I don’t disagree with what has been written – I just tend to take a different approach. English, a very special language that has changed and evolved, and continues to over the years – has semantic and grammatical ebbs and flows. Upon isn’t what I would call “archaic”. I would reserve that term for really older or ancient terms no longer in use – like Thou and Thine.
Here’s an example of a pop hit from the late 70’s – by no other than Michael Jackson:
So tonight Gotta leave that nine to five upon the shelf An’ just enjoy yourself Groove Let the madness in the music get to you Life ain’t so bad at all If you live it off the wall Life ain’t so bad at all Live your life off the wall
What is upon anyway? It’s basically connecting the two words and making them into one, like “outside” and “indoors.”
If the shelf is right in front of you – then you put something on it. If it is high up, and you want to stress that, put it upon the shelf.
In the other meaning, i.e. together with “rely” or lean upon, I think one should use poetic license; up – which means higher, above – lends a loftiness – a certain something to the expression – and if you need to lean upon your friend, you is in a higher position than you (simply because it is thou who leanest upon him) then why not say upon, rather than on.
There is simply that added syllable, and for music’s sake, one would use either on, or upon, depending on the meter.