The English prepositions in, on, and at are some of the most common words in our language, but they can easily get mixed up. Confusion can arise because not only are they all prepositions of place, but they’re also all prepositions of time; being prepositions of both time and place can make these two-letter words difficult to use.
In this guide, we explain how to use in, on, and at. We discuss the rules for each as prepositions of both time and place and share some examples of in, on, and at sentences. Let’s start with reviewing how English prepositions work in general.
English prepositions: in, on, and at
In English, prepositions are a type of word class that shows relationships between other words in a sentence. Prepositions can describe when something happened (“in the morning”) or where something happened (“at the office”), as well as explain connections (“mother of three puppies”) or give extra details (“a movie with subtitles”).
Prepositions are always followed by a noun. This noun acts as the object of a preposition because it is what the preposition refers to. Combining the preposition and the object of the preposition creates a prepositional phrase, which also includes any adjectives or determiners the noun uses.
For example, the prepositional phrase “behind the tall tree” includes the preposition behind, the object of the preposition tree, the article the, and the adjective tall.
There are four types of prepositions:
- prepositions of time
- prepositions of place
- prepositions of direction
- prepositions of space
What makes in, on, and at challenging is that they are prepositions of both time and place. That means each one has at least two different meanings, and all of those meanings can easily get mixed up. To make things more difficult, in, on, and at are not interchangeable—you have to learn all the usages for each to avoid confusing them.
English preposition: in
In: preposition of time
As a preposition of time, in is used with the following words and concepts:
- instant and moment
- seconds, minutes, and hours
- amounts of days
- months
- seasons
- years
- groups of years (decades, centuries, etc.)
- the past, present, and future
- times of day: morning, afternoon, evening
- night (specific time)
In: preposition of time examples
- in a few moments
- in a couple of minutes
- in five days
- in August
- in the summer
- in 3200 BCE
- in less than a decade
- in the future
- in the evening
- in the middle of the night
In: preposition of place
As a preposition of place, in is used with the following words and elements:
- general locations
- locations within large places like cities, countries, and continents
- class
- the sky and atmosphere
- outer space
In: preposition of place examples
- in the dining room
- in Tanzania
- in my third class
- in the blue sky
- in the farthest reaches of space
English preposition: on
On: preposition of time
As a preposition of time, on is used with the following words and concepts:
- days of the week
- times of day used with days of the week
- yearly events like birthdays and holidays
- specific dates
- weekend (American English)
On: preposition of time examples
- on Tuesday
- on Saturday evening
- on our anniversary
- on Lunar New Year
- on January 19 (on the 19th of January)
- on the weekend
On: preposition of place
As a preposition of place, on is used for the following words and ideas:
- things on the surface of something else (tables, walls, etc.)
- locations near a body of water
- mountains
- floors of a building
- corners
- streets
- planets
On: preposition of place examples
- on the ceiling
- on the Amazon River
- on Mount Hood
- on the fifth floor
- on Main Street
- on Mars
English preposition: at
At: preposition of time
As a preposition of time, at is used for:
- clock times
- mealtimes
- times of day: dawn, dusk
- night (unspecific time)
- weekend (British English)
At: preposition of time examples
- at 8 p.m.
- at dinner
- at dusk
- at night
- at the weekend
At: preposition of place
As a preposition of place, at is used with these categories:
- precise locations
- events
- specific addresses
At: preposition of place examples
- at the dinner table
- at the homecoming dance
- at 720 Main Street
When not to use in, on, or at
Don’t use with next and a time
When using next as an adjective before a time, you can omit in, on, or at. The sentence will work without a preposition of time.
Don’t use the last and a specific time
Similarly, you can also omit in, on, or at when using last as an adjective before a time period, as long as you are talking about a specific time.
However, if you’re using last with an unspecified time, you still need a preposition. Typically, if the phrase with last uses an article or other determiner, it is unspecific and should include in, on, or at.
Keep in mind that the phrase “at last” acts as an adverb, so these rules for prepositions don’t apply to it.
Last night, at our last meeting, we picked a group name at last!
In, on, and at FAQs
What are English prepositions?
In English, prepositions are a type of word class that shows relationships between other words in a sentence. Prepositions can describe when something happened (“in the morning”) or where something happened (“at the office”), as well as explain connections (“mother of three puppies”) or give extra details (“a movie with subtitles”).
What type of prepositions are in, on, and at?
The words in, on, and at are prepositions of both time and place. That means each one has at least two different meanings, and all of those meanings can easily get mixed up.
Can in, on, and at be used interchangeably?
The prepositions in, on, and at are not interchangeable. Each has its own rules and suggested usages. However, sometimes the same words or sentence can use different prepositions, although the meaning will change slightly.
