24 Unit 2 Critical thinking: the basics
However, this does not mean we can never
use the words ‘know’ or ‘certain’
appropriately. It is perfectly appropriate to say
of some claims that they are certain. The
truths of mathematics and logic are usually
spoken of as certainties. No one doubts that
7 + 5 = 12 or that a triangle has three sides, or
that an object cannot be red and black all over
at the same time. Claims like these are often
said to be true by definition. For example, ‘12’
just means the same as ‘the sum of 7 and 5’.
Also there are claims which are practically
certain even if they are not logically true. The
old favourite is that the sun will rise tomorrow
(as it has always done on previous days). It
would be foolish to dispute this claim, despite
the fact that some freak of nature could
conceivably spell the end of the solar system in
the next 24 hours. If you had to bet on winning
the lottery or the sun not rising, you would bet
on winning the lottery every time!Complex claims
Sentences such as ‘Katya just ran a marathon’
or ‘Dinosaurs were reptiles’ express simple
claims. The following, by contrast, are
complex sentences, each expressing two or
more connected claims:[D] Katya just ran a marathon and
completed the distance in under four
hours.
[E] The dinosaurs were reptiles, yet they
were warm-blooded.
[F] Sea levels are rising around the world
because global warming is melting the
polar ice caps.
[G] Many parts of the world will soon be
submerged if nothing is done to reverse
climate change.Grammatical note
A simple sentence, when it becomes part of a
complex sentence, is called a ‘clause’. Words
or phrases which express the relation between
clauses are called ‘connectives’: for example,a criminal case there is an imbalance between
the standards that must be met by the
prosecution and the defence respectively.
The ‘burden of proof’, it is often said, ‘lies with
the prosecution’.The balance of probability
Outside the criminal law we may find
standards lower than proof being needed to
justify a claim or decision. For instance, in a
civil case, where both sides are treated
equally, a verdict is justified ‘on the balance
of probability’. Obviously it is much harder
to justify a claim beyond reasonable doubt
than on the balance of probability.
What this means is that there are degrees of
justification, depending on context. For
critical thinking it means that when we judge
a claim to be justified (warranted), or
unjustified (unwarranted), we need to qualify
the judgement by stating what standard we
are applying. Expressions like ‘wholly
(completely, entirely) justified’ are stronger
than ‘well supported’ or ‘highly likely’; and
‘unwarranted’ is stronger than ‘open to
question’ or ‘unlikely’. Choosing the right
qualification for the judgements we make
about claims and their justification is
one of the most important critical skills to
develop – arguably the most important.Knowledge and certainty
With certainty, on the other hand, there are
no degrees. It is true that people often talk
about the degree of certainty that can be
given to some claim or other; but what they
really mean by this is the degree to which the
claim falls short of certainty. The claim that
you will never win the lottery is so highly
probable that it can be stated as a near-
certainty. But near-certainty is not certainty.
Likewise, you don’t know that you won’t win
the lottery. If everyone who bought a lottery
ticket claimed to know that they would not
win, sooner or later one of them would
be wrong!