Should I use on or upon in the following sentence?
I remembered the story years later when I investigated the incident it was based on.
Usage note from Thefreedictionary:
In their uses to indicate spatial relations, on and upon are often interchangeable.
To indicate a relation between two things, however, instead of between an action and an end point, upon cannot always be used.
Similarly, upon cannot always be used in place of on when the relation is not spatial.
In this particular case, it makes no real difference. And if you’re one of those who feels that whenever you have the choice of two words of unequal lengths, indistinguishable in meaning, that you should always select the shorter of the two, then the choice is clear.
Others have noted that despite claims that on and upon are completely interchangeable, that there many places where you cannot use upon at all. It turns out there are also a few places where the reverse is true, that you cannot use on and must upon.
One such place is with phrasal verbs involving upon; there are also several non-verbal formulaic constructs associated with upon. Here are some of them:
The sentence shouldn't end in "on". It should be ".. on which the incident was based."
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