简要回答
if是一个英语单词，既可以作名词又可以作连词，作名词意为不确定的情况，作连词意为如果、假若、倘若、当、无论何时、每次，与will或would连用，表示客气地请求。
if仅由两个字母组成，是一个看上去很简单的单词，但是实际它的意思和用法都是很多的，那么接下来就来跟大家说一说if究竟包含有哪些意思。
详细内容
if
英 [ɪf] 美 [ɪf]
conj.如果;假若;倘若;当;无论何时;每次;与will或would连用，表示客气地请求
n.不确定的情况
复数： ifs
语法说明
【if】 【whether】
Both if and whether are used in reporting questions which expect ‘yes’ or ‘no’ as the answer if和whether均用于要求以yes或no作答的转述疑问句中：
She asked if/whether I wanted a drink.
她问我要不要喝点什么。
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. 不过whether与discuss、consider和decide等动词连用听起来更自然。提供选择时用if或whether均可：
We didn’t know if/whether we should write or phone.
我们不知道是写信好还是打电话好。
In this last type of sentence, whether is usually considered more formal and more suitable for written English. 在最后这一句型中，一般认为whether较正式，更适用于书面英语。
双语例句
She gets very upset if I exclude her from anything
要是有什么事情我不让她参加，她会非常难过。
He asked if I had left with you, and I said no
他问我是否和你一块儿离开的，我说不是。
Sometimes, that standard is quite difficult, if not impossible, to achieve
有时即便有可能达到那个标准，那也是非常困难。
If I could just make another small point about the weightlifters in the Olympics
请允许我就有关奥运会举重运动员的问题再补充一点。
I wonder if you'd be kind enough to give us some information, please?
请问您能不能给我们提供一些信息？
If there was any disappointment it was probably temporary
即便有点儿失望，也肯定是暂时的。
