一、两者在用法上的相同点
两者都可用作表语,表示“一定”或“确信”,有时可互换.互换的场合应注意以下几点用法:
1.表示说话者的态度或看法
即表示说话者自己的态度或看法,其意为“一定会”“肯定会”.此时主要用法有:
(1) 单独用作表语.如:
One thing was sure [certain]:they’d be late.有一件事是确定无疑的,他们会迟到.
(2) 后接不定式.如:
He’s certain [sure] to win.他一定会成功.
They’re certain [sure] to need help.他们肯定需要帮助.
If you do this,you are certain [sure] to be found out.如果你这样做一定会被发现.
2.表示句子主语的判断或信念
即表示句子主语对某一情况的判断或信念,其意为“相信”“确信”“有把握”等.此时通常用于以下结构:
(1) 后接of [about] sth.如:
He is certain [sure] of success.他确信会成功.
Are you certain of [about] that?你对此有把握吗?
(2) 后接 of doing sth.如:
Our team is certain [sure] of winning.我们队有把握赢.
You can be sure [certain] of his agreeing.你可以放心他会同意.
比较同义句:
He is certain [sure] of winning.
=He is sure [certain] that he will win.他自信会赢.
(3) 后接 that / whether / if 从句.如:
I am sure [certain] that he is honest.我肯定他是诚实的.
I’m sure [certain] that it’s not your fault.我敢肯定这不是你的错.
Are you certain [sure] that this is the right road?你肯定这条路对吗?
注:当be sure [certain]为肯定式或疑问式时,后接that从句;当be sure [certain]为否定式时,后接whether [if]从句.如:
I’m not sure [certain] whether he still works there.我不能肯定他是否还在那里工作.
I wasn’t sure [certain] whether he would agree.我不太肯定他是否会同意.
He wasn’t sure [certain] whether he would be able to get back in time.他不能肯定他是否能准时回来.
(4) 后接其他从句.如:
I’m not sure [certain] where she lives.我不能肯定她住在哪里.
I’m not certain [sure] who wrote it.我不太清楚这是谁写的.
二、只能用certain的情形
以下情况通常只用certain,而不用sure:
1.当句中用了形式主语或形式宾语 it 时.如:
It’s certain that he’ll come tomorrow.他明天肯定会来.
I thought it certain that he would be late.我肯定他会迟到.
It’s certain that prices will go up.价格肯定会上涨.
It’s not certain how much it will cost.这要花多少钱还不确定.
2.当表示“某一”“某些”时.如(from www.***.com):
A certain Mr Green wants to see you.有个叫格林先生的人想见你.
Certain plants are good to eat but others are not.有些植物好吃,而其他一些则不好吃.
三、只能用sure的情形
在 Be sure (not) to do sth.(一定要或不要做某事)这类祈使句中通常不用 certain.如:
Be sure not to forget it.千万别忘记啦.
Be sure to get there before nine.务必在九点前到达.
Be sure to turn off the light when leave.离开时一定要关灯.
四、两者在习语中的用法
1.用于 for certain / for sure,意为“肯定地”“确切地”等,两者可互换.如:
I can’t say for certain [sure] when he will come.我不敢肯定地说他什么时候来.
No one knows for sure [certain] what happened to her.没有人确切地知道她出了什么事.
2.用于 make certain / make sure,意为“弄清楚”“弄得有把握”,两者可互换.如:
They made certain [sure] (that) they weren’t late.他们有把握不迟到.
I think there’s a train at 10:40,but you’d better make certain [sure] of it.我想10:40有趟火车,但你最好去核实一下.