cer‧tain‧ly S1 W1 /ˈsɜːtnli $ ˈsɜːr-/
adverb [sentence adverb] [
Word Family: noun:
certainty ≠
uncertainty;
adverb:
certainly ≠
uncertainly;
adjective:
certain ≠
uncertain]
1. without any doubt
Synonym : definitely:
I certainly never expected to become a writer. They’re certainly not mine.it is certainly true/possible etc It is certainly true that there are more courses on offer. The girl was almost certainly murdered. ‘Not smoking has made a real difference.’ ‘It most certainly has.’2. spoken used to agree or give your permission:
‘I’d like a beer, please.’ ‘Certainly, sir.’ ‘Can I come along?’ ‘Certainly.’3. certainly not spoken used to disagree completely or to refuse to give permission:
‘May I go?’ ‘Certainly not!’
REGISTERIn everyday English, people usually say
of course or
sure rather than
certainly when agreeing or giving permission:
‘Can I sit down?’ ‘Of course.’ [TahlilGaran] Dictionary of Contemporary English ▲
certainlyadverb1. 
BAD: All of a sudden the engine started to make a strange noise. Certainly, I stopped the car at once to see what had happened.
GOOD: All of a sudden the engine started to make a strange noise. Naturally, I stopped the car at once to see what had happened.
Usage Note:Certainly is mainly used to emphasize that something is really true, really happened, etc: 'I'm sorry if I upset you. I certainly didn't mean to.' 'The file certainly wasn't given to me or it would be on my desk.'
When you mean 'as anyone would expect', use
naturally or
of course : 'It was the first time the little boy had seen an elephant and naturally he was a little scared.'
2. BAD: Are you sure that you certainly don't want to go?
GOOD: Are you sure that you definitely don't want to go?
BAD: If they certainly can't find a job, they should be given further training.
GOOD: If they definitely can't find a job, they should be given further training.
Usage Note:When you mean 'absolutely certain and without even the slightest doubt', use
definitely . This word gives very strong emphasis and is often used in connection with intentions and future events: 'He definitely wants to be a vet.' 'Do you think that you'll definitely be able to come?'
3. BAD: Certainly I think so.
GOOD: I certainly think so.
BAD: The car can be repaired certainly.
GOOD: The car can certainly be repaired.
BAD: Certainly, it was a pleasant surprise.
GOOD: It was certainly a pleasant surprise.
GOOD: It certainly was a pleasant surprise.
Usage Note:Certainly is usually used like a middle position adverb: 'She certainly likes you.' 'His work has certainly improved this year.'
For extra emphasis, however,
certainly may be placed before the first auxiliary verb and before
be when this is the main verb: 'His work certainly has improved this year.' 'She certainly is one of the best teachers on the staff.'
[TahlilGaran] Dictionary of Common Errors ▲
certainly used when saying that you are sure about something:
Amy’s certainly growing, but she’s not gaining weight. It’s certainly not the cheapest way of getting to New York. ‘Is this his signature?’ ‘Almost certainly.’undoubtedly used when saying that you are completely sure about something.
Undoubtedly sounds more certain and a little more formal than
certainly:
They are undoubtedly the better team. Undoubtedly it will be a huge shock for him. The furniture, although undoubtedly fashionable, was a little too plain for my taste.there is no doubt used when you are completely sure about something:
There is no doubt that violence on TV influences children. He’s definitely innocent. There’s no doubt about that.without (a) doubt used when you are completely sure about something:
She was without doubt one of Mexico’s finest artists. There would be, without a doubt, some perfectly ordinary explanation for his behaviour. [TahlilGaran] English Thesaurus ▲