if与whether这两个连接词均含“是否”之意。
if : 作“是否”解时，多用于口语，引出宾语从句，不能直接跟or not连用。
- Mrs Kramer called half an hour ago to ask if her cake was ready.
克雷默夫人半小时前来电话问她的蛋糕做好了没有。 - I don't care if he likes it or not - I'm coming!
我不在乎他乐不乐意，我反正要来！ - I was wondering if you'd like to come to the cinema with me this evening?
不知你今晚想不想与我一起去看电影？
whether : 多用于书面语中，可与or或or not连用，除引出宾语从句外，还可引出主语从句、表语从句、同位语从句或与不定式连用。
- I wasn't sure whether you'd like it.
我拿不准你是否喜欢它。 - She asked me whether I was interested in working for her.
她问我是否有兴趣为她工作。 - I'm wondering whether to have the fish or the beef.
我正在考虑是吃鱼还是吃牛肉。 - I doubt whether it'll work.
我怀疑这是否能起作用。
