SHL is right.

As far as I know, the only two fixed phrases where 'upon' is obligatory are the very outdated exclamation "Upon my word!" and the traditional opening line of fairy tales "Once upon a time...".

In every other situation, you can - and usually should - use 'on' instead of 'upon'. In some phrases, it's OK to use either: for example, you can rely on something or you can rely upon something, and there's no difference in meaning. In other cases, especially everyday situations such as SHL's example of the spoon on the table, it would be strange, old-fashioned or even wrong to use 'upon'.

Here's my advice:

Listening and reading: If you come across the word 'upon', just accept that it always means the same as 'on'.

Speaking and writing: Don't worry about 'upon': Use 'on', and it'll always be right.

(Unless of course, you feel a burning desire to exclaim "Upon my word!" or start writing a fairy story...)

Im a native English speaker from the San Francisco area. The difference between on an upon is hard in a way. Upon does sound weird in some situations, but okay in others. Like „The spoon is on (not upon) the table“ is correct and upon would sound strange. Frankly I can’t think of a case where you couldn’t just forget about upon and say on instead and be fine. There could be some phrase but nothing comes to mind.

But su.ki. is really the one that would know a rule for learners to follow. I just go by what sounds right.

Thanks su.ki. At least I get it right sometimes using my „It just sounds right or wrong test.“

I tried thinking on a phrase where I could say upon and make it sound right and couldn’t find one, I thought about saying „put the spoon upon the table“ and I knew that sounded terrible and no one would says that. Just set the spoon on the table.

Upon does sound literary as in „once upon a time.“ In those kinds of sentences is about the only time I’ve seen it.

As i read they both have the same meaning but " upon " is more formal than " on" .