on

on — preposition

1. touching the top or outer side of something, or moving into that place.

1.prepositionA1
Definition

touching the top or outer side of something, or moving into that place.

Example

The keys are on the kitchen table beside Dad's newspaper.

on + surface noun

Lina dropped her wet towel on the chair by the window.

movement onto a surface

Common collocations
  • on the table
  • on the floor
  • on the chair
  • land on
  • put on
Synonyms
  • upon

    more formal and less common in everyday speech

  • onto

    used only for movement into contact, not for a static position

Antonyms
  • under

    in a lower position beneath something

  • off

    not touching or no longer on the surface

Grammar Patterns

on + surface/body-part noun

put/place/land + on + noun

Usage Note

The noun after 'on' is usually a physical surface or body part. Distinguish from sense 2: this sense is about simple position or movement into contact, while sense 2 often involves covering, wearing, or attachment.

Common Mistakes

The keys are in the table.
The keys are on the table.
use 'on' when something touches the surface.
Put your bag over the chair.
Put your bag on the chair.
'on' is the normal choice for resting on top of a surface.

2. spread across a surface, worn or carried by someone, or fixed to another thing.

2.prepositionA1
Definition

spread across a surface, worn or carried by someone, or fixed to another thing.

Example

Sophie wore a silver ring on her smallest finger.

wear + thing + on + body part

There was mud on the dog's paws after the river walk.

covering a surface

Common collocations
  • on your finger
  • on your lap
  • on the wall
  • on the radio
  • mud on
Synonyms
  • with

    can describe accompanying features ('a man with a hat'), but not direct surface contact in the same way

  • upon

    formal alternative in some writing, though less natural for clothing or machine parts

Antonyms
  • off

    removed from the body, surface, or object

Grammar Patterns

wear/have/carry + thing + on + noun

something + on + machine/body/surface noun

Usage Note

Common with clothes, body parts, surfaces, and parts of machines. Distinguish from sense 1: here the thing is often worn, hanging, covering, or attached rather than simply resting in a place.

Common Mistakes

She wore a ring in her finger.
She wore a ring on her finger.
use 'on' for something attached to a body part.
There was mud at his shoes.
There was mud on his shoes.
'on' shows that a substance covers the surface.

3. marking the day, date, or occasion when something happens.

3.prepositionA1
Definition

marking the day, date, or occasion when something happens.

Example

We always eat noodles on Friday nights after basketball practice.

on + day + part of day

Ken's visa ends on 30 June, so he must renew it.

on + date

Common collocations
  • on Monday
  • on Friday night
  • on my birthday
  • on 30 June
  • on national holidays
Synonyms
  • during

    works for longer periods, but not usually for exact days or dates

  • at

    used for clock times rather than days or dates

Grammar Patterns

on + day/date noun

on + day + part of day

on + special occasion noun

Usage Note

Use this sense with days, dates, and named occasions. Compare 'at' for clock times ('at six') and 'in' for months, years, and longer periods ('in June', 'in winter').

Common Mistakes

The meeting is in Monday.
The meeting is on Monday.
use 'on' with days.
Her birthday is at 12 May.
Her birthday is on 12 May.
dates take 'on', not 'at'.

4. marking the surface where words, numbers, or pictures appear.

4.prepositionA2
Definition

marking the surface where words, numbers, or pictures appear.

Example

Mia drew a red star on the corner of the map.

draw + on + surface

The nurse wrote Daniel's temperature on a paper bracelet.

write + on + surface

Common collocations
  • write on
  • print on
  • draw on
  • sign on
  • paint on

Grammar Patterns

write/print/draw/sign + on + surface noun

Usage Note

The noun after 'on' is the surface carrying the marks, such as paper, a wall, a sign, a page, or a screen. Distinguish from sense 2: in this sense, the important idea is that information or a picture appears there.

Common Mistakes

Please write your name in the form.
Please write your name on the form.
use 'on' for the surface that carries the writing.
The number is printed at the box.
The number is printed on the box.
'on' shows where the words or numbers appear.

5. marking the vehicle or other means a person uses to move from place to place.

5.prepositionA2
Definition

marking the vehicle or other means a person uses to move from place to place.

Example

We reached the lake on foot because the road was flooded.

fixed phrase: on foot

Nina reads comic books on the bus to school.

on + the + vehicle noun

Common collocations
  • on foot
  • on the bus
  • on the train
  • on horseback
  • on bikes
Synonyms
  • by

    names the travel method in a more general way: 'by bus', 'by train'

Grammar Patterns

on + the + vehicle noun

on foot

on horseback

on + plural vehicle noun

Usage Note

Use this sense for travel by bus, train, horse, bicycle, and in the fixed phrase 'on foot'. Compare 'by bus' or 'by train', which name the method more generally and not the experience of being on the vehicle.

Common Mistakes

We came by foot.
We came on foot.
'on foot' is the fixed phrase.
She read on bus.
She read on the bus.
with most vehicles in this sense, English normally needs the article.

6. showing that a person or thing is in a temporary state or going through a formal

6.prepositionB1
Definition

showing that a person or thing is in a temporary state or going through a formal or public process.

Example

The garage is on fire, so call the fire station.

be on + dangerous state

Several nurses stayed on duty through the stormy night.

be on + duty

Common collocations
  • on fire
  • on duty
  • on trial
  • on strike
  • on leave
Synonyms
  • under

    used in some nearby collocations such as 'under pressure' or 'under repair', but not with the same set of fixed phrases

Grammar Patterns

be on + state/process noun

go on strike

be on leave/trial/duty/fire

Usage Note

Usually appears in fixed phrases after 'be', 'go', or 'stay'. The noun after 'on' names the state or process itself, not the thing providing support. Distinguish from sense 15: sense 6 is about being in a condition or action ('on strike', 'on trial'), while sense 15 names what someone or something lives or runs on.

Common Mistakes

The nurses were in duty all night.
The nurses were on duty all night.
'on duty' is the fixed expression.
The workers made strike.
The workers went on strike.
English uses the pattern 'go on strike'.

7. used before a medium or instrument to show what something is recorded, broadcast

7.prepositionA2
Definition

used before a medium or instrument to show what something is recorded, broadcast, or played through.

Example

The interview was recorded on video for the school news website.

recorded on + medium

Lina heard the weather report on the radio before breakfast.

on the radio — broadcast medium

Common collocations
  • on video
  • on the radio
  • on film
  • on TV
  • on the violin
  • on the piano
Synonyms
  • via

    more formal and mostly for the medium, not for musical instruments

  • with

    can name an instrument or tool, but it does not sound as fixed as 'play on the piano'

Grammar Patterns

recorded on + medium noun

play + piece on + musical instrument

Usage Note

The noun after 'on' is usually a medium or instrument: radio, video, film, TV, piano, guitar. Distinguish from sense 4 (WRITING), which marks the surface where words or pictures appear.

Common Mistakes

I heard the news in the radio.
I heard the news on the radio.
English uses 'on' for broadcast media.
Mika played the song with the violin.
Mika played the song on the violin.
use 'on' before the instrument in this pattern.

8. used after a verb of contact to name the thing that hurts or injures you when yo

8.prepositionB2
Definition

used after a verb of contact to name the thing that hurts or injures you when you touch it.

Example

Noah banged his elbow on the bus door this morning.

bang + body part + on + object

Emma cut her finger on a broken jar in the sink.

cut + body part + on + sharp object

Common collocations
  • hit your head on
  • bang your elbow on
  • cut your finger on
  • scrape your knee on
  • bruise your shin on

Grammar Patterns

hit + body part + on + object

cut/scrape + body part + on + sharp object

Usage Note

Usually follows verbs such as hit, bang, cut, bruise, or scrape. The noun after 'on' is often a hard edge, rough surface, or sharp object.

Common Mistakes

Lina hit on the table her knee.
Lina hit her knee on the table.
put the injured body part before 'on + object'.
Marcus cut his hand by the broken glass.
Marcus cut his hand on the broken glass.
use 'on' for accidental injury from contact.

9. in the direction of a person, place, or target, especially when moving at it or

9.prepositionA2
Definition

in the direction of a person, place, or target, especially when moving at it or attacking it.

Example

Before dawn, the soldiers marched on the border town.

march on + place

The rebels opened fire on the bridge from the trees.

fire on + target

Common collocations
  • march on
  • move on
  • open fire on
  • turn on
  • set [someone] on
Synonyms
  • toward

    general direction word; less tied to attack and pressure than this sense

  • against

    often used for hostile action, but it does not cover forward movement toward a place

Antonyms
  • away from

    shows movement in the opposite direction

Grammar Patterns

verb of movement + on + place

verb of attack + on + target

Usage Note

Most common after verbs of attack or forward movement, such as march, fire, turn, or set. Distinguish from sense 1 (ABOVE), where 'on' describes physical contact with a surface.

Common Mistakes

The rebels opened fire to the bridge.
The rebels opened fire on the bridge.
the target of attack takes 'on' in this pattern.
The soldiers marched to on the town.
The soldiers marched on the town.
do not add 'to' before this use of 'on'.

10. about a particular subject, issue, or area of study.

10.prepositionB1
Definition

about a particular subject, issue, or area of study.

Example

Professor Lin gave a short talk on sea turtles.

talk on + topic

Maya needs your advice on the flat before signing.

advice on + matter

Common collocations
  • a book on
  • a talk on
  • advice on
  • an opinion on
  • a paper on
  • a discussion on
Synonyms
  • about

    the closest everyday equivalent

  • concerning

    more formal, especially in writing

Grammar Patterns

noun of communication + on + topic

book/paper/talk + on + subject

Usage Note

Common after nouns or verbs of speaking, writing, teaching, and thinking: book on, talk on, opinion on, advice on, lecture on. Distinguish from sense 12, which follows verbs of dependence or basis such as depend on or base on.

Common Mistakes

We had a discussion about on the budget.
We had a discussion on the budget.
use one preposition, not both.
She wrote a paper for climate change.
She wrote a paper on climate change.
after 'paper', 'book', or 'talk', 'on' marks the topic.

11. used after money words or spending verbs to name what the money is paying for.

11.prepositionA2
Definition

used after money words or spending verbs to name what the money is paying for.

Example

Maya spent all her birthday money on art paper.

spend money on + thing

Dad put a deposit on the blue van yesterday.

put a deposit on + purchase

Common collocations
  • spend money on
  • waste money on
  • save money on
  • put a deposit on
  • more on ... than on ...
Synonyms
  • for

    used with some payment verbs such as 'pay', but not with the fixed pattern 'spend money on'

  • toward

    used when money covers only part of a cost, not the whole spending target

Grammar Patterns

spend money on + thing

put a deposit on + purchase

Usage Note

Usually appears after spend, waste, save, or nouns such as money, cost, and deposit. The noun after 'on' is the item, service, or event that receives the payment.

Common Mistakes

Maya spent all her birthday money for art paper.
Maya spent all her birthday money on art paper.
'spend money' takes 'on' before the thing bought.
Dad put a deposit for the van.
Dad put a deposit on the van.
use 'on' after 'deposit' when naming the purchase.

12. used after verbs like depend, rely, or base to show the person, thing, or fact t

12.preposition
Definition

used after verbs like depend, rely, or base to show the person, thing, or fact that something needs or comes from.

Example

Saturday's match depends on the weather after lunch.

depend on + condition

The twins rely on their aunt for after-school care.

rely on + person

Common collocations
  • depend on
  • rely on
  • based on
  • rest on
  • hang on
  • hinge on
Synonyms
  • because of

    shows cause, but it does not express dependence or support as clearly as this sense

  • from

    can mark origin with some verbs, but not with fixed patterns such as 'depend on' or 'based on'

Grammar Patterns

depend on + condition/person

rely on + person/thing

base + noun + on + source

Usage Note

Common after depend, rely, base, rest, hang, and hinge. A following clause is often introduced by 'whether' or an -ing form, as in 'depends on whether it rains' or 'depends on Maya arriving early'.

Common Mistakes

The trip depends from the weather.
The trip depends on the weather.
'depend' takes 'on', not 'from'.
Our plan is based in last year's map.
Our plan is based on last year's map.
use 'on' when naming the source or basis.

13. used with a task, case, programme, or project to show that someone has a job or

13.preposition
Definition

used with a task, case, programme, or project to show that someone has a job or active role there.

Example

Marcus is on the airport case with two senior detectives.

be on + case for active involvement

Three nurses are on night duty during the holiday weekend.

on duty = assigned task

Common collocations
  • on duty
  • on the case
  • on the project
  • on the exchange program
Synonyms
  • involved in

    a fuller phrase that states participation more directly

  • working on

    common with projects and cases, but less natural with duties or programmes

  • taking part in

    best for events and activities rather than assigned tasks

Antonyms
  • off

    used for duties or schedules when someone is not assigned

  • out of

    used when someone is excluded from an activity or programme

Grammar Patterns

be on + case/duty/program

work on + project

stay on + story

Usage Note

Often follows verbs such as 'be', 'work', or 'stay'. The object is usually a task, duty, case, project, programme, or trip rather than a formal organization. Distinguish from sense 17, which is more about membership in an established group.

Common Mistakes

Marcus is in the airport case.
Marcus is on the airport case.
use 'on' for taking part in a case or task.
Nina worked in the museum project all summer.
Nina worked on the museum project all summer.
use 'on' with projects someone is involved in.

14. used before a wage, pension, allowance, or other source of money to show what so

14.preposition
Definition

used before a wage, pension, allowance, or other source of money to show what someone depends on in order to live.

Example

After the factory closed, the family lived on Mei's small salary.

live on + income source

Grandpa gets by on a farm pension and free meals.

Common collocations
  • live on a salary
  • get by on a pension
  • survive on one income
  • be on a scholarship
Synonyms
  • from

    a neutral source word, but it does not always imply dependence for living

  • off

    informal, especially in phrases like 'live off'

Grammar Patterns

live on + salary

survive on + income

be on + scholarship

Usage Note

Usually follows 'live', 'survive', 'get by', or 'be'. The object is a source of money such as a salary, pension, allowance, scholarship, or customer base, not food or fuel; compare sense 15.

Common Mistakes

The family lived from Mei's salary.
The family lived on Mei's salary.
'on' is the usual preposition for the money you depend on.
Rosa was in a music scholarship.
Rosa was on a music scholarship.
say 'on' when a scholarship supports you financially.

15. used before food, fuel, or medicine to show what keeps a person, animal, machine

15.prepositionB2
Definition

used before food, fuel, or medicine to show what keeps a person, animal, machine, or treatment going.

Example

The old bus runs on diesel from a farm station.

run on + fuel

Baby goats can live on milk for several weeks.

Common collocations
  • run on diesel
  • live on milk
  • be on antibiotics
  • feed on rice
Synonyms
  • with

    possible with some tools or fuels, but less idiomatic for diet or medicine

  • off

    informal, especially in phrases like 'live off the land'

Grammar Patterns

run on + fuel

feed on + food

be on + medicine/diet

Usage Note

Common after 'live', 'feed', 'run', 'work', or 'be'. The object names what provides nourishment, power, or treatment, so it can be food for living things, fuel for machines, or medicine for patients. Distinguish from sense 14, where the support is money.

Common Mistakes

The bus runs by diesel.
The bus runs on diesel.
use 'on' for the fuel that powers something.
Wild ducks feed from rice left in the fields.
Wild ducks feed on rice left in the fields.
'feed on' means eat something regularly.

16. used for a place beside a road, river, coast, wall, or similar line, often follo

16.prepositionB1
Definition

used for a place beside a road, river, coast, wall, or similar line, often following its side.

Example

The Chen family rented a small cabin on the river near Hualien.

on + river = beside it

A row of shops stands on both sides of the road.

on both sides of

Common collocations
  • on the river
  • on the beach
  • on the road
  • on the border
Synonyms
  • beside

    very close in meaning for nearby position

  • along

    emphasizes following the side or length of something

Antonyms
  • away from

    shows separation from the road, river, coast, or other line

Grammar Patterns

on + river/coast/beach

on + road/path

on + border

Usage Note

The object is usually a road, river, coast, beach, path, wall, or border, and the subject is often a place located beside it. If one thing is touching the surface of another, use sense 1 or 2 instead.

Common Mistakes

Their cabin is in the river near Hualien.
Their cabin is on the river near Hualien.
here 'on' means beside the river, not inside it.
Several farms are in the French border.
Several farms lie on the French border.
use 'on' for places along a border line.

17. used with a committee, team, jury, or similar group to show that someone belongs

17.prepositionC1
Definition

used with a committee, team, jury, or similar group to show that someone belongs to it as a member.

Example

Aiko serves on the city arts committee this year.

serve on + committee

Two parents sit on the school board this year.

sit on + board

Common collocations
  • serve on a committee
  • sit on the board
  • on the jury
  • on the team
Synonyms
  • in

    more neutral for belonging to organizations, but less idiomatic with committees and juries

  • part of

    an explicit phrase for membership, though less compact

Antonyms
  • outside

    shows that someone is not included in the group

Grammar Patterns

serve on + committee

sit on + board/panel

be on + jury/team

Usage Note

Frequently used after 'be', 'serve', and 'sit'. The object is normally a committee, board, panel, jury, or team with recognized membership. Distinguish from sense 13, which can describe temporary involvement in a task or project.

Common Mistakes

Aiko serves in the city arts committee.
Aiko serves on the city arts committee.
committees and boards usually take 'on'.
Marcus was in the jury for the robbery trial.
Marcus was on the jury for the robbery trial.
the fixed phrase is 'on the jury'.

18. used before a device, instrument, machine, or system to show what someone uses t

18.prepositionB1
Definition

used before a device, instrument, machine, or system to show what someone uses to do something.

Example

Mina booked the tickets on her phone during lunch.

do something on + device

The children learned their first song on the piano.

play or learn on + instrument

Common collocations
  • on your phone
  • on the app
  • on the piano
  • on a tablet
Synonyms
  • with

    everyday choice for a physical tool, though less common with apps and systems

  • through

    good for platforms and systems, especially online services

Grammar Patterns

do/buy/pay on + device or app

play/learn on + instrument

enter on + system

Usage Note

The object is a device, instrument, machine, platform, or system used to do the action. Distinguish from sense 4 when 'on' marks where words or pictures appear, and from sense 7 when it marks the form or medium of a performance or record.

Common Mistakes

Mina booked the tickets in her phone.
Mina booked the tickets on her phone.
use 'on' for the device or platform used.
The children learned their first song in the piano.
The children learned their first song on the piano.
instruments commonly take 'on' here.

19. used with the same noun repeated to show one similar event or thing following an

19.preposition
Definition

used with the same noun repeated to show one similar event or thing following another.

Example

Loss on loss followed the club through a miserable spring.

repeated noun pattern: loss on loss

Wave on wave crashed against the harbor wall all night.

wave on wave for repeated movement

Common collocations
  • loss on loss
  • wave on wave
  • question on question
  • day on day
Synonyms
  • after another

    used in phrases such as 'one after another'; less compact than repeating the noun with 'on'

  • repeatedly

    gives the general idea, but it does not create the same stacked pattern

Grammar Patterns

loss on loss

wave on wave

day on day

Usage Note

Mostly appears in repeated-noun patterns such as 'loss on loss' and 'wave on wave'. It emphasizes one similar event after another, rather than simple frequency.

Common Mistakes

The club lost on and on after April.
The club suffered loss on loss after April.
this pattern repeats the noun, not the preposition by itself.

20. used to measure one result, amount, or version against another.

20.preposition
Definition

used to measure one result, amount, or version against another.

Example

This year's sales are up on last year's even without ads.

up on for comparison with an earlier figure

Mina's second sketch improves on her first one in every way.

improve on + earlier version

Common collocations
  • improve on the original
  • up on last year
  • down on Monday
  • better on paper
Synonyms
  • compared with

    more explicit and neutral, especially in formal writing

  • against

    common when figures or results are set beside a standard

Grammar Patterns

improve on [thing]

up on [earlier figure]

down on [earlier figure]

Usage Note

Most common after verbs such as 'improve' or with phrases like 'up on' and 'down on'. Distinguish from sense 10, where 'on' shows topic or relation rather than a direct comparison.

Common Mistakes

This year's sales are up than last year's.
This year's sales are up on last year's.
in this pattern, 'on' introduces the thing you compare with.

21. used to say that someone has an item physically with them, for example in a pock

21.prepositionC2
Definition

used to say that someone has an item physically with them, for example in a pocket, wallet, or handbag.

Example

Do you have any cash on you for the night market?

have + thing + on you

Rosa never keeps her passport on her during school trips.

keep + item + on her

Common collocations
  • have cash on you
  • have ID on me
  • keep a passport on her
  • have medicine on them

Grammar Patterns

have [thing] on me

have [thing] on you

keep [thing] on + pronoun

Usage Note

Usually follows 'have', 'keep', or 'carry', and the object after 'on' is normally a person pronoun such as 'me', 'you', or 'her'. It points to things physically with the person, not things they own in general.

Common Mistakes

I don't have my card on myself.
I don't have my card on me.
this pattern normally uses object pronouns like 'me', 'you', and 'him'.

22. used before an event or piece of information that another action follows from, o

22.preposition
Definition

used before an event or piece of information that another action follows from, often both later in time and because of it.

Example

On hearing the fire bell, the cooks ran into the street.

on + -ing for action after a trigger

On losing their father, the twins moved in with Aunt May.

Common collocations
  • act on information
  • on hearing the news
  • on losing a parent
  • on coming back
Synonyms
  • after

    gives the time order, but it often lacks the same idea of cause

  • following

    more formal and common before noun phrases

Grammar Patterns

act on [information]

on hearing [news]

on returning [place]

Usage Note

Often appears in phrases like 'on hearing...' or after verbs such as 'act'. The event after 'on' is usually the trigger for what happens next, unlike sense 3, which only marks time.

Common Mistakes

On hear the bell, the boys ran out.
On hearing the bell, the boys ran out.
after 'on' here, use a noun phrase or an -ing form.

23. used after a person or organization to mark who pays the bill or cost.

23.preposition
Definition

used after a person or organization to mark who pays the bill or cost.

Example

Don't reach for your wallet; lunch is on me today.

be on + person paying

The repairs were on the landlord after the pipe burst.

Common collocations
  • on me
  • on the company
  • on public insurance
  • on the house
Synonyms
  • paid by

    a more explicit passive phrase for the same payer idea

  • at [someone's] expense

    more formal and often used in writing rather than casual offers

Grammar Patterns

be on me

be on [person/company]

on public insurance

Usage Note

Most common after 'be', especially in short offers such as 'It's on me.' The noun after 'on' names the person or group paying, not the thing being bought.

Common Mistakes

Lunch is on I today.
Lunch is on me today.
after a preposition, use the object pronoun 'me', not 'I'.

24. used after the affected person to show who is left in trouble when something sud

24.preposition
Definition

used after the affected person to show who is left in trouble when something suddenly stops working properly.

Example

My old laptop froze on me during the class talk.

verb of failure + on + affected person

The rental car broke down on us outside Hsinchu.

break down on + person

Common collocations
  • freeze on me
  • break down on us
  • die on him
  • quit on the cashier
Synonyms
  • let [person] down

    broader and often figurative; it can describe people as well as machines

Grammar Patterns

freeze on [person]

break down on [person]

quit on [person]

Usage Note

Common with verbs for breakdown or sudden failure, such as 'freeze', 'die', 'quit', and 'break down'. The noun or pronoun after 'on' names the unlucky person affected by the problem.

Common Mistakes

The printer stopped to me during the test.
The printer stopped on me during the test.
use 'on' to show who suffered from the failure.

25. showing how many points a player or team has at that stage of a competition.

25.preposition
Definition

showing how many points a player or team has at that stage of a competition.

Example

After three rounds, Taiwan Blue are on 18 points.

be on + number + points

Marcus moved into first place when he went on 27 points.

go on + number + points

Common collocations
  • on 18 points
  • on 42 points
  • go on 27 points
  • finish on 9.8 points
  • end the day on 11 points
Synonyms
  • with

    used in some reports to state a total, but less fixed than this sports-table pattern

  • having

    can paraphrase the idea, but it does not replace the set 'on + points' pattern

Grammar Patterns

be + on + number + points

go/stay/finish/end + on + number + points

Usage Note

Usually follows verbs like 'be', 'go', 'stay', 'finish', or 'end' in sports and competition reports. The phrase after 'on' is normally a number plus 'points'.

Common Mistakes

The Tigers are with 12 points.
The Tigers are on 12 points.
sports reports use 'on' before a points total.
Lina finished in 18 points.
Lina finished on 18 points.
use 'on' for the score someone ends with.

on — adverb

on — adjective

on — noun

Synonym discussion

Sense: preposition/1

For preposition sense 1, on is the normal everyday choice when something touches a surface: 'The keys are on the table.' Upon can replace it in many cases, but it sounds more formal or literary and is much less common in speech. Onto is different because it highlights movement to a surface: 'The cat jumped onto the wall' focuses on the change of position. Over can mean higher than something without contact, so a lamp may hang over a desk but not be on it. Against is used when something touches the side of another thing, especially a wall, window, or fence. Say The cup is on the shelf, but The bike is against the fence.

Etymology

Proto-GermanicOld EnglishMiddle EnglishModern English

'On' goes back to Old English on, a very old form that already covered ideas such as position, contact, movement, and time. That word came from Proto-Germanic *ana and is related to words such as German an and Dutch aan. Because English has used it since its earliest stages, on gradually spread into many grammar patterns, which is why modern English uses it for place, time, state, support, and progress.