VOA一分鐘英語：辨析連詞 when 和 if

在陳述事實和描述重復性的動作時，連詞 “when” 和 “if” 都適用于一般現(xiàn)在時的句子中。但使用 “when” 時，句意卻和使用 “if” 時不同。哪個詞用來引導未知的、假設的情況？哪個詞引導確定會發(fā)生的事情？
 
Hi, I'm Roy and today I'm going to tell you the difference between when and if.
Firstly, you can use when or if with the present simple when it is a fact, or a repeated action.
If or when you put water in the freezer, it becomes ice.
We use if for unknown or possible situations.
If it rains today, I'll take my umbrella.
We use when to say we are certain something is going to happen in the future.
When I go home, I'll watch a film.
Compare these two sentences:
If I eat breakfast today, I'll have toast.
I might not eat breakfast.
When I eat breakfast today, I'll have toast.
I will eat breakfast.
Anyway, that's everything for today. I've got go because I'm hungry. If I don't eat breakfast, I get grumpy.
Bye.
 
用法總結(jié)
1 在陳述事實或描述重復性動作時，“when” 和 “if” 都適用于一般現(xiàn)在時的句子里。
When I go home, I have dinner.
If I go home, I have dinner.
 
2 我們用 “if（如果）” 來描述未知的或可能發(fā)生的情況。
If it snows this year, I'll go skiing.
If I see your dad, I'll say hello.
 
3 我們用 “when（當……時）” 來談論確定未來會發(fā)生的事情。
When I graduate, I'll get a job.
When I get home, I'll watch a film.