“Double Negative: The use of two negatives in a sentence where one will suffice, e..g., ‘It doesn’t mean nothing’; reiterated denial that is tantamount to an affirmative of positive statement.
In substandard speech, however, double negatives often reinforce a strongly negative color in an assertion. ‘I don’t want nothing from nobody is a threefold declaration of independence, not a logical seesaw.” G.W. Turner, Stylistics“
Excerpted from: Grambs, David. The Random House Dictionary for Writers and Readers. New York: Random House, 1990.