Double negatives

The Oxford philosopher J. L. Austin was giving a lecture in New York to a group of fellow philosophers. In it he raised the question of double negatives. ‘In some languages,’ said he in his precise Oxford voice, ‘a double negative yields an affirmative. In others it yields a more emphatic negative. But I know of no language in which a double affirmative yields an negative.’ From the back of the hall came a drawling professorial Brooklyn accent: ‘yeah, yeah’.