Keep the key until Friday describes continued possession. Return it by five sets a deadline: returning it earlier is allowed, and five is the latest time.
The idea
Use until for a state or activity continuing up to a time. Use by for completion no later than a time. Not…until blocks an action before the named point: do not remove the clamps while the glue is wet.
Examples
- I'll keep the key until Friday.
- Please return the key by five.
- We waited until the rain eased.
- The reception desk is staffed until six.
- Send the form by Wednesday.
- Don't remove the clamps until the glue is dry.
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Watch out
By five does not mean exactly five. Before five excludes five itself, while by five includes that deadline. In future until-clauses use a present form: until the glue is dry.
Try it yourself
Five is the latest acceptable return time. Please return the key ___ five. (by / until)
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by
By five gives the latest acceptable return time. The key can be returned earlier; until would describe something continuing.
Staff work continuously up to six. The reception desk is staffed ___ six. (until / by)
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until
Until six describes continuous staffing up to six. By six would instead set a latest time for a situation to be established.
Don't remove the clamps until the glue is dry. According to the instruction, may you remove the clamps while the glue is wet? (No. / Yes.)
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No.
No follows the instruction: removal is forbidden while the glue is still wet. Not…until sets the earliest permitted point.
Practice round
Answer questions and rebuild English sentences to practise. Your score is shown.
Five is the latest acceptable return time. Please return the key ___ five. (by / until)
Staff work continuously up to six. The reception desk is staffed ___ six. (until / by)
Don't remove the clamps until the glue is dry. According to the instruction, may you remove the clamps while the glue is wet? (No. / Yes.)
Tap the words in the right order.
Tap the words in the right order.
Tap the words in the right order.
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Write a note with one availability period and one return deadline. Use until for the continuing period and by for the deadline, then explain whether an earlier return is acceptable.