if和weather引导宾语从句的区别

if和weather引导宾语从句的区别

if和weather引导宾语从句的区别： 
  引导动词后面的宾语从句时，一般情况下二者可以通用；引导形容词后面的宾语从句时， 二者可以通用（如：He is not sure whether/if it is right or wrong.）。但是以下 几种情况只能使用whether而不能使用if： 
A）引导主语从句时：Whether we shall attend the meeting hasn’t been decided yet.   注意：如果使用it作形式主语，则whether和if都能引导主语从句。如： It hasn’t been decided whether/if we shall attend the meeting. 
B) 引导表语从句时：The question is whether the film is worth seeing. 
C) 引导同位语从句时：Please answer my question whether you are coming. 
D）引导动词后面的宾语从句置于句首时：Whether she is married I don’t know.   E) 引导动词后面的宾语从句表示选择概念时： 
1) He wondered whether he should wait for them or go on. 2) He wondered whether he should go there by air or by sea. 
F）引导动词后的宾语从句，后面紧接or not时：He asked me whether or not I would come.     注意：当or not置于句末时，也可使用if。如：He asked me whether/if I would come or not. 
当宾语从句是否定句时，要用if，而不能使用whether。如：He asked me if I wouldn’t come. G) 引导discuss后面的宾语从句时：They discussed whether John could attend the meeting. H) 引导介词后面的宾语从句时：It all depends on whether they will support us.   I) 后接动词不定式作宾语时：He doesn’t know whether to stay (or not).    J) 为了避免与表示条件的if重复或为了避免产生歧义时，常使用whether： 1) He asked whether, if I got the job, I’d move to Beijing. 
2) Please let me know if you like it. 该句可译为“请告诉我你是否喜欢。”或“如果你喜欢，请告诉我。” 如果使用whether就可以避免产生歧义。  
注意：whether可以引导让步状语从句，意为“不论是否…，不管是…还是…”。例如：  Whether I am busy or not, I shall spare no effort to learn English well.