58 Unit 2 Critical thinking: the basics
grounds (or evidence) for arguing that global
warming is taking place. The phrase ‘must be’
helps us to see that the author is urging the
reader to accept the claim. But even without
this clue it is quite obvious that rising seas
could not be the cause of global warming,
whereas it makes good sense to offer rising
seas as evidence of global warming. It may not
be conclusive evidence, but it is supportive.
What we learn from this is that the word
‘reason’ is ambiguous, depending upon
whether it is a reason why (as in an
explanation), or a reason for (as in an
argument). This can make it quite hard on
occasions to be sure whether a set of
sentences is expressing an argument or giving
an explanation, especially if there are no
indicator words (such as ‘because’, ‘therefore’,
‘for this reason’) to label the sentences.Reasons as premises
Premises are claims from which a conclusion is
said to follow. But ‘follows’ in this sense means
more than just coming after. When we say a
conclusion follows from certain premises, we
mean that it follows logically. In natural-
language arguments the premises can appear
before or after the conclusion: it is only in
standard form that the conclusion is always at
the end.
What we mean by ‘follows from’ is that if
the premises are true, the conclusion must be
true too. If the conclusion does not follow
from the premises, then even if the premises
are true, the conclusion might be false. So a
really good argument is one in which the
premises are true and the conclusion does
follow. That is why, in a good argument, the
premises are reasons for believing, or agreeing
with, the conclusion.Reasons are expressions which tell us why
something is as it is. Their primary function
is to explain. Recall the example you first
considered in Chapter 2.2:
[1] Sea levels are rising around the world
because global warming is melting the
polar ice caps.
This complex claim offers an explanation for
rising sea levels. As you have seen, it consists of
two simple sentences joined by the connective
‘because’. Grammatically, therefore, [1] looks
very much like an argument, with the second
sentence being given as a reason for the first. It
could even be rephrased with ‘so’ or ‘therefore’
as the connective:
[1a] Global warming is melting the polar ice
caps and therefore sea levels are
rising . . .
But the claim that global warming is melting
the ice is not a reason in the sense of a premise.
[1] and [1a] do not make the argument that sea
levels are rising: they assert why sea levels are
rising. This is an important difference. The
claim that the seas are rising is not a
conclusion in need of support, but a claim to
fact in need of an explanation.
Compare:
[2] Global warming must be happening
because the polar ice is melting and sea
levels are rising.
Superficially there is not a lot of difference
between [1] and [2]. Again in [2] we see two
claims connected by the word ‘because’,
indicating that the second is being given as a
reason for the first. But this time global
warming is not being explained by rising sea
levels: rising sea levels are being offered as