Synonyms sure
These words all describe somebody who knows without doubt that something is true or will happen.
sure not before noun without any doubt that you are right, that something is true, that you will get something or that something will happen: ‘Is that John over there?’ ‘I’m not sure.’
Are you sure about that?
England must win this game to be sure of qualifying.
Sure is often used in negative statements and questions, because there is some doubt or worry over the matter. If there is no doubt, people often say quite sure: I’m quite sure (that) I left my bag here (= I have no doubt about it).
confident completely sure that something will happen in the way that you want or expect: I’m quite confident that you’ll get the job.
The team feels confident of winning.
Confident is a stronger and more definite word than sure and is more often used in positive statements, when you feel no worry.
convinced not before noun completely sure that something is true or right, especially because the evidence seems to prove it or somebody else has persuaded you to believe it: I’m convinced that she’s innocent.
Are you absolutely certain about this?
sure or certain?
Like sure, certain is often used in negative statements and questions. It is slightly more formal than sure; sure is more frequent, especially in spoken English.
She was positive that he’d been there.
‘Are you sure?’ ‘Positive.’
clear (often used in negative statements and questions) having no doubt or confusion about something: My memory isn’t really clear on that point.
Patterns
sure/confident/convinced/certain/positive/clear about something
sure/confident/convinced/certain of something
sure/confident/convinced/certain/positive/clear that…
sure/certain/clear who/what/how, etc.
to feel sure/confident/convinced/certain/positive
quite/absolutely/completely/fairly/pretty sure/confident/convinced/certain/positive/clear
not altogether sure/confident/convinced/certain/clear