if

Từ điển Oxford Advanced Learner 8th

if [if ifs] conjunction, noun BrE [ɪf] NAmE [ɪf]
conjunction
1. used to say that one thing can, will or might happen or be true, depending on another thing happening or being true
• If you see him, give him this note.
• I'll only stay if you offer me more money.
•If necessary I can come at once.
•You can stay for the weekend if you like.
•If anyone calls, tell them I'm not at home.
•If he improved his IT skills, he'd (= he would) easily get a job.
•You would know what was going on if you'd (= you had) listened.
•They would have been here by now if they'd caught the early train.
•If I was in charge, I'd do things differently.
• (rather formal)If I were in charge…
•Even if (= although) you did see someone, you can't be sure it was him.
2. when; whenever; every time
• If metal gets hot it expands.
• She glares at me if I go near her desk.
3. (formal)used with will or would to ask sb politely to do sth
• If you will sit down for a few moments, I'll tell the manager you're here.
• If you would care to leave your name, we'll contact you as soon as possible.
4. used after ask, know, find out, wonder, etc. to introduce one of two or more possibilities
Syn: ↑whether
• Do you know if he's married?
• I wonder if I should wear a coat or not.
•He couldn't tell if she was laughing or crying.
•Listen to the tune and see if you can remember the words.
5. used after verbs or adjectives expressing feelings
• I am sorry if I disturbed you.
• I'd be grateful if you would keep it a secret.
•Do you mind if I turn the TV off?
6. used to admit that sth is possible, but to say that it is not very important
• If she has any weakness, it is her Italian.
•So what if he was late. Who cares?
7. used before an adjective to introduce a contrast
•He's a good driver, if a little over-confident.
•We'll only do it once— if at all.
8. used to ask sb to listen to your opinion
• If you ask me, she's too scared to do it.
• If you think about it, those children must be at school by now.
•If you remember, Mary was always fond of animals.
9. used before could, may or might to suggest sth or to interrupt sb politely
•If I may make a suggestion, perhaps we could begin a little earlier next week.

Word Origin:
Old English gif, of Germanic origin; related to Dutch of and German ob.

Grammar Point:
if / whether
Both if and whether are used in reporting questions which expect ‘yes’ or ‘no’ as the answer: ▪ She asked if/whether I wanted a drink., although whether sounds more natural with particular verbs such as discuss, consider and decide. When a choice is offered between alternatives if or whether can be used: ▪ We didn’t know if/whether we should write or phone. In this last type of sentence, whether is usually considered more formal and more suitable for written English.
Idioms: ↑if I were you ▪ ↑if and when ▪ ↑if anything ▪ ↑if not ▪ ↑if only ▪ ↑it's not as if ▪ ↑only if
 
noun (informal)
a situation that is not certain
• If he wins— and it's a big if — he'll be the first Englishman to win for fifty years.
• There are still a lot of ifs and buts before everything's settled.

Word Origin:
Old English gif, of Germanic origin; related to Dutch of and German ob.