Must we have a theory of proof?

JurisdictionSouth Africa
Citation2003 Acta Juridica 113
AuthorAndrew Paizes
Published date15 August 2019
Pages113-138
Date15 August 2019
Must we have a theory of proof?
ANDREW PAIZES*
University of the Witwatersrand
It is common, when writing a legal textbook, to begin with a general
introductory chapter in which the theoretical foundations of the subject
are expounded and explained. Chapters of this kind usually hold little of
interest for those who are concerned primarily with f‌inding practical
answers to legal problems. They are, typically, ignored by them as being
the province of academics who amuse themselves and each other by
posing and solving riddles that stimulate the mind but have little bearing
on the often prosaic world of legal practice. The question that forms the
title of this chapter would, no doubt, suggest to some, this kind of
exercise. ‘Who cares,’ one can imagine some people thinking, ‘about
competing ‘‘theories of proof?’’’
‘Evidence is lawyers’law. We know what we want to achieve, and we make
sure that our evidentiary rules deliver the results we need. There is little to be
gained by exposing what we do to penetrating analysis or by trying to
construct sophisticated models that rely on metaphysical distinctions, syn-
thetic metaphors or scientif‌ic precision, since most of the things we do when it
comes to legal proof take place at a visceral level where everything rests on
such unscientif‌ic and non-academic notions as intuition, experience, ‘‘gut-
feeling’’and observations on human nature. It is of such things that the world
of forensic fact-f‌inding, the so-called real world, are made, and any attempt to
contain them within a coherent scientif‌ic theory, while it may dignify the
subject and lend it a certain intellectual veneer, are bound to be artif‌icial,
unhelpful and, as a result, tend toward sophistry.’
My purpose in writing this chapter is to show that such views are
harmful and wrong. I hope to show that the selection of one or other
‘theory’ of proof is of the greatest practical importance and that
fundamental every-day problems of proof cannot adequately be addressed
without making such a selection. I propose to indicate, too, what the
implications of the chief competing theories are, and, f‌inally, to put
forward some ideas on how we might go about determining which of the
theories might best serve us in particular cases.
I THE FIRST PROBLEM: IS THE COURTROOM LIKE A
CASINO?
The unlikely starting point for this exploration of theories of proof is
the casino. Imagine that you wish to play a game of roulette. Imagine a
*BCom LLB PhD (Witwatersrand); Professor of Law, University of the Witwatersrand,
Johannesburg.
113
2003 Acta Juridica 113
© Juta and Company (Pty) Ltd
roulette wheel of 36 numbers, 18 of which are marked in red, the
remaining 18 in black; 18 of which are odd, the remaining 18 even. If you
were to place a single token on a bet that the spin of the wheel will yield,
say, an odd number, it is accepted that your chance of success is one in
two, or, to express this in the language of probability theory,0.5. A bet on
a black number would have the same chance of success. A bet that
combined these outcomes, one that, in other words, is taken on an odd
and black number resulting, would yield a probability of 0.25 (or one in
four), a ratio that is the product of the other two ratios.
That it is entirely appropriate to employ this product rulein cases of
this kind is plain. It is a simple application of the classical or mathematical
system of probability that has come to be referred to as Pascalian, after
Blaise Pascal,
1
who developed the early analysis of the probabilities
involved in gambling. But what is much more controversial is whether it
is appropriate to engage in this kind of reasoning in the legal context.
It should be emphasised that the inquiry is not a synthetic one. One is
frequently required, in law, to consider the probability of the truth of an
entire series of propositions taken together where none of the preposi-
tions may be considered, in itself, to be certain. To take but one example:
2
X disappears in mysterious circumstances while hunting in a remote area
of bushveld. He was in the company of Y who returns with an
implausible account of the disappearance. Y had a motive to kill X, who
has not re-appeared in the intervening two years, and Y comes back with
some of Xs valuable personal possessions giving, again, an implausible
account as to how they came into his possession. The area in which X
disappeared is, however, notoriously dangerous, with countless natural
and other hazards, including wild animals, marshes, rivers, f‌loods,
extreme weather conditions, and human occupants hostile to tourists.
The propositions that would have to be established by the prosecution in
a case of murder against Y would include the following:
1. X is dead;
2. Y killed X;
3. The killing was unlawful (and, therefore, carried out in the
absence of defences such as self-defence, compulsion, and neces-
sity); and
4. the killing was intentional.
A probability ratio may be allocated to each of these propositions, none
of which may be taken to be certain, each ratio being determined,
however, on the assumption that the preceding propositions are certain.
1
16231662.
2
This example is taken from a murder trial that took place some 15 years ago in Botswana.
It is, to my knowledge, unreported.
114 CRIMINAL JUSTICE IN A NEW SOCIETY
© Juta and Company (Pty) Ltd

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