On and upon are interchangeable, however, in some instances each has gained preference.
For example
row upon row of seats;
once upon a time;
on no account;
on good authority;
Once Upon a Time - 2011 Second Star to the Right 2-21 is rated/received certificates of: Netherlands:9 USA:TV-PG
once upon a time
When you wish upon a star, it makes no difference who you are. Once upon a time, I read a bedtime story to my little nephew. The frog is poised upon a lilypad.
You'll know when its the right time..
It usually begins with "Once upon a time,".
"Upon" is typically used when referring to a specific time, event, or condition that triggers or precedes another action. For example, "Upon receiving payment, the item will be shipped." It can also be used more formally to indicate a time or event is happening or will happen soon, such as "He arrived upon the hour."
Once upon a time, One Morning and more...
Because it wasn't the right thing to do
the usual opening line of fairy tales is the "once upon a time"
then they will learn how to use their left hand and after a long period of time forget how to use their right hand.
When does once upon a timesOnce Upon a Time Season 4 come on Netflix
No adverb is better than any other; each adverb has its particular use, to convey a specific meaning. Choosing the right word depends upon what you are trying to say. There is no single right word which is always the right one to use in all cases.