条件状语从句时态

条件状语从句时态根据主句决定。主句是一般将来时态，祈使句或情态动词，从句要用现在时态；主句如果是过去的某种时态，则从句要用过去的某种时态。

条件状语常用的引导词是if和unless

1、用if引导：if意为“如果”。

例句：I don’t know if it will rain tomorrow. But if it rains tomorrow, I’ll stay at home.不知道明天是否会下雨，但要是下雨的话，我就呆在家里。

2、用unless引导：unless的意思是“如果不”“除非”。

但除了这两个以外，条件状语从句也拥有一些其他的引导词，这些引导词出现频率较低，用法偏复杂，所以不如if和unless知名度那么高。

1. on condition(that)...在……条件下

eg.I can tell you the truth on condition that you promise to keep a secret.
　　You can eat ice cream on condition (that) you won't eat too much.

2. supposing conj.如果，假如

osing it rains,shall we continue the sports meeting?
　 Supposing anything should go wrong,what would you do then?

3. provided conj.假如，除非，以……为条件 provided (that) +从句表示一种假设条件。

eg. He will sign the contract provided we offer more favorable terms.
　　He won't be against us in the meeting provided that we ask for his advice in advance.

for 若非，要不是

for the rain,we should have a pleasant journey.
　 But for your help,we should not have finished in time.

5. in case 如果，万一

case I forget, please remind me about it.

6. as/so long as 只要

long as you’re happy,it doesn’t matter what you do.
　 As long as it doesn't rain, we can go.