surely
- definitely - certainly - naturally
‘surely’
You use surely for emphasis when you are objecting to something that has been said or done.
‘I can have it ready for next week.’ – ‘Surely you can get it done sooner than that?’
Their lawyers claim that they have not broken any rules, but surely this is not good practice.
‘definitely’ and ‘certainly’
Don't use ‘surely’ simply to give strong emphasis to a statement. Use definitely.
They were definitely not happy.
The call definitely came from your phone.
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.
Ellie was certainly a student at the university but I'm not sure about her brother.
‘You like him, don’t you?' – ‘I certainly do.’
American speakers use both surely and certainly to agree with requests and statements.
‘It is still a difficult world for women.’ – ‘Oh, certainly.’
Surely, yes, I agree with that.
Don't use ‘surely’ to say emphatically that something will happen in the future. Use definitely or certainly.
The conference will definitely be postponed.
If nothing is done, there will certainly be problems.
‘naturally’
Don't use ‘surely’ to emphasize that something is what you would expect in particular circumstances. Use naturally.
His sister was crying, so naturally Sam was upset.
Naturally, some of the information will be irrelevant.