as, when & while (simultaneous events)

To talk about actions or situations that take place at the same time, we can use as, when or while. There are some differences.

'backgrounds': as, when or while

We can use all three words to introduce a longer 'background' action or situation, which is/was going on when something else happens/happened.

As I was walking down the street I saw Joe driving a Porsche.

The telephone always rings when you are having a bath.

While they were playing cards, somebody broke into the house. As-, when- and while-clauses can go at the beginning or end of sentences, but os-clauses usually introduce less important information, and most often go at the beginning.

A progressive tense is usually used for the longer 'background' action or situation (was walking; are having; were playing). But as and while can be used with a simple tense, especially with a verb like sit, lie, or grow which refers to a continuous action or state.

As I sat reading the paper, the door burst open.

simultaneous long actions: while; as

We usually use while to say that two longer actions or situations go /went on at the same time. We can use progressive or simple tenses.

While you were reading the paper, I was working.

John cooked supper while I watched TV. As is used (with simple tenses) to talk about two situations which develop or change together.

As I get older I get more optimistic. We prefer when to refer to ages and periods of life.

When I was a child we lived in London, (not As/While I was a child...)

His parents died when he was twelve, (not ... while he was twelve.)

simultaneous short actions: (just) as; (just) when

We usually use (just) as to say that two short actions or events happen/ happened at the same time.

As I opened my eyes I heard a strange voice.

Mary always arrives just as I start work. (Just) when is also possible.

7 thought of it just when you opened your mouth.

reduced clauses with when and while

It is often possible to leave out subject + be after when (especially when it means 'whenever'), and after while.

Don't forget to signal when turning right.

(=... when you are turning right.)
Climb when ready (=... when you are ready.)
While in Germany, he got to know a family of musicians

(= While he was...)