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as, when and 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.

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 ‘state’ verb like sit, lie, or grow.

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

We can also describe situations like these by using when to introduce the shorter action or event. As and while cannot be used in this way.

  • When the telephone rang I was having a bath. (not As/While the telephone rang …)
  • When the burglar broke into the house, they were playing cards.

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.
  • Jack 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.
  • Emily always arrives just as I start work.

(Just) when is also possible.

  • I thought of it just when you opened your mouth.

Future reference​

As with other time conjunctions, we use present tenses with as, when and while when talking about the future.

  • As you get used to the work you’ll find it quite easy.
  • I’ll wash some clothes while you’re out.
  • We’ll feel a lot better when we’re lying on the beach next week.

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. This is rather formal.

  • 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 …)
note

For other uses of as, when and while, search the Index.