certain /ˈsə:tn/ adj. 1.有把握，肯定 (多作表语，可跟从句、of/about 短语和不定式)：I was certain (that) he had seen me. 我肯定他看见我了。I am not certain whether he will come. 究竟他来不来,我没有把握。I am not certain who he is (where he went, etc.).我说不准他是谁(他去哪儿等)。You can be certain of success. 你可以相信肯定能成功。Are you absolutely certain about this? 这事你能绝对肯定吗？The duties before me are certain to be heavy.摆在我前面的任务一定是很重的。［注］ be certain of… 表示句子主语对某事有把握；be certain 跟不定式，表示说话人的一种看法，如： He is certain of living to 100. 他坚信自己能活到100岁。He is certain to live to 100.他一定能活到100岁。 2.某个，某些，某种(作定语)：for a certain reason 为了某种理由；on certain conditions 附带某些条件；make certain concessions作某些让步 To a certain degree it served his purpose. 在某种程度上这是为他的目的服务的。There was a certain coldness in her attitude towards me.她对我的态度有某种程度冷淡。
certainly /ˈsə:tnli/ adv. 1. 确实，的确 （紧跟系动词be、助动词或情态动词或放在主要动词或否定的助动词或情态动词前）：Something was certainly wrong with him. 他肯定出问题了。I will certainly see you into the train. 我肯定送你上火车。I certainly wish them victory. 我当然希望他们获胜。We certainly mustn’t forget that. 我们当然不能忘记那件事。 2.(用在答话中表示同意)当然，可以，没问题：— Will you help me? — Certainly I will.“你愿意帮我的忙吗?”“当然愿意。” — Do you mind if I sit here? — Certainly not.“我坐这儿你介意吗?”“当然不。”
certainty /ˈsə:tənti/ n. 1.［u］确信，确实，确定性: say with certainty 断言；have the certainty of success 确信能成功 2.［c］必然的事，确定的事实: know for a certainty that…确实知道 The horse will win the race; that is a certainty. 这匹马会赢得比赛，这是必然的。
