the.com/double negative

means A sentence that cancels itself out by stacking two negatives, like 'I don't know nothing,' which technically claims you know something.

from The term comes from grammar's straightforward Latin-rooted vocabulary — 'negative' from Latin 'negare,' to deny — paired with 'double' from Latin 'duplus.' The construction itself is ancient; languages like Old English and Chaucer's Middle English used piled-up negatives freely for emphasis, not confusion ('He never yet no vileynye ne sayde'). The modern taboo against double negatives in standard English is largely an 18th-century invention, when grammarians, leaning on the logic of mathematics (two negatives make a positive), decided the construction was 'illogical' and began policing it out of polite usage — even though plenty of the world's languages still use double negation as standard emphasis, no contradiction implied.