The Purpose of Dialogue
What is the purpose of dialogue in a story? Is it to tell things to other characters? No. Is it to tell things to the audience? Sometimes this is the only way to let the audience in on something, but no, this isn't the purpose of dialogue. Is it to make the story move forward? It should move the story forward, but no this is not it. Is it to show conflict? Conflict is very important, but no.
Dialogue may do all of these things, but these are not what dialogue is for. Dialogue is your character's reaction to other characters, and the purpose of dialogue is communication between characters.
Make Your Characters Say Something
When someone says something to another person, unless he is just making conversation, he wants the other person to react to what he is saying. Bill wants Paul to be impressed with him, to leave him alone, to give him money, to let him do something, etc.
When Paul hears something from Bill, he reacts. The first reaction is internal and Paul absorbs the words and the meaning he perceives. Paul may be unimpressed, have no intention of leaving Bill alone, understand that Bill wants money and be unwilling to give it, and Paul may not be willing to let Bill do whatever he is wanting to do. But internally Paul reacts.
Paul's external reaction usually will match his internal reaction. He reacts outwardly by responding in some way, most often with more words. Paul verbally insults Bill to make him know he is unimpressed. Paul grabs Bill and shouts in his ear to make him know he won't leave him alone. Paul tells Bill that he is not going to give him any money. Paul replies with a simple "no" to Bill's request to do something. Paul's actions and dialogue communicate something to Bill.
The process doesn't stop there. Bill hears Paul's words and goes through his own reactions.
Dialogue is one form of dramatic action, and the way dialogue proceeds is action, reaction, reaction, reaction, reactionů adding new actions as needed, until the scene concludes.
Dialogue and physical action work out each characters motivation as they try to get what they want. If you are having difficulty writing dialogue, it may be because you don't know what your character wants. Writing stories works best when you know your characters.- Scott