形容词 “certain” 可以表示 “确定的，肯定的”。常用搭配有 “for certain” 和 “be certain about something”。此外，“certain” 还可以用来在不提供细节的前提下表示 “某个特定的人或事物”。

用法总结

1 形容词 “certain” 可以表示 “百分百确定的，有把握的”。

I am certain that Tuesday is the day before Wednesday.

Are you certain we are at the right place?

2 搭配 “for certain” 表示 “肯定地，确定无疑地”。

Tuesday comes before Wednesday, for certain.

He can't say for certain whether they'll be on time or not.

3 搭配 “be certain about something” 表示 “对某事有把握、很确定”。

I am certain about the length of this video. It's one minute long.

She is certain about the date of the event. 

4 “Certain” 还可以表示 “某个，某些，某位”，代指 “事物或人”，但不提供具体细节。

Hello? Boss? For certain personal reasons I can't come to work today.

Certain foods are easier to buy than others.