Chapter 5
Deduction
Introduction
Nature
Applying Law
Interpreting Law
Ascertaining Values
Ascertaining Causal Laws
Proving Facts
There are more things in heaven and earth, Horatio, than are dreamt of in
your philosophy.
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Introduction
Deduction is a form of reasoning based on a syllogism. Deduction is used or
allegedly used in several tasks in or connection with law. First, the task of
applying law to facts is unquestionably deductive.
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Second, according to
some it is used in forming law. There are three aspects to this. (i) Interpreting
law, according to one view, is based on a syllogism. (ii) There is some
argument that ‘reason,’ which could include deduction, is a means of
ascertaining values that are deployed in the policy process. (iii) The process of
verifying or establishing the causal laws that are used in the policy process
relies in part on syllogistic reasoning. Third, deductive reasoning is used in fact
finding where the court relies on scientific evidence.
Nature
How often have I said to you that when you have eliminated the impossible,
whatever remains, however improbable, must be the truth.
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Introduction
A syllogism is a form of argument in which a conclusion logically follows from
two propositions or premises. A syllogism, however, does not discover new
truths. Instead, it merely exposes, in the conclusion, a truth that is inherent in
two other propositions, the major and minor premises, which are themselves
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William Shakespeare Hamlet v I 4 166
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Kirby (1991) p 2; published in revised form as Kirby (1995); Kirby (1990) p
697, citing R v Trade Practices Tribunal; Ex parte Tasmanian Breweries (1970) 123 CLR
361, 374-375; New South Wales Bar Association v Muirhead (1988) 14 NSWLR 173, 197
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Arthur Conan Doyle A Study in Scarlet
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