Along with the written constitution and unwritten principles, constitutional power is expanded upon, and more clearly defined, in the common law.
The common law is ‘judge-made law’, or law that is developed in the court system. Judges interpret the law based on an analysis of past court decisions and have the opportunity to create new causes of action, if necessary, for the facts at hand.
Over the years, the courts have been called on to interpret the Constitution, to resolve disputes about seemingly contradictory ideas, to define vague terms or to answer other big questions. The courts have also helped to define certain constitutional principles.
One of the most important constitutional principles that was developed by the courts is known as the living tree doctrine. The living tree doctrine was first developed in the case of Edwards v Canada (Attorney General), otherwise known as the “Persons Case.”  In this case, the Privy Council of England, then the highest court in the Canadian legal system, was asked to decide whether women should be permitted to sit in the Canadian Senate. In a particularly groundbreaking decision, the Privy Council found that women were considered to be ‘persons’ for the purposes of the Senate and stated that, “the British North America Act, planted in Canada [is] a living tree capable of growth and expansion within its natural limits.”  This idea meant that although the original framers of the Constitution were not thinking about women when they designed the Canadian Senate, times have changed and the original meaning would have to be expanded to fit the current social and political climate.
Since that ground-breaking decision, the living tree doctrine has been used to expand and interpret our Constitution in more modern and relevant ways, understanding that the framers of the Constitution were living in a different world than the one we live in today and may not have anticipated all of the social and technological advancements that have come our way.
This idea is particularly important for environmental law because although the environment was not recognized as needing regulation in 1867, it has certainly become necessary today.
 Edwards v Canada (AG),  A.C. 124, 1929 UKPC 86.
 Edwards v Canada (AG).
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