Adapted from the Sherlock Holmes story: The Priory School)

PUZZLE of THE WEEK Only one of the following statements about a particular hand of cards is true: 1. There is a king in the hand, or an ace or both. 2. There is a queen in the hand, or an ace or both. 3. There is a jack in the hand, or a ten or both Assuming that the above information is true, is it possible there is an ace in the hand?

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