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Judicial decision making
Judicial decision making

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2.2 Legal fact-finding

Fact-finding in a legal case is just like common-sense fact-finding in everyday life. The fact-finder has to use the evidence that is available at the trial to infer what they think happened in the past. For example, the court might use skid marks on the road to infer how fast a vehicle was travelling before it was involved in an accident, or medical evidence to infer how likely it was that the claimant’s disease was caused by exposure to toxic particles in the workplace, or chemical analysis to infer how likely it was that a particular company polluted a river.

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Figure 5 (a) skid marks; (b) medical evidence; (c) chemical analysis

However, when making findings of fact, the fact-finder also has to follow legal rules contained in common-law cases and parliamentary statutes. For example, in the previous section on everyday fact-finding, we noted how fact-finding is never certain, only probable, and a fact may be found with varying degrees of probability ranging from 0% (impossible) to 100% (dead certain). In everyday life, it is up to us what degree of likelihood we want to rely upon in making decisions, but in law there are legal rules that impose very strict requirements on what degree of probability is acceptable.

The standard of proof

The law generally treats fact-finding as a simple yes or no question, so we have to translate the grey scale of probabilities into a straight black-and-white answer. This is called the ‘standard of proof’ and in civil law context this standard is ‘on the balance of probabilities’. The balance of probabilities means more likely than not. Therefore anything with a probability of 50% or less is taken not to have happened, and anything with a probability of 51% or more is taken to have happened. In criminal cases the standard is much higher, ‘satisfied so that you feel sure’ or the famous ‘beyond reasonable doubt’. However, there is disagreement about what exact percentage this equates to.

The burden of proof

The standard of proof still does not tell us which way round to apply it (does the claimant need to show that something is 51% likely, or does the defendant need to show it is 51% likely?), so we also need the ‘burden of proof’. In civil law, the law is that the burden of proof is on the side alleging that a particular fact is true. So a claimant who says that a defendant polluted a river will need to show that it was at least 51% likely that the defendant did so. And if the defendant says that the pollution was instead caused by a factory further up the river, the defendant will need to show this with 51% probability. In criminal cases the burden is generally on the prosecution.

There are other legal rules that must be followed when fact-finding. Sometimes these rules have a drastic effect on the fact-finding process. For example, ‘public interest immunity’ is a process recognised by common law rules where the government can apply to a court to exclude evidence that would otherwise be used because the government believes it would harm the public interest. The evidence might put an informer’s life at risk if disclosed, or it might harm national security. Just before World War II, an experimental submarine sank while being tested, killing 99 sailors. When a claim was brought against the shipbuilders, the House of Lords upheld a certificate from the government that it would damage national security if the designs for the submarine were disclosed. This meant that the plans could not be used as evidence (Duncan v Cammell Laird and Co Ltd Footnote 1). Public interest immunity is controversial because it can affect the fairness of the trial. Nonetheless, the tribunal of fact is obliged to follow these laws because if it does not, its decision will be overturned on appeal.


  1. 1 Duncan v Cammell Laird and Co Ltd [1942] AC 624.Back to main text