According to standard English grammar, a double negative used to express a single negative, such as I don't know nothing （rather than I don't know anything）, is incorrect. The rules dictate that the two negative elements cancel each other out to give an affirmative statement, so that I don't know nothing would be interpreted as I know something. In practice this sort of double negative is widespread in dialect and other non-standard usage and rarely gives rise to confusion as to the intended meaning. Double negatives are standard in certain other languages such as Spanish and they have not always been unacceptable in English, either. It was normal in Old English and Middle English and did not come to be frowned upon until some time after the 16th century, when attempts were made to relate the rules of language to the rules of formal logic.Modern (correct) uses of the double negative give an added subtlety to statements: saying I am not unconvinced by his argument suggests reservations in the speaker's mind that are not present in its 'logical' equivalent: I am convinced by his argument.