These words all describe sb who knows without doubt that sth is true or will happen. 以上各词均指确信、肯定、有把握。

• sure [not before noun] without any doubt that you are right, that sth is true, that you will get sth or that sth will happen 指确信、肯定、有把握、必定：◆'Is that John over there?' 'I'm not sure.' “那边那个人是约翰吗？” “我说不准。”◆Are you sure about that? 这事你肯定吗？◆England must win this game to be sure of qualifying. 英格兰队必须拿下这场比赛才能确保获得资格。 NOTE Sure is often used in negative statements and questions, because there is some doubt or anxiety over the matter. If there is no doubt, people often say quite sure. * sure 常用于否定句和疑问句，表示有所怀疑或担忧。毫无疑问时常用 quite sure：◆I'm quite sure (that) I left my bag here(= I have no doubt about it). 我肯定是把包丢在这儿了。
• confident completely sure that sth will happen in the way that you want or expect 指肯定、确信、有把握：◆I'm quite confident that you'll get the job. 我肯定你能得到那份工作。◆The team feels confident of winning. 这个队觉得有把握取胜。 NOTE Confident is a stronger and more definite word than sure and is more often used in positive statements, when you feel no anxiety. * confident 较 sure 语气强，而且更肯定，在无所担忧的情况下较常用于肯定句中。
• convinced [not before noun] completely sure that sth is true or right, especially because the evidence seems to prove it or sb else has persuaded you to believe it 指坚信、深信、确信，尤指有证据证明或经说服：◆I'm convinced that she's innocent. 我坚信她是清白无辜的。
• certain [not usually before noun] sure that you are right or that sth is true 指确信、肯定、无疑：◆Are you absolutely certain about this? 你对这事绝对确信无疑吗？

sure or certain? 用 sure 还是 certain？

Like sure, certain is often used in negative statements and questions. It is slightly more formal than sure; sure is more frequent, especially in spoken English. * certain 与 sure 一样，常用于否定句和疑问句中，但比 sure 稍正式些。sure 较常用，尤其是在口语中。

• positive [not before noun] (rather informal) completely sure that sth is true 指有绝对把握、确信、肯定：◆She was positive that he'd been there. 她确信他曾到过那儿。◆'Are you sure?' 'Positive.' “你肯定吗？” “绝对肯定。”
• clear (often used in negative statements and questions) having no doubt or confusion about sth （常用于否定句与疑问句中）指无疑的、清楚的、明白的：◆My memory isn't really clear on that point. 那一点我记不太清楚了。

Patterns

• sure/confident/convinced/certain/positive/clear about sth
• sure/confident/convinced/certain of sth
• sure/confident/convinced/certain/positive/clear that…
• sure/certain/clear who/what/how, etc.
• to feel sure/confident/convinced/certain/positive
• quite/absolutely/completely/fairly/pretty sure/confident/convinced/certain/positive/clear
• not altogether sure/confident/convinced/certain/clear