upon/on

[Bridget]

What is the difference between:

impose on
impose upon

[Pete]

What is the difference between:

impose on
impose upon
I don't think that there is a strict difference between them. I may be wrong, but I can't think of a sentence using one of the phrases where you couldn't substitute the other phrase and have a correct sentence with the same meaning. A Google search shows similar numbers of hits (about 1.5 million) for each, with slightly more for the "on" version.

However, without proof, my feeling is that "impose on" is used more often when the meaning is "to take advantage of":
- My friend imposed on me frequently when he was too tired to drive home after a long day in my city.

whereas I feel that "impose upon" is used more often when the meaning is to force something on someone:
- The legislature enacted a new tax to impose upon all people who smoke.

(But even in these cases, the other term would not be wrong.)