Thinking Skills: Critical Thinking and Problem Solving

30 Unit 2 Critical thinking: the basics

of belief or opinion. An argument that the Earth

is not flat makes practical sense only if

someone – past or present – thinks that it is

flat, or needs proof that it is.

Evaluating argument

We have seen then that an argument is a

complex claim, made up of simpler claims –

the reasons (premises) and the conclusion. It

is a good argument if the reason or reasons

justify the conclusion. It is a poor argument if

they do not. Evaluating argument means

distinguishing good ones from bad ones.

Much of the content of this book is about the

critical evaluation of reasoned argument. But

here is a taste of what it is like.

We have established that [3] is a weak

argument; a bad one. Compare it with [1]:

the argument that since ships appear to sink

out of sight as they sail away, the Earth

cannot be flat. Is [1] a good argument, or

not? Would it persuade you that the Earth’s

surface was curved if you had previously

believed it was flat?

Activity

Commentary

Argument [1] might seem like a strong

argument now, because we already accept that

the Earth is not flat. But, as we also know from

history, arguments like [1] were not enough to

convince the general public straight away.

People needed more reasons if they were

going to give up a belief that had persisted for

centuries. Judged critically it becomes clear

that [1] is no better than [3], because [1] also

argues from appearances. If the flat

appearance of the Earth does not mean that it

is flat, then surely the appearance of ships

sinking does not prove that they are dropping

out of sight; nor that the curvature of the

Earth is the cause of this appearance. It could

be some kind of optical illusion; a kind of

mirage perhaps. It isn’t a mirage: it is perfectly

However, it would be wrong to think that

the two meanings of ‘argument’ are completely

divorced from one another. As stated at the

beginning of the chapter, arguments typically

exist to persuade, and it is clear that in a dispute

like [2] each of the participants is trying to

change the mind of the other. In [1] there is no

context given, but the argument being made is

obviously aimed at some real or imagined

opposition. Why else would its author feel any

need to give reasons to support the claim? You

don’t hear people nowadays arguing that the

Earth is spherical, because it is no longer

disputed. Arguments of the first kind occur

typically when some opposition to the

conclusion has been expressed or is anticipated.

Conversely, most arguments of the second

kind have some elements of reason-giving in

them. Even in [2], which is predominantly a

quarrel, both men are arguing on the grounds

of what they claim to see – the evidence of

their senses.

Bart: Anyone can see the Earth is flat.

Kris:... my eyes . . . tell me the Earth is

round.

If we wanted to interpret Bart’s words as an

argument, we could write it as follows:

[3] The Earth looks flat (to me); therefore it

is flat.

You may not think much of this argument now

because you happen to know that, because of

the size of the Earth, appearances are

misleading. The Earth does look flat. Therefore

the premise of [3] is true; but the conclusion is

not. So the conclusion does not follow from the

reason. [3] is an argument, but it is a bad one.

In some textbooks the impression is given

that critical thinking is concerned only with

arguments of type [1], and not with argument

in the sense of dispute. But for reasons just

given, we cannot understand the full meaning

and purpose of arguments if we ignore their

most obvious context. Much of our reasoning –

perhaps all of it – arises in or from differences