Which preposition would you use ?

- It's impossible to be sure about/of the value of the land.

- I heard he caught a big trout on Sunday, but I am not sure about/of its size. All I know is that it was quite big.

- My co-worker must have stolen the money. I am sure of/about it!

I think that "sure of" would only work in the third sentence. I'd choose "sure about" for the other two, but who knows... When would you choose one and not the other?

Thank you. Emotion: smile

Gene93I think that "sure of" would only work in the third sentence. I'd choose "sure about" for the other two, but who knows... When would you choose one and not the other?

I assess the situation as you do; however, the "why" is a matter for students in linguistics looking for papers to do to earn their doctorate degrees. Emotion: smile

I don't think it would stand out as really awful if you used 'of' for all of them. The difference is so subtle that it defies description. Still, there may be other posts which help to disentangle the mysteries.



You are asking about a phrase that illustrates the evolution of the English language.

"Sure about" did not exist before about 1860; "sure of" usage peaked in 1900 and has been in decline since then. However, it is still more common than "sure about."


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Thank you, Jim. Fair enough. I think that a very similar distinction exists in my native language. As far as I know, "sure about" means "certain about something", and "sure of" means "confident that something's true". However, if I am sure about something, then I must be confident that it's true. Emotion: smile That's where they start to look similar. "I am not sure of the trout's size" = "I don't have confidence in its size"? Hmm... I should have become a linguist. Emotion: smile

Gene93I should have become a linguist.

Yes, indeed. You've already got a start on your advanced degree. Emotion: smile


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Thank you. Hah, I hope I will be able to complete it. Emotion: smile

 AlpheccaStars's reply was promoted to an answer.

Should I use "sure of" instead? I tend to use "sure about" more frequently, but it doesn't seem to be as common as "sure of".

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These are my personal observations:

"Sure of" is still required in some contexts:

Reflexive pronouns: He is very sure of himself.
Gerunds: He is sure of winning the match.
It is more common with pronouns: I am sure of it.

Sure about is more common with content clauses.

He is so sure about what his mother said that he's willing to bet all his money on it.
He is sure about how the magician tricked the audience.

Thank you for your help and time. Yes, indeed. There are contexts in which only "sure of" would work. I think it does have a slightly different meaning, though. That's all. Emotion: smile

I'd definitely say "...sure of it", "...sure of himself", etc.