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Unit 17
Prepositions of Time
In / On / At — when
Overview
Prepositions of time tell us when something happens. The three most important ones are in, on, and at — and each one is used for a different type of time expression.
Getting these right is essential for talking about schedules, habits, dates, and plans.
AT — Specific Clock Times & Fixed Expressions
| Use | Examples |
|---|---|
| Clock times | at 7 o'clock / at 9:30 / at midnight / at noon |
| Mealtimes | at breakfast / at lunch / at dinner |
| Fixed expressions | at the weekend / at night / at the moment / at Christmas / at Easter |
| Age | She got married at 25. / He retired at 60. |
ON — Days & Dates
| Use | Examples |
|---|---|
| Days of the week | on Monday / on Friday / on weekdays |
| Specific dates | on 14 March / on the 1st of January |
| Named days | on my birthday / on New Year's Day / on Christmas Day |
| Parts of a specific day | on Monday morning / on Friday night |
IN — Longer Periods
| Use | Examples |
|---|---|
| Months | in January / in March / in October |
| Seasons | in summer / in winter / in spring |
| Years | in 2024 / in 1990 / in 2001 |
| Decades / centuries | in the 1990s / in the 20th century |
| Parts of the day | in the morning / in the afternoon / in the evening |
| Periods of time | in an hour / in two weeks / in a few days |
Quick Reference: AT / ON / IN
| AT | ON | IN |
|---|---|---|
| at 6 o'clock | on Monday | in the morning |
| at night | on 5 April | in January |
| at the weekend | on my birthday | in 2020 |
| at Christmas | on New Year's Day | in summer |
| at the moment | on Friday evening | in the 1990s |
No Preposition Rule
- Never use in / on / at before this, last, next, every, each, one, some, any, all.
- ✅ I will call you next Monday. ❌ on next Monday
- ✅ We go swimming every summer. ❌ in every summer
- ✅ She arrived last night. ❌ at last night
At Night or In the Night?
- at night = during the night in general, as a habit: I don't drink coffee at night.
- in the night = at some point during one particular night: The baby woke up twice in the night.
- British: at the weekend · American: on the weekend. Both are correct.
Examples
Subject
Verb
Auxiliary
Object
Adjective
Adverb
Preposition
Hover over any word to see its role.
subjectThe filmverbstartsadverbat 8 p.m.
↳ "at" — clock time
subjectWeverbhaveobjecta testadverbon Friday
↳ "on" — a day
subjectMy birthdayverbisadverbin June
↳ "in" — a month
subjectIverbwill callobjectyouadverbin ten minutes
↳ "in" — after a period from now
subjectSheverbvisitsobjectusadverbevery summer
↳ no preposition before "every"
Common Mistakes
I will see you on next Friday.
→
I will see you next Friday.
Never use "on" before "next / last / this / every".
She was born in 14 May.
→
She was born on 14 May.
Specific dates → "on".
He always sleeps at the afternoon.
→
He always sleeps in the afternoon.
Parts of the day → "in" (except "at night").
We met at 2019.
→
We met in 2019.
Years → "in".
I'll be ready on an hour.
→
I'll be ready in an hour.
"In" = after a period of time.
She called me in midnight.
→
She called me at midnight.
"Midnight" → "at" (specific time point).
He was born on summer.
→
He was born in summer.
Seasons → "in".
The bus comes after 5 minutes.
→
The bus comes in 5 minutes.
"5 minutes from now" → in.