These questions ask you to match a time expression with at, on, in or no preposition. First classify the time phrase, then check whether the sentence describes an exact point, a broad period or a future point measured from now.
Classify the time expression
Think from the smallest point outward. At marks a clock time or another fixed point: the doors open at 7:15, and birds settle at sunset. On marks a named day or a complete date: the class meets on Wednesday, and the pass expires on 14 February. In holds a broader period: flowers appear in April, the bridge opened in 2006, and the lake freezes in winter. For a general part of the day, use in the morning, in the afternoon or in the evening, but the fixed general expression is at night.
| Signal | Choice and example |
|---|---|
| Clock time, noon, midnight, sunrise or sunset | Use at: at 6:45, at noon. |
| Weekday, full date or named day plus part of day | Use on: on Saturday, on 3 May, on Tuesday evening. |
| Month, year, season, century or general daytime period | Use in: in October, in 2012, in spring, in the morning. |
| General night period | Use the fixed phrase at night. |
| Last, next, this or every before a time noun | Use no preposition: every Friday, this afternoon. |
| A period counted forward from the present | Use in: The parcel will arrive in three days. |
| Festival period versus its named single day | Use at for the festival period, but on when Day is part of the name: at Easter, on Easter Day. |
Common traps
| Tempting route | How to reject it |
|---|---|
| Using by for an event scheduled at an exact clock time | By creates a deadline and permits an earlier time. Choose at when the event begins at that precise clock reading. |
| Using in because a date contains a month | A month alone takes in, but a day number turns the phrase into a full date, which takes on. |
| Using in before a weekday morning or evening | The named day controls the whole phrase, so keep on even though a general morning or evening takes in. |
| Adding on before next or every | These determiners already attach directly to the time noun. Remove the preposition rather than treating the phrase like an ordinary weekday. |
| Treating a festival period and its named Day alike | Ask whether the meaning covers the holiday period or one calendar day. The period takes at; the name ending in Day takes on. |
Try it
The clinic is scheduled to reopen specifically on Tuesday, not earlier. Which sentence uses the standard weekday preposition?
- The clinic reopens at Tuesday.
- The clinic reopens in Tuesday.
- The clinic reopens on Tuesday.
- The clinic reopens by Tuesday.
Select all that apply: which statements correctly use at, on or in for seasons and longer periods?
- Many swallows migrate on winter.
- The valley is quiet in winter.
- The device was invented at the nineteenth century.
- Rail travel expanded in the nineteenth century.
It is 2.00 now, and the train leaves at 2.20. Complete with either the in construction or an equivalent from-now phrase; write twenty as a word or digits: The train leaves ___