22 Unit 2 Critical thinking: the basics
Judging which of these is the right way to
respond to a claim is at the heart of the
discipline of critical thinking, and is part of
what we mean by ‘evaluation’.Recall the example in the last chapter: the
claim that the prehistoric dinosaurs were
cold-blooded. Two facts are often cited in
support of this:
[A] The dinosaurs were reptiles.
[B] Modern reptiles, e.g. snakes and
lizards, are all cold-blooded.Discuss whether these two facts between
them justify the claim that the dinosaurs
were cold-blooded.Activity
Commentary
The two facts give some support to the claim,
but only some. They are grounds for the
hypothesis that the dinosaurs were cold-
blooded inasmuch as they add some weight to
that side of the debate. If you knew nothing
else about dinosaurs, or reptiles, or evolution
generally, you might be tempted to accept the
grounds as sufficient. But it would be a big
step to take. For one thing it would mean
assuming that what is true of reptiles now
must have been true of reptiles 70 million
years ago, and earlier. It is not at all impossible
that there were once warm-blooded reptiles
running around, including some of the
dinosaurs; but that these reptiles became
extinct, leaving only the cold-blooded species
surviving today. (Being cold-blooded may
have given certain reptiles a survival
advantage over the warm-blooded ones.
Warm-blooded species use more energy than
those with cold blood, and food sources may
have become scarce.) This possibility alone
means that the assumption is questionable,
though not necessarily false.At first sight it may seem that truth and
justification amount to the same thing: a
claim is justified if it is true, and unjustified
(or unwarranted) if not. But neither of these
is correct. A claim can be true but unjustified
if the person making it does not have good
grounds for believing it – or in extreme cases
may not believe it at all. Suppose, for
example, a crime has been committed. The
victim (we’ll call her Vera) claims that her
neighbour (Nick) was the one who did it,
perhaps because she doesn’t like him, or
perhaps because she wants to see someone
convicted, and anyone will do. Other than
this she has no reason for making the
allegation, and certainly nothing that would
count as evidence. But then suppose it is
discovered that Nick, just as Vera has claimed,
is guilty of the crime! Would the discovery of
Nick’s guilt justify Vera’s accusation? No. It
would just be chance that the claim she had
made was true. Given her motives her claim
would still be a lie.
Conversely, a false claim can be justified in
some circumstances. Someone may make an
assertion on the basis of all the information
available at the time of making it. If that
information gives convincing grounds for the
claim, then it is fair to say that it is a justified
claim to have made, even if it later turns out
to be false on the basis of some new
information.
In other words, truth and justification are
different. Justification is provided by the
reasons that can be found and given for a
claim, but truth or falsity belong to the claim
itself. We may never know for certain whether
a particular claim is true, but we may be able to
say that there is sufficient evidence or grounds
or support to justify asserting it. Alternatively
we may say that a claim is unjustified, because
there are not sufficient grounds or support for
it, or because there are sufficient grounds to
cast doubt on it. This is different from saying
that it is actually false.