Assumptions underlying basic reasons

The following argument (used in a slightly different form on p.7 as an example of
an argument without a conclusion indicator word) provides an example of the use of an
assumption in the first sense, that is to say as something which is intended to support one
of the basic reasons of the argument.
One-third of the population still smokes. Everyone must know that smoking causes
lung cancer and heart disease. So, knowing the dangers of smoking is not sufficient
to stop people from smoking.
This piece of reasoning presents two (basic) reasons for its conclusion:
Reason 1: One-third of the population still smokes.
Reason 2: Everyone must know that smoking causes lung cancer and heart disease.
In such arguments, the basic reasons may be well-established facts, or they may make the
kind of factual claim which we could easily check. Reason 1 seems to be of this nature –
that is to say that either it is a generally accepted fact, backed up by reliable statistics, or the
author of the argument has made an error about the statistics, and the fraction of the
population who smoke is something other than one-third. But we do not need to worry
about the reasonableness or unreasonableness of assumptions in relation to Reason 1,
because we would be able to seek confirmation as to the correct figure, and in any case,
the exact figure is not crucial to establishing the conclusion. Provided that some of the
population still smoke – and our own experience confirms the truth of this – and provided
Reason 2 is true, then Reason 1, taken together with Reason 2, gives support to the
conclusion.
Reason 2, however, seems a less straightforward factual claim than Reason 1. What lends
support to this statement? The claim that ‘everyone must know . . .’ suggests that there
is an underlying reason for expecting people to be well-informed on this topic, and the
obvious candidate is that there has been widespread publicity on the dangers to health
of smoking – on television, in newspapers and by means of posters in the waiting rooms of
doctors and hospitals. Yet, the move from the doubtless true claim that there has been
publicity about the dangers to the further claim – that everyone must know about the
dangers – depends upon an assumption that everyone has absorbed this information, is
capable of understanding the messages which are being put across, and accepts the truth
of those messages.
This may seem a reasonable assumption to make, but there may well be those who would
wish to challenge it by pointing out that, despite publicity campaigns, some people may
not believe that there is a causal link between smoking and ill-health, because they think
that the statistics are inconclusive. Even if you do not regard this assumption as controversial,
the example illustrates the way in which we can attempt to identify potentially
controversial assumptions underlying the basic reasons presented in an argument. Clearly
the identification of such assumptions is closely associated with evaluating the truth of
reasons, which will be discussed further in the next chapter.
Another example of assumptions which underlie basic reasons is provided by the passage
below:
Occupational accidents will never be eliminated because all human activity entails
risk. But the total number of accidents could be greatly reduced, and the surest way
of achieving such a reduction is to penalise, with fines or even imprisonment, those
employers on whose premises they occur. Such a policy might result in cases of
individual injustice, but it would be effective in securing safer workplaces.
Before reading on, ask yourself what this passage is recommending, and why.
The passage is recommending the imposition of penalties on employers on whose premises
occupational accidents occur, on the grounds that this would be the best way to reduce the
number of such accidents. There is an obvious unstated assumption here that the threat of
penalties would influence the behaviour of employers. But there is a further assumption,
since the existence of penalties would not reduce the number of accidents if it were
beyond the power of employers to prevent some of the accidents which now occur. So the
argument assumes that it is possible for employers to take measures which will prevent the
occurrence of some accidents.
Both these assumptions function as reasons which need to be taken together in order to
support the claim that the threat of penalties would reduce accidents; and both are reasonable
assumptions to make. However, even with these assumptions, the conclusion is too
strong, since nothing has yet been said to support the idea that introducing penalties is the
surest way of achieving a reduction in accidents. So there is yet another assumption – that
no other method would be as effective in reducing the number of accidents – and this
assumption is more controversial than the others, since it may be possible to get employers
to take appropriate action by offering them incentives.