if和whether都可译为"是否"，二者引导宾语从句时通常可以互相替换，口语中多用if代替whether。例如：Ask if/whether he plans to come to the meeting. 而以下几种情况中, 只能用whether:1. 强调两方面的选择，特别是句中有or not时。如：Let me know whether you can come or not.2. 宾语从句前置时。如：Whether this is true, I can't say.3. 引导主语、表语、同位语从句时。如：Whether the football game will be played depends on the weat...
