When we talk about something that happened in the past (or which will happen in the future), we can use the words “when”, “while”, “as” and “during”.
Here are some rules to help you use these words correctly.
For background situations and activities
Use ”when”, ”while” and ”as” to introduce a background situation or activity. Usually we use the past continuous tense to talk about this background situation, but you can also use the past simple tense (especially after “as).
Shorter and longer background activities
We use ”when” to talk about shorter actions.
When two longer situations or activities happen at the same time, we usually use ”while” rather than ”when”.
Talking about the future
When you use words like ”when”, ”as”, ”before”, ”after” etc to refer to a future action or situation, use the present tense – not a future form. (”When he finishes school” and not ”when he will finish school”.)
For changing situations
We use ”as” to talk about two situations that are changing at the same time.
For actions happening at the same time or immediately after
We can use ”just as” or ”just when” (not ”just while”) when one action happens at the same time or immediately after another.
We use ”during” with a noun to talk about when something happened. We don’t use it with a number (NOT ”during four weeks”) because we use ”for” to talk about the length of time.
We also use ”during” to emphasise the duration of something. (”It snowed during the winter” – either throughout the whole of the winter, or at some time in the winter). Remember: you still need a noun after ”during”.
When, While, As, During
Choose the correct answer.