English — Time conjunctions
Words like when, while, before, after, until, since and as soon as join two clauses and say when the action happens. The key rule: in a clause about the future, use the present tense, not will — I'll call you when I arrive, not when I will arrive.
How it works
The time clause can come first or second: When it rains, we stay in = We stay in when it rains. When talking about the future, normally use a present form rather than will in the time clause: As soon as she calls, I'll leave. The main clause can use will, another future construction or an imperative. To stress that an action will be finished first, use the present perfect after after, once or when: After I've eaten, I'll help you. After by the time with future reference, use the present simple: By the time you arrive, I'll have left. With as you often stress two things happening together: As I left, it started to snow.
Examples
| Conjunction | Use and tense | Example |
|---|---|---|
| when | at the time that; use the present for the future | I'll call you when I arrive. |
| while | during the same time; often with a continuous tense | She read while I was cooking. |
| as | just as two things happen together | As I opened the door, the phone rang. |
| before / after | one action earlier / later than another | Wash your hands before you eat. We left after it stopped. |
| until / till | up to the moment when something happens | Wait here until the rain stops. |
| since | from a past point until now; with the present perfect | I've lived here since I was ten. |
| as soon as | immediately when; present for the future | Call me as soon as you get home. |
| by the time | before another moment; often with the past perfect | By the time we arrived, the film had started. |
Good to know
The most common mistake is putting will in the time clause: not I'll call you when I will arrive, but I'll call you when I arrive. The same holds after as soon as, before, after, until and by the time: As soon as it stops raining, we'll go — never As soon as it will stop raining.