Critical thinking for Students (3 page)

Interestingly, we have an example here in which a large number of possible explanations can be seen as being part of ‘the explanation’. Our previous work on left-handed US presidents is also very likely to fit with this type of explanation. An explanation made up of a series of contributory explanations has implications for
any inferences drawn from it. Thus, an inference on the claim about the high proportion of left-handed US presidents will have to be judged against the range of possible explanations for the claim.

We can now see explanations as a way of focusing us on to the significance of evidence-claims. By doing this, they help us to draw useful inferences and to assess inferences that others have drawn.

Where we have (or use) only one explanation for evidence, then this sequence will follow:

Where we have more than one explanation for evidence, then more than one inference could be drawn, depending on which explanation is used.

Where we have (and use) more than one explanation for evidence, then the inference will be drawn accordingly.

	+ explanation 1
Evidence-claim	+ explanation 2    →	inference
	+ explanation 3

 

In an important sense, inference must wait its turn until explanation allows it in. Explaining evidence-claims is necessary to give them a significance, which is then made concrete by inference.

We’ve now restored explanations to their rightful place at the heart of Critical Thinking. What we’ve seen is that, until we’ve looked at explanations, we very often can’t do much with a claim.

What follows is an opportunity for you to do some explanation work with another evidence-claim.

Here’s the evidence for you to consider.

What else do you need to know to see if this evidence is, in any way, significant?

If it is significant, what might be an explanation for it?

Given an explanation, is there any inference that could be drawn from it? (Therefore what?) (You can find some analysis to help you on p.112.)

In the previous chapter we saw that, by looking at evidence-claims and their significance, we highlighted the importance of explanations. And, by highlighting explanations, we found that we opened the door to inference. Indeed, for inference to force its way in before explanations have opened the door risks inferences that have considerable problems.

This point is particularly well illustrated with predictions, where we find explanations have an especially important role. Indeed, with prediction-claims, explanations move forwards as the starting point, such that the prediction itself is the inference.

You will remember the example we gave in Chapter 1.

You can see that this prediction can be viewed as an inference from claims that make up an explanation. This explanation is concerned with (presumably) changes in medical knowledge. These changes could be detailed to include greater understanding of genetic diseases and how to slow down the ageing process.

Here’s another prediction.

The prediction is again based on an explanation, this time that the Sun has been getting progressively hotter for millions of years and will continue to do so, such that its heat will eventually make plant life (and thus all life) on Earth impossible.

The prediction could then be used to support an inference.

We’ll keep returning to this link between claims, explanations, and inferences. But, for the rest of this chapter, we’re going to focus on the process of inference itself.

You’ll remember that we represented the process of inference as claim → claim. The arrow sign shows that the second claim is being
drawn from
the first. Take out the arrow sign and we have just two separate claims. This shows the importance of the relationship between the two. It also shows that there is an important thing going on. Whoever draws the inference is saying that the first claim is enough for the second one to be drawn. We’ll be coming back to this point time and time again throughout the book.

We’ll now look at some examples of inference.

This is based on a letter to
The New York Times
in May 2009. Because we have the second claim drawn from the first, we have inference. In other words, we have an argument. The author is arguing that it’s good that young people hug each other
because
there is an understandable need for people to hug each other. This shows that we can turn round the argument, without the direction of inference being changed.

In this way, we can see that, however the direction of the inference is presented, the argument as such remains the same.

Interestingly, we have here another example where the argument flows out of an explanation.

The first sentence is an explanation (as used in the letter), and it’s used here as support for the second sentence. In other words, we have here an example of

Claim (explanation) → claim (inference from explanation) → claim (inference from inference).

You can see how arguments can be built up, step by step.

Here’s another argument on the same subject (based on another letter):

In this argument, the same inference is drawn from a different claim.

By the way, you will have noticed that we’ve used the word ‘argument’ time and time again. At no point did we fret about what it isn’t, so long as we understood what it is. An ‘argument’ might well be a disagreement, a quarrel, a debate. It might sometimes involve shouting or insults. We don’t really care, as long as we remember that, for us, in this subject, an argument has to have the process of claim → claim going on. There has to be at least one claim being drawn from at least one other.

We’ve been using the word ‘
so
’ to indicate that an inference is going on (except when we reversed the sentences and connected them with a ‘because’). You’ll find lots of other words that can be used:
therefore, thus, in consequence, as a result, it follows
that
. You might find that no words are used at all. 

In the second version above, the inference can still be seen as the second claim being drawn from the first. Even though it’s not actually there, a word like ‘so’ or ‘therefore’ sort of shouts at us to say ‘I’m here’ when we read the two sentences together.

Look at the next example.

What’s going on here?

You will probably have spotted that the inference was given first. The claim that the use of sunbeds should be banned is drawn (inferred) from evidence on skin cancer and its link with sunbeds. An interesting thing is that no words such as ‘so’ (or ‘because’) were used, but there was a different word which gave us a big hint that an inference was being drawn. This was the word ‘should’. Words like this – ought to, must, and their negatives shouldn’t, ought not to, must not – often indicate that an inference has been drawn. Note the word ‘often’: these words don’t
always
indicate an inference.

In this example, though the first sentence contains the word ‘should’, it is the claim that’s used to support the inference.

There was something else to note in the first version of the sunbed argument. Look at the second sentence again.

What we have in the second sentence are really two claims.

So what we have are two claims from which the inference is drawn:

If you look at this sentence, the inference certainly needs the second claim, although the first gives some extra significance to the second.