standard of proof requires proof on the balance of probabilities. This is a
standard of 51%. For a criminal case the common law standard of proof is
proof beyond all reasonable doubt. This does not translate directly into a
percentage as does the civil standard. However, a reasonable measure would
be 99%.
Because these rules reject absolute truth in favour of a defined standard of
truth, probability is fundamental to the task of finding facts. This is why the
“logical rules for thinking about facts in legal cases are those of probability”.
227
To explain this more it is necessary outline the task of fact finding. It is
explained here by a model constituted by three steps –
Step 1. Versions of
Truth, Step 2. Probability of Truth and Step 3. Standard of Truth.
228
Step 1. Versions of Truth
Step 1 involves each party presenting to the court their version of the facts. At
the same time they have to make a case to the court that this version of the
facts is true.
Step 2. Probability of Truth
Step 2 involves the court assessing the probability that each version of facts is
true.
229
This sets up Step 3 where the court compares the probability it has
assessed in Step 2 with the probability required by the operative standard of
proof.
Ideally the court would estimate this probability by giving it a numerical
measure. However, in most undertaking there are often problems in putting a
figure on a probability with any sort of confidence. With fact finding additional
problems because considerations “for and against particular findings of fact”
___________________
227
Robertson and Vignaux (1993) p 478
228
The part of the fact finding based on observation is discussed in Chapter 26
Observing Facts. For a basic account how the rules of probability are deployed in
fact finding see Christopher Enright Legal Method (2008) Chapters 21-25.
229
Under the common law rules the party who initiates proceedings, such as
the plaintiff or prosecutor, carries the burden or onus of proof. Strictly the court is
concerned only with the probability that their case is true because they are the
party who must meet the standard. There is, however, a good reason for
describing this step as requiring the court to assess the probability of truth for all
versions and not just that of the initiating party. It is difficult for a court to assess
the probability of one case on its own because it has before it two (or more)
competing versions of the truth. As the probability of one version increases, the
probability of one or more other versions decreases to accommodate the increase.
This reasoning is formally encapsulated in the complementarity rule under which
the sum of the probabilities for all outcomes must total 100%. The
complementarity rule is discussed later in the chapter.
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