Pendulum Swing
A theory suggesting that trends in culture, politics, etc., tend to swing back and forth between opposite extremes, much like the pendulum of a lock.
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Origin
The phrase entered political vocabulary through Arthur M. Schlesinger Sr., who argued in his 1939 Yale Review essay "Tides of American Politics" that the nation's mood oscillated between liberal and conservative phases. His son, Arthur M. Schlesinger Jr., extended the model in his 1986 book The Cycles of American History, popularizing the pendulum image for a mass audience — though the elder Schlesinger privately preferred the spiral as a more accurate metaphor.
Updated February 22, 2026