How to express certainty and uncertainty

*Asking for certainty

-Are you sure?

-Really?

-Are you certain?

-Do you think so?

*Expressing certainty

-Iam certain about it....

-Iam positive....

-No doubt...

-It is confirmed....

-Iam sure that...

-It must be.....

-I feel certain about...

-Definitely

*Expressing uncertainty

-Well,it’s possible,I suppose,but I’m not sure

-It could happen ,but it’s doubtfull

-Well,I can’t tell you for sure

-No one can know for certain

-It might be,I suppose,but I doubt it

-I’m not(quite)sure about it

-I’m not sure if....

-I doubt about this information

-I’m not sure/certain that....

-There’s surely some doubt about....

-Iam afraid I can’t be certain about....