Q: News writers seem to have dropped the word “probably” in favor of “likely.” Now you hear sentences like this: “The President will likely sign the bill.” In fact, “likely” seems to have completely replaced “probably.” Is this grammatically correct?
A: “Likely,” according to traditional usage, can be either an adjective (“that’s not likely”; “a likely story”), or an adverb (“he’ll very likely quit”). But when it’s used as an adverb, tradition says, “likely” should be modified by a word like “very” or “most” or “rather” or “quite.”
The use of “likely” as an adverb all by itself, unadorned, has long been considered substandard or dialect. The New York Times stylebook still subscribes to this belief. However, some recent dictionaries say it’s acceptable in all but the most formal writing. Here’s what The American Heritage Dictionary of the English Language has to say about “likely.”
I’m with you, though. I think “the President will likely sign the bill” is slangy. I’d prefer “the President will very likely sign the bill” or “the President is likely to sign it” or even “it’s likely that the President will sign.”
So the answer is no. People who use “likely” as an adverb all by itself, in place of “probably,” are not using the word in its traditionally accepted sense.