Thinking Skills: Critical Thinking and Problem Solving

126 Unit 4 Applied critical thinking

4.1

Unit 4 Applied critical thinking

Inference

The verb ‘infer’ means to draw a conclusion,

usually from some factual (or supposedly

factual) information. The information

provides the grounds for the inference. If the

grounds are good, we say that the inference is

sound, or reliable. Another word that is often

used is ‘safe’. If the grounds for an inference

are poor, we have to say that the inference is

unsafe: it cannot be relied upon.

Judging whether an inference is safe is

therefore similar to judging whether an

argument is sound. The main difference is that

in a standard argument the conclusion is

stated. In many texts and documents,

however, there is no explicit conclusion. There

may be claims; there may be information. But

unless some further inference is drawn from

the information, there is no argument.

Sometimes there may be an implicit

conclusion, where the information is clearly

leading in one particular direction, and it is

obvious what we are meant to infer. There is an

example in Chapter 2.4, item [7] (page 34).

Here is another example (the subject may

sound familiar):

[1] These banknotes all have the same

serial number. All genuine banknotes

have different numbers.

This time the conclusion has been left unsaid.

But it is clear what the author is getting at. If

asked what can be inferred from [1] most

people would probably answer that:

[2] The banknotes are not all genuine.

Moreover this would be a safe inference,

because [1] provides very good grounds for [2].

Of course [2] is not the only inference that

could be drawn from [1]. Nor is it the only safe

one. [1] also gives good grounds for inferring

that I would be committing an offence if I

tried to spend these banknotes. I would need

to know that passing false currency is illegal,

but that is such common knowledge that it

practically goes without saying.

It would be fairly safe, too, to infer from [1]

that

[3] The banknotes are forgeries,

on the reasonable assumption that only

forgeries could have duplicate numbers. By

contrast it would be entirely unsafe to infer

that

[4] The banknotes are the work of terrorists,

intent on destabilising the economy.

Inferring [4] from [1] would be a blatant

example of jumping to a conclusion.

Inference and science

Drawing inferences, and judging the reliability

of inferences, are especially important in

scientific contexts. Scientists typically base

their claims to knowledge on the information

they collect from observation and experiment.

Because we cannot confirm the truth of such

claims without supporting evidence, we have

at least to be sure that the evidence is strong

and the inference is reliable. Assessing what

can and cannot be inferred from a given

document is therefore a key component of

critical thinking.

Here is a short introductory example:

DOC 1

Ice ages last for roughly 100,000 years,

going by the record of the past half-million

years. The warm phases in between are

called interglacials. The standard view,

until quite recently, has been that we are