Some techniques for controlling pacing are universal to writing: sentence length, content, etc. (See 206 Pacing for more information about pacing in general.) But dialogue also has two unique technique for managing its pacing: manner of speech, and collaborative vs conflicting dialogue.
How does each character express themselves? Much like foreshadowing, good dialogue primes audience expectations, using questions and vague remarks to hint at what comes next. For example, whenever you ask someone “How are you?”, you may not know exactly what they’re going to say, but you have a concept of what they might say (great, good, okay, eh, bad, very bad). You may even try to predict which response they will choose.
Questions frame our expectations. Granted, a character could defy expectations and offer a strange answer, but over time audiences learn to “expect that” from specific characters. Consider the following:
“What do you think?”
“I like the look of it, but it’s a little too heavy.”
“How about this one?”
“Nice. What’s it made of?”
Alternating between question and answer provides a natural back and forth. Each sentence is a small piece of the whole, dependent upon the others for its meaning.
Another technique is when two characters share something (typically knowledge and/or similar experiences). They both understand the topic so well that they can almost finish each other’s sentences. Consider this excerpt from Well of Ascension:
“They hate you,” she said quietly. “They hate you because of your powers, because they can’t make you break your word, or because they worry that you are too strong to control.”
“They become afraid of you,” he said. “They grow paranoid—terrified, even as they use you, that you will take their place. Despite the Contract, despite knowing that no one would break his sacred vow, they fear you. And men hate what they fear.”
Look at how the two blend together, how one character could have said all of it. Writing like this creates a strong sense of momentum, while simultaneously deepening connections between the characters.
Conflict & Collaboration