A Diamond Is Forever

Why it works

Four words that invented a social custom. Copywriter Frances Gerety scribbled "A Diamond Is Forever" late one night in 1947, defended it against colleagues who objected to the grammar, and watched it run in every De Beers ad from 1948 onward. The line fused an arbitrary product with the idea of eternal commitment so completely that the diamond engagement ring — a marginal tradition when N.W. Ayer took the account in 1938 — became a near-universal Western norm, and a resale market that might undercut prices never formed, because you don't sell 'forever.' Ad Age named it the No. 1 advertising slogan of the 20th century. It is studied as the outer limit of what advertising can do: not shift share within a market, but manufacture the market's meaning itself.