Sure of means certain about something: I'm sure of it. It's used for facts (sure of the date), results (sure of success) and yourself: sure of yourself means confident, sometimes even overconfident. You can also use about instead of of: I'm sure about it.
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be sure of + noun/-ing; sure of yourself; be sure (that) + clause; be sure to + verb
- I'm not sure of the exact date, but the course starts in March.
- If you're not sure of the answer, skip the question and come back later.
- He sounded very sure of himself in the job interview.
What changed
First versionI'm sure in my answer, so I won't change it.
RevisionI'm sure of my answer, so I won't change it.
In can seem logical by analogy with confident in or believe in, which gives sure in. But sure takes of or about. One preposition was replaced: sure of my answer.
Be sure to + verb doesn't mean being certain; it means “make sure you do it”, a gentle piece of advice or a request. Be sure to lock the door means don't forget to lock it. Compare: She's sure of passing means she's certain she'll pass.
Your turn
Our team won every match this season, so the coach is ___ victory in the final.
Show the answer
sure of — The coach is certain of victory, so it's sure of victory. In may seem logical, but it isn't used after sure.
Describe a decision you were completely sure of. Say what the decision was and why you had no doubts.
I was sure of my choice to study medicine because I had volunteered at a hospital for two summers.
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