英語(yǔ)中的sure和certain是近義形容詞,均有“肯定的；確信的；有把握的”的意思,它們的用法也大體相似,許多情況下可以通用,但它們之間也有一些差別,現(xiàn)歸納如下：
一、相同點(diǎn)
1. 兩者都能用于“be sure/certain + about /of短語(yǔ)”句型中,表示“對(duì)（某事）有把握”.主語(yǔ)必須是人,about/of之后多跟名詞、代詞.如：
I am sure/certain of his returning. 我確信他會(huì)回來(lái).
He is quite sure/certain of /about it. 他對(duì)這事很有把握.
2. 兩者都能用于be sure/certain to do sth句型中,表示“一定會(huì)做某事”,主語(yǔ)可以是人,也可以是物.如：
Spring is sure/certain to follow winter. 冬天過(guò)后一定是春天.
They are sure/certain to come. 他們一定會(huì)來(lái)的.
3. 兩者都能用于“be sure/certain +從句”句型中,表示“確信……”,主語(yǔ)只能是人,而不能是物.如：
Tom is sure/certain that I put the key on the table. 湯姆確信我把鑰匙放在桌子上了.
We are sure/certain that the book will be of great help to us.我們相信這本書(shū)對(duì)我們會(huì)有很大幫助.
4. 兩者都能用于“make sure/certain +從句”結(jié)構(gòu)中,表示“確定；弄清楚”,主語(yǔ)只能是人.如：
You must make sure/certain when the bus will leave. 你必須弄清汽車(chē)何時(shí)出發(fā).
5. “I ' m not sure…”與“I ' m not certain…”意思相同.如：
I ' m not sure/certain where he is. 我不能確定他在哪兒.
I ' m not sure/certain how to do it. 我不能確定如何做這件事.
二、不同點(diǎn)
1. “I ' m sure…”與“I ' m certain…”均可譯為“我深信（確）信……”,但兩者的含義卻不同.前者表示一種主觀上的判斷或感覺(jué),事實(shí)并不一定如此.后者強(qiáng)調(diào)的則是客觀事實(shí),意為主語(yǔ)已經(jīng)知道后面的內(nèi)容是既定的事實(shí).試比較下面一組句子：
I ' m sure he didn ' t steal it. He isn ' t that kind of person. 我確信他沒(méi)偷,他不是那種人.
I ' m certain he didn ' t break the cup. I broke it myself. 我敢肯定他沒(méi)有打碎那個(gè)茶杯,（因?yàn)椋┠莻€(gè)茶杯是我打碎的.
2. 如果it作為形式主語(yǔ)代替從句時(shí),則其后的表語(yǔ)用certain,而不能用sure.如：
It isn ' t certain whether he will give us a report next Monday. 下星期一他是否來(lái)為我們作報(bào)告還不能確定.
3. 兩者在作定語(yǔ)時(shí)含義不同：sure意為“可靠的；無(wú)誤的”；而certain若修飾可數(shù)名詞,意為“某一；某些；某種；一些”,若修飾抽象名詞,表示程度,意為“有點(diǎn)；有些”.如：
The letter was sent by a sure hand. 信已由一位可靠的人寄出了.
He made a sure answer. 他回答得準(zhǔn)確無(wú)誤.
A certain person called on me yesterday. 昨天有個(gè)人來(lái)找過(guò)我.
4. 在祈使句中常用sure,不宜用certain.如：
Be sure and remember what I told you. 千萬(wàn)要記住我對(duì)你講的話.
Be sure to write and tell me all the good news. 務(wù)必寫(xiě)信告訴我所有的好消息.
5. 口語(yǔ)中,sure常作副詞,用在肯定答語(yǔ)中替代surely,這時(shí)與of course,certainly意思相當(dāng),而certain不可作副詞用.如：
—Would you please turn down the radio a little bit? 請(qǐng)你把收音機(jī)音量擰小點(diǎn),好嗎?
—Sure/of course/certainly. 當(dāng)然可以.
certainly與surely用法比較

區(qū)別一
表示客觀論斷,意為“無(wú)疑地”、“肯定地”、“確實(shí)地”,兩者?？蓳Q用(注：通常用于被修飾詞語(yǔ)之前).如：
He will surely [certainly] fail. 他肯定會(huì)失敗.
The results are surely [certainly] satisfactory. 結(jié)果確實(shí)令人滿意.

區(qū)別二
表示主觀看法, 意為“想必”、“一定”、“我相信”等義,通常只用 surely.此時(shí)它表示既相信又不肯定或感到驚訝(有時(shí)幾乎相當(dāng)于一疑問(wèn)句,書(shū)寫(xiě)時(shí)可用問(wèn)號(hào)),通常置于句首或句末,若主語(yǔ)是人稱代詞,有時(shí)也可緊跟在主語(yǔ)之后.如：
You can do something to help him, surely. 你總可以想點(diǎn)辦法幫他一下吧.
Surely that’s Jim over there? I thought he was in Paris. 那邊想必是吉姆吧? 我還以為他在巴黎呢!
You surely [Surely you] don’t believe that. 想必你不會(huì)相信那種話吧.
比較：
That’s certainly a plain-clothes policeman. 那肯定是個(gè) 便衣警察.(表客觀論斷)
Surely that’s a plain-clothes policeman. 那一定是個(gè)便衣警察吧.(表示主觀看法)
注：若用于否定句,則更強(qiáng)調(diào)說(shuō)話者的懷疑態(tài)度,可譯為“不見(jiàn)得會(huì)”、“不一定會(huì)”.如：
Surely you are not going alone. 你不見(jiàn)得會(huì)一個(gè)人去吧!
of course
一定,當(dāng)然
=without doubt
of course在口語(yǔ)中的用法
表示：當(dāng)然；自然.如：
He was late again, of course. 自然他又遲到了.
Of course I‘ll help you. 我當(dāng)然會(huì)幫你.
Of course, I wish both of you well. 當(dāng)然我希望你們倆身體健康.
He was joking. Of course I‘m not a poet. 他是在開(kāi)玩笑,我當(dāng)然不是詩(shī)人.
通常在對(duì)話中用作回答.如：
A：Are you coming with us? 你和我們一起去嗎?
B：Of course. 當(dāng)然啦.
A：Will you be able to come to the meeting? 你能來(lái)開(kāi)會(huì)嗎?
B：Of course. 當(dāng)然能來(lái).
A：May I book your dictionary? 我可借你的字典嗎?
B：Yes, of course. 當(dāng)然可以.
有時(shí)與not連用.如：
A：Were you glad to leave? 你愿意離開(kāi)嗎?
B：Of course not. 當(dāng)然不愿意.
A：Do you want lost the game? 你起輸?shù)暨@場(chǎng)比賽嗎?
B：Of course not. 當(dāng)然不想.