if做连词,主要有两个意思,一是“是否”,引导宾语从句,一是“如果”,引导状语从句
一、if作为连词,引导条件状语从句,它表示的意思是“假如”“如果”等.在复合句中如果主句用将 来时,则if引导的状语从句用一般现在时.例如:
1.If itdoesn’train,we will go to the park next Sunday.如果天不下雨,下周星期天我们将去公园.
2.If you ask him,he will help you.如果你求他,
if从句中用过去式,表示不可能实现,大概不会实现或提出作为考虑的假定条件.此时需要用虚拟语气,例如:
1.If you were a bird,you could fly.假使你是只鸟,你便会飞了.
2.If I asked him(if I were to ask him) for a loan,would he agree?如果我向他借贷,他会答应吗?
另外,if从句中用过去完成式,表示过去未实现的条件(例如由于不可能实现或某人之未能实行).例如:
1.If they had startedearlier,they would have arrivedin time.要是他们早些动身,他们便可及时到达了.
2.If they had not started when they did,they would not be here now.如果他们那时不动身,现在他们就不会在此地了.
二、if还可以引导让步状语从句.这时if当作“即使是”,“虽说”解.例如:
1.If she’s poor,at least she’s honest. 虽说她很穷,但至少她还是诚实的.
2.If I am wrong,you are wrong,too. 即使说我错了,那么你也不对.
3.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.
三、if作为连词还可以引导宾语从句.引导宾语从句时和whether意思相同.例如:
1.Lily asked if / whether she liked it.莉莉问她是否喜欢它.
2.She asked if / whether they had a cotton one. 她问是否他们有一件棉织的.
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