Today, class, we shall talk about dialogue.  More specifically, expositional dialogue.  What’s expositional dialogue, you say?  Well gather round while we discuss it.

Even if you don’t know it by the fancy name I used for it, you are no doubt familiar with it.  When you are reading a novel and the characters start telling each other things they would obviously know for the sake of revealing the information to the reader, like this:

Mother:  "When I had you on April 20, 1992, you were the cutest baby I ever saw.  I just don’t know what happened."

Daughter: "You know, mother, my life changed when Dad walked out on us.  Now all I want to do is smoke pot and watch TV all day long."

That is expositional dialogue.  I exaggerate, but you get the point.  Obviously, when the mother mentions her daughter’s birthdate, it is information her daughter already knows.  And when the daughter replies with choice bits about her own life, it is, again, information her mother knows. 

Expositional dialogue makes readers groan.  Avoid it.  Usually expositional dialogue is a lot less obvious than the above example.  Writers sometimes use it unwittingly in their never-ending efforts to show, not tell, so the impulse behind it is pure.

I was reminded of the issue of informational dialogue when reading a post on Trashionista, which gives a great example of it here.