A French speaker who says “Je ne sais rien” raises no eyebrows among the educated, but an English speaker who says “I don’t know nothing” is immediately marked as semi-literate. (French ne corresponds to English not and rien to nothing.)
Some languages, like French and Spanish, have what is called “negative concord,” usage that allows two negatives to express a single negation without being considered incorrect. Double negatives in English came to be seen as ungrammatical after the Middle Ages.
Considering the wide use of double negatives in nonstandard English dialects of English,
one might wonder why the double negative is disdained in the standard dialects.
In 1762 a very learned English bishop named Robert Lowth (1710-1787) published A Short Introduction to English Grammar. The bishop stated this rule:
Two Negatives in English destroy one another, or are equivalent to an Affirmative.
Lowth was a scholar of Latin and Hebrew. Both those ancient languages lack negative concord.
Bishop Lowth’s opinion has become our rule. Never use not in the same sentence as the following:
only (in some contexts; does not apply to “not only…but also”)
Here are some examples of sentences that rarely cause confusion in nonstandard dialects, but which are incorrect in standard English:
Note: the asterisk indicates that the sentence is nonstandard.
*She was so weak she couldn’t hardly sit up.
*Scarcely nobody came to my party.
*I can’t stay only a few minutes.
*I didn’t know neither her telephone number nor her address.
*I never saw no one I thought prettier.
*I don’t know nothing about building a compost pile.
*We don’t need no education
*I don’t want none of those escargots.
Here are the same thoughts expressed in standard English:
She was so weak she could hardly sit up.
Scarcely anybody came to my party.
I can stay only a few minutes.
I knew neither her telephone number nor her address.
I never saw anyone I thought prettier.
I don’t know anything about building a compost pile.
We don’t need an education
I don’t want any of those escargots.
Note: Not all double negatives in English earn an F from grammarians. The “not un-” construction popular in the 17th century is still acceptable in standard English. For example, here’s a comment from a travel article: “the flavor was unusual, but not unappealing.” Both not and unappealing are negatives. The idea is that the flavor is too strange to actually be “appealing,” but is nevertheless palatable. To state the thought otherwise would alter the writer’s intended meaning.