C1 The tuna population will vanish unless the tuna industry is regulated more stringently

This is easier to read, and it saves you having to write things out unnecessarily. Henceforth, whenever an argument draws an inference from a conditional premise, feel free to abbreviate in this way.

CHAPTER This chapter was concerned to address some of the main logical

SUMMARY problems encountered in the reconstruction of arguments.

In many cases, one or more premises upon which a conclusion depends is left implicit by the arguer. A necessary part of reconstruction is to make such premises explicit. Implicit premises are usually, though not always, connecting premises: these are either conditionals or generalisations. Where an argument contains a conditional amongst its premises, the conditional is often regarded by the arguer as being supported by a covering generalisation. In reconstruction, we should take care to include a suitable covering generalisation where appropriate. Covering generalisations may be either hard or soft generalisations.

Not everything explicitly stated by an arguer is relevant to the argument. A proposition asserted by an arguer may be completely irrelevant; that is, the arguer does not advance that proposition as support for the conclusion. Such propositions should not be included in the reconstruction. In other cases, a proposition explicitly stated does provide some support for the conclusion, but is such that if it were ignored, the arguer would still, by virtue of other propositions put forward, have given an argument for the intended conclusion. If that proposition is false, then it should be removed from the argument.

Where possible, ambiguity and vagueness should be coped with by removing them. If it is possible to do so, the ambiguous or vague language should be replaced by language that is not ambiguous or vague. If a word in a premise or conclusion is ambiguous (can be read as expressing either of two meanings), and it is not clear which meaning is intended, then two reconstructions of the argument should be given, each reflecting one of the two meanings.

All generalisations in reconstructed arguments, whether hard or soft, should have explicit quantifiers. Where a premise is a generalisation, the scope of a generalisation should be as narrow as possible, but not so narrow that the inference to the conclusion is no longer valid (or inductively forceful, as the case may be).

Practical reasoning, or means-end reasoning, is embodied in arguments that specify an outcome as being either desirable or undesirable, along with an action said to be either necessary or sufficient for bringing about that outcome. Such arguments can take any of eight basic forms. In order to reconstruct such arguments as valid or inductively forceful, we often have to add a premise stating that the proposed action is the most efficient means of bringing about the outcome, and a premise stating that the benefit of the outcome outweighs the cost of the action (or, in the negative case, that the cost of an action would outweigh the benefit of the outcome). But sometimes the outcomes of actions are only probable. This may require us to calculate the expected value of an action.

Arguments are distinct from explanations, but many arguments have explanations as conclusions: such arguments attempt to establish which, of various possible causes of a given fact or event, is the actual cause. Arguments that attempt to establish causal generalisations present more difficulty. It is common to see causal generalisations fallaciously inferred from mere correlations. Causal generalisations are not as informative as one might be tempted to think: what they tell us is that one type of event or state of affairs increases the probability of another type of event or state of affairs.

EXERCISES 1 As given, the arguments below are invalid. But each can plausibly be thought to contain either a generalisation or conditional as an implicit premise - a proposition that the arguer is assuming but has not explicitly stated. The arguments can easily be made deductively valid by making the implicit premise explicit. Do so: identify the conclusion and explicit premises, then add the premise needed to make the argument valid. Reconstruct the argument in standard form. Use a hard generalisation if you can think of one that is plausible; otherwise settle for a conditional. You should write all conditionals in the 'if-then' form.

a Mr Bean is an idiot. You shouldn't marry him.

b All men are idiots. You shouldn't marry one.

c Johnny will like the Blandings Castle books; he likes the Jeeves books.

d Pavarotti is going to sit in that chair! It's going to break!

e Prices are not going to rise, because the savings rate is not decreasing.

f Häkkinen won't win unless Schumacher's car breaks down. So Häkkinen won't win unless Schumacher's mechanic is inept.

g Wagner was greater than Verdi, so obviously Wagner was greater than Puccini.

h Since only democracies are just, no socialist countries are just.

i If he doesn't accept the offer, then we will either withdraw the offer or raise it. If we raise it, then we will incur financial risk. Therefore, if he doesn't accept the offer, then either we give up trying to acquire another company, or we will incur financial risk.

j Unless John brought wine, there isn't any. John didn't bring wine. So everyone will drink water.

k Cigarette advertisements don't encourage people to smoke more? Ha. I think it safe to say that ads for chocolates encourage people to eat chocolate.

2 Find appropriate covering generalisations for the following conditionals. Choose a hard or soft generalisation as seems appropriate.

a If John is under 18, then he cannot legally purchase alcohol in the UK.

b If that is a scorpion, then it is poisonous.

c If that wine is not French, then it is probably not overpriced.

d That picture is not likely to be an oil painting if it is not Dutch or Flemish.

e He is good at analysing arguments if he is a successful lawyer.

f If the patient is now haemorrhaging, then his blood pressure is decreasing.

a Suppose you know that Doctor Bowes does not own or drive a new Mercedes-Benz. Reconstruct the argument in accordance with the Principle of Charity.

Doctor Bowes, the candidate, drives a new Mercedes-Benz. Furthermore, he has over £6 million in a personal Swiss bank account. Of course he is wealthy.

b The following passage includes the assertion that the defendant has been addicted to cocaine for two years. Suppose you know this assertion to be entirely false (that is, the defendant has never used any illicit drug). Reconstruct the argument in accordance with the Principle of Charity. In order to reconstruct it, you will have to rephrase some of the sentences, ignore some material, and also to make implicit premises explicit. The conclusion is also implicit.

The evidence is very compelling. The defendant has been addicted to cocaine for over two years. Her blood and fingerprints were found on the murder weapon. She was seen emerging from the victim's flat not more than half an hour after the murder took place. She boarded a flight for

Greece only twelve hours after the murder. And finally, the victim had recently ended the sexual relationship between himself and the accused.

4 We very frequently hear of claims or actions being criticised on the grounds that they are politically motivated. Sometimes this is put by saying that someone is 'playing polities', or using something as a 'political football'. What does this mean? Why is it a criticism? Find examples in the print media, and try to explain what the point is, in such cases, in calling something 'political'.

5 Reconstruct the following arguments, taking care to eliminate vague or ambiguous terms. You will have to rewrite sentences, ignore some material, and make implicit propositions explicit.

a Ms Jones has demonstrated her commitment to feminism by supporting an across-the-board pay rise for female academics. If she is elected MP, then no doubt she'll support a reduction of the evidential standard for rape convictions.

b Make no mistake: whatever their keepers say, these so-called

'domesticated' wolves are wild. Wild animals are too dangerous to be kept as pets.

c Researchers have found that heroin use in teenagers is linked to parents with histories of depression. Parents under psychiatric care for depression should therefore be told the symptoms of heroin use.

6 For this argument, reconstruct it twice: once retaining the vague term 'political correctness', and once eliminating it.

When the Bunbury Women's Group proposes that the City Council bar men from the 'Women's Safe House', we realise that we must not allow them to have influence on the council. For this makes it obvious that the virus of 'political correctness' has infected the women's group, and we know what 'political correctness' stands for - they would promote such horrors as homosexuality being taught in schools and legal prohibitions against language deemed 'incorrect'.

7 Reconstruct the following arguments, making implicit propositions explicit as needed. If the argument is not deductively valid, increase its inductive force by decreasing the scope of the generalisation. If the argument is deductively valid, increase its chances of being sound by decreasing the scope of the generalisation.

a Of course your yearling can be trained without much difficulty. Most horses can be.

b Most men marry. Therefore most men have, have had or will have a mother-in-law.

c No primates can learn to talk. Bobo is a chimpanzee, hence a primate; therefore he cannot learn to talk.

d All countries can be attacked by sea. If so, then all countries require naval defence.

8 Reconstruct the argument about compulsory military service discussed at the beginning of this chapter (pp. 155-156). Take into account the advice given in the section on practical reasoning.

9 Look at argument-pattern (1) in the section on practical reasoning. In order for such arguments to be valid, we need to add two premises: first, that the benefit of increasing the amount of chocolate outweighs the cost of performing action X; second, that action X is the most efficient way of increasing the amount of chocolate. What similar premises are needed to make argument-patterns (2)-(8) valid?

10 The following argument contains a fair amount of rhetoric, stage-setting and explanation, but also a practical argument. Decide which of the eight patterns of practical reasoning the central argument of the passage fits, and reconstruct it. Don't worry too much about including every point that might be relevant; your main task should be to get the central argument laid out before you (then you can add sub-arguments, if you find any). Part of the first paragraph is concerned to reply to a point made by the correspondent referred to; think carefully about whether, and in what way, this contributes to the writer's intended argument.

I despair of your correspondent who responded to the article on otters and mink (Letters, 9 July). Mink are certainly not playful and delightful animals. She must be confusing them with ferrets. While I agree it is no fault of their own that they are with us, it is not a question of survival. Mink are in paradise here in the wild: no harsh winter; no natural predators, a vast range of prey.

In the Mustelid family they have found a niche halfway between otters and pine martens with the aquatic ability of the former and the natural aggression of the latter. Mink are consequently able to reach nesting colonies of ducks and seabirds, formerly secure from predation, wiping them out and rendering the island sanctuaries untenable by birds. I would invite your correspondent to come to Argyll and see for herself. Mink are a scourge on our environment and should be eliminated at every opportunity.7

11 Another practical argument, this time giving you more practice identifying implicit premises and conclusion. Reconstruct according to the instructions on practical reasoning. The letter is humorous, but contains a serious (though implicit) argument.

Sir, Having read your report on how the police plan to test drivers for drugs, I and both my children in their early twenties attempted the tests described, without having taken any illegal substances.

We consistently failed the second test (on one leg, head tilted back, eyes closed, other leg off the ground, arms extended, touch nose with each index finger). Swaying and giggling helplessly at each other's attempts, we would have given every appearance of intoxication.

We have therefore decided that, if we are stopped and invited to perform these tests at the roadside, we will first ask the officer for a demonstration.8

12 A friend offers you a wager: if you draw an ace out of a (normal) pack of playing cards, he'll give you £10. If you don't, you pay him £1. What is the expected value of accepting the wager? Should you do it?

7 Michael Murray, The Independent, 16 July 2000.

8 John Tayler, The Times, 4 August 2000.

13 There is a sweepstakes draw: all you have to do is post a letter with your name and address to the address given, and your name will go into the draw. The lucky winner, drawn from a barrel containing 400,000 names, will receive £100,000! Assuming that a second-class stamp costs 26p, what is the expected value of posting your letter, thereby entering the sweepstakes?

14 The following are not simply explanations, but rather arguments that have explanations as conclusions. Reconstruct them, eliminating extraneous material and making implicit material explicit as needed.

a At your last visit I said that the pain in your abdomen is caused either by a kidney infection, a musculoskeletal injury, or cancer in the pancreas or liver. But no indicators for a kidney infection showed up in the urinalysis, and if it were musculoskeletal, the pain would have subsided, not grown, by now. I'm afraid you have cancer.

b The stress of modern life is not because we work more than our parents did - we don't - but because we no longer go to church. Instead, we shop: the world's most stressful activity.

c Nietzsche's going irrevocably mad was caused either by his tortured intellectual life - as romantically-minded people would like to believe - or by the syphilis he contracted as a young man. But if it were the former, then we should expect a great many other notable intellectuals to have gone irrevocably mad. The truth -again contrary to romantic fantasies - is that very few have.

d We read with horror that the age of the onset of puberty in girls is getting younger. We don't believe this has to do with artificial hormones in the milk or anything like that - surely in these more environmentally aware times, there are fewer artificial hormones and suchlike in our food than there were say, twenty years ago. The real reason is the unprecedented onslaught of sexualised images to which children are now subjected, especially on television.

e Mr Jenkins blames the high unemployment rate on Britain's high interest rates: these strengthen the pound, making British exports uncompetitive, which in turn forces British manufacturers to cut costs by means of redundancies. We blame it on the ease with which people out of work can go on the dole. Jenkins' argument assumes that the non-manufacturing sector of the economy is not growing as fast as the manufacturing side shrinks. Manifestly, it is.

f The president says that greenhouse gases are mostly produced by trees, not by industry. That makes sense. Global warming is on the rise, and we all see how, all over the world, people are busy planting trees and closing down factories, getting rid of their cars, and so on. The world of our pre-industrial ancestors must have been a real hothouse.

15 Review the section on causal generalisations. Every example below is a case either of (1) assuming that a causal relation entails a hard generalisation or a generalisation of the 'most' type; or (2) too readily inferring a causal relationship from a statistical correlation. In a short paragraph, criticise the following arguments: say whether each argument is a case of either (1) or (2) and explain your answer.

a It is just not true that exposure to the sun causes skin cancer. If it did, then everyone who has ever had a suntan or a sunburn would get skin cancer.

b I am so tired of hearing that social and economic deprivation 'cause' teenage criminality. Plenty of teenagers suffer from social and economic deprivation without turning to crime.

c Taking lots of vitamin C makes my colds go away. I always take vitamin C when I get a cold, and it always goes away.

d A causal link between violent video games and juvenile violence has been demonstrated. A study has shown that the incidence of violence is much higher amongst teenage boys who play violent video games regularly than it is amongst those who do not.

e Oxbridge representatives claim that their admission procedures are not biased against students from poor backgrounds. How can they maintain this obvious falsehood, when their own figures show that the proportion of Oxbridge undergraduates from impoverished backgrounds is far lower than the proportion of applicants from impoverished backgrounds? Oxbridge continues to exclude the poor because they are poor.

16 Reconstruct the following arguments, and say whether they are valid, inductively forceful, or neither.

a The sharp increase in the death rate in ancient Antioch, in the year ad 364, has been ascribed to many factors: to famine, to an influx of disease brought by soldiers returning from the Persian campaign, and to problems with the city's water supply. It was probably the water supply: if it were food shortages, it is unlikely both that no contemporary historian mentions it, and that there should be no record of similar sufferings in the lesser towns of the area or the surrounding countryside. And if the soldiers had contracted disease in Mesopotamia, then, since they were seriously weakened by hunger and the strain of a long and arduous campaign, they would have died of disease in significant numbers. And then it is certain that Ammanius, an eyewitness, would have recorded those fatalities - so cruel after the humiliations and losses they had endured in battle - in his history. But he is silent on the point.

b Jepsen's Neural Syndrome - JNS - seems to be caused in dolphins by an excessive intake of heavy metals. A genetic cause is ruled out, because if the cause were genetic, then the correlation discovered between JNS and the presence of abnormally high levels of heavy metals in dolphins would be extremely unlikely. True, the correlation between JNS and abnormally high levels of heavy metals is no greater than that of JNS with the consumption of large amounts of squid. But squid, as we know, tend to retain, over time, large concentrations of the trace heavy metals that pass through their bodies. Dolphins tend to eat the larger, therefore older squid. It is very probable that if squid did not retain heavy metals, then the correlation between JNS and squid consumption would not exist. Since there are no other significant correlations with JNS, the heavy metals diagnosis looks highly probable.

c If alcoholic behaviour in parents - as opposed to genetic predispositions to alcoholism - caused alcoholism in children, then we would find that children whose parents are not alcoholic, and who are adopted at a very early age by alcoholic parents, were significantly more likely to become alcoholics. But our study shows that they are not. Therefore mere heavy drinking in parents does not, despite the well-known correlation, cause children to grow up to be alcoholic.

Rational

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