The rule of law is the tradition's first principle. It means that power can only be exercised under legal authority; that laws are public, prospective and general rather than secret, retroactive or targeted; and that independent courts stand ready to hold anyone — minister, police officer, corporation — to the same rules as everyone else.
It is an ideal as much as a doctrine. No system satisfies it perfectly, and much of public law is an argument about what it requires: how much discretion officials may have, how clear laws must be, and what happens when the state itself breaks the rules.
The Supreme Court of Canada has called the rule of law a foundational constitutional principle, implicit in the preamble to the Constitution Act, 1867 and explicit in the preamble to the Charter.