Critical Reasoning

A Practical Introduction

Anne Thomson

• Publisher: Routledge
• Year: 2009
• eBook ISBN: 9781135267414
• Edition: 3
• Topic: Philosophy
• Subtopic: Logic in Philosophy

We all engage in the process of reasoning, but we don't always pay attention to whether we are doing it well. This book offers the opportunity to practise reasoning in a clear-headed and critical way, with the aims of developing an awareness of the importance of reasoning well and of improving the reader's skill in analyzing and evaluating arguments.

In this third edition, Anne Thomson has updated and revised the book to include fresh and topical examples which will guide students through the processes of critical reasoning in a clear and engaging way. In addition, two new chapters on evaluating the credibility of evidence and decision making and dilemmas will fully equip students to reason well. By the end of the book students should be able to:

• identify flaws in arguments
• analyze the reasoning in newspaper articles, books and speeches
• assess the credibilty of evidence and authorities
• make sound decisions and solve dilemmas
• approach any topic with the ability to reason and think critically.

1
• analysing reasoning

We cannot begin to evaluate someone’s reasoning if we do not understand it, or if we understand the words but fail to grasp that reasons are being offered for accepting a point of view. The skills upon which this chapter focuses – recognising reasoning, and identifying conclusions, reasons and assumptions – are the most basic abilities; upon them the important skills involved in evaluating reasoning (the focus of our next chapter) depend.

• RECOGNISING REASONING AND IDENTIFYING CONCLUSIONS

Reasoning is, of course, presented in language, but not all communications in language involve reasoning, so we need to be able to pick out those features of language which tell us that reasoning is taking place. It is clear that we use language for a variety of purposes. For example, we may use it to tell a joke, to insult someone, to report factual information, to describe a scene or a personality, to tell a story, to express our feelings, to explain why we have acted in a particular way, to ask questions, to issue orders. What most uses of language have in common is the attempt to communicate something to others.

Sometimes we want to persuade others to accept the truth of a statement, and one way of doing this is to offer them reasons or evidence in support of this statement. This is the essence of argument. The simplest examples of arguments occur when someone who believes some statement will present reasons which aim at persuading others to adopt this same point of view. In more complex cases, someone may wish to assess and evaluate someone else’s reasoning, or someone may be reasoning about their own or someone else’s reasoning. We all use language in this way, often without thinking of what we are doing as being something as grand as ‘presenting an argument’. For example, someone might say:

He must be older than he says he is. He told us he was forty-two, but he has a daughter who is at least thirty years old.

Here reasons are being offered for the conclusion that ‘he must be older than he says he is’. So this simple, everyday piece of communication is an argument.

Here are some more very simple examples of argument. As you read through these examples, think about which statement the author is trying to get you to accept (that is, the conclusion), and which statements are being offered as reasons for accepting the conclusion:

The bus is late. It must have broken down.

That bird can’t be a robin. It doesn’t have a red breast. You should try to appear confident in your job interview. The employers are looking for someone who can speak confidently in public.

Children learn languages much more quickly and speak them more fluently if they start to learn them at an early age. So if you want your children to be bilingual, you should speak two languages to them from the time they are born.

She didn’t turn up for their date. She obviously doesn’t really want to be his girlfriend. If she’d wanted a serious relationship with him she wouldn’t have missed the date.

‘Argument indicator’ words

The language of reasoning can be very complex, but there are some relatively simple linguistic clues which can signal that reasoning is taking place. Certain characteristic words are used to indicate that someone is presenting a conclusion, the most commonly used being ‘therefore’ and ‘so’. For example, the argument presented in the first paragraph of this section could be written as:

He told us he was forty-two, but he has a daughter who is at least thirty years old. So, he must be older than he says he is.

‘Hence’ and ‘thus’ can also function in the same way as ‘so’ and ‘therefore’, though they are less commonly used. Other words may indicate the presence of a conclusion, for example, ‘must’, ‘cannot’. In the original version above, the word ‘must’ is used to show that the reasons offered force us to draw the conclusion. The word ‘cannot’ could function in a similar way, since the conclusion could have been expressed as follows: ‘He cannot be as young as he says he is’. Sometimes the word ‘should’ can signal that someone is presenting a conclusion, because arguments often make a recommendation. This is shown in two of the examples above; the third, which recommends appearing confident in a job interview, and the fourth, which recommends speaking two languages to babies. All of these ‘conclusion indicator’ words have other uses in addition to their function in arguments, so their presence in a written passage does not guarantee that an argument is being offered. However, they are useful indicators in assessing whether a passage contains an argument.

Recognising arguments without argument indicator words

Some passages which contain arguments have no argument indicator words. In order to recognise them as arguments, it is necessary to consider the relationships between the statements in the passage, to assess whether some of the statements can be taken to support a statement expressing a conclusion. For example, the following passage can be construed as an argument:

Knowing the dangers of smoking is not sufficient to stop people from smoking. One-third of the population still smokes. Everyone must know that smoking causes lung cancer and heart disease.

This passage is clearly presenting as a statistical fact that one-third of the population smokes, and as an obvious truth that everyone must know the dangers of smoking. It is using these reasons to support the conclusion that knowing the dangers is not sufficient to stop smokers from smoking.

Note that the only candidate for a conclusion indicator – the word ‘must’ – appears not in the conclusion, but in one of the reasons. Yet, we can be clear that the last sentence is not the conclusion, because no appropriate evidence (for example, that there have been programmes to educate the public about the dangers) is offered. Note also that in this example, as well as in our first example, the conclusion does not appear at the end of the passage. We need to be aware that conclusions can appear anywhere within a passage, even though it is possible for us to ‘tidy up’ an argument by writing out the reasons first and ending with a conclusion introduced by ‘so’ or ‘therefore’.

We have now considered two things we might look for to identify the conclusion of an argument:

• conclusion indicator words;
• the claim for which reasons appear to be offered.

Note that if we have identified a conclusion, we have also identified the passage as an argument or as something which is intended to be an argument. If we have identified the conclusion by finding conclusion indicator words, then it is reasonable to regard the author as intending to present an argument. Earlier, we introduced the term ‘argument’ as one way in which people use language when they are attempting to persuade or convince others of the truth of something – that is to say, when they have a particular purpose. However, when trying to assess whether a written passage presents an argument, we are not solely trying to guess the purpose of the author in writing the passage. We can also attempt to interpret the way in which this piece of language functions: this is what we are doing when we identify the conclusion by the second method, that is to say by looking for the claim for which reasons appear to be offered. If a passage can be written out as a series of reasons supporting a conclusion, then it can be construed as an argument, even if the author did not quite intend it in that way.

Nevertheless, it is often useful as a first step to consider the purpose of a passage when trying to decide whether it is an argument. If you ask yourself, ‘What is the main point which this passage is trying to get me to accept or believe?’, you can then underline the sentence which you think expresses the main point. The next step is to check whether the rest of the passage contains a reason or series of reasons which support the main point. You do not need to worry too much at this stage about whether they give conclusive support, because you are not yet attempting to evaluate the reasoning. Consider whether they are relevant to the main point, and whether they support it, rather than counting against it. Do they provide the kind of evidence or reasoning which one would need to present in order to establish the truth of the main point? If you are satisfied on these matters, then you can take it that you have identified a conclusion of an argument, and thereby decided that the passage is an argument. You may find it useful to tidy up the argument by writing it out as a series of reasons, followed by your chosen conclusion, introduced by ‘so’ or ‘therefore’.

Identifying conclusions

In this section are some examples in which we put these recommendations into practice.

The new miracle drug Amotril has caused unforeseen side effects of a devastating nature. Careful testing of the drug prior to its marketing could have prevented the problems caused by these side effects. Therefore, no new drugs should be released for public consumption without a thorough study of their side effects.

(Law School Admission Test, 1981)

This argument presents its conclusion in a straightforward way, and this helps to make it an easy passage to analyse. We first notice that the word ‘Therefore’ introduces the last sentence, so it is obvious that the conclusion we are being led to accept is:

no new drugs should be released for public consumption without a thorough study of their side effects.

The reason given for this is that careful testing of Amotril before it went on sale could have prevented the problems caused by its devastating side effects. In this case, we do not need to tidy up the argument, since it is clear what claim is being made. Moreover, the reason gives good support for the conclusion, provided we assume that one could not find out about a drug’s side effects without thorough study, and that it is never worth taking the risk of offering a drug for sale unless we are as certain as we can be that it has no serious side effects.

Here is another example:

People who diet lose weight. Falstaff cannot have dieted. He hasn’t lost weight.

In this case, we do not have a conclusion indicator such as ‘so’ or ‘therefore’, but we do have the word ‘cannot’. Is it being used to signal a conclusion? We must consider whether the sentence in which it occurs is the main point which the passage is trying to establish. It seems that the passage is trying to convince us that Falstaff cannot have dieted, and we seem to have a clear argument if we rearrange it to read:

People who diet lose weight. Falstaff hasn’t lost weight. Therefore, he cannot have dieted.

This is the most natural way to read the passage.

But suppose we had started out by assuming that the main point which the passage was aiming to get us to accept was that Falstaff has not lost weight. Then, we would have set out the argument as follows:

People who diet lose weight. Falstaff cannot have dieted. Therefore, he hasn’t lost weight.

But this is an unnatural reading of the passage, in two respects. First, it would not be natural to use the words ‘cannot have dieted’ in the second sentence if the meaning it aimed to convey was that Falstaff has been unable to diet. Second, even if we replaced ‘cannot have dieted’ with ‘has been unable to diet’, the first two sentences would be insufficient to establish the conclusion, since Falstaff may have lost weight by some means other than dieting, for example by taking exercise. Moreover, the kind of evidence which one would have to use in order to establish that Falstaff had not lost weight would be evidence, not about whether or not he had dieted, but about what he weighed in the past compared with what he weighs now.

Here is another example in which there are no conclusion indicators such as ‘so’ and ‘therefore’:

We need to make rail travel more attractive to travellers. There are so many cars on the roads that the environment and human safety are under threat. Rail travel should be made cheaper. Everyone wants the roads to be less crowded, but they still want the convenience of being able to travel by road themselves. People will not abandon the car in favour of the train without some new incentive.

What is the main point which this piece of reasoning tries to get us to accept? Clearly it is concerned with suggesting a way of getting people to switch from using cars to using trains, on the grounds that it would be a good thing if people did make this switch. We could summarise the passage as follows:

Because the large numbers of cars on the roads are bad for the environment and human safety, and because people will not abandon the car in favour of the train without some new incentive, we need to make rail travel more attractive. So, rail travel should be made cheaper.

Notice that the word ‘should’ appears in the conclusion. This may have helped you to see which sentence was the conclusion. Now that we can see more clearly what the argument is, we may question whether it is a good argument. For example, is it the cost of rail travel which deters motorists from switching to using trains, or is it because rail travel is less convenient? Would reducing rail fares really make a difference? Are there any alternative measures which would better achieve the desired effect? Setting out the argument in this way can help us to see what questions we need to ask when we begin to evaluate arguments.

Judging whether a passage contains an argument

Sometimes the subject matter of a passage may make it appear at first sight that an argument is being presented when it is not. Consider these two passages, one of which can be construed as an argument, whereas the other cannot.

The number of crimes reported to the police is rising. The overall crime rate may not be rising. Traditionally, only a quarter of what most people regard as crime has been notified to the police.

Most crime is committed by those aged under 21. But most people aged under 21 are not criminals. Some people aged over 21 are persistent offenders.

Let us consider the first passage and ask what main point it is making. Does it try to convince...

Table of contents

• Cover Page
• Title Page
• Copyright Page
• Acknowledgements
• INTRODUCTION
• 1 ANALYSING REASONING
• 2 EVALUATING REASONING
• 3 RECOGNISING IMPLICATIONS
• 4 EVALUATING EVIDENCE AND AUTHORITIES
• 5 TWO SKILLS IN THE USE OF LANGUAGE
• 6 EXERCISING THE SKILLS OF REASONING
• 7 CONSTRUCTING REASONING
• ANSWERS TO EXERCISES
• Bibliography and further reading