1. if引导条件状语从句
If you mix yellow and blue, you get green.
你将黄色与蓝色混合，便会得到绿色。
If she wants the servant, she rings the bell.
每当她需要仆人时，她便按铃。
If I forget something, my mother reminds me of it.
每当我忘记了某件事情，我妈妈就会提醒我。
If he comes to the countryside, he sees his old friend.
如果他来乡下，他总是来看他的老朋友。
2. if +not
We should do it with all our heart, if not we will leave it unfinished.
我们应该全心全意地做这件事，不然的话，我们将会半途而废。
I should go to school earlier, if not my teacher will criticize me.
我应该早点上学，不然我的老师会责备我的。
He should tell me the truth, if not I will get angry.
他应该告诉我真相，不然我会生气的。
Mary should give me a call, if not she couldn't get the news.
玛丽应该给我打个电话，不然的话她就没办法得到这个消息了。
3. if引导让步状语从句
If she's poor, at least she's honest.
虽说她很穷，但至少她还是诚实的。
If I am wrong, you are wrong, too.
即使说我错了，你也不对。
I'll do it, even if it takes me all the afternoon.
虽然会花费我一下午的时间，我还是要做这事。
I'll insist on doing it even if they scold me.
即使他们责怪我，我也会坚持做下去。
4. if作连词，引导否定的条件状语从句
If we are not healthy, happiness is impossible.
没有健康，我们就不可能有幸福.
If he does not study hard, he will never pass the examination.
如果他不努力学习，考试就绝不会及格。
This baby seldom cries if he is not tired.
这个婴儿很少哭，除非是累了。
If I do not understand what he says，I always ask him.
要是我不明白他所说的，就总是问他。