At, In and On are commonly confused because they are used in similar situations – mostly to demonstrate time and place. These notes will help you to identify the different uses of these prepositions, and to use them correctly.

Describing Time

At, in and on are used to describe different points in time.

at describes a specific time: Let’s meet at 12.15.
in describes a period of time: Let’s meet in four hours.
on describes a days and specific dates: Let’s meet on Thursday.

The specific time of at can be any defined moment in time, either a clock time or a time defined by something more general, such as dinner time: Let’s talk at dinnertime.

The period of time for in could be minutes, hours, days, months, years or more – as long as the event happens within a larger time period. It is therefore most common for time expressions with units of time. It can also refer to general areas of time, such as mornings and afternoon: Let’s meet in the afternoon.

On can refer to periods of time on a specific day or date, when we want to show it happens on a specific day or date: Let’s meet on Tuesday morning.

These examples should help demonstrate the differences:

At (specific time)	In (period of time)	On (specific day/date)
We will watch a film at 3pm.	We will watch a film in the afternoon.	We will watch a film on Tuesday.
Jim ate at lunchtime.	Jim ate in the afternoon.	Jim ate on Monday afternoon.
The party starts at 10pm.	The party starts in an hour.	The party is on the 1^st of December.
Water the plants at noon.	Water the plants in summer.	Water the plants on the 2^nd day of each week.
Do you think it will be raining at 5 o’clock?	Do you think it will rain in the night?	Do you think it will rain on the day of the festival?

Fixed time expressions using at

Some fixed expressions use at to show general periods of time or specific dates. These should be learnt separately, as exceptions:

at night: They only come out at night.
at the weekend: What are you doing at the weekend?
at the same time: I can sing and dance at the same time.
at present: He doesn’t know the answer at present.
at Christmas/Easter: Will you visit your parents at Christmas?

Last, this, next, every

When we use last, this, next or every to describe time, we do not need at, in or on.

I visited Brighton last summer.
She brushes her teeth every night.

Describing Location

At, in and on can describe different locations.

at describes an exact/specific point.
in describes a point within a larger area
on describes a point on top of a surface

When we use these prepositions to describe the same location, they give us specific details about the location. This is mostly possible with at and in, as the use of on requires a surface.

Meet me at the restaurant. (At this location.)
Meet me in the restaurant. (Inside the building.)
Meet me on the restaurant roof. (On top of the building.)

Look at the following examples to compare the different uses:

At (specific point)	In (point within an area)	On (point on a surface)
Turn right at the lights.	Drive in the second lane.	Don’t drive on the side of the road.
There’s someone at the door.	There’s someone in the house.	There’s someone on the floor.
Write your name at the top of the form.	Write your name in the empty space.	Write your name on the paper.
Ask for me at the front desk.	Ask for me in the reception area.	Ask for whatever is on the menu.

There are many fixed expressions that do not stick to these rules, however, so be careful to learn these. These examples from at refer to being in a general area, but require at:

at home: I’ll do the work at home.
at work: I’m at work all day.
at school: I left my book at school.
at university: I am studying at Brighton university.

In often describes specific, smaller areas, such as inside vehicles, or large areas such as books, or the sky. For example:

in a taxi: I left my umbrella in the taxi.
in a lift: I met my wife in a lift.
in the newspaper: I read about the new school in the newspaper.

On is often used in fixed expressions describe using transport (including using animals as transport), or for broadcast media, and for some directions:

on a bus: I’ll arrive on the bus.
on an elephant: We went through the mountain on an elephant.

(also on a train, on a plane, on a ship, on a bike etc.)