if, whether

1. She glares at me if I go near her desk.
   我一走近她的辦公桌，她就瞪我。
2. Do you know if he's married?
   他結(jié)婚沒結(jié)婚，你知道嗎？
3. I'm not sure whether to resign or stay on.
   我拿不準(zhǔn)主意是辭職還是留任。
4. I wonder if I should wear a hat.
   我不知道該不該戴帽子。
5. Even if you saw him pick up the money, you can't be sure he stole it.
   就算你看見是他拾起的錢，你也不能肯定錢就是他偷的。
6. If he wins and it's a big if he'll be the first Englishman to win for twenty years.
   假使他贏了－－是否能贏還是一大疑問－－他將是二十年來第一個(gè)獲勝的英國(guó)人。
7. Listen to the tune see if you can remember the words.
   請(qǐng)聽這曲子－－看你能不能想得起歌詞來。
8. If weather permit, we will go to the park tomorrow.
   如果天氣好的話，明天我們?nèi)ス珗@。

if

conj.（連接詞）

In the event that:
如果，倘若：在…的情況下：
例句：
If I were to go, I would be late.
倘若我去，就要遲到

Granting that:
假設(shè)，如果：
例句：
If that is true, what should we doô
假設(shè)那是真的我們?cè)撛趺崔k呢ô

On the condition that:
如果，只要：在某種條件下：
例句：
She will play the piano only if she is paid.
只有付給她報(bào)酬，她才愿意演奏鋼琴

Although possibly; even though:
雖然；即使：
例句：
It is a handsome if useless trinket.
雖然無用卻很漂亮的小飾物

Whether:
是否：
例句：
Ask if he plans to come to the meeting.
問問他是否要來參加會(huì)議

Used to introduce an exclamatory clause, indicating a wish:
但愿，要是…該多好?。河脕硪鲆粋€(gè)表達(dá)愿望的感嘆句，表達(dá)一個(gè)愿望：
例句：
If they had only come earlier!
如果他們?cè)鐏硪徊皆摱嗪冒?

n.（名詞）
A possibility, condition, or stipulation:
條件：可能性、條件或設(shè)想：
例句：
There will be no ifs, ands, or buts in this matter.
這件事不允許有假設(shè)、拖延或反對(duì)

來源：
Middle English
中古英語
from Old English gif * see i-
源自 古英語 gif *參見 i-

In informal writingbothif and whether are standard in their use to introduce a clause indicating uncertainty after a verb such as ask, doubt, know, learn, or see:
在非正式的寫作中，可以使用if 或 wether 兩個(gè)詞來表達(dá)不定性，兩者都算標(biāo)準(zhǔn)，例如 ask,doubt,know,learn, 或 see這樣的動(dòng)詞后：
例句：
We shall soon learn whether (or if ) it is true.
我們很快就會(huì)知道這是否（或 if ) 是真實(shí)的。

In such contexts, however,the use ofif can sometimes create ambiguities. Depending on the intended meaning, the sentenceLet her know if she is invited might be better paraphrased asLet her know whether she is invited or If she is invited, let her know. · In conditional sentences the clause introduced byif may contain either a past subjunctive verb (if I were going ) or an indicative verb ( if I am going; if I was going ), depending on the intended meaning.According to the traditional rule,the subjunctive should be used to describe an occurrence that is presupposed to be contrary to fact,as inif I were ten years younger or if Napoleon had won at Waterloo. The main verb of such a sentence must then contain the modal verbwould or (less frequently) should:
不過在這種情況下，用if 就可能會(huì)造成歧義。 Let her know if she is invited 這句話最好根據(jù)所要表達(dá)的意思， 分開說成告訴她她是否被邀請(qǐng)了 或 如果她被邀請(qǐng)了，就讓她知道 兩句話。 用if 引起的條件狀語從句中， 可以含有一個(gè)過去式的虛擬動(dòng)詞(倘若我去 )或一個(gè)一般陳述動(dòng)詞( 如果我就去；如果我去了 )， 這得依據(jù)所要表達(dá)的意思而定。根據(jù)正統(tǒng)的原則，虛擬語氣用來表達(dá)一個(gè)與事實(shí)相反的假設(shè)，例如如果我再年輕十歲 或者 如果拿破侖在滑鐵盧戰(zhàn)役中獲勝。 于是在這樣的句子里，主要?jiǎng)釉~必須包含情態(tài)動(dòng)詞會(huì) 或（在較少情況下） 應(yīng)該：
例句：
If America were still a British colony,
如果美國(guó)現(xiàn)在還是英國(guó)的殖民地，

we would have an anthem that human voices could sing.
我們就會(huì)有一支人人都會(huì)唱的國(guó)歌。
例句：
If I were the President,
如果我是總統(tǒng)，

I should (or would ) declare November a national holiday. When the situation described by theif clause is not presupposed to be false, however, that clause must contain an indicative verb,and the choice of verb in the main clause will depend on the intended meaning:
我就（或 會(huì) ) 宣布十一月一日為國(guó)家休假日。 而只要if 引起的從句描述的條件不是事先就被認(rèn)為是不可能的， 從句中就必須使用直陳動(dòng)詞，而主句中詞的形式就要依所要表達(dá)的意義而定：
例句：
If Hamlet was really written by Marlowe, as many have argued, then we have underestimated Marlowe`s genius.
如果就象很多人猜測(cè)的那樣，《哈姆雷特》一劇是由馬洛寫的，那我們就一直低估了馬洛的才能。

例句：
If Kevin was out all day, then it makes sense that he couldn`t answer the phone.
如果確實(shí)一直在外面，打電話找不著他是很正常的。

Note also that the presence of the modal verbwould in the main clause should not be taken as a sign that the verb in the if clause must be in the subjunctive, if the content of that clause is not presupposed to be false:
另須注意，在主句中使用情態(tài)動(dòng)詞would 并不表明 if 從句中一定使用虛擬語氣，因?yàn)閺木涞膬?nèi)容并不一定原先就認(rèn)為是錯(cuò)誤的：
例句：
If I was (not were ) to accept their offer—which I`m still considering—I would have to start the new job on May 2.
如果我去（不是 were ) 接受他們的盛情——我還在這樣考慮——那么我必須在5月2日開始新工作。

例句：
He would always call her from the office if he was (not were ) going to be late for dinner. ·
如果他（不是 were ) 晚餐會(huì)遲到，就會(huì)從辦公室打電話給她。 ·

Again according to the traditional rule,the subjunctive is not correctly used following verbs such asask or wonder in if clauses that express indirect questions, even if the content of the question is presumed to be contrary to fact:
另外還是根據(jù)傳統(tǒng)規(guī)則，在動(dòng)詞ask 或 wonder 中 if 引導(dǎo)的間接問句， 即使其內(nèi)容被認(rèn)為與事實(shí)相反，也不能使用虛擬語氣：
例句：
We wondered if dinner was (not were ) included in the room price.
我們想知道晚餐費(fèi)用是否被（不是 were ) 包括在房間費(fèi)中。

例句：
Some of the people we met even asked us if California was (not were ) an island. ·
我們碰到的一些人甚至問我們加利福尼亞是否是（不用 were ) 一個(gè)島嶼。

With all deference to the traditional rules governing the use of the subjunctive,it should be noted that a survey of the prose of reputable writers over the past 200 years would reveal a persistent tendency to use the indicativewas where the traditional rule would require the subjunctive were. A sentence beginningIf I was the only boy in the world, while not strictly correct, is wholly unremarkable. But the corresponding practice of using the subjunctive in place of the indicative may be labeled a hypercorrection. ·In spoken Englishthere is a growing tendency to usewould have in place of the subjunctive in contrary-to-fact clauses, as inif I would have been the President, but this usage is still widely considered incorrect.See Usage Note at doubt ,should ,wish
在與指導(dǎo)虛擬語氣使用方法的傳統(tǒng)規(guī)則相沖突的一系列不同用法中，我們應(yīng)注意到一項(xiàng)對(duì)過去200年散文作家的調(diào)查顯示，在傳統(tǒng)語法要求使用虛擬式的were 的情況下，有一種持久的使用直陳式 was 的趨勢(shì)。 一句用假如我是世界上唯一的男孩 開頭的句子不會(huì)引起人們的注意。 而一定要把其中的直陳式換成虛擬式就顯得矯正過了頭。在英語口語中，在與事實(shí)相反的從句中，使用would have 一詞的趨勢(shì)有所增加， 例如如果我會(huì)是總統(tǒng)， 但這種用法仍然被大多數(shù)人認(rèn)為是不正確的參見 doubt,should,wish