Should a constitution mean what it meant when it was written?

It is a live dispute in constitutional law, with judges on both sides. Originalism is a US legal theory that bases the interpretation of constitutions and statutes on the original understanding at the time of adoption. Its rival, the Living Constitution view, holds that the Constitution has a dynamic meaning even if the document is not formally amended. Originalists say the aim is to stop judges inserting their own values; critics reply that the original intent cannot be found.

Each camp has its founding voices. Robert Bork, credited with proposing the first modern theory of originalism in 1971, argued that where a text is silent, judges are free to input their own values. Defenders of a living constitution answer that the document was meant to grow. The phrase traces to a 1927 book by Howard Lee McBain, and Woodrow Wilson wrote that living political constitutions must be "Darwinian in structure and in practice". Justice Holmes wrote in 1920 that a case must be considered in the light of our whole experience, and not merely of what was said a hundred years ago.

Each side has a pointed reply. Opponents of the living view argue that the Constitution should change by amendment, because allowing judges to change its meaning undermines democracy. Justice Scalia put it more bluntly: the Constitution is not a living organism; it is a legal document. Critics of originalism reply with doubts about the method: Justice Brennan argued that the Founders' intent was indiscernible.

The argument is not only American. Canada calls its version the living tree doctrine, and in 2004 its Supreme Court held that Parliament could define marriage to include same-sex unions, rejecting the argument that this was ruled out because the notion had not been conceived in 1867.