In English grammar, a flat adverb, bare adverb, or simple adverb[1] is an adverb that has the same form as the corresponding adjective,[2] so it usually does not end in -ly, e.g. "drive slow", "drive fast", "dress smart", etc. The term includes words that naturally end in -ly in both forms, e.g. "drive friendly". Flat adverbs were once quite common but have been largely replaced by their -ly counterparts. In the 18th century, grammarians believed flat adverbs to be adjectives, and insisted that adverbs needed to end in -ly. According to the Merriam-Webster Dictionary, "It's these grammarians we have to thank for ... the sad lack of flat adverbs today".[3] There are now only a few flat adverbs, and some are widely thought of as incorrect.[4] Despite bare adverbs being grammatically correct and widely used by respected authors, they are often stigmatized.[5] There have even been public campaigns against street signs with the traditional text "go slow" and the innovative text "drive friendly."[1]