You use surely for emphasis when you are objecting to something that has been said or done.
Don't use 'surely' simply to give strong emphasis to a statement. Use definitely.
In British English, you don't use 'surely' when you are agreeing with something that has been said, or confirming that something is true. Use certainly.
American speakers use both surely and certainly to agree with requests and statements.
Don't use 'surely' to say emphatically that something will happen in the future. Use definitely or certainly.
Don't use 'surely' to emphasize that something is what you would expect in particular circumstances. Use naturally.
| Adv. | 1. | surely - definitely or positively (`sure' is sometimes used informally for `surely'); "the results are surely encouraging"; "she certainly is a hard worker"; "it's going to be a good day for sure"; "they are coming, for certain"; "they thought he had been killed sure enough"; "he'll win sure as shooting"; "they sure smell good"; "sure he'll come" colloquialism - a colloquial expression; characteristic of spoken or written communication that seeks to imitate informal speech |