赖世雄教你学英语语法
虚拟语气
5-5：if
if=in case(that)，on condition that,provided(that),suppose (that),supposing (that)，so long as（只要），as long as（只要），此类连接词通常只用在表纯条件的虚拟语气中。换言之，其引导的从句时态均为现在时。
例：if it is fine, we will start to do it.
（如果天气好，我们就开始着手做这件事。）
in case he comes, let me know.= in case he should come, let me know.
（如果他来了，让我知道一下。）
i will undertake it on condition that you bear the expenses.
（如果是你出钱，这件事我就做。）
i will pardon him provided (that) he acknowledges his mistake.
（如果他认错，我会原谅他。）
suppose/supposing i meet him, what shall i tell him?
（要是我遇见他，要跟他说什么呢？）
any book will do, as long as it is interesting.
（哪本书都可以，只要有趣就好。）
注意
in case+(that)从句 万一……
in case of+名词 万一……
例：in case an accident happens, don't panic.
= in case of an accident, don't panic.
（万一有意外发生，不要惊慌。）