Impose on or Impose upon?

[Iloveenglish]

Sometimes I see 'on' used after impose, and sometimes 'upon'. Can anyone explain the difference please?

[Alan]

Hi,

'Impose' is usually followed by 'on' when used to mean 'place on somebody/something' in the sense of 'impose a fine on someone or impose a tax on goods'. The use of 'impose upon' has a rather formal use as in: 'I hate to impose upon you but I wonder if you could help me.' Less formally we would simply say: Sorry to impose on you... They both have the sense of asking someone a favour/asking someone to help you.

Alan
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[Jordan]

synonyms for impose, force upon, compell? are not they?