Page 199 - Advanced English Grammar in Use

A d v e r b i a l c l a u s e s o f t i m e ( 2 ) : a s , w h e n a n d
w h i l e

We can use as, when or while to mean 'during the time that...', to talk about something that is
or was happening when something else took place:
• As/When/While Dave was eating, the doorbell rang, or
• The doorbell rang, as/when/while Dave was eating.
The word whilst can also be used in this way, but is today considered rather literary.

We use when (not as or while):
• to talk about an event that takes place at the same time as some longer action or event
(described in the main clause):
• They were playing in the garden when they heard a scream.
• Dave was eating when the doorbell rang, (compare A)
• to talk about one event happening immediately after another:
• When the lights went out, I lit some candles.
• I knew there had been an accident when the police arrived.
• to talk about periods of our lives or periods of time past:
• His mother called him Robbie when he was a baby.
• to mean 'every time':
• I still feel tired when I wake up in the morning.
• When I turn on the TV, smoke comes out the back.

We use either as or when (not while):
• to talk about two short events that happen at the same moment, or if we want to emphasise
that two events that in fact occur one after the other happen almost at exactly the same time,
particularly if one causes the other:
• You'll see my house on the right as/when you cross the bridge.
• As/When the can is opened, the contents heat automatically.
• when we want to say that when one thing changes, another thing changes at the same time.
However, we prefer as to express this meaning:
• As the cheese matures, its flavour improves, (rather than When the cheese matures...)
• Her eyesight worsened as she grew older, (rather than ...when she grew older.)

We prefer while or as (rather than when):
»• to talk about two longer actions that go on at the same time:
» • I went shopping while/as Linda cleaned the house.
We use while (or when) rather than as if 'as' could also mean 'because':
• While you were playing golf, I went to the cinema. ('As you were playing golf...' could mean
'Because you were playing golf...')

Particularly in formal speech and writing, we can often leave out subject + be in clauses with
when and while if the main and subordinate clause refer to the same subject:
• The President was on holiday in Spain when told the news. (= when he was told)
• When in doubt about taking the medicine, consult your doctor. (= when you are in doubt)
• Mr Thomas found the coins while digging in his back garden. (= while he was digging)
• While on the boat, always wear a lifejacket. (= while you are on the boat)

Adverbial time clauses (1) = As: giving reasons =