“On” and “upon” are synonyms. However, “upon” is considered very formal and not that commonly used in conversational English.

Overview
OnUpon
CommonVery formal
Common idiomatic expressions
“On” + specific time“Upon” + event
Emphasise a large amount

Differences

1.   “Upon” is very formal compared to “on.”

Although interchangeable, “upon” is often too formal for conversational English—”on” is more common and acceptable.

Compare the following:

  • “I left the books on the table.”
  • “I left the books upon the table.”

Although both sentences are the same, using “upon” sounds quite old-fashioned and less natural.

a. Very formal and legal language.
  • “The title was bestowed upon him by the Queen in 1998.”
  • “The proceedings were served upon the defendant last week.”
b. Literary use or period literature, movies and tv shows.
  • “I sincerely believe we were put upon this planet for this very purpose.”
  • “He put his bowler hat upon his shiny, bald head and briskly walked away without so much as a farewell.”
2.   There are some common idiomatic expressions with “upon.”

Using “on” is possible, but less common.

“Once upon a time” 
– (expression) used at the beginning of children’s stories to mean “a long time ago.”

This cannot be used with “on.”

  • “Once upon a time, there lived a beautiful maiden.”
    Not – “Once on a time, there lived a beautiful maiden.”

“Chance upon/on (someone/something)” 
– (idiom) to find something or meet someone by accident.

“On” can be used, but this is less common.

  • “We chanced upon a fossil while taking a stroll on the beach.”
  • “I chanced upon an old friend at the supermarket yesterday. We hadn’t seen other in years.”

“Take (something) upon/on (onself)” 
– (idiom) to accept responsibility for doing something without being asked.

“On” can be used, but this is less common.

  • “Thanks for taking it upon yourself to organise the event.”
  • “She’s taken it upon herself to care for him but I’m not sure if that’s such a good thing.”

“Be upon (somebody)
– (formal expression) something will happen very soon.

“On” cannot be used.

  • “It won’t be long before winter is upon us again.”
    Not – “It won’t be long before winter is on us again.”

“Be put upon”
– (informal phrasal verb) to be treated badly by someone who takes advantage of your desire to be helpful.

To me, this is not very common.

  • “I don’t mind but I can’t help being put upon.”
    Not – “I don’t mind but I can’t help being put on.”
Similar expression: “Put on”

“Put on” has a number of different meanings but requires difference sentence structures, which is why the previous example does not work. 

“Put on someone” 
– (informal phrasal verb) to tease or playfully deceive someone.

  • “I don’t mind but I can’t help like he’s putting me on.”

“Put-on” 
– (informal noun) an attempt to deceive someone into believing something that is not true.

  • “I don’t mind but I can’t help feeling like it’s a put-on.”

3. “Upon” can mean “immediate/soon after.”

This is sometimes interchangeable with “on.”

  • “Visitors will be tested upon arrival.”
  • “Visitors will be tested on arrival.”
  • Upon his return, he realised he lost his wallet.”
  • On his return, he realised he lost his wallet.”
+ Gerund phrase – using “on” can sometimes sound weird.
  • “We congratulated Wally upon hearing the good news.”
  • “We congratulated Wally on hearing the good news.”

These sound okay to me.

  • “Wally’s son moved out upon leaving school.”
    Not – “Wally’s son moved out on leaving school.”
  • Upon watching the documentary, we decided to change our diets.”
    Not – “On watching the documentary, we decided to change our diets.”
a. “On” can be used to show when something happens, so this refers to a specific time.
  • “We visited my grandmother on Friday.”
    Not – “We visited my grandmother upon Friday.”

4. “Upon” can be used to emphasise a large number or amount of something.

“Upon” is placed between two of the same nouns. This can sound more literary and poetic.

  • “All I saw were thousands upon thousands of bright pink flowers.”
    Not – “All I saw were thousands on thousands of bright pink flowers.”
  • “He waited for her year upon year, but never heard from her.”
    Not – “He waited for her year on year, but never heard from her.”

* Please note: “year-on-year” is a finance term to compare the financial results in the previous year.


Original posts: 19 April 2021