2 IntroductionWhat is a valid argument?A valid argument is one in which the conclusion follows from the reasons or premises. So if the premises of a valid argument are true, the conclusion must also be true.The other side of the coin is that if an argument has premises that are true but has a conclusion that is false, then it, the argument, is invalid because it is unreliable.An invalid argument is one that has reasoning errors – or flaws.A flaw is sometimes referred to as a fallacy
3 So what is a flaw?A flaw is a fault in a pattern of reasoning which weakens the support given to the conclusion of the argument.
4 Flaw of Cause and Correlation Example 1 Some people attempt to smuggle a pet into Britain because of the quarantine regulations which are aimed at preventing rabies from entering the country. If there were no such regulations, there would be no reason to smuggle pets. Since the most likely source of a rabies outbreak in Britain is a smuggled pet, if the quarantine regulations were abolished, the danger of a rabies outbreak would be reduced.Is this argument valid or invalid?What is the reasoning error or flaw in this argument?CR3
5 Example 2RBecause people step over the railings which are meant to keep people off the grass, if you took away the railings fewer people would walk across the grass.C
6 CommentsExamples 1 and 2 make exactly the same error, they wrongly assume that the cause of the danger is some regulation or preventative measure rather than people breaking the regulations, which of course is the real cause. The railings themselves don’t make people cross the grass, they just make people who are going to walk on the grass anyway, step over them, just as the quarantine regulations make people smuggle, who are going to import pets anyway.
7 Which of the following identifies the flaw in example 1 Rabies is not likely to enter Britain in a wild animal.The quarantine regulations cannot prevent owners from smuggling their pets.If there were no quarantine regulations, pets with rabies could enter Britain easily.If people did not want to travel with their pets, there would be no need for quarantine regulations.If pets were inoculated against rabies, there would no need for quarantine regulations.Answer: C
8 Confusing Cause with Correlation Example 3 There have been improvements in the health of the population over the past thirty years, a period during which there has been an increase in the affluence of the country. So the increased affluence of the country has produced the improvements in the health of the population.Explain the flaw in this argument?
9 CommentsConfusing cause with correlation is a dangerous error that can be made. Just because two things are both observed to occur together, it does not mean that they are connected, and in particular it does not mean that one caused the other.The question as to whether increased affluence has or has not produced improvements in the health of the population cannot be settled without more evidence – both about the incidence of all illnesses in the population and about whether any improvements in health could not have occurred without greater affluence.The argument simply assumes, without producing any evidence for it, that because two things have occurred together, one of them must have caused the other.
10 Confusing Cause with Correlation Example 4Crimes and outrages of all sorts have been committed under a full moon by a wide variety of people. The advice to derive form this is clear: when the moon is full, trust no-one, not even yourself.CommentThe fact that crimes have been committed when the moon is full is not a good reason to believe that the full moon causes people to commit crimes
11 Arguing from the Particular to the General Example 4A. Ted’s car, which is red, has been stolen three times, and my blue car has never been stolen. Red cars are therefore more likely to be stolen than blue ones.B. Red cars are more likely to be stolen than cars of other colours. My car is blue, so it is less likely to be stolen than Ted's red one.C. Ted’s car is red and red cars are the most likely to be stolen. Therefore he is more likely to have his car stolen than mine, which is blue.One of the arguments is invalid. Which one is it.?What reasoning error or flaw is illustrated in this example?
12 CommentsThe error lies in arguing from the particular to the general. This is an error because a single case, or a small number of cases of something happening, cannot justify concluding that it happens all the time, or as a general ruleHere the flawed argument is A. It argues from the particular case of Ted's experience to the general conclusion about car colour and the likelihood of theft. To establish a generalization like conclusion A, you would need to have some statistical evidence involving hundreds or thousands of cases. A single piece of anecdotal evidence- which this is – is certainly not enough for such a strong conclusion.
13 Appeal to HistoryExample 5In 1914 and in 1939, when the two world wars broke out, therewere no weapons of mass destruction on the scale that there were after The possession of ever-more–powerful nuclear weapons by the major powers has made the prospect of a third world war potentially so destructive that if could destroy the human race, but for that reason it has also prevented such a war from starting. Therefore we should continue to stock-pile nuclear weapons as a safe-guard against another world war.What is the reasoning error in this argument?The common error here is in arguing from the past to the future or otherwise known as making an appeal to history.
14 Confusing Necessary for Sufficient Conditions Example 6 In order to succeed in academic examinations it is necessary to study. Therefore, if a student studies hard in a particular subject, that student should succeed in examinations in that subject.Which of the following identifies the flaw in the above argument?Assumes that it is necessary to study in order to succeed.Overestimates the value of studying in preparation for examinations.Ignores the fact that some examinations are more difficult than others.Assumes that studying hard is a sufficient condition for academic successIgnores the fact that some students do not need to study very much in order to succeedAnswer: DWhat is the flaw here?
15 CommentsThe correct answer is D.The argument has the following structureR - X is necessary in order for Y to happenC – Therefore, if X happens, Y will happen.However the fact that something will not happen unless some other thing has already happened does not guarantee that the second thing will happen if the first one does. So in this case the fact that you need to study in order to succeed does not guarantee that you will succeed if you do study.This is another case of mistaking necessary for sufficient conditions.
16 We should do further research on the nuclear technology… Ad HominemWe should do further research on the nuclear technology…WAIT,,BUSH IS A BAD MAN,,THEREFORE,,THE RESEARCH ON NUCLEAR TECHNOLOGY IS RUBBISH!!!
17 Ad HominemAn ad hominem flaw involves criticing some feature of theoriginator of an idea so that people dismiss his argumentwithout giving it serious consideration. This applies frequently to politicians.For example, people might be disillusioned with George Bush’s policy on Iraq. If they gave this as a reason and did not even consider a new policy advocated by him, this would be an ad hominem flaw.The phrase is Latin and means ‘to the man’, suggesting that the man himself is the focus of the criticism, when in fact, his new ideas should be examined more neutrally.
18 Ad Hominem (Flaw of Emotion) Example 7Dan Quayle would be a totally unsuitable governor of the USA. How can I take an interest in his policies when I hear that during his visit to a primary school it emerged that he incorrectly spelt the word ‘potato’.Dan Quayle’s inability to spell a word is used as a reason for dismissing his policies without giving them any consideration.
19 Ad Hominem (Flaw of Emotion) Example 8The managing director insisted that the company could not increase its pay offer since profits were expected to fall substantially over the coming year, but she had been convicted of drink driving in the past three years, so the union should not believe her profits forecast. They should press ahead with the strike.The managing director’s personal problem is used to dismiss her claim of falling profits. This is irrelevant to the issue and cannot be accepted.
20 Ad Hominem (Flaw of emotion) Example 9Tony Blair was less than honest about the incidents that led to David Kelly’s suicide. I don't trust Blair enough to consider his recommendations on extending the number of city academies.Blair’s possible lack of integrity is used as a reason for not considering his recommendations for city academies on their own merits.
22 Straw man Fallacy (Flaw of Emotion) This flaw entails criticizing some minor weakness in the author's argument and using this as a means of discrediting the whole argument or study, often in a mocking way. The name is metaphorical. It relates to the notion of building up a fragile model of just one negative aspect of the argument or set of ideas and then blowing it down, with the implication that the rest of the argument should then be abandoned. Good schemes usually have one or two weaknesses, and opponents may use these as straw men.
23 Strawman Fallacy Example 11 My optician cannot repair my glasses in the shop because of the EU legislation about the dangers of soldering. What right have people in Europe to interfere with my glasses? The sooner we leave the EU, the better.One minor drawback about EU legislation is used to discredit the EU membership as a whole.
24 Straw man Fallacy (Flaw of Emotion) Example 10 The system of welfare benefits is exploited by scroungers. Moonlighters, people who work secretly without telling the authorities, are claiming unemployment pay that they are not entitled to. The whole welfare system should be abolished.One small group of people who exploit the system is used to argue for the abolition of the welfare system.
25 Straw man Fallacy (Flaw of Emotion) Example 11 The Hare Krishna movement is too absurd to consider seriously. It is ridiculous for followers of Hare Krishna to wear saffron robes, and their topknots are really unsightly. Their teachings are likely to be just as absurd.The writer focuses on a true but minor aspect of the Hare Krishna movement. i.e. their clothes and topknot. The writer then uses this to dismiss the movement entirely.
27 Slippery slope (Flaw of Emotion) This is a chain of arguments that starts with a moderate claim and ends with an alarming one. These are often the cause of moral panics in the media. The flaw lies in the fact that at one or more links in the chain, the author makes an imaginative leap that might not be justified. The author assumes something negative is bound to happen, when it might not, or that it will affect huge numbers, when it might only happen to a few. Hence the term slippery slope
28 Slippery slopeExample 12The increasing number of immigrants and asylum seekers coming into Britain is a threat to our national traditions. Few of them speak English as their native tongue, so they are unable to appreciate our literary heritage such as Shakespeare, Jane Austen and the King James Bible. As these texts become increasing less relevant to the populations as a whole, they will be lost. Bangra and Bollywood will replace them in our media and school syllabus. Traditional English culture will be as dead to us as that of the ancient Greeks.
29 Slippery Slope Example 13 Examination results for 2005 showed an alarming decline in the number of students studying modern foreign languages for GCSE. This trend will result in fewer students taking languages at A-level and far fewer taking language degrees. Without language graduates, in several years there will be no language teachers availabel for schools. Eventually langauge learning will stop although – a disaster for international understanding and world peace.Each step is not inevitable, since just as many students might take languages at A-level if it is mainly the less enthusiastic and less able ones who have opted out of GCSE.
31 Begging the Question (Flaw of logic or unclear reasoning) This fallacy consists of circular reasoning whereby the argument appears at first to offer useful, new information but the line of reasoning only leads back to the beginning so that nothing is learned or proved. This is also known as begging the question because, despite appearances, it avoids the question rather than addressing it.
32 This restaurant serves the best food in the town, because it has the best chef. It has attracted the best chef because it has the best reputation. It has the best reputation because the chef cooks the best food.Best foodBest ChefReputation
33 Because it has the best chef!! (me) Best foodWhy does the restaurant serve the best food?Best ChefBecause it has the best chef!! (me)
34 Because it has the best reputation Why does the restaurant attract the best chef?ReputationBecause it has the best reputation
35 Because it has the best food ReputationWhy does the restaurant have the best reputation??Best foodBecause it has the best food
37 Begging the Question (Flaw of logic or unclear reasoning) I am convinced that my sister is suffering from a mental illness. She says that she is perfectly sane, but delusions are a symptom of schizophrenia. Her adamant denial confirms she is mentally ill.
38 Tu Quoque (Flaw of emotion) This Latin phrase means ‘you too’. The technique is a common ‘bad habit’. It involves deflecting what might be a sound criticism by accusing the critic of being guilty of the same or similar fault. For example, a student reprimanded for being late might point out that the teacher too is sometimes late for lessons. Although this might be true it does not excuse the student's own lateness. ‘Two wrongs do not make a right’.
39 Tu Quoque (Flaw of emotion) My Weight Watchers leader told me off for eating so many chips while I was on holiday. She’s one to talk. I saw her eating a chocolate bar on the way home.Here instead of acknowledging and explain her lapse, the slimmer is accusing her accuser also of eating fattening food.
40 There are two main categories of flaws: Flaws of logic and Flaws of emotion.Flaws of Logic:Flaw of cause and correlation or Post Hoc FlawConfusing Necessary for Sufficient conditionsArguing from the Particular to the GeneralAppealing to History or arguing from the PastBegging the Question or Circular ArgumentFlaws of Emotion:Ad HominemStrawman FallacySlippery SlopeTu Quoque