UK:*UK and possibly other pronunciationsUK and possibly other pronunciations/ˈs3ːrtən/US:USA pronunciation: IPA and respellingUSA pronuncation: IPA/ˈsɝtən/ ,USA pronunciation: respelling(sûrtn)

WordReference Collins English Usage © 2020
certain - sure
having no doubts
If you are certain or sure about something, you have no doubts about it.
He felt certain that she would disapprove.
I'm sure she's right.
definite truths
If it is certain that something is true, it is definitely true. If it is certain that something will happen, it will definitely happen.
It is certain that he did not ask for the original of the portrait.
It seemed certain that they would succeed.
Be careful
Don't say that it is ‘sure’ that something is true or will happen.
‘be certain to’ and ‘be sure to’
Instead of saying that it is certain that someone or something will do something, you can say that they are certain to do it or are sure to do it.
I'm waiting for Cynthia. She's certain to be late.
The growth in demand is certain to drive up the price.
These fears are sure to go away as the baby gets older.
The telephone stopped ringing. ‘It’s sure to ring again,' Halle said.
Instead of saying that it is certain that someone will be able to do something, you often say that they can be certain of doing it or can be sure of doing it.
I chose this hospital so I could be certain of having the best care possible.
You can always be sure of controlling one thing -- the strength with which you hit the ball.
Don't use words such as ‘very’ or ‘extremely’ in front of certain or sure. If you want to emphasize that someone has no doubts or that something is true, you use words such as absolutely and completely.
We are not yet absolutely certain that this report is true.
Whether it was directed at Eddie or me, I couldn't be completely certain.
Can you be absolutely sure that a murder has been committed?
She felt completely sure that she was pregnant.
negative structures
Sure is more common that ‘certain’ in negative structures.
‘Are you going to the party tonight?’ – ‘I’m not sure. Are you?'
'certain' also found in these entries:

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