牛津?qū)嵱糜⒄Z語法:226 if，even if，whether，unless，but for，
A even if(=even though即便)
請(qǐng)比較下面兩個(gè)例句：
You must go tomorrow if you are ready.
如果你準(zhǔn)備好了，明天你必須走。
You must go tomorrow even if you arent ready.
哪怕你沒有準(zhǔn)備好，明天你也得走。
B whetheror(=ifor是否)
You must go tomorrow whether you are ready or not.
無論你明天是否準(zhǔn)備好了，你都必須走。
C unless+肯定動(dòng)詞(=if+否定動(dòng)詞除非)
Unless you start at once youll be late.相當(dāng)于：
If you dont start at once youll be late.
除非你立即動(dòng)身，否則你就會(huì)遲到。
Unless you had a permit you couldnt get a job.相當(dāng)于：
If you hadnt a permit you couldnt get a job.
除非你有執(zhí)照，否則你就找不到工作。
注意下面兩個(gè)例句間的區(qū)別：
(a) Dont call me if you need help.
如果你需要幫助的話，別打電話找我。
(b) Dont call me unless you need help.
除非你需要幫助否則別打電話找我。
在例句(a)中，即使在對(duì)方需要幫助的時(shí)候，說話人也不愿意去幫助對(duì)方。在例句(b)中，在對(duì)方需要幫助的時(shí)候，說話人愿意幫助對(duì)方，但說話人不愿意對(duì)方在不要緊的時(shí)候打電話找自己。
unless+hed/youd like/prefer等通常可用來代替 if he/you wouldnt like等：
Ill ask Tom，unless youd prefer me to ask/unless youd rather I asked Bill.
我去問湯姆，除非你寧愿叫我去問比爾。
D but for(=if it were not for/if it hadnt been for不然)
My father pays me fees.But for that I wouldnt be here.
我父親給我一筆補(bǔ)貼費(fèi)。不然我就不會(huì)在這里了。
The car broke down. But for that we would have been in time.
汽車出毛病了。要不是那個(gè)我們會(huì)及時(shí)趕到的。
E otherwise(=if this doesnt happen/didnt happen/hadnt happened否則)
We must be back before midnight; otherwise well be locked out.
我們必須在午夜之前趕回去，否則我們就會(huì)被鎖在門外。相當(dāng)于：
If we are not back by midnight well be locked out.
如果我們不在午夜之前趕回去，我們就會(huì)被鎖在門外。
Her father pays her fees;otherwise she wouldnt be here.
她的費(fèi)用是她的父親付的，否則她就不會(huì)在這里。相當(dāng)于：
If her father didnt pay her fees she wouldnt be here.
要是她的父親不付她的費(fèi)用，她就不會(huì)在這里了。
I used my calculator; otherwise Id have taken longer.
我用了計(jì)算器，不然我花的時(shí)間就會(huì)更多。相當(dāng)于：
If I hadnt used my calculator Id have taken longer.
要是我沒用計(jì)算器，我花的時(shí)間就會(huì)更多。
F 在日常英語中 or(+else)可以代替 otherwise：
We must be early or(else) we wont get a seat.
我們必須早去，否則就不會(huì)有座位了。
G 存在強(qiáng)烈的限制或約束的意思時(shí)，provided(that)可以代替if。它主要用來表示允許：
You can camp here provided you leave no mess.
你們?nèi)绻３终麧嵉脑挘梢栽谶@里宿營。
H suppose/supposing?(=what if?假如)
Suppose the plane is late?相當(dāng)于：
What if/What will happen if the plane is late?
假如飛機(jī)誤點(diǎn)的話，將會(huì)出現(xiàn)什么情況?
Suppose no one had been there?相當(dāng)于：
What if no one had been there?
假如沒有人去過那里的話，會(huì)怎么樣?
suppose也可以引出建議：
Suppose you ask him?/Why dont you ask him?
假如你問一問他呢?/你為什么不問一問他呢?
A even if(=even though即便)
請(qǐng)比較下面兩個(gè)例句：
You must go tomorrow if you are ready.
如果你準(zhǔn)備好了，明天你必須走。
You must go tomorrow even if you arent ready.
哪怕你沒有準(zhǔn)備好，明天你也得走。
B whetheror(=ifor是否)
You must go tomorrow whether you are ready or not.
無論你明天是否準(zhǔn)備好了，你都必須走。
C unless+肯定動(dòng)詞(=if+否定動(dòng)詞除非)
Unless you start at once youll be late.相當(dāng)于：
If you dont start at once youll be late.
除非你立即動(dòng)身，否則你就會(huì)遲到。
Unless you had a permit you couldnt get a job.相當(dāng)于：
If you hadnt a permit you couldnt get a job.
除非你有執(zhí)照，否則你就找不到工作。
注意下面兩個(gè)例句間的區(qū)別：
(a) Dont call me if you need help.
如果你需要幫助的話，別打電話找我。
(b) Dont call me unless you need help.
除非你需要幫助否則別打電話找我。
在例句(a)中，即使在對(duì)方需要幫助的時(shí)候，說話人也不愿意去幫助對(duì)方。在例句(b)中，在對(duì)方需要幫助的時(shí)候，說話人愿意幫助對(duì)方，但說話人不愿意對(duì)方在不要緊的時(shí)候打電話找自己。
unless+hed/youd like/prefer等通常可用來代替 if he/you wouldnt like等：
Ill ask Tom，unless youd prefer me to ask/unless youd rather I asked Bill.
我去問湯姆，除非你寧愿叫我去問比爾。
D but for(=if it were not for/if it hadnt been for不然)
My father pays me fees.But for that I wouldnt be here.
我父親給我一筆補(bǔ)貼費(fèi)。不然我就不會(huì)在這里了。
The car broke down. But for that we would have been in time.
汽車出毛病了。要不是那個(gè)我們會(huì)及時(shí)趕到的。
E otherwise(=if this doesnt happen/didnt happen/hadnt happened否則)
We must be back before midnight; otherwise well be locked out.
我們必須在午夜之前趕回去，否則我們就會(huì)被鎖在門外。相當(dāng)于：
If we are not back by midnight well be locked out.
如果我們不在午夜之前趕回去，我們就會(huì)被鎖在門外。
Her father pays her fees;otherwise she wouldnt be here.
她的費(fèi)用是她的父親付的，否則她就不會(huì)在這里。相當(dāng)于：
If her father didnt pay her fees she wouldnt be here.
要是她的父親不付她的費(fèi)用，她就不會(huì)在這里了。
I used my calculator; otherwise Id have taken longer.
我用了計(jì)算器，不然我花的時(shí)間就會(huì)更多。相當(dāng)于：
If I hadnt used my calculator Id have taken longer.
要是我沒用計(jì)算器，我花的時(shí)間就會(huì)更多。
F 在日常英語中 or(+else)可以代替 otherwise：
We must be early or(else) we wont get a seat.
我們必須早去，否則就不會(huì)有座位了。
G 存在強(qiáng)烈的限制或約束的意思時(shí)，provided(that)可以代替if。它主要用來表示允許：
You can camp here provided you leave no mess.
你們?nèi)绻３终麧嵉脑挘梢栽谶@里宿營。
H suppose/supposing?(=what if?假如)
Suppose the plane is late?相當(dāng)于：
What if/What will happen if the plane is late?
假如飛機(jī)誤點(diǎn)的話，將會(huì)出現(xiàn)什么情況?
Suppose no one had been there?相當(dāng)于：
What if no one had been there?
假如沒有人去過那里的話，會(huì)怎么樣?
suppose也可以引出建議：
Suppose you ask him?/Why dont you ask him?
假如你問一問他呢?/你為什么不問一問他呢?
