certain
单词辨析：
指确定无疑的，表示说话人有确切的理由或不容置疑的证据，语气较强，通常作表语，多用于肯定句或正式的书面语中，常可与positive 换用，但不可单独用作回答。
He is absolutely certain/positive that he has met her before.
他绝对肯定他以前见过她。
She's not certain/positive when the movie will begin.
她不确定电影何时开始。
It is certain/positive that every effect must have a cause.
毋庸置疑，有果必有因。
He is certain/positive that the fruit is ripe.
他确信水果熟了。
指确信某事会以自己想要或期望的方式发生的，通常作表语。
They are confident next year's profits will be higher.
他们确信明年的利润会增加。
The French football team is confident of victory.
法国足球队对取胜很有把握。
The committee is confident of success.
委员会对成功很有把握。
指对某事深信不疑的，通常作表语，常后接介词 of 或 that 从句。
I am convinced that we are doing the right thing.
我确信我们做的事情是正确的。
I am fully convinced we can do it.
我完全确信我们能做这件事。
He is firmly convinced of the possibility of life on other planets.
他坚信在其他行星上可能存在生命。
指对某事物的正确性或真实性绝对肯定的，通常作表语，可单独用作肯定回答，常后接介词 about/of 或 that 从句。
She is absolutely positive that she opened the window.
她绝对肯定她开窗户了。
He can't be positive where he lost his key.
他说不准是在哪里丢的钥匙。
-Are you sure about that?
—-那事你能肯定吗？
-Positive.
—-能。
We'll benefit from this deal -I'm positive of that.
我们会从这笔交易中赚到钱的，对此我有把握。
指主观上对某事物的正确性或真实性没有疑虑的，常可与 certain 换用，但语气稍弱，通常作表语。
I am sure/certain that he is honest.
我肯定他是诚实的。
Are you sure/certain that this is the right road?
你肯定这条路对吗?
He wasn't sure/certain whether he would be able to get back as planned.
他不能肯定他是否能如期回来。
相关例句：
Certain guidelines can be given. First, have a heating engineer check the safety of the system.
可以提供一些指导原则：第一，找位供暖工程师检查系统的安全性。
Hill had to find out for certain.
希尔得弄个清楚。
It wasn't a balloon — I'm certain of that.
那不是气球，这点我敢肯定。
It's not certain they'll accept the Front's candidate if he wins
即便来自阵线的候选人获胜，他们能否接受他还说不准。
There is a certain impatience among some of the soldiers
有些士兵有点儿不耐烦。
She managed to arrange for them to be hidden in the house of a certain Father Boduen.
她设法安排他们藏在一个叫博迪恩的神父家里。