Some Basic Principles of Common Law Reasoning

Last updated: October 18, 2012

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Different jurisdictions may have different laws.
Individual decisions must be consistent with the general rules of law of the jurisdiction.
General rules must be consistent with individual decisions, except for cases which were wrongly decided, or cases decided prior to a change in the law.
Legislatures may change the law, although occasionally they do say they are only declaring it.
Courts generally do not purport to change the law, although there are exceptions.
A court may ignore unconstitutional or ultra vires legislation.
A court may give temporary force to unconstitutional or ultra vires legislation, in order to maintain the rule of law.
On very rare occasions, a court will find that the law applicable to former circumstances no longer applies in current circumstances.
Courts make uncertain areas of the law more certain when they decide cases.
Like cases within the same jurisdiction should be decided alike, unless the law in that jurisdiction has been changed in the meantime.
Two cases are unlike when they can be distinguished.
On appeal, a higher court may reverse the decision of a lower court within the same jurisdiction.
A higher court, in a later case, may say that the decision of a lower court in a previous case was wrong, even though the previous decision was not appealed.
A lower court should not say that the decision, in a previous like case, of a higher court in the same jurisdiction, was wrongly decided.
A lower court should not say that the decision, in a previous like case, of the same or of a same level court in the same jurisdiction, was wrongly decided, except in the clearest of cases.
The decisions of courts of other jurisdictions, and the writings of learned authors, are not binding, but may be persuasive, depending on the reputation of the authors and the quality of the reasoning.