When / While / As

Also see past continuous tense.

We use when, while and as to talk about situations or actions that occur simultaneously.

1. They can be used to introduce a longer action or situation, which was / is going on when another situation occurred / occurs. As I was sleeping, the door bell rang.
While you were studying, your friend called you.
Note: The main clause and as / while clauses can be in reversed order.

The doorbell rang as I was sleeping.
Your friend called you while you were studying.


Continuous tense is preferred for the longer action or situation (was eating / are walking) however note that we can use “as and while” with a simple tense with a state verb. (sit, grow, be)

As I was at home, the postman came.

2. We prefer while to talk about two simultaneous actions that go / went on together.

While I was a taking shower, my mother was cleaning the attic.
My mother was cleaning the attic while I was taking a shower.

Note: we can also use simple tenses for the same meaning.

While I took a shower, my mother cleaned the attic.

3. We prefer as to talk about two things that change together in time.

As you eat more, you will gain more weight.
As you study more, you will get better grades.

4. We use when to talk about phases of life.

When you were a kid, you used to be so shy. (not while or as)

5. We prefer (just) as to talk about two consecutive events or actions that occurred simultaneously.

As he opened the drawer, he took out an old photo.
Just as my father came in, the phone rang.

6. We use reductions with when and while.

Don’t forget to take a map with you when going camping.
Tell me when ready.
While a student, I used to live with me family.

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