来自中国的托尼写道：
Hi! I am an English learner from China. I want to know the difference between when and while. Thanks!
你好！我是一名来自中国的英语学习者。我想知道when和while之间的区别。谢谢！
Answer:
回复：
Dear Tony,
亲爱的托尼：
This is a very interesting question, because both words are what grammar experts call "subordinating conjunctions." That means we use them to connect subordinating clauses to the main clause of a sentence. A subordinating clause is a part of a sentence that adds additional information to the main clause. Here is an example:
这个问题很有趣，因为这两个词都是语法专家所说的从属连词。这意味着我们使用它们将从句跟句子的主句连接到一起。从句是句子中用于补充附加信息的部分。举例如下：
I read Tony's email when I started work today.
我今天开始工作时读到了托尼的电子邮件。
The main clause is "I read Tony's email." The additional information is "when I started work today." The subordinating conjunction "when" tells us that the time of the second event was almost at the same time or very close to the time of the first event.
主句是“我读到了托尼的电子邮件”。附加信息是“我今天开始工作时”。从属连词when告诉我们，第二个事件发生的时间与第一个事件发生的时间几乎相同或非常接近。
Note that both these actions – "start" and "read" are single actions, using verbs in the simple past tense. That is an important thing to remember as we look for the difference between "when" and "while."
请注意这两个动作，开始和阅读都是单一动作，使用动词的一般过去时态。当我们寻找when和while之间的区别时，这是要记住的重要一点。
While
Now, look at this example:
现在我们来看这个例子：
While I was making lunch, the phone rang.
当我正在做午饭的时候，电话铃响了。
Here, the first action is in the present continuous tense. That means the action, making lunch, took place over a period of time. The main clause, "the phone rang" is in the simple past tense, and it is a single action taking place at a point in time.
在这里，第一个动作用过去进行时。这意味着做午饭这个动作发生在一段时间之内。主句“电话铃响了”用一般过去时，它是在某个时间点发生的单一动作。
When
The order of the events in a sentence with subordinating conjunctions can affect the choice of "when" or "while. If we change the order of our example above, we get:
在具有从属连词的句子中，事件发生的顺序可能会影响到when或是while的选择。如果我们更改上面例句的顺序，则会得到：
When the phone rang, I was making lunch.
当电话铃响的时候，我正在做午饭。
Here, the conjunction "when" is in the clause with the single action, "the phone rang."
在这里，when这个连词用在具有“电话铃响了”这个单一动作的从句中。
So as a general rule, you should use "while" in a clause with a continuous action, using a verb in a continuous tense. Use "when" in a clause with a single action, using a simple past or present tense.
所以作为一般规则，我们应该在带有连续动作的从句中使用while，动词用进行时态。在具有单一动作的从句中使用when，动词用一般过去时或现在时。
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以上就是本期名师答疑的全部内容。
I'm Jill Robbins.
我是吉尔·罗宾斯。(51VOA.COM原创翻译，请勿转载，违者必究！)