As, when and while

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When, while and as can be used to talk about actions or situations that take place at the same time. There are some differences.

When and while

We can use when and while to introduce a longer background action or situation, which is/was going on when something else happens/happened. Note that we usually use a continuous tense for the longer background action or situation.

When- and while-clauses can go at the beginning or end of sentences.

When can mean at the same time as something else.

When and while: differences

When is used to refer to ages and periods of life. As and while are not possible in this.


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

When and while in reduced clauses

It is often possible to drop subject + be after when and while.


To talk about two short actions or situations that happen/happened at the same time, we usually use as. When is also possible.

As can also be used to talk about two situations that develop together. We normally use simple tenses.

As can be used to introduce a longer background action or situation.


Can you use as, when and while correctly? Test your understanding of these conjunctions with this exercise.

See Also

As, since, because and for
A lot of, lots of, plenty of, a great deal of
Below and under
Above and over
Both and both of
As if and as though
Fairly, quite, pretty and rather
Finally, at last, in the end and at the end
No and none