- introducing a conditional clause［引导条件状语从句］如果。
- on the condition or supposition that; in the event that如果：
if you have a complaint, write to the director
如果你想投诉, 就给厂长写信
if you like I'll put in a word for you.
如果你愿意, 我就替你说句好话。
- (with past tense) introducing a hypothetical situation后跟过去时态, 表示假设要是, 假如：
if you had stayed, this would never have happened.
要是你当时留了下来, 就不会发生这件事。
- whenever; every time无论何时; 每当：
if I go out she gets nasty.
每逢我出门, 她就发脾气。
- despite the possibility that; no matter whether虽然; 即使：
if it takes me seven years, I shall do it.
即使花上7年时间, 我也要做这件事。
- (often used in indirect questions) whether常用于间接疑问句是否：
he asked if we would like some coffee
他问我们想不想来点咖啡
see if you can track it down.
看看你是否能追查到。
- with modal expressing a polite request［表示礼貌的问询］是否：
if I could trouble you for your names?
麻烦能否问一下你们的姓名？
if you wouldn't mind giving him a message?
你是否介意带个口信给他？
- expressing an opinion表示看法如果：
that's a jolly long walk, if you don't mind my saying so
那是一次愉快的长途散步, 如果你不介意我这么说
if you ask me, he's in love.
如果你问我, 他是在恋爱了。
- expressing surprise or regret表示惊讶、遗憾这不是…; 要是…多好：
well, if it isn't Frank!
哟, 这不是弗兰克吗！
if I could just be left alone.
要是没人来管我多好。
- with implied reservation暗示有所保留：
- and perhaps not或许不：
the new leaders have little if any control.
新任领导们很少或许根本就没有控制力。
- used to admit something as being possible but regarded as relatively insignificant［表示虽有可能, 但不重要］就算：
if there was any weakness, it was naivety
就算有什么缺点, 也只是天真而已
so what if he did?
就算是他做的又怎样？
- despite being (used before an adjective or adverb to introduce a contrast)［置于形容词或副词前表示对比］尽管：
she was honest, if a little brutal.
她是诚实的, 尽管有点不讲情面。
- a condition or supposition条件; 假设：
there are so many ifs and buts in the policy.
这项政策里有那么多假设和例外。
if and only if
- used to introduce a condition which is necessary as well as sufficient表示所述条件是充分且必要的惟一可能是, 当且只当…时：
witches are real if and only if there are criteria for identifying witches.
只有在有标准确认什么是女巫的条件下, 女巫才是真实存在的。
if and when
- at a future time (should it arise)如果, 万一：
if and when the film gets the green light, be sure you've read the book first.
万一电影获准（放映）, 千万保证你事先已读过原书。
if anything
- used to suggest tentatively that something may be the case (often the opposite of something previously implied)甚至可以这样说（常与已提及的情况相反）：
I haven't made much of this - if anything, I've played it down.
对它我一直未多加重视——甚至可以这样说, 我是在贬低它。
if I were you
- used to accompany a piece of advice表示建议换作是我：
I would go to see him if I were you.
换作是我, 我会去见他。
if not
- perhaps even (used to introduce a more extreme term than one first mentioned)用于提出更极端的说法甚至可能：
hundreds if not thousands of germs.
数以百计甚至可能数以千计的细菌。
if only
- even if for no other reason than即使只为：
Willy would have to tell George more, if only to stop him pestering.
即使只是为了不要让乔治继续纠缠, 威利也得多告诉他一点。
- used to express a wish, especially regretfully要是…就好了：
if only I had listened to you.
如果我听你的话就好了。
if so
- if that is the case若是这样。