In common law systems, the duty of a judge is to apply the law to the facts which are presented to them. They will need to apply both the existing case law (common law) as well as any relevant statutes.
When the meaning of a statute isn’t immediately obvious, it will be necessary for them to interpret what its meaning is and how it should be applied to the case before them. However, in doing so, they must respect the intention of Parliament as closely as possible.
In order to do this, they may in some cases need to study external aids which are not included in the statute (such as Hansard).
Rules of interpretation
There are four different rules of interpretation which can be used by judges. Each rule will potentially result in a different outcome.
Sometimes referred to as the plain-meaning rule. When using the literal rule, the judge reads the statute using the plain meaning of the words contained in it. The advantage of this method is that it avoids the judicial legislation, adhering as closely as possible to the drafting of the original statute. The disadvantage is that it can sometimes create absurdities, particularly when the drafting of the statute has not taken certain circumstances into account.
Whiteley v Chappell is a good example of how applying the literal rule can result in an absurdity.
This rule allows the judge to vary of modify the language of the statute to avoid an absurd or unjust outcome which may arise from a literal reading of the drafting.
When using the mischief rule, the judge will look back to see which mischief (gap or fault in the law) Parliament intended to fix by passing the statute.
When using the purposive approach, rather than looking at the state of the law before the statute was passed as used in the mischief rule, the judge will instead look forward to see what outcome Parliament hoped to achieve by passing the statute.