I'm sure that you're very handsome!中文釋義為“我確定你非常英俊”I'm sure意為“我確定...”或?yàn)椤拔覉?jiān)信”.that引導(dǎo)后面的從句.
I’m not sure意思相反.
sure 是形容詞,意為“肯定的,當(dāng)然的”.常用來回答一般疑問句,等于 Yes或Certainly.sure的用法：
（1）be sure＋不定式.常用于祈使句,表示要求,意為“務(wù)必、請(qǐng)一定”.指外界的看法.例如：
I think he's coming,but I'm not quite sure.
Be sure to telephone me and give me all the news.
（2）be sure＋of或about.意為“相信,對(duì)……有把握”,后接名詞、代詞或動(dòng)詞的-ing形式.常用來表示“人對(duì)某事的看法”,指主觀上的看法.例如：
Are you sure of that meeting?He is sure about this answer.
（3）be sure＋從句.表示“某人對(duì)……有把握”.例如：
I'm sure that he is coming to help me.
The teacher is sure that these books are interesting.
（4）make sure意為“務(wù)必、確信”,其后也可接of或about或動(dòng)詞不定式或that從句.例如：
I made sure (that) he was badly ill.
Will you make sure of his return?
Make sure to come to the party on time.