Dialogue Is Talk With Purpose

My sister is over from abroad, and I've been spending a lot of time with her and my mother - and jolly nice it's been too, as we chat about family things past and present.  I think anyone else listening to our conversations would be bored to tears, but for us they are serving a purpose - that of cementing family bonds in a pleasant way.  They are not intended to entertain anyone else, just us.

It's a distinction writers need to bear in mind.  Dialogue, as written in fiction, has a primary function of entertaining the reader (or viewer or listener).  Let's suppose you have a scene of a mother and her two adult daughters talking about family.  It's serving a purpose, that of showing how the family bonds are being cemented.  But once that's been established - and it should happen pretty quickly, within half a page I'd have thought - the scene will need a new purpose.

The new purpose could be anything - a hidden agenda for one of the participants, preferably a hidden agenda for ALL of the participants, which they're trying to promote.  Secrets, long established grievances, revelations for the future - all suitable purposes to move the story on and make it interesting.

In real life, we're quite happy to ramble on all weekend about family stuff, but no reader/viewer/listener is going to put up with that.  Dialogue in fiction constantly needs new purposes or it won't work.