Ken l. Manktelow
Neil Fairley
Steve G. Kilpatrick
David E. Over

This chapter is concerned with the strategic role of pragmatics in practical
reasoning. Three studies are reported. In Study 1, scale of violation of deontic rules
was explored, along with aggravating and mitigating circumstances for the
specified offenses (road traffic violations). It was found that these factors all had
significant, systematic effects on inference. In Study 2, problem components were
presented serially: Inferences from deontic rules varied qualitatively and
quantitatively as relevant information was encountered. In Study 3, a well-known
effect in deontic reasoning, the perspective effect, was shown to extend to causal
reasoning. Both effects are attributed to uncertainty about the condition relations
of necessity and sufficiency. A modified account based on the theory of mental
models is proposed. These studies show that pragmatic factors help to define initial
representations, determine the sorts of inferences made, and motivate the search
through problems which is at the heart of the connection between these elements
of thought.

Philosophers have for many years made a broad distinction between two forms of
reasoning: pure or theoretical reasoning on the one hand, and practical reasoning
on the other. Pure reasoning is largely about matters of fact: It is the kind of
thinking we are doing when we try to figure out what is the case, as when we
consider whether a certain statement is true or not. For instance, suppose we
assume that the following statement about students is true:

If one works hard, then one does well on tests.

We learn that a certain student, Jasper, works hard. We conclude, validly, that he
does well on tests. Practical reasoning, by contrast, is largely concerned with
inferences about which actions may be performed or not. Suppose now that one
accepts the following statement:

If one works hard, then one should rest on Sundays.

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