282 Unit 7 Critical reasoning: Advanced Level
Depending on other relevant factors – the
weather, the terrain, how tired you feel, the
distance remaining and so on – you might
decide that an 80 : 20 chance of getting wet
outweighed the certainty of having to trek
eight extra and unnecessary kilometres.
But next imagine a similar situation, only
this time you are practically certain you can
jump the gap. The difference is that this time
the river is a raging torrent and there is a large
waterfall just below the crossing point. Falling
in would carry a serious risk of fatality. In
both cases there is a long walk at stake if you
decide not to jump. But in the first case the
probability of failure is high and the
seriousness of a bad outcome low; in the new
one the risk is very low and the seriousness of
a bad outcome very high. What is the right
decision now?
How a real person would decide would
depend to a degree on temperament. Some
people are natural risk-takers and even
thrive on adrenalin; others are naturally
cautious. But we are not talking here about
feelings or personalities, but about rational
choices. Most people would say it was
perfectly rational to avoid a long trek at even
a high risk of falling into a slow-moving
river, but irrational to take even a tiny risk
when the consequence of failure could be
death. We cannot put fixed numerical values
on the seriousness of the chance of death
compared with the annoyance of wet
clothes, but we can say with justification
that a small risk of death outweighs a big
risk of wet clothes. Although the actual
values, and the ways of expressing them, may
differ, the underlying principle of measuring
seriousness against likelihood is broadly
unchanged. To summarise:
1 Consider the available options.
2 For each option consider the
consequences – the pluses and the
minuses.
3 For each consequence think ‘likelihood
versus seriousness’.to give a more general, verbal account of the
factors affecting our decision, we might say
something along these lines:
‘If you buy the cheaper car you run a bigger risk
of wasting your money; but then you have less to
lose if it lets you down. Buy the newer one, and
you’ve much less chance of wasting your money,
but a lot more to lose if the worst does happen.’Although the numbers have been left out, it is
clear that this statement still applies the same
basic principle (or methodology) of balancing
risk against cost, probability against value.Quality not quantity
The principle can be seen at work even when
we consider a very different kind of scenario,
and one in which qualitative rather than
quantitative judgements have to be made.
Imagine you are on a trekking holiday:
With 5 km to go to your next camp you come
to a river-crossing with wet, slippery rocks.
Partway across there is a large gap. You are
not confident that you can jump the gap, but
the water is slow-moving, so in the likely event
of falling short, you will just have to walk the
remaining 5 km in wet clothes. There is of
course some risk of a minor injury: cut,
bruise, strain. You would have to be extremely
unlucky for there to be anything more serious,
though it is not strictly speaking impossible.
Freak accidents do happen: you could slip and
crack your head, or break your leg. A rational
decision must allow for this, but must be kept
in perspective too. The alternative option is a
4 km walk upstream to the nearest bridge,
which would add 8 km to an already long day’s
trek. Basically you have to decide whether the
risk of wet clothes, or worse, is a less
desirable consequence than the longer hike.Can you quantify this? Perhaps not with the
precision with which we were able to assess
monetary values in the previous case, but
there is nothing to stop you making
qualitative judgements in the same way.