if 1 S1 W1 / ɪf / 连词

1 used when talking about something that might happen or be true, or might have happened :

We’ll stay at home if it rains.

If you need money, I can lend you some.

If I didn’t apologize, I’d feel guilty.

If you had worked harder, you would have passed your exams.

What would happen to your family if you were to die in an accident?

If Dad were here, he would know what to do.

Taste the soup and add salt and pepper if necessary .

I want to get back by five o’clock if possible .

I think I can fix it tomorrow. If not , you’ll have to wait till Friday.

Is the book available, and if so, where?

The missiles can be fired only if the operator types in a six-digit code.

We’ll face that problem if and when it comes along (= if it happens or when it happens ) .

If by any chance you can’t manage dinner tonight, perhaps we can at least have a drink together.

2 used to mention a fact, situation, or event that someone asks about, or is not certain about :

He stopped to ask me if I was all right.

I don’t know if what I am saying makes any sense.

I doubt if anyone will remember me.

I’m not sure if this is the right road or not.

3 used to mention a type of event or situation when talking about what happens on occasions of that type :

If I go to bed late, I feel dreadful in the morning.

Plastic will melt if it gets too hot.

4 used when saying what someone’s feelings are about a possible situation :

You don’t seem to care if I’m tired.

I’m sorry if I upset you.

It would be nice if we could spend more time together.

5 spoken used when making a polite request :

I wonder if you could help me.

I’d be grateful if you would send me further details.

Would you mind if I open a window?

If you would just wait for a moment, I’ll try to find your papers.

6 used when you are adding that something may be even more, less, better, worse etc than you have just said :

Brian rarely, if ever, goes to bed before 3 am.

Their policies have changed little, if at all, since the last election.

Her needs are just as important as yours, if not more so.

The snow was now two feet deep, making it difficult, if not impossible, to get the car out.

7 even if used to emphasize that, although something may happen or may be true, it will not change a situation :

I wouldn’t tell you even if I knew.

Even if she survives, she’ll never fully recover.

8 if anything used when adding a remark that changes what you have just said or makes it stronger :

It’s warm enough here in London. A little too warm, if anything.

9 spoken used during a conversation when you are trying to make a suggestion, change the subject, or interrupt someone else :

If I might just make a suggestion, I think that the matter could be easily settled with a little practical demonstration.

If I could just take one example to illustrate this.

10 if I were you spoken used when giving advice and telling someone what you think they should do :

I wouldn’t worry about it if I were you.

11 if only

a) used to express a strong wish, especially when you know that what you want cannot happen :

If only he had talked to her sooner!

If only I weren’t so tired!

b) used to give a reason for something, although you think it is not a good one :

Media studies is regarded as a more exciting subject, if only because it’s new.

12 used to say that, although something may be true, it is not important :

If he has a fault at all, it is that he is too generous.

Her only problem, if you can call it a problem, is that she expects to be successful all the time.

13 used when adding one criticism of a person or thing that you generally like :

The eldest son was highly intelligent, if somewhat lazy.

Lunch was a grand if rather noisy affair.

→ as if at as 2 ( 9 ) , → if ever there was one at ever ( 15 ) , → what if … ? at what 1 ( 18 )

Grammar

When you are using if to talk about something that might happen in the future, use the present tense or the present perfect in the if-clause, not ‘will’ or ‘shall’ :

If I see him (NOT will see him), I’ll tell him.

If she hasn’t come home by midnight, call the police.

You can use won’t to talk about someone being unwilling to do something in the future :

If the bank won’t listen, say that you are going to move your account.

When you are using if to talk about something that is unlikely to happen or is impossible, use the past tense in the if-clause, not ‘would’ :

If someone gave me (NOT would give me) the money, I’d buy a car tomorrow.

In formal English or in writing, use were , not ‘was’, even when the subject of the clause is singular :

If I were in that position, I’d get legal advice.

In normal conversation, you can use was with a singular subject :

If I was ten years younger, I’d go out with him.

When you are using if to talk about something that did not happen, use the past perfect tense in the if-clause :

If they had tried (NOT would have tried) to stop the demonstration, there would have been a riot. if, whether

If and whether are both used to introduce clauses mentioning things that someone asks about or is uncertain about :

I’m not sure if I heard him correctly.

I don’t know whether he is guilty.

Whether can also be used after a 介词 , before the 短语 ‘or not’, and before a ’to’ infinitive, but if cannot :

the question of whether (NOT if) the injuries had caused Mary’s death

Nobody knew whether or not the technique worked.

He won’t decide whether to become a candidate until next year.

THESAURUS

if used when talking about the possibility that something might happen or be true : He faces a long prison sentence if the court finds him guilty. | If scientists’ predictions are correct, average global temperatures could rise by 6 degrees.

unless if something does not happen, or if someone does not do something : The star is difficult to see unless the sky is very clear. | Doctors said they could not treat the boy unless his parents gave their permission.

whether or not used when saying that it does not matter if something happens or not, or if something is true or not : Most people will get better on their own, whether or not they receive medical treatment. | I’m still going, whether she likes it or not.

otherwise used when saying that there will be a bad result if someone does not do something, or if something does not happen : Drink plenty of water – otherwise you will become dehydrated.

in case in order to deal with something that might happen : She did not think it would rain, but she took her umbrella just in case. | It is best to keep a medical kit ready in case of emergency.

as long as/provided that only if something else happens or is true : Visitors are welcome, as long as they bring their own tent. | Anyone can join the course, provided that there is space available. | As long as you can find a computer, you can access an internet-based bank account wherever you are.

on condition that used when you agree to do something only if someone first agrees to do something else : He was offered the job on condition that he went on a month-long training course.