Learn English – Difference between “Are you sure to continue?” and “Are you sure you want to continue?”

It depends on the context in which both words are used. Generally, there is little to no difference. However, a person may use certain to add more power to his statement when he is completely positive. For example:

I am certain that Costa Rica beat Italy in the World Cup match today.

A greater emphasis is added to one's sentence when using the word certain. On the other hand, when using sure it does not always sound confident, and you can tell that in the way it is pronounced most of the time. For example:

I'm sure Costa Rica beat Italy in the World Cup match today.

or

I'm sure I left my mobile at home.

I'm certain I left my mobile at home.

With certain you completely believe that you left your mobile at home. I hope this has answered your question.

The first one is a question but should include a question mark:

Which bike are you using?

The second one is incorrect as written but could form part of a correct sentence:

I want to know which bike you are using.