Hello

Thank you for your clear explanation every time.
Now would you help me with this?
How to use an article is very difficult. Especially to choose a definite article or an indefinite article is so.

Would you take a look at the following sentences?

#1 What were you doing when the earthquake happened last night?
#2 What were you doing when an earthquake happened last night?
#3 What were you doing when we had an earthquake last night?
#4 What were you doing when we had the earthquake last night?

I wonder which I should choose "a" or "the." Does the way of choosing the article change whether the person who are asked a question know the earthquake last night itself? Or how to change depends on the speaker's mind?

I suppose we usually choose "a/an" for the things which is not specific. But I'm not sure in this situation.

I'll be happy to have some guidance.
Thank you.

# 1 is correct. We assume that both the speaker and the hearer knew of and probably experienced the earthquake. "The earthquake" is correct.

We know this because of "last night," which pinpoints the time of the earthquake. The speaker wants to know what the hearer was in the middle of doing at the time – a very short time – that the earthquake occurred.

#1 and # 4 contain "the." However, # 4 with "had" is incorrect. It's incorrect idiomatically. "Have an earthquake" would mean "experience an earthquake," and in this case, "have" would be an action verb and need –ing: "What were you doing when we were having the earthquake?" This would indicate that the speaker wants to know what the hearer was doing all during the earthquake, and that is not likely; the speaker most probably wants to know what the hearer was in the middle of doing at the moment that the earthquake struck.
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You are correct in your statement that generally, we use "a/an" for something that is not specific. In this case, however, the earthquake is very specific: it's the earthquake that the speaker and the hearer, as well as many others, experienced.

Rachel

Dear Rachel

Thank you for your helpful explanation. I understood I should choose "the" in this case.

But there is what I want to confirm I understand precisely or not.
If #4 is used -ing form like "What were you doing when we were having the earthquake?" , it will become grammatically correct but it is not likely to be asked. Do you mean that? Does "when we were having he earthquake " mean a long period the earthquake began and end and not at a certain moment?

I'm sorry I'm not sure I get what you said precisely.

Thank you.

Yes. "What were you doing when we were having the earthquake" would ask about your activity all during the earthquake.
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Some sentences that might express what you were in the middle of doing at the moment the earthquake struck:

"¢ What were you doing when the earthquake began?
"¢ What were you doing when the earthquake struck?

Some sentences to express what you did as soon as (immediately after) the earthquake struck, as soon as you realized it:

"¢ What did you do when the earthquake began?
"¢ What did you do when the earthquake struck?

Some sentences that express your activity that went on simultaneously with the earthquake:

"¢ What were you doing while/ when the earthquake was happening?
"¢ What were you doing while/ when we were having the earthquake?
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Hope this helps. Please feel free to write more, or again.

Rachel

Dear Rachel
Thank you so much for your kind explanation. May I ask more?

Reading your examples " What did you do when the earthquake began?" and "What did you do when the earthquake struck?", I came to know I should change the expression according to the moment what I ask.

If I want to ask about the ongoing-action at the moment when the earthquake just
began and not after the moment , can I use the following expression?
The answer might be " I was watching TV then."

1) What were you doing when the earthquake struck (/ began) last night?
2) What were you doing when the earthquake happened last night?

Plus,in this case can I imply the moment " when the earthquake began" by using " when we had the earthquake last night" like this?
3) What were you doing when we had the earthquake last night?

(I know you said I should use "when we were having the earthquake " for another meaning.)
I'm sorry I ask a little confusing question.

Thank you.

No. Even if you say "when we had the earthquake," it appears as though you are talking about the entire duration of the earthquake.

If you want to use "when we had the earthquake," use it this way:

"¢ What did you do when we had the earthquake?

This would mean:

What was the activity / were the activities that you did all during the time that the earthquake was happening.

In addition, the earthquake in this case probably took place at a more distant past.

A conversation could be like this:

A: I am so dependent on electricity! When our electricity goes off, I can't do my work. I need my computer for all my work, which I do at home.

B: What did you do when we had the earthquake last year?

A: I became very anxious. I couldn't do my work for a week, the whole week we didn't have electricity.

B: You should get a laptop with a long-life battery.

Rachel