if是一个英语单词，名词、连词，作名词时意思是“条件，设想；不确定的情况”，作连词时意思是“（表条件）如果；（表假设）要是，假如；无论何时；虽然，即使；（用于间接疑问）是否；（用于礼貌问询）是否；当，每次；（与情态动词连用）表婉转客气；这不是……，要是……多好；或许不；就算；尽管”。

根据《柯林斯英汉双解大词典》，意为：

1.CONJ You use if in conditional sentences to introduce the circumstances in which an event or situation might happen, might be happening, or might have happened. (引导条件从句) 如果

2. CONJ You use if是非问句中) 是否

3. CONJ You use if to suggest that something might be slightly different from what you are stating in the main part of the sentence, for example, that there might be slightly more or less of a particular quality. (表示与主句所述事实可能有少许不同) 即使

4. CONJ You use if情态动词连用，表示婉转客气

5. CONJ You use if at or near the beginning of a clause when politely asking someone to do something. (用于从句句首或靠近句首的位置，表示礼貌的请求) 是否 [礼貌]

6. PHRASE You use if not in front of a word or phrase to indicate that your statement does not apply to that word or phrase, but to something closely related to it that you also mention. 即便不

7. CONJ You use if to introduce a subordinate clause in which you admit a fact that you regard as less important than the statement in the main clause. (引导从句，提出次要的事实) 即使

8. PHRASE You use if ever with past tenses when you are introducing a description of a person or thing, to emphasize how appropriate it is. (与过去式连用，强调对人或事物的描述极为恰当) 如果有…的话 [强调]

9. PHRASE You use if only with past tenses to introduce what you think is a fairly good reason for doing something, although you realize it may not be a very good one. 即使仅仅 (与过去式连用，引出能勉强说明做某事的原因)

10. PHRASE You use if only to express a wish or desire, especially one that cannot be fulfilled. (尤指不能实现的愿望) 要是…多好 [情感]

11. PHRASE You use as if when you are making a judgment about something that you see or notice. Your belief or impression might be correct, or it might be wrong. (表示判断) 好像

12. PHRASE You use as if to describe something or someone by comparing them with another thing or person. (表示类比) 仿佛

13. PHRASE You use as if to emphasize that something is not true. (强调某事不是真的) 好像…一样 [口语]

if any

如果有的话；即便要

if so

如果这样；要是那样的话

as if

(强调某物不是真的)好像…一样,仿佛,似乎；(表示判断)好像,仿佛,似乎；(表示类比)好像，仿佛，似乎

if only

(与过去时连用，引出一个相对合理的理由)即使仅仅为了(或因为)…；要是…多好

if ever

(用于过去时,加强语气)如果真的…

even if

即使；尽管；纵然

if so

如果这样；要是那样的话

if necessary

如果必要的话

if not

要是不;即使不

1、If you do not know me, nothing.

如果你不认识我，什么也没有。

2、If you can do it , so can I.

所以，如果我能做到，我知道你可以。

3、Yes. What do you do if that happens?

是的。那当他发生时你该怎麽做?。