We use “Are you sure that…?” when we want someone to confirm that something is a good idea.
Are you sure that this is going to work?
Are you sure that you want to go to University?
Are you sure that this is the right decision for you?
If your friend is trying to make a decision in his/her life you can ask questions like “Are you sure” to help them express certainty.
Your friend can respond with something like:
Yes, I am sure.
No, I am not sure.
“Do you sure” is incorrect. We need to use the verb to be because sure is an adjective.
Are you sure (that)?
“That” is optional in this phrase, you can choose to use it or not. It is more common when there is a full sentence after “that”.
Are you sure he did it?
Are you sure it was him?
Are you sure you can trust him?
Are you sure that the fire was started by the children?
Are you sure that Mr. Roberts will approve the project?
You can even just say “Are you sure?”
You can also change the subject of the sentence:
Are we sure that this is the right thing to do?
Are John and Mary sure that this is the right move for them?
Is he sure he wants to go?
“Are you sure that” Alternatives
You can also ask questions like:
Are you certain that this is a good idea?
Are you positive that this is a good idea?
“How sure are you that…?”
How sure are you that? Is a question we ask to know the degree of certainty that someone has.
How sure are you that this will work?
You can respond to “How sure are you that?” with a percentage or an adverb of degree(very, quiet etc)
Let’s look at some answers to the question “How sure are you that this will work?”
I am about 50% sure.
I am 100% sure it will work.
I am quite sure.
I am very sure that it will work.