State courts used to read their own constitutions to mean exactly what the federal Constitution means. Many no longer do.
For much of the twentieth century, many state courts interpreted their state constitutional rights 'in lockstep' with the parallel federal provision, whatever the U.S. Supreme Court said the Fourth Amendment meant, the state's search-and-seizure clause meant the same.
In a 1977 Harvard Law Review article, Justice William Brennan urged state courts to rely on their own constitutions as an independent source of rights. The resulting movement, New Judicial Federalism, saw state courts increasingly interpret their constitutions to protect rights beyond the federal minimum.
Approaches vary: some courts still default to lockstep; others use a 'primacy' approach (interpret the state constitution first, on its own terms); others depart only when state-specific text, history, or tradition justifies it (an 'interstitial' or criteria-based approach).
For a state decision to be safe from U.S. Supreme Court review, it must rest on an 'adequate and independent state ground.' Under Michigan v. Long (1983), if a state court relies on its own constitution, it must say so plainly, otherwise the Supreme Court presumes the decision turned on federal law and may review it. That plain statement is the mechanism by which a state genuinely departs.
