What phrase did C.S. Lewis use for judging the past by the assumptions of the present?

C.S. Lewis called the habit of judging the past by present-day assumptions “chronological snobbery.”

Lewis defined the phrase as the uncritical acceptance of the intellectual climate common to one’s own age, combined with the belief that ideas from earlier periods are automatically outdated. He discussed the idea in Surprised by Joy, his 1955 autobiography.

The phrase does not mean that every old idea is correct or that progress is impossible. Lewis’s point was methodological: readers should examine current assumptions rather than treating them as self-evidently superior. He encouraged encountering older books as serious arguments that can challenge modern habits of thought.

The term is often used outside Lewis’s religious writing, including discussions of history, literature, and philosophy. It is also sometimes confused with simple nostalgia for the past. Lewis’s argument was not to idealize earlier centuries, but to seek an intellectual “cleaning of the windows” by comparing different ages.