70 Unit 2 Critical thinking: the basics
‘fallacies’. A fallacy is a flawed line of
reasoning. Because it is very often not possible
to know the truth or otherwise of the
premises, most of the critical evaluation of
arguments focuses on the reasoning, and
whether it is sound or fallacious. (If you know
that either the reasons or the conclusion is
false, there is no further critical thinking to do
on the argument!)
Note: the word ‘fallacy’ is often used
casually to mean a false or mistaken claim.
For example, after 1912 a person might have
said, ‘It was a complete fallacy that the Titanic
was unsinkable.’ In critical thinking, or any
formal context, ‘fallacy’ is never used that
way. A fallacy is always a defective argument.Read the following argument and decide
whether or not the reasoning is flawed. If it is
flawed, explain what you think the flaw is.
[1] The outstanding success of Amulk’s
company, which was launched against
the advice and without the support of
bankers, business consultants and
financiers, just goes to show that one
person’s vision can prove all the experts
in the world wrong. Anyone thinking of
setting up in business should therefore
trust their own judgement, and not be
influenced by the advice of others.Activity
Commentary
First we need to analyse the argument so as to
identify the conclusion and the reasons. Then
we need to ask whether or not the conclusion
follows from the reasons, according to Rule 2.A good argument is one that satisfies
two rules.
Rule 1 is that the reasons should be true.
We cannot trust an argument that is based on
false premises. If we know that one or more
of the premises are false, we must reject
the argument.
Rule 2 is that the conclusion must follow
recognisably from the reasons, meaning that if
the reasons are all true, the conclusion cannot
be false.
An argument that passes both these tests is
said to be sound. An argument that fails one or
both of them is unsound. Interestingly we use
the same words to talk about structures like
boats or buildings, and more abstract objects
such as ideas, advice or plans. When you
describe something as sound, what you are
saying about it is that it is safe, reliable, free of
faults. You would not call a boat sound if it had
a hole in it and sank ten minutes after setting off
from the shore. You would not call a plan sound
if it led to a disaster. And you don’t call an
argument sound if it leads to a false or dubious
conclusion. (A bad argument is often said to
have a hole in it – something missing from the
reasoning.) Nor do you call an argument sound
if you know, or have reason to believe, that one
or more of its premises are false.
Another word for an unsound argument is
‘flawed’. A flaw is a fault. There are two main
ways in which you can find fault with an
argument. You can disagree with one or more
of the reasons; and/or you can show that,
whether the reasons are true or not, the
conclusion doesn’t follow from them.
Arguments that are unsound for this second
reason are said to contain ‘reasoning errors’, or
‘flaws in the reasoning’. They are also called