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Aids to statutory interpretation
To assist judges in interpreting statutes there exist various aids that they may refer to. Aids to statutory interpretation are divided into internal aids and external aids. These are  sometimes referred to as intrinsic aids and extrinsic aids to interpretation.
Internal aids
Internal aids are those contained in the statute itself and consist of:
  • The long title of the Act
  • Explanatory notes
  • Other sections of the Act
  • Definition sections in the Act 

External aids
  • Dictionaries
  • text books
  • Academic writings
  • Law Commission Reports
  • Case law from other jurisdictions
  • Hansard
Previously reference to Hansard was not allowed by the courts:
Davis v Johnson [1978] 2 WLR 553         Case summary
However this position was changed in:
  • European Convention of Human Rights
Since the introduction of the Human Rights Act 1998 in October 2000 the courts are now obliged as far as is possible to do so to interpret legislation in line with Convention Rights under s.3(1) HRA 1998.
The courts must also take into account any judgments made by the European Court of Human Rights under s.2(1) HRA 1998.


Other aids


Where a statute does not expressly provide otherwise, it is presumed the following apply:

  • Statutes do not affect the monarch
  • Statutes do not operate retrospectively
  • Existing rights are not to be interfered with
  • Statutes do not change the common law
  • mens rea is required for criminal liability

Sweet v Parsley [1970] AC 132    (Case summary)
Rules of language
There are three rules of language applied by the courts:
  • Ejusdem generis rule
  • Expressio unius est exclusio alterius
  • Noscitur a sociis
Ejusdem generis rule
This applies where a statute contains a list of items followed by and 'other...'. When the courts are determining what is counts as 'other' they will look at the context of the things in the list. Eg a statute which states it applies to  lions, tigers, cheetahs and other animals would apply also to leopards but not to a horse. See:
Powell v Kempton Park [1897] 2 QB 242           Case summary
Expressio unius est exclusio alterius
This means the express mention of one thing excludes all others. So if a statute stated it applies to lions and tigers (without stating and other) it would only apply to lions and tigers and not leopards and cheetahs. See:
R v Inhabitants of Sedgely (1831) 2 B & Ad 65            Case summary
Noscitur a sociis
This applies where there is a list of items in the statute and the item under consideration is included in the list, but the context of the items in the list suggest that the item should not be in the list. Eg if a statute stated it applied to cat baskets, toy mice, flea collars and food, under this rule a loaf of bread would not be within the remit of the statute. See:
Inland Revenue v Frere [1964] 3 All ER 796                                  Case summary

Aids to Statutory Interpretation