certain和certainly的用法：中文意思不同、词性不同、用法不同。certain可作代词和形容词，含义为“某些”、“肯定”、“确信”、“某种”、“无疑”；certainly只作副词，含义为“当然”、“确定”、“行”。
一、certain的含义及用法介绍
1、作为代词时，译为(不提及人或事物的名称时用)某些。
例句：Certain of those present were unwilling to discuss the matter further.
某些在场的人不愿意进一步讨论这个问题。
Those beliefs still prevail among certain social groups.
这些信念在某些社会群体中仍很盛行。
Society is knit together by certain commonly held beliefs.
社会是靠某些共同的信念来维系的。
2、作为形容词时，译为肯定;确定;确实;确信;无疑;(不提及细节时用)某事，某人，某种。
例句：It is certain that they will agree/They are certain to agree.
他们肯定会同意。
She wasn't certain (that) he had seen her.
她不敢肯定他见过她。
For certain personal reasons I shall not be able to attend.
由于某种个人原因，我将不能出席。
It was a certain Dr Davis who performed the operation.
是一位叫戴维斯的医生做的手术。
I felt there was a certain coldness in her manner.
我觉得她的态度有点冷淡。
One thing is certain, both have the utmost respect for each other...
有一点可以肯定，那就是双方都非常尊重对方。
二、certainly的含义及用法介绍
certainly作为副词，译为当然;肯定;无疑;确定;行。
例句：Without treatment, she will almost certainly die.
要是不治疗，她十有八九会死。
The public is certainly getting tired of hearing about it...
关于此事，公众当然已经听腻了。
We've certainly improved on last year's figures.
我们的业绩的确超过了去年的数字。
I'm certainly never going there again.
我肯定不会再去那里了。
Since he left his wife he's certainly gone down in my estimation.
他离弃妻子后我对他的看法便不如以前了。
She certainly had me fooled ─ I really believed her!
她确实把我骗了——我真的相信了她的话！
