/ɪf ||; ɪf/conj 1 used in sentences in which one thing only happens or is true when another thing happens or is true 如果；假如；要是: If you see him, give him this letter. 你看到他的话，把这封信交给他。We won't go to the beach if it rains. 要是下雨，我们就不去海滩了。If I had more time, I would learn another language. 如果有时间，我会再学一种语言。I might see her tomorrow. If not, I'll see her at the weekend. 我明天或许会见到她，要不就会在周末见到。
2 when; every time 当；每次: If I try to phone her she just hangs up. 每次我给她打电话，她都把电话挂断。If metal gets hot it expands. 金属遇热就膨胀。
3 used after verbs such as ‘ask’, ‘know’, ‘remember’ （用于ask、know、remember等动词之后）是否: They asked if we would like to go too. 他们问我们是不是也想去。I can't remember if I posted the letter or not. 这封信我记不清寄了没有。 ☞Look at the note at whether. 参看whether的注释。
4 used when you are asking sb to do sth or suggesting sth politely （用于礼貌的请求或建议）: If you could just come this way, sir. 先生，请跟我来。If I might suggest something... 我想提个建议…
as if→
AS→
EVEN²
if I were you used when you are giving sb advice （用于提出忠告）:
If I were you, I'd leave now. 我要是你，现在就走。 if it wasn't/weren't for sb/sth if a particular person or situation did not exist or was not there; without sb/sth 要不是；若非:
If it wasn't for him, I wouldn't stay in this country. 要不是因为他，我不会待在这个国家。 if only used for expressing a strong wish （用于表达殷切的愿望）:
If only I could drive. 我会开车就好了。If only he'd write. 要是他写信给我就好了。