如目的所指的人與主句中的主語不同，或原主語再次被提到，則必須使用目的從句：

　　Ships carry lifeboats so that the crew can escape if the ship sinks.

　　大船上帶有救生艇，萬一船下沉船員可以逃生。

　　This knife has a cork handle so that it will float if it falls overboard.

　　這把刀的柄是用軟木做的，萬一從船上掉下去，它可以浮在水面上。

　　A 目的從句常由so that+will/would或can/could+動詞原形結構來表示。

　　這里can/could意為will/would be able to：

　　They make￡10 notes a different size from￡5 notes so that blind people can(=will be able to)tell the difference between them.

　　他們把十英鎊的紙幣和五英鎊的紙幣做成不同大小，以便使盲人可以區(qū)分開來。

　　They wrote the notices in several languages so that foreign tourists could (=would be able to)understand them.

　　他們把通知用幾國文字寫出來，以便讓各國游客都能看得懂。

　　如句子的主要動詞是一般現(xiàn)在時、一般完成時或一般將來時，則都可用can和will。如主要動詞是一般過去時，則使用could和would。請看上面和下面這些例句：

　　I light/am lighting/have lit/will light the fire so that the house will be warm when they return.

　　我點著/正在點著/已點著/將要點著爐子，以便等他們回來時屋子就暖和了。

　　I have given/will give him a key so that he can get into the house when- ever he likes.

　　我已經(jīng)給/會給他一把鑰匙，好讓他能隨時進來。

　　I pinned the note to his pillow so that he would be sure to see it.

　　我把紙條用針別在他的枕頭上了，好讓他一定能看得見。

　　There were telephone points every kilometre so that drivers whose cars had broken down would be able to/could summon help.

　　每公里都有求援電話點，以便汽車出了毛病時司機可隨時呼喚幫助。

　　如果帶can/could的目的從句中省去that，那么這一目的性可能隨之消失。He took my shoes so that I couldnt leave the house(他把我的鞋拿走了，好讓我出不了門)意為He took my shoes to prevent my leaving(他把鞋拿走是為了阻止我離開)。但是He took my shoes，so I couldnt leave the house(他把鞋拿走了，我出不了門)意為He took my shoes;therefore I wasnt able to leave(他把我的鞋拿走了，所以我不能夠出門)。

　　B so that/in order that/that+may/might或shall/should+不定式結構也可構成目的從句。這種結構僅比上面A中所示的結構更為正規(guī)，在意思上是相同的。

　　注意：so that之后可跟will/can/may/shall或它們的過去式。

　　in order that或that之后只限跟may/shall或它們的過去式。

　　that除在戲劇、詩歌及文章中外極少單獨使用。

　　關于時態(tài)一致的規(guī)定與上文所述相同。下文的句子是很正式的：

　　We carved their names on the stone so that/in order that future genera- tions should/might know what they had done.

　　我們把他們的名字刻在石頭上，為的是讓后代們知道他們的事跡。

　　These men risk their lives so that/in order that we may live more safely.

　　這些人甘冒生命危險，為的是讓我們生活更安全。

　　在一般現(xiàn)在時中may比shall更常見，shall現(xiàn)已很少用。但在一般過去時中might或should都可使用。對上述形式要有所了解，但并不見得需要用，因為在一般情況下，用so that+ can/could或will/would就足夠了。

　　C 表示否定目的的從句由助動詞(will/would或should)變?yōu)榉穸ㄊ綐嫵桑?/p>

　　He wrote his diary in code so that his wife wouldnt be able to read it.

　　為了不讓妻子看懂，他用密碼寫日記。

　　He changed his name so that his new friends wouldnt/shouldnt know that he had once been accused of murder.

　　為了不讓新朋友們知道他曾被控犯有謀殺罪，他改了名字。

　　Criminals usually telephone from public telephone boxes so that the police wont be able to trace the call.

　　罪犯常在公用電話亭打電話，好讓警察追查不到電話是從哪兒打來的。

　　表示否定目的的從句常可用to prevent+名詞/代詞+動名詞或to avoid+動名詞來代替：

　　He dyed his beard so that we shouldt recognize him/to prevent us rec- ognizing him/to avoid being recognized.

　　他染了胡子，好讓我們認不出/為了阻止/為了避免我們認出他。(被動態(tài)動名詞)

　　She always shopped in another village so that she wouldnt meet her own neighbours/to avoid meeting her own neighbours.

　　她經(jīng)常去另外一個村子購買東西，以免碰到她的鄰居/為了避免碰到她的鄰居。

　　與表示否定目的的從句相比，人們更喜歡用這些不定式短語。

　　如目的所指的人與主句中的主語不同，或原主語再次被提到，則必須使用目的從句：

　　Ships carry lifeboats so that the crew can escape if the ship sinks.

　　大船上帶有救生艇，萬一船下沉船員可以逃生。

　　This knife has a cork handle so that it will float if it falls overboard.

　　這把刀的柄是用軟木做的，萬一從船上掉下去，它可以浮在水面上。

　　A 目的從句常由so that+will/would或can/could+動詞原形結構來表示。

　　這里can/could意為will/would be able to：

　　They make￡10 notes a different size from￡5 notes so that blind people can(=will be able to)tell the difference between them.

　　他們把十英鎊的紙幣和五英鎊的紙幣做成不同大小，以便使盲人可以區(qū)分開來。

　　They wrote the notices in several languages so that foreign tourists could (=would be able to)understand them.

　　他們把通知用幾國文字寫出來，以便讓各國游客都能看得懂。

　　如句子的主要動詞是一般現(xiàn)在時、一般完成時或一般將來時，則都可用can和will。如主要動詞是一般過去時，則使用could和would。請看上面和下面這些例句：

　　I light/am lighting/have lit/will light the fire so that the house will be warm when they return.

　　我點著/正在點著/已點著/將要點著爐子，以便等他們回來時屋子就暖和了。

　　I have given/will give him a key so that he can get into the house when- ever he likes.

　　我已經(jīng)給/會給他一把鑰匙，好讓他能隨時進來。

　　I pinned the note to his pillow so that he would be sure to see it.

　　我把紙條用針別在他的枕頭上了，好讓他一定能看得見。

　　There were telephone points every kilometre so that drivers whose cars had broken down would be able to/could summon help.

　　每公里都有求援電話點，以便汽車出了毛病時司機可隨時呼喚幫助。

　　如果帶can/could的目的從句中省去that，那么這一目的性可能隨之消失。He took my shoes so that I couldnt leave the house(他把我的鞋拿走了，好讓我出不了門)意為He took my shoes to prevent my leaving(他把鞋拿走是為了阻止我離開)。但是He took my shoes，so I couldnt leave the house(他把鞋拿走了，我出不了門)意為He took my shoes;therefore I wasnt able to leave(他把我的鞋拿走了，所以我不能夠出門)。

　　B so that/in order that/that+may/might或shall/should+不定式結構也可構成目的從句。這種結構僅比上面A中所示的結構更為正規(guī)，在意思上是相同的。

　　注意：so that之后可跟will/can/may/shall或它們的過去式。

　　in order that或that之后只限跟may/shall或它們的過去式。

　　that除在戲劇、詩歌及文章中外極少單獨使用。

　　關于時態(tài)一致的規(guī)定與上文所述相同。下文的句子是很正式的：

　　We carved their names on the stone so that/in order that future genera- tions should/might know what they had done.

　　我們把他們的名字刻在石頭上，為的是讓后代們知道他們的事跡。

　　These men risk their lives so that/in order that we may live more safely.

　　這些人甘冒生命危險，為的是讓我們生活更安全。

　　在一般現(xiàn)在時中may比shall更常見，shall現(xiàn)已很少用。但在一般過去時中might或should都可使用。對上述形式要有所了解，但并不見得需要用，因為在一般情況下，用so that+ can/could或will/would就足夠了。

　　C 表示否定目的的從句由助動詞(will/would或should)變?yōu)榉穸ㄊ綐嫵桑?/p>

　　He wrote his diary in code so that his wife wouldnt be able to read it.

　　為了不讓妻子看懂，他用密碼寫日記。

　　He changed his name so that his new friends wouldnt/shouldnt know that he had once been accused of murder.

　　為了不讓新朋友們知道他曾被控犯有謀殺罪，他改了名字。

　　Criminals usually telephone from public telephone boxes so that the police wont be able to trace the call.

　　罪犯常在公用電話亭打電話，好讓警察追查不到電話是從哪兒打來的。

　　表示否定目的的從句常可用to prevent+名詞/代詞+動名詞或to avoid+動名詞來代替：

　　He dyed his beard so that we shouldt recognize him/to prevent us rec- ognizing him/to avoid being recognized.

　　他染了胡子，好讓我們認不出/為了阻止/為了避免我們認出他。(被動態(tài)動名詞)

　　She always shopped in another village so that she wouldnt meet her own neighbours/to avoid meeting her own neighbours.

　　她經(jīng)常去另外一個村子購買東西，以免碰到她的鄰居/為了避免碰到她的鄰居。

　　與表示否定目的的從句相比，人們更喜歡用這些不定式短語。