It is often quite easy to think up a plausible explanation, or combination of plausible explanations, for some observed fact. But it is often very difficult to come to a confident decision as to the best explanation. Moreover, as we have just seen, even the most plausible explanation, which seems to tick all the boxes,
Summary
• Explanations differ from arguments, despite resemblances.
• There may be many possible explanations for an outcome or event, though some are more plausible than others.
• The best explanations are those that are simple and that explain the most (have the widest ‘scope’).
• Even the best explanations may be wrong:
they are, strictly speaking, hypotheses.
was weightless. But in all three locations the amount of matter remains the same, and this constant amount is what is meant by its mass.
D He did it for sure, because no one else had the opportunity, the motive or the training to do such a thing.
E He did it because he needed the money and because an opportunity came his way.
2 Study the following information and then answer the question that follows.
Measurements were taken showing the growth of 16 fir trees planted at the same time but at different altitudes on a hillside. The results were recorded as shown in the graph.
25
Height of tree (m)
Altitude (m above sea level) 500 0
1 Which of the following short passages are arguments, and which are explanations?
A Icebergs are formed from glaciers breaking off into huge chunks when they reach the sea. The process is known as ‘calving’. The glacier is formed from snow, so it consists of freshwater ice. The oceans consist of brine (salt water), which has a significantly lower freezing point than fresh water. Therefore the sea around icebergs remains in a liquid state.
B Ice is less dense than liquid water.
Consequently, ice forms on the surface of lakes and ponds, instead of sinking to the bottom.
C In our ordinary everyday lives we use the word ‘weight’ as if it meant the same as ‘mass’. For example, we
‘weigh’ cooking ingredients in the kitchen to tell us how much to use, not to measure how much downward force they exert on the scales. But there is a distinction, and in science-teaching it must be preserved and stressed. A bag of flour on the surface of the Earth has a different weight from the same bag on the moon: here it is
approximately six times heavier. And in an orbiting spacecraft we would say it
End-of-chapter assignments
die. Leaving a climber to his fate, just to get to the summit of a mountain, was unthinkable in Hillary’s day. Then people climbed as members of large, organised expeditions and knew each other as friends and colleagues. Not all of them were expecting, nor even attempting, to reach the summit, because it was the purpose of the expedition just to get one or two climbers to the top. It was a team effort, and the credit was shared. Once the mountain was beaten they could all go home, satisfied that they had achieved their shared goal. Today Everest is besieged by swarms of individuals who have paid thousands of pounds for their one chance to make it, personally, to the top. No wonder traditional mountaineering morals have been thrown to the 80-mile-an-hour winds.
Is this passage an argument or an
explanation? (Give a reason or reasons for your interpretation.)
• If it is an argument, identify its conclusion and summarise the reasoning.
• If it is an explanation, state what is being explained, and what the explanation is.
Answers and comments are on page 324.
Which of the following, if true, would be a plausible explanation for the data recorded in the graph? (There may be more than one.)
A The fir trees planted at higher altitudes tended to be shorter.
B The higher up a hillside you go, the poorer the soil tends to be.
C Air temperature decreases with altitude.
D The higher a tree is planted, the smaller its growth.
3 Re-examine the data in Doc 3 in Chapter 4.1 (pages 131–2) and the statistics discussed in this chapter from Doc 4 (page 134). Suggest one or more explanations for the widespread public perception (shown by the charts) that claims for injury are up, when official statistics suggest that they are stable or falling. Which is the best explanation, in your view, and why?
4 (Harder task) Study the following short article and complete the task below.
In 1953, New Zealander Edmund Hillary and the Nepalese Sherpa Tenzing Norgay became the first climbers to reach the summit of Mount Everest and survive. That was then.
Now Sir Edmund has come out in forthright criticism of some 40 climbers who passed a dying man on the upper slopes of Everest, and left him there to
Evidence
4.3
Practically anything can be evidence: a footprint, a bloodstain, a written or spoken statement, a statistic, a chance remark, an email, some CCTV footage . . . the list could run to pages.
There is good and bad evidence, just as there are good and bad reasons (for a conclusion).
Judging whether or not a piece of evidence is
‘good’ depends on what it is being used as evidence for. There is nothing good or bad about a percentage of people saying they think that false claims for personal injury are on the increase. That is just raw data; a fact. It becomes evidence when it is used as a reason for some conclusion or verdict; or, to put it another way, when something is inferred from it.
From this we can see that ‘evidence’ and
‘reason’ have some overlap in meaning.
However, there are subtle differences in the way we use the terms in connection with arguments. Recall once more the evidence underlying the discussions in the previous two chapters. The charts in Doc 3 in Chapter 4.1 (pages 131–2) could be cited as evidence for the claim that:
[A] The vast majority of people believe that more compensation payments are being made than previously, and that more false claims are being made.
But we could just as well say that the data in the charts gave reasons for inferring [A]. It is useful therefore to think of the numbers and percentages reflected in the charts as raw evidence (or raw data) which has been extracted and processed into the statement, [A]. [A] expresses the evidence in a form that could be used as a reason (or premise) in an argument. It also interprets the data, by
summarising the figures and connecting the information from Charts 1 and 2.
Similarly, the figures in Doc 4 in Chapter 4.1 (page 134) are evidence for the claim that:
[B] Overall, more than 3000 fewer claims were notified in 2007/8 than in 2000/1.
These two claims between them could then be used to argue that, for example:
[C] The public perception of a dishonest
‘compensation culture’ is completely mistaken.
Expressed as an argument:
[1] According to a report by the UK House of Commons Constitutional Affairs Committee the vast majority of British people believe that more
compensation payments are being made than previously. However, the Compensation Recovery Unit reported that over 3000 fewer claims were made in 2007/8 than in 2000/1. The widespread perception among the British public that there is a growing, and increasingly dishonest,
compensation culture is completely mistaken.
Whether we want to call [A] and [B] ‘evidence’
for [C] or ‘reasons’ for [C] is a matter of preference. They are evidence because they are factual and statistical; they are reasons because they are used in support of a conclusion. The distinction is maintained when we say that the reasons (or premises) in [1] are based on the evidence provided by two sources. If [A] and [B] are warranted by the evidence from those sources, then [1] is well founded, and
hand may also be telling the truth about what she was told, but the receptionist may not be telling the truth about what happened. Of course, either of the two witnesses might be lying or mistaken. But in the second case there are two ways in which the evidence may be unreliable; in the first case only one.
Circumstantial evidence
By ‘circumstantial evidence’ we mean a fact, or set of facts, which may be used to support a conclusion or verdict indirectly. The facts themselves – the circumstances – are not in question. What is in question is what they signify, or permit us to infer. Wherever an inference is needed to get to the truth, the evidence cannot be accepted as direct, even if it is strong.
The classic example is the ‘smoking gun’. A detective rushes into a room after hearing a shot. He sees a body on the floor and a man standing holding a gun with smoke still coming from the barrel, indicating that it has just been fired. The natural assumption is that the man holding the gun is the murderer. The detective testifies at the trial, reporting exactly what he has seen. The suspect pleads not guilty because, he says, he too heard the shot and rushed into the room, and picked up the still-smoking gun from the floor where it was lying. The facts – the gun, the smoke, the man holding the gun, the body on the floor – are identical. The inferences are totally opposed.
‘A likely story!’ you may say of the suspect’s explanation. But in the absence of any other evidence, even the smoking gun is insufficient for a conviction. It is (merely) circumstantial.
Corroboration
If, however, it were also known that the suspect knew the dead man, that in the past he had threatened to kill him, that he owed the dead man money, and/or that he had recently visited a gun shop, then his guilt would be rather more probable. Each of these on its own is another piece of circumstantial evidence, but now the various items
strengthened. Hence the evaluation of an argument like [1] ultimately comes down to evaluating the evidence from which it draws its premises. However good the reasoning may be, if the evidence base is false, then the argument is groundless.