Critical Thinking: A Concise Guide by Kemp Gary & Tracy Bowell

Author:Kemp, Gary & Tracy Bowell [Kemp, Gary]
Language: eng
Format: mobi
Tags: Humanities
Publisher: Taylor and Francis
Published: 2009-07-29T16:00:00+00:00

C)

If you smoke, then, probably, you will get cancer.

What, then, does ‘Smoking causes cancer' mean? Roughly, what it means is that each person is more likely to develop cancer if they smoke than that person would be if they did not smoke. Smoking raises the probability of getting cancer. So this argument is deductively valid:

P1)

Smoking causes cancer.

C)

You will be more likely to get cancer if you smoke than if you don't.

But note that the statement about smoking does not tell us to what degree smoking raises the probability of getting cancer. In that respect it is vague. A more precise causal generalisation would take the form: ‘Smoking raises the probability of cancer by such-and-such per cent.'

This connects with another important issue regarding generalisations. Consider:

A recent study of primary school children has discovered a strong correlation between diet and school performance: better diets were strongly linked to better test marks. One of the simplest things we can do to improve performance in primary schools, then, is simply to improve the foods on offer at school refectories.

To discover a ‘correlation' between X and Y is to discover that the proportion of things that exhibit the feature Y is higher among things that exhibit feature X than it is among things that do not exhibit feature X. The arguer here seems to infer a causal relationship from the correlation of better test marks with better diets. In the language to be introduced in Chapter 7, this is the fallacy of confusing correlation with cause. The inference goes like this:

P1)

X is strongly correlated with Y.

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