150 Unit 4 Applied critical thinking
4.4 Credibility
Whilst we are often unable to say with
confidence whether or not a claim is true, we
can make a judgement as to its credibility – how
justified we are in believing it. Credibility is
determined by two main factors. The first is
the plausibility of the claim itself. A wildly
improbable claim is less credible than an
unsurprising claim that fits in well with our
other beliefs. But, as we all discover from time
to time, something wildly improbable can on
occasions be true, and something highly
plausible can be false.
You may recall your role as the imaginary
time-traveller in Chapter 2.3, attempting to
convince a pre-Copernican population that the
Earth is not a flat dish but a large ball whirling
like a bucket on an invisible rope around a
distant nuclear furnace... You can imagine
their incredulity, given their other beliefs at
that time. The account of the solar system that
we now regard as fact was once so far beyond
people’s understanding as to be fantastical. If
the Earth were a ball, surely the people on the
sides and underneath would fall off! Isaac
Newton’s theory of universal gravity was not
yet formulated; and that too was treated with
derision when it was first announced.
Likewise some of today’s new scientific
theories seem improbable. Some of the
implications of quantum physics are more like
science fiction than science fact, especially to a
non-scientist. They don’t make ordinary sense,
any more than the solar system made ordinary
sense in the middle ages. The point of this is
that plausibility and justification do not
always correspond. Just because a claim seems
implausible we should not reject it out of
hand; nor should we accept a claim just
because it seems plausible. We need methodsof evaluating claims that are more critical than
merely relying on common sense.The sources of claims
A second factor in judging the credibility of a
claim is its source. If the claim comes from a
trusted source, we have more grounds for
believing it than if we do not know where it
comes from. ‘Source’ in this context may be an
individual making an assertion; or it may be a
book, an article in a newspaper, a website; or it
may be a publisher. If you have found two
conflicting claims, one from a book published
by, say, Harvard University Press, the other
from a blog or tweet by some anonymous
individual, you would be likely to put your
trust in the former rather than the latter.
When deciding the extent to which we can
trust a source, we are looking for qualities such
as honesty and possession of knowledge.
There are other qualities, but those are
probably the most important. We need the
first for obvious reasons: we cannot trust a
known liar. But however honest an author
may be, we also have to be assured that he or
she is well informed. An honest mistake is no
more true than a deliberate lie, even though
one may be more excusable than the other.Judging credibility
However, there is an obvious problem when it
comes to judging who to believe. It is no easier
than judging what to believe. Suppose
someone says to you: ‘Look, I’m telling you
the truth and I know what I’m talking about.’
This is just a claim like any other. To believe in
the source of the claim, you have to believe the
claim; and to believe the claim, you have to
believe the source. All you are doing is going
round in circles! What is needed is a set of