Chapter 9
Probability
Introduction
Measuring Probability
Applying Probability
Assigning Probability
Deriving Probability
Fallacies in Probability
I feel like a fugitive from the law of averages.
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Introduction
Probability
Probability caters for uncertainty. Probability is widely used in the human
sciences such as management and psychology and also the physical sciences.
As Professor Alan Hájek neatly puts it, “[p]robability is virtually ubiquitous”
since it is used in so many disciplines of both academic and practical
importance.
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It is, therefore, relevant to
any study of law from the human
sciences perspective.
Commonly but loosely people treat probability as referring to the likelihood of
an event occurring. In fact, this is a fallacy, called the mind projection fallacy.
It is a fallacy that probability is
“a property of objects and processes in the
real world”.
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Probability is a state of mind, not the state of the world. It is a
measure of the strength of our belief that an event will occur or has
occurred.
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There are two aspects to this. One is a descriptive function. It
describes how certain we are about the truth of something. A second function
of probability is derivative. When one or more probabilities are known and
quantified further probabilities can be derived by rules based on deduction.
This chapter uses the standard symbols that are utilised in the mathematics of
probability. These are set out in the preliminary pages to this book under
“Labels”.
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Bill Maudlin Up Front (1946) p 39
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Alan Hájek’s “Interpretations of Probability”
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Robertson and Vignaux (1993) p 460
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Robertson and Vignaux (1993) p 462
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