Thinking Skills: Critical Thinking and Problem Solving

2.5 Analysing arguments 39

If the next train would do just as well, then

there is no need to set off within ten minutes.

Where possible, analysis abbreviates a text, but

nothing essential can be left out. Sometimes

for clarification purposes an analysis may even

need to add explanatory detail.

How reasons relate to a conclusion

There is more to analysis, even of simple

arguments like [1], than simply listing

premises. We also need to know how the

premises operate in supporting the

conclusion.

In some arguments the reasons function

independently of one another, each giving

support to the conclusion in its own right. If

one premise is taken out, or found to be false,

it doesn’t fatally affect the argument because

the other, or others, may still be sufficient. The

argument may be a little weaker for the loss of

a premise; but like a plane with two or more

engines, the failure of one does not necessarily

knock it out of the sky.

There are other structures, however, in

which the reasons work together in support of

the conclusion. They are interdependent. This is

more than just an interesting detail. It is an

important factor when we come to evaluation.

In an argument with interdependent premises,

both or all of them are necessary for the

conclusion to follow. If one is omitted, or found

to be false, the conclusion cannot be inferred

from the other (or others) on their own.

In [1] the reasons are interdependent. It is

the train time together with the time it can take

to get to the station and the time it is now

that justifies the conclusion. If any of these

three reasons turned out to be unwarranted,

then the argument would fail. For example, if

the train were not due until 5.24, then the

other two, on their own, would not establish

the need for setting off at 3.40. Or if R2 was

an exaggeration, and it never took 40 minutes

to get to the station, leaving in ten minutes

would not be necessary. The remaining

premises would be true, but the conclusion

Commentary
The prime purpose of analysis is to identify
each of the claims that comprise the argument
and to separate the reasons from the
conclusion. Since there are three main
reasons, we can label them R1 to R3, and the
conclusion we can label C:

R1 The train leaves at 4.24.

R2 It can take 40 minutes to get to the

station.

R3 It’s 3.30 now.

C We need to set off within ten minutes to

be sure of catching the train.

(You can use ‘P’ for premise to replace ‘R’
if you prefer.)
Notice that in [1] there is no argument
indicator, such as ‘therefore’, ‘so’ or ‘because’.
That is because none is needed. It is obvious
which of the claims is the conclusion: it is
because of R1, R2 and R3 that the speaker
claims C, not the other way round.
Also notice that there are more claims in [1]
than there are sentences. The first two reasons
are connected by ‘but’ to form a single
compound sentence. Part of the job of analysis
is to identify each of the individual claims. So,
in standard form, these need to be listed
separately. Logically ‘but’ means the same as
‘and’ in that both R1 and R2 have to be true
for the whole compound sentence to be true.
‘But’ has a different meaning from ‘and’ in the
natural-language version. But as far as the
reasoning is concerned all that matters is that
the train leaves at 4.24 and that the journey
can take 40 minutes. Nor does it really matter
to the argument why the journey to the station
sometimes takes 40 minutes: it is sufficient
that it sometimes does. So, when you are
analysing an argument, it may not be
necessary to include every detail.
On the other hand, not all detail is
extraneous: some is essential. For example, the
conclusion of [1] is incomplete without the
phrase: ‘... to be sure of catching the train’.