as if only if even though

一、 as if (= as though) 用来引导行为方式状语从句
as if比as though较为常用,一般译为“好像,像……似的”
例如:
They are talking as if/as though they had seen a ghost.他们谈着话,就像是见了鬼似的
使用as if时应注意以下几点:
1.as if从句叙述的并不是事实或真实性极小时,该从句中的谓语动词应为虚拟形式,如上例
再如:
It seemed as if the good man were trying to teach us all he knew at his last lesson.这个好心人仿佛要把自己的全部知识在这
最后一堂课里都教给我们.
2.as if从句叙述的内容真实性较大时,该从句中要用直陈语气
例如:
When the spaceship leaves the earth at very high speed,the astronauts feel as if they are being crushed against the
spaceship floor.宇宙飞船高速离开地球时,宇航员感到自己似乎是被压着贴在飞船的地板上.
3.as if后面还可以直接跟动词不定式短语、分词短语或介词短语
例如:
The fat man threw himself on the ground,and held his breath as if to be dead.那位胖人扑倒在地,屏住气,就像死了一样.
Our teacher,Mr Zhang,was sitting at the desk,as if thinking about something.我们的张老师坐在桌子旁,好像在思考着什么.
4.在非正式文体中,特别在美国英语中,可用like代替as if
例如:
It looks like it’s going to rain today.看来今天要下雨
二、even if (= even though) 用来引导让步状语从句,所表达的事情往往是实现的可能性不大,可译为“尽管,即使,纵然,就算”
例如:
I’ll help you,even if I don’t sleep for the whole night.即使我一夜不睡觉,也要帮你一把.
有时even if可用if代替,意义上与as if相同
例如:
Now he had a safe place,if the wolf came.即使狼来了,他现在也有一个安全的地方了
三、 what if常用来表示建议或担心,用于疑问句时,等于“What will happen if ...”,“What shall we do if ...”,“What
will you do if ...”,可译为“要是……怎么办?”,“万一……将会怎样?”
例如:
What if it rains while we have a long way from shelter?万一天下雨,而我们又离躲雨的地方很远,该怎么办呢?
四、 only if可用来引导条件状语从句,可译为“如果,只有”
例如:
You will be able to speak English fluently only if you practise constantly.只有通过经常练习,你的英语才能讲得很流利.
I’ll lend you my book only if you return it by 5:00.如果5点钟之前能把书还给我,我就把它借给你.
五、if only后面从句中的谓语动词通常为过去时或过去完成时,可以表达强烈的愿望或遗憾,一般译为“只要,要是……就好了”.
例如:
If only I had more money,I could buy a computer.我要是有更多的钱就好了,那样我就可以买部电脑了.
注意:1.if only从句常常单独使用,若省去主句,可用来表示较为强烈的感叹意义
例如:
If only I were younger!要是我年轻点儿就好了!
2.if only与would连用,可表示意图,意愿等情态意义.
例如:
If only the postman would come earlier!要是邮递员能早点来该多好啊!