Upon vs. Once — What's the Difference?
By Maham Liaqat & Fiza Rafique — Updated on May 9, 2024
Upon refers to something that happens immediately after another event, emphasizing a conditional relationship. Once means "as soon as" or "after one time," highlighting a single occurrence or a specific point in time.
Difference Between Upon and Once
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Key Differences
Upon indicates an action that follows directly after a specified event or condition. In contrast, once emphasizes that an action occurs after a particular point or one instance.
Upon is often formal and conditional, used for emphasizing a sequence of events. While, once is more versatile, signaling a specific event that may or may not repeat.
Upon typically leads into another clause or idea immediately connected to the first event. Whereas, once often serves as a standalone adverb or a conjunction for a singular time-based condition.
Upon often implies a more immediate or expected reaction, as in "upon arrival." Once, however, can denote a flexible period after a specified event, like "once completed."
Upon is generally followed by a noun or gerund, creating a prepositional phrase. On the other hand, once functions as a conjunction or adverb that leads to a clause.
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Comparison Chart
Meaning
Immediately following another event
As soon as or after a single event
Formality
More formal
Less formal, more conversational
Part of Speech
Preposition
Adverb or conjunction
Structure
Usually followed by a noun/gerund
Leads to a dependent clause
Frequency
No frequency indication
Specifies one instance or point
Compare with Definitions
Upon
At the moment of arrival or occurrence.
The team began the meeting upon arrival.
Once
In the past, previously.
He once lived in Spain but has since moved back.
Upon
Immediately following or depending on a specific event.
Upon receiving the letter, she called her attorney.
Once
As soon as or after a specific point in time.
Once the cake cools, you can ice it.
Upon
On top of or in a position over something.
The cat leaped upon the table to catch the mouse.
Once
One single time or instance.
She only asked him for help once.
Upon
Indicating dependence or reliance on.
Success depends upon careful planning.
Once
At the same time, simultaneously.
They all spoke at once, creating confusion.
Upon
On or immediately after an action or event.
The guards were called upon discovering the breach.
Once
Used for emphasis to mean "even one time."
I never saw her once during the vacation.
Upon
On
The leaves are scattered upon the grass. He put the book upon the table. Upon hearing the news, we all cheered.
Once
One time only
Once a day.
Upon
Physically above and in contact with.
Place the book upon the table.
Once
At one time in the past; formerly.
Upon
Physically directly supported by.
The crew set sail upon the sea.
She balanced upon one foot.
Once
At any time; ever
Once known, his face is never forgotten.
Upon
Being followed by another so as to form a series.
Hours upon hours, years upon years, mile upon mile of desert
Once
By one degree of relationship
My first cousin once removed.
Upon
At (a prescribed point in time).
The contract was rendered void upon his death.
Once
A single occurrence; one time
Once will have to do. You can go just this once.
Upon
On.
Once
As soon as; if ever; when
Once he goes, we can clean up.
Upon
On; - used in all the senses of that word, with which it is interchangeable.
Our host upon his stirrups stood anon.
Thou shalt take of the blood that is upon the altar.
The Philistines be upon thee, Samson.
As I did stand my watch upon the hill.
He made a great difference between people that did rebel upon wantonness, and them that did rebel upon want.
This advantage we lost upon the invention of firearms.
Upon the whole, it will be necessary to avoid that perpetual repetition of the same epithets which we find in Homer.
He had abandoned the frontiers, retiring upon Glasgow.
Philip swore upon the Evangelists to abstain from aggression in my absence.
Once
Having been formerly; former
The once capital of the nation.
Once
(frequency) One and only one time.
I have only once eaten pizza.
Once
(temporal location) Formerly; during some period in the past.
He was once the most handsome man around.
I once had a bicycle just like that one.
Once
At any time; ever.
If the facts once became known, we'd be in trouble.
Once
(obsolete) One day, someday.
Once
(mathematics) Multiplied by one: indicating that a number is multiplied by one.
Once three is three.
Once
As soon as; when; after.
We'll get a move on once we find the damn car keys!
Once you have obtained the elven bow, return to the troll bridge and trade it for the sleeping potion.
Once he is married, he will be able to claim the inheritance.
Once
The ounce.
Once
For one time; by limitation to the number one; not twice nor any number of times more than one.
Ye shall . . . go round about the city once.
Trees that bear mast are fruitful but once in two years.
Once
At some one period of time; - used indefinitely.
My soul had once some foolish fondness for thee.
That court which we shall once govern.
Once
At any one time; - often nearly equivalent to ever, if ever, or whenever; as, once kindled, it may not be quenched.
Wilt thou not be made clean? When shall it once be?
To be once in doubtIs once to be resolved.
Once
Belonging to some prior time;
Erstwhile friend
Our former glory
The once capital of the state
Her quondam lover
Once
On one occasion;
Once I ran into her
Once
As soon as;
Once we are home, we can rest
Once
At a previous time;
Once he loved her
Her erstwhile writing
Common Curiosities
What does "upon" mean?
Upon means immediately following or depending on a specific event.
Is "upon" the same as "once"?
No, "upon" emphasizes a conditional or immediate relationship, while "once" highlights a single event.
What does "once" mean?
Once indicates a single occurrence or the point after a particular event.
Is "upon" only used in time-based contexts?
No, "upon" can also mean "on top of" or "depending on."
Can "once" start a sentence?
Yes, "once" is often used to start sentences, like "Once he finished, he left."
Can "upon" be used like "once"?
Not exactly, as "upon" is a preposition, while "once" is typically an adverb or conjunction.
Can "once" refer to multiple occurrences?
Not usually; "once" generally means a single time or event.
Can "once" mean "previously"?
Yes, "once" can mean "at some point in the past."
Is "once" always a conjunction?
No, it can also function as an adverb or noun.
Is "upon" more formal than "once"?
Yes, "upon" tends to sound more formal than "once."
Can "once" be used for emphasis?
Yes, "once" is sometimes used for emphasis, meaning "even a single time."
Does "upon" indicate immediacy?
Yes, it suggests that one event follows another right away.
Is "upon" always followed by a noun or gerund?
Yes, it's typically followed by a noun phrase or gerund.
Does "upon" imply dependence?
It can, as in "relying upon."
Can "upon" imply a metaphorical position?
Yes, as in "called upon for advice."
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Written by
Maham Liaqat
Co-written by
Fiza RafiqueFiza Rafique is a skilled content writer at AskDifference.com, where she meticulously refines and enhances written pieces. Drawing from her vast editorial expertise, Fiza ensures clarity, accuracy, and precision in every article. Passionate about language, she continually seeks to elevate the quality of content for readers worldwide.
