English Prepositions: “In,” “On,” and “At”

Understanding Prepositions in English

The words in, on, and at are among the most frequently used prepositions in English, yet they are often confusing. The reason for this confusion is that these prepositions can function in two different ways—indicating both time and place. Since they serve dual purposes, it’s easy to misuse them.

This guide provides a clear explanation of how to use in, on, and at correctly. We’ll outline the rules for each when used as prepositions of time and place and provide practical examples. But first, let’s briefly discuss how prepositions work in English.

What Are English Prepositions?

Prepositions are words that connect different parts of a sentence, establishing relationships between them. They help indicate time (in the morning), location (at the office), relationships (mother of three puppies), and additional details (a movie with subtitles).

A preposition is always followed by a noun, which serves as its object. Together, they form a prepositional phrase, which may also include adjectives or determiners. For example, in the phrase behind the tall tree, behind is the preposition, tree is the object, the is the determiner, and tall is an adjective.

There are four main types of prepositions:

Prepositions of time
Prepositions of place
Prepositions of direction
Prepositions of space
The challenge with in, on, and at is that they fall into both the time and place categories. Because they each have multiple meanings, they are not interchangeable, making it essential to understand their correct usage.

How to Use In, On, and At

Using In
In as a Preposition of Time

The preposition in is used when referring to:

Moments or brief periods (in a moment, in an instant)
Small time units like seconds, minutes, and hours (in two minutes)
Periods spanning multiple days (in five days)
Months (in August), seasons (in summer), and years (in 2020)
Extended timeframes such as decades and centuries (in the 18th century)
Broad time references (in the future, in the morning)

Examples:

I’ll call you in a few minutes.
We met in December.
It happened in the 19th century.
In as a Preposition of Place

In is used to describe locations that are:

General (in the city, in a room)
Inside large areas like cities, countries, and continents (in Africa, in New York)
Within groups (in my third class)
In atmospheric or cosmic spaces (in the sky, in space)

Examples:

She lives in Canada.
The stars shine brightly in the sky.

Using On
On as a Preposition of Time

The preposition on is used with:

Days of the week (on Monday)
Specific dates (on July 4th, on January 1st)
Holidays and annual events (on Christmas, on my birthday)
Weekend references (in American English)

Examples:

I have a meeting on Wednesday.
They got married on Valentine’s Day.
On as a Preposition of Place

On is used to refer to:

Surfaces (on the table, on the wall)
Areas near bodies of water (on the lake)
Locations on mountains (on Mount Everest)
Floors of buildings (on the third floor)
Streets and planets (on Main Street, on Mars)

Examples:

The book is on the desk.
They built a house on the hill.
Using At
At as a Preposition of Time

The preposition at is used for:

Exact times (at 5 p.m.)
Mealtimes (at breakfast, at dinner)
Specific points of the day (at dawn, at dusk)
The night (without a specific time) (at night)
Weekend references (in British English)

Examples:

We’ll meet at noon.
I like to read at night.
At as a Preposition of Place

At is used when talking about:

Precise locations (at the door, at the airport)
Events (at the concert, at the conference)
Specific addresses (at 123 Main Street)

Examples:

She is at the bus stop.
We had dinner at a fancy restaurant.

When Not to Use In, On, or At

Avoid prepositions with “next” and a time reference
If next is used before a time expression, you don’t need in, on, or at.
❌ Let’s meet on next Friday.
✅ Let’s meet next Friday.
Avoid prepositions with “last” when referring to a specific time
When last is used to describe a definite time, prepositions should be omitted.
❌ We stayed home at last night.
✅ We stayed home last night.
❌ They went on vacation in last June.
✅ They went on vacation last June.
However, when last refers to an unspecified time, a preposition is needed.

✅ On the last day of school
✅ At our last meeting
Additionally, the phrase at last is an adverb, so prepositions are not required in that context.

At last, we found the missing keys!

FAQs About In, On, and At

What are prepositions in English?
Prepositions are words that establish relationships between parts of a sentence. They help describe time (in the morning), location (at the station), connections (father of two kids), and additional details (a book with illustrations).

How are in, on, and at categorized?
These words function as both prepositions of time and place. Since they each have distinct uses, learning their differences is essential.

Can in, on, and at be used interchangeably?
No, they cannot be swapped freely. Each has specific rules, and while some phrases allow for different prepositions with slight changes in meaning, using them incorrectly can lead to confusion.