VOA一分鐘英語：In case 還是 if？

“In case（以防）” 和 “if（如果）” 都可以用來談?wù)?“一件事情發(fā)生在特定的條件或情況下”，但兩者的用法不同。
 
Hi, everyone! I'm James. We're going to look at the difference between in case and if in today's English In A Minute.
Look at these examples:
1 I'll call you if I need help with my homework.
2 I'll call you in case I need help with my homework.
In the example with if, it means that I might call you in the future, but it depends if I need help or not. The second sentence with in case means I'm going to call you before I do my homework to prevent any problems.
Let's take a look at another example:
1 I'll take an umbrella in case it rains.
2 I'll take an umbrella if it rains.
Just like in our first example, in case means I'm going to take my umbrella anyway to prevent any problems. But in the example with if, this means that you only take an umbrella because it is raining when you leave.
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用法總結(jié)
1 當我們想談?wù)?“為以后可能發(fā)生的事情或后果采取預(yù)防措施” 時，用 “in case”，表示 “以防，免得”。換言之：做事件 A 是為了防備事件 B 的發(fā)生。 
I'll call you in case I need help with my homework.
I'll take an umbrella in case it rains.
 
2 我們用 “if” 談?wù)?“如果特定的條件或情況已發(fā)生，則針對這個情況采取相應(yīng)的行動”。換言之：只有事件 B 發(fā)生了，才會做事件 A。
I'll call you if I need help with my homework.
I'll take an umbrella if it rains.