Due Process

From the Magna Carta (1215): nisi per legale judicium parium suorum vel per legem terrae — 'except by lawful judgment of his peers or by the law of the land.' The phrase 'due process of law' appeared in a 1354 statute of Edward III and was carried into the Fifth and Fourteenth Amendments to the U.S. Constitution.

Appears in two constitutional amendments because the founders understood it needed saying twice — once to limit the federal government, once to limit the states. In practice, contested at every edge: who gets it, when it applies, what procedures satisfy it. Governments under pressure tend to find ways to suspend it while insisting they haven't.