(1)一(必)定，肯定(without any doubt;definitely)： He will～come.他肯定会来。She is～pretty.她当然漂亮。I～wish them victory.我当然希望他们取得胜利。〖同〗surely;

(2)当然(yes;of course)(用于回答问题)：“Can I try it on?” “C～(=Yes).”“我可以试穿一下吗?”“当然可以。”“Are you paying for him?” “C～not(=No，definitely not).”“你是在替他付钱吗?”“当然不是。”

【辨异】certainly与surely语义相近，但有区别。当确知真相时用certainly，当仅仅是有强烈的希望和信念时，用surely，如：He certainly didn't steal the money.I stole it myself.(他肯定是没偷那钱。是我自己偷的。)Surely he didn't steal the money. He's not that kind of person.(当然他没偷那钱。他不是那种人。)此外，在回答问题时，BrE中用certainly(见(2))，AmE中则用 surely(或 sure)，如：“Can I try it on?”“Sure(ly).”“我可以试穿一下吗?”“当然。”