Welcome to Ask the Editor. I'm Emily Brewster, an Associate Editor at Merriam-Webster.
The other night, my parting words to a friend were, “Drive safe,” at which point another friend chimed in, “-ly!”—which made me think about how attached some of us are to the idea that an adverb should end in -ly. Should it? Should I have said, “Drive safely”? Or was “Drive safe” okay?
The adverb “safe” is what's called “the flat adverb,” that is, an adverb that has the same form as its related adjective. So, “safe” in “drive safe,” “slow” in “go slow”; “easy” in “take it easy.”
Flat adverbs used to be much more common than they are now. In Robinson Crusoe, Daniel Defoe spoke of weather that was “violent hot.” In his famous diary, Samuel Pepys wrote of being “horrid angry.” But most of these adverbs have long since been abandoned.
In Middle English, adverbs like these had case endings that distinguished them from their related adjectives, but those gradually disappeared.
18th-century grammarians didn't even identify flat adverbs as adverbs. They considered them adjectives, and the adverbial used to be a mistake. It's these grammarians we have to thank for the still repeated injunction that adverbs end in -ly, and for the sad lack of flat adverbs today.
We still have some, but most of them compete with an -ly form—there's “slow” and “slowly,” “safe” and “safely”; “bright” and “brightly.” But then we have “tight” and “tightly,” with “tight” used in a few places “tightly” is not—“sit tight”; “sleep tight.” “Near” and “nearly” also do different jobs—“The day is drawing near” versus “It's nearly over.”
A few flat adverbs survived without any competition from an -ly version. “Fast” is one—“Time goes so fast”; “fast asleep.” So is “soon,” as in “We'll be there soon.”
I admit, I like flat adverbs. Maybe I'll start ignoring the competing -ly versions entire.
Tune in again soon for future installments of Ask the Editor here at merriam-webster.com, and in the meanwhile, surf safe.