Partir, sortir, quitter.

Question

Questions on ‘partir, sortir, quitter’ which comprise one, some or all answers are so inconsistent, I find it very irritating. Sometimes when I choose all three (excluding ‘laisser’ of course), only ‘partir’ is the answer deemed acceptable. sometimes, when I select ‘partir’ only, all three are given as correct. More context please.

Accepted Answer

Bonjour Richard,
I agree that this is a particularly tricky grammar point.
One way to eliminate options is to look at what follows the verbs: partir is an intransitive verb (can't have a direct/indirect object), whereas quitter and laisser are always transitive verbs (i.e. have a direct object) and sortir can be either. 
So, to come back to "they are leaving soon", there is no direct object present but an adverb "soon" (= bientôt). Therefore, of all the options, only "partir" and "sortir" are possible. But, when "sortir" is used on its own, it actually means to go/come out (unless it is used with "de" + [place] - in which case it implies "leaving somewhere"/"coming out of a place"). Therefore, here, only "partir" is possible.
I hope this is helpful.
Bonne journée !

Answer

This is in response to the question  ‘Are they leaving soon?’