二者的不同点:
1.在"It is certain that…/ to do something"结构中,It是形式主语,此时一般不用sure.如:
It is certain to take him a lot of time.肯定会占用他很多时间.
It is certain that two plus two makes four.二加二得四是确定无疑的.
2."Be sure +to do something"结构,用于祈使句,这时一般不用certain.如:
Be sure not to forget it.千万别忘了.
3.作定语时,sure表示"可靠的,无疑的".而certain修饰可数名词时,意为"某一,某些",修饰抽象名词时,意为"有点,有些".如:
The student made a sure answer.学生做出了确凿的回答.
A certain Brown is waiting for you at the gate.门口有个叫布朗的在等着你.
Certain students have failed in the test.有些学生测验没及格.
There was certain coldness in her attitude towards me.她对我的态度有点冷淡.
4.在口语中,sure可作副词,用在肯定答语中,相当于surely,certainly,of course,而 certain不能用作副词,如:Are you going Sure/Certainly.你去吗 当然啦