Proposition or proposal?

M'interrogeant sur la différence en anglais entre 'proposition' and 'proposal', je surfe un peu sur Internet et je tombe là-dessus :


Un internaute s'interroge :

I am wondering what differences there can be between these two words : a proposition and a proposal. I just heard a line at the end of the Hitchcock movie North by NorthWest the hero asking to the girl :

"let's go back to New York on the train together

- is that a proposition?

- it's a proposal, sweety"

Cet autre lui répond :

A very cute line. 

is that a proposition? - are you offering to sleep with me?

it's a proposal, sweety - no, I'm offering to marry you.

In the context of sex/love, a proposition is an offer of sex, while a proposal is an offer of marriage.

Bon c'est très mignon tout ça, mais ce que je cherchais, c'est plutôt ce qui suit : 

In the business context, proposition is hardly used while proposal is very common and is used for the formulation of all sorts of future plans. For example, I'm meant to be writing a funding proposal right now, but I'm procrastinating instead.