used to show that you are almost certain of what you are saying and want other people to agree with you
Surely we should do something about it?
It's surely only a matter of time before he is found, isn't it?
used with a negative to show that sth surprises you and you do not want to believe it
Surely you don't think I was responsible for this?
‘They're getting married.’ ‘ Surely not! ’
They won't go, surely?
without doubt; certainly
He knew that if help did not arrive soon they would surely die.
used to say ‘yes’ to sb or to agree to sth
making slow but definite progress
We'll get there slowly but surely.
You use surely , especially in BrE , to show that you are almost certain about what you are saying and you want other people to agree with you.
Surely this can’t be right?
Surely in negative sentences shows that something surprises you and you do not want to believe it.
You’re surely not thinking of going, are you?
Certainly usually means ‘without doubt’ or ‘definitely’, and is used to show that you strongly believe something or to emphasize that something is really true.
I’ll certainly remember this trip!
In informal NAmE this would be
I’ll sure remember this trip!
The meal was certainly too expensive (= there is no doubt about it) .
The meal was surely too expensive? (= that is my opinion. Don’t you agree?)
In formal language only surely can be used to mean ‘without doubt’.
This will surely end in disaster.