連詞的分類：
連詞分為并列連接詞和從屬連接詞兩種。
1、并列連接詞連接并列的詞、短語(yǔ)、從句或句子。常見(jiàn)的并列連接詞有：and(和),but(但是),or(或者,否則),nor(也不), so(所以), however(然而,無(wú)論如何),for(因?yàn)?,still(可是),as well as(也),both..and...(...和...), not only ...but also...(不但…而且…), either… or…(或…或…),neither… nor…(既不…也不…)等。
2、從屬連接詞用于引導(dǎo)從句,常見(jiàn)的從屬連接詞有：
when(當(dāng)…時(shí)候), while(正當(dāng)…時(shí)候), after(在…之后), before(在…之前), since(自從), until(直到), although/though(雖然), if(假如), as(如…一樣;由于), as …as…(和…一樣), as far as(就…而言), as long as(只要), as soon as(一…就…), even if(即使), because(因?yàn)?, unless (除非), than(比…), whether (是否…), in order that…(為了), so…that…(如此…以致), so that…(以便), now that…(現(xiàn)在既然), by the time…(到…時(shí)候), every time…(每當(dāng)), as if…(仿佛),no matter when(或whenever)(無(wú)論何時(shí)),no matter where(或wherever)(無(wú)論在哪里)等。
[辨析]
(1) because、as、since、for的用法：because(因?yàn)?表示原因的語(yǔ)氣最強(qiáng),常表示必然的因果關(guān)系,從句一般放在主句后面;另外,回答why的問(wèn)句只能用because.
as(因?yàn)?表示一般的因果關(guān)系,語(yǔ)氣比because弱,說(shuō)明比較明顯的原因,它引導(dǎo)的從句可以放在句首也可以放在句尾。since(既然)表示對(duì)方已經(jīng)知道、無(wú)需加以說(shuō)明的原因或事實(shí)。for(因?yàn)?是并列連詞,語(yǔ)氣較弱,用來(lái)補(bǔ)充說(shuō)明理由或提供一種解釋。如：He is not at school today because he is seriously ill.(他今天沒(méi)有上學(xué)因?yàn)樗〉脜柡?/ As all of you have got here, now, let’s go to the zoo.(既然大伙兒都到了我們就去動(dòng)物園吧)/ I will ask Lin Tao to go with me since you are very busy.(既然你很忙我就叫林濤和我一起去吧)/ We must be off now for the match starts at 7：00.(我們得走了因?yàn)楸荣愒谄唿c(diǎn)開(kāi)始)
(2)if、whether的區(qū)別：表示“是否”時(shí),if和whether同義,引導(dǎo)賓語(yǔ)從句,另外,whether還可以引導(dǎo)主語(yǔ)從句、表語(yǔ)從句(以及同位語(yǔ)從句)等名詞性從句或者讓步狀語(yǔ)從句;而if還可以表示“如果”,引導(dǎo)條件狀語(yǔ)從句,(主句與從句遵循主將從現(xiàn)的原則)。如：I don’t know if/whether he will arrive on time.(我不知道他是不是會(huì)按時(shí)到達(dá))/ I will ring you up if he arrives on time.(如果他按時(shí)到達(dá)我會(huì)給你打電話的)
[注意]
下列情況只能用whether不能用if：
①引導(dǎo)主語(yǔ)從句,
②引導(dǎo)表語(yǔ)從句,
③引導(dǎo)從句作介詞賓語(yǔ),
④引導(dǎo)不定式短語(yǔ),
⑤引導(dǎo)讓步狀語(yǔ)從句,
⑥在動(dòng)詞discuss之后,
⑦在wonder / not sure之后,
⑧在if與whether含義易混時(shí)。如：Whether it is a fine day next Sunday is still a question.(下個(gè)星期天是不是個(gè)好天還是個(gè)問(wèn)題)(引導(dǎo)主語(yǔ)從句) / Please ask him whether to go there with a raincoat or not.(請(qǐng)問(wèn)一下帶不帶雨衣去那兒)(作動(dòng)詞的賓語(yǔ)) / Hainan is the place to be, whether it’s summer or winter.(海南是個(gè)該去的地方無(wú)論冬夏)(引導(dǎo)讓步狀語(yǔ)從句)/ Please let me know whether you need my help.(請(qǐng)告訴我你是否需要我的幫助)(引導(dǎo)賓語(yǔ)從句)(如果換成if則還可能表示“如果你需要我的幫助請(qǐng)告知”)
(3)while、when、as的用法區(qū)別：while常表示一個(gè)較長(zhǎng)的動(dòng)作,它引導(dǎo)的從句動(dòng)作與主句的動(dòng)作是同時(shí)發(fā)生的、是平行的;when可以表示較短的動(dòng)作也可以表示較長(zhǎng)的動(dòng)作,主句和從句的動(dòng)作可以同時(shí)發(fā)生也可以先后發(fā)生;as與上兩詞同義,可替換while和when, 表示主句和從句的動(dòng)作同時(shí)發(fā)生,常譯為“一邊……一邊……”。如：Please do not trouble me while I am writing my homework.(我寫作業(yè)時(shí)請(qǐng)不要打擾我)/ I’ll go home when I have finished my job.(我干完了活兒就回去)/ They were running quickly across the road when they heard the sound of a truck coming.(他們正快速地穿過(guò)馬路忽然聽(tīng)到了卡車開(kāi)來(lái)的聲音)/ As we walked in the dark street, we sang songs and talked loudly.(當(dāng)我們?cè)诤诙炊吹慕稚献呗窌r(shí)我們高聲地唱歌說(shuō)話)
(4)till/until與not…till/until的區(qū)別：前者表示一個(gè)延續(xù)性的動(dòng)作,后者表示一個(gè)才開(kāi)始的動(dòng)作。如：I will stay here and watch the baby until you return.(我會(huì)呆在這里看著娃娃直到你回來(lái))(stay這個(gè)動(dòng)作一直進(jìn)行到你return) / They won’t go on working until they get what they think is reasonable.(他們要到獲得了他們認(rèn)為合理的東西時(shí)才會(huì)繼續(xù)干下去的)
另外till與until基本可以互換,但是在句首時(shí)只能用until,不能用till. 如：Until the last minute of the match we kept playing.(我們堅(jiān)持到比賽的最后一分鐘)/ Not until he had finished his work did he go home.(直到做完工作他才回家)(倒裝句)
(5)though與although的區(qū)別：兩個(gè)詞都表示“雖然”,均不可以與but同時(shí)使用,但在句中可加still或yet連用。although“盡管、雖然”僅作連詞,比較正式,一般可以換為though; though“雖然、盡管、即使”,還可以與even連用(=even if),表示“即使、縱然”,作副詞時(shí)意思是“然而、不過(guò)”,不能放在句首。如：He passed the exams although illness prevented him from going to classes.(盡管疾病使他無(wú)法上課但是他還是通過(guò)了考試)/ she won’t leave the TV set,even though her husband is waiting for her for the supper.(她不愿離開(kāi)電視機(jī)雖然丈夫在等她吃飯)/ It was a quiet party. I had a good time, though.(這是個(gè)不熱鬧的聚會(huì)盡管如此我還是玩得很開(kāi)心)
(6)prefer to…rather than…與prefer…to…的區(qū)別：prefer to…rather than…后面都是用動(dòng)詞原形,prefer…to…都是用動(dòng)名詞或名詞。如：I prefer English to Japanese.(與日語(yǔ)相比我更喜歡英語(yǔ))/ I prefer to learn English rather than learn Japanese. (與日語(yǔ)相比我更喜歡學(xué)英語(yǔ))
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