大家在舉例的時候常常會這么說“如果………”，”假設………..”，即if………
先不說這種舉例的好還是壞,就本身的句子而言，很多都是有問題的。
總結了一些if的用法，大家考前看看
先看兩個托福作文例子:
[Scenery]Sue has lost her watch. She think it may be at Ann’s house.
SUE: I think I left my watch at your house. Have you seen it?
（1） ANN: no, but I’ll have a look when I get home. If I find it, I’ll tell you.
If I find…., I’ll……
（2） Ann says: If I found a wallet in the street, I’d take it to the police.
If I found……, I’d（=I would）……..（而不是if I find, I’ll…..）
這里兩個句子有著不同的意思,前者表示Ann覺得她有找到手表的真實可能性.因此才說if I find….., I’ll…..
而后者是完全不同的'情況.在這里Ann沒有考慮真實的可能性;她在虛擬這一個托福 作文 情景,并不認為真的可以在街上揀到手表.于是才說：if I found……,I’d……
if I do……….和if I did………的區別
用if+過去式（if I found / if you were / if we didn’t等）表示虛擬的事情,而不是指過去時間發生的事情:
What would you do if you won a million pounds?
I don’t really want to go to their party, but I probably will go. They’d be offended if I didn’t go
Sarah has decided not to apply for the job. She isn’t really qualified for it, so she probably wouldn’t get it if she applied.
If從句中一般不用would：
I’d be very frightened if somebody pointed a gun at me.（而非if somebody would point）
If I didn’t go to their party, they’d be offended（而非if I wouldn’t go）
If …….would可以表示用來請求某人做某事：
I would be grateful if you would send me your brochure as soon as possible.
“Shall I close the door?” “yes, please, If you would.”
Would（‘d） / wouldn’t用于句子的主句（不是if從句）
If you took more exercise, you’d （=you would） probably feel healthier.
Would you mind if I used your phone?
I’m not tired enough to go to bed yet. I wouldn’t sleep.
另外,if引導的條件句也能引起倒裝,如果要是在作文里用到,也是一個加分點：
先看正常語序。
It would be a serious setback, if the talks were to fail.
If you should need more information, please telephone our main office.
If Alex had asked, I would have been able to help.
倒裝是要省略if
it would be a serious setback, were the talks to fail.
Should you need more information, please telephone our main office.
Had Alex asked, I would have been able to help
倒裝句比if-從句更加正式。
但是在否定句里面,不可以用縮寫。
e.g.
Had he not resigned, we should have been forced to sack him（不用hadn’t he…..）
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