Learner's definition of IF
1
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used to talk about the result or effect of something that may happen or be true假如，如果，要是（用于描述可能发生的事或真实事件的结果或影响） -
If it rains, (then) we won't go to the park.要是下雨，我们就不去公园了。
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If he actually did commit the crime, he deserves to be punished.倘若他真犯了罪，就应该受到惩罚。
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If you believe that, you'll believe anything!要是你连那件事都信，你就会相信一切。
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Come to the party if you can.你如果可以就来参加聚会吧。
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If you really want to know, you should ask.要是你真想知道，就应该问问。
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What will happen if I fail the test?如果我考试没通过，会怎么样呢？
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You should study. If not, you won't pass the test. = If you don't (study), you won't pass the test.你应该学习。否则，就没法通过考试。
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Please arrive early if possible. = Please arrive early if it is possible.如果可能，请早点到。
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I'll do the work myself if necessary. = I'll do the work myself if it is necessary.如果有必要，我会亲自做这个工作。
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If and when he comes, you can ask him. = When and if he comes, you can ask him.倘若他来，你可以问他。
2
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used to discuss the imaginary result or effect of something that did not happen or that is or was not true假如，如果，要是（用于描述没有发生或不真实的事件的结果或影响） -
If you had studied, you would have passed the test.你如果之前好好学习的话，就会通过这次考试了。
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The situation would be funny if it weren't so tragic. = (informal) The situation would be funny if it wasn't so tragic.这情形如果不是如此悲惨，会是很可笑的。
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The harvest would have been good if it had rained.要是下过雨，收成本该很好。
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The news would be interesting if (it were) true, but it's not true.消息要是真的本该很有趣，但它不是真的。
3
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used to say that something must happen before another thing can happen只有，只要（用于描述某事件是另一事件发生的先决条件） 4
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used to indicate a result that always occurs when something happens每当，无论何时（用于表示某事件的必然结果） 5
: even though : although虽然；即使 -
It was an interesting if unbelievable story.那故事虽然不可信却很有趣。
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Her actions were understandable, if not forgivable.她的行为虽然不可饶恕却可以理解。
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He had to perform an annoying, if necessary, task.他不得不执行一项虽有必要却令人讨厌的任务。
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a fair, if tough, boss虽然严厉但公平的老板
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The weather was good, if not great.天气即使不算非常好却也还不错。
6
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used to introduce a statement or question about something that is not certain是否 -
I'll see if [=whether] I can come.我会看看我是否能来。
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Do you know if he'll come to the party?你知道他是否会来参加聚会？
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I wonder if it's true (or not).我想知道这是不是真的。
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Frankly, I doubt if he'll pass the exams.坦率地说，我怀疑他能否通过这些考试。
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She asked if the mail had come.她问邮件到了没有。
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We should determine/decide if it is safe to go swimming.我们应该确定去游泳是否安全。
7
a —
used to make a polite request or suggestion用于礼貌地提出请求或建议 -
Would you mind if I sat here? [=may I sit here?]我可以坐这里吗？
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If you will/would (be good enough to) follow me, ladies and gentlemen, I'll take you to your seats.女士们、先生们，请跟我来，我带你们就座。
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If I could make a suggestion, why don't we sit closer to the front of the theater?我可以提个建议吗，我们为什么不坐得离剧场前台近点呢？
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I'd like to stay a little longer, if you don't mind. = I'd like to stay a little longer, if it's/that's all right with you.如果你不介意，我想再待一会儿。
b —
used to state an opinion in a polite way用于礼貌地表达观点 8
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used in statements that describe feelings (such as regret) about a possible situation用于描述对可能出现的情形的感受（如后悔等） -
I'm sorry if you think I insulted you.如果你觉得我侮辱了你，我很抱歉。
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I'd be sorry if you thought I had insulted you.如果你觉得我侮辱了你，我很抱歉。
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I don't care if we're late.我不在意我们会迟到。
9
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used in statements and questions that express doubt用于表示怀疑的陈述句和疑问句 -
I met Brenda last week—if that is/was in fact her real name.我上星期见过布伦达——如果那是她的真名。
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If you're so smart, why aren't you rich?要是你真如此聪明，为什么你不富有？
10
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used to introduce an even stronger alternative to what has just been said用于引出比已说的话更有力的话 -
These changes will have little if any impact on the problem.这些变革对此问题即使有影响也只是一丁点而已。
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Few if any of the town's original settlers are left.这个镇子最初的移民即便有留下来的也很少。
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Rarely, if ever, does that happen.即使有那种事，也很少发生。
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His efforts have helped to save thousands, if not millions, of lives.他的努力即使没有救助数百万人的性命，也有成千上万了。
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My car is as fast as yours if not (even) faster.我的车即使不比你的车快那也一样快。
11
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used to express surprise about meeting someone when it is not expected用于表达意外遇见某人的惊讶 -
So I went to the game and who should I see there if not [=but] my old friend Tom!于是我去看了比赛，竟然在那儿遇到了老朋友汤姆！
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Well, if it isn't my old friend Tom!啊，这不是我的老朋友汤姆吗！
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So I went to the game and who did I see there if it wasn't my old friend Tom!于是我去看了比赛，竟然在那儿遇到了老朋友汤姆！
12
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used to emphasize the truth of a statement用于强调一句话的真实性 -
The idea is true if any idea has ever been! [=the idea is certainly true]这个想法绝对正确！
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“He claims that he's never met her.” “Well, if that isn't the biggest load of nonsense I've ever heard!” [=that is a lot of nonsense; that is completely untrue]“他说他从未见过她。”“啊，简直是胡说八道！”
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I'll get my revenge if it's the last thing I do! [=I am determined to get my revenge]我一定会报仇的！
if anything
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used to make a statement that strongly disagrees or contrasts with a preceding statement用于表达对前述内容的强烈反对 -
We don't see each other too often—if anything we don't see each other often enough!我们见面不太频繁——其实是我们不怎么见面！
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The economy has not improved. It has gotten worse, if anything.经济情况没有改善，反而变得更糟糕了。
if it comes to that
— see 1come
if I were you
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used when giving advice to people about how they should behave如果我是你（用于劝告别人应该如何做）
if not for
: in the absence of (something or someone) : without要不是；若非 -
If not for modern medicine, fewer babies would survive.要不是有现代医学，幸存的婴儿会更少。
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If not for him, I wouldn't be where I am today.要不是他，我不会有今天的成就。
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often used in the phrases if it were not for and if it had not been for常用于短语if it were not for和if it had not been for -
If it were not for your donations, many more children would go hungry.要不是有你的捐赠，会有更多的孩子挨饿。
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If it hadn't been for him, I wouldn't be where I am today.要不是他，我不会有今天的成就。
if nothing else
: at least至少；起码 —
used to stress that an approving statement is true even though a stronger statement might not be用于强调某个好处是确实存在的，即使除此之外别无其他好处 -
If nothing else, he's polite!至少，他有礼貌！
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The food was hot, if nothing else. [=the food may not have been very good, but at least it was hot]最起码，食物是热的。
if only
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used to talk about something that you want to happen or be true但愿；要是…多好
if you ask me
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used in statements that express an opinion依我看；要我说 2 if /ˈɪf/ noun
plural ifs
plural ifs
Learner's definition of IF
[count]
: something that is not certain : something that could either happen or not happen不确定的事 -
There are too many ifs in this proposal.这一提议有太多不确定因素。
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They could win if everyone plays his best, but that's a big if. [=it is not likely that everyone will play his best]要是每个人都竭尽全力，他们就能获胜，但那是个很大的未知数。
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(US) She's the most qualified candidate, and there are no ifs, ands, or buts about it! = (Brit) She's the most qualified candidate, and there are no ifs and buts about it! [=it is certain that she is the most qualified candidate]她是最有资格的候选人，这一点毋庸置疑！