Good cop dialogue, bad cop dialogue ...

I like good dialogue in a book.

It brings the characters alive, moves the story on, adds depth to the milieu in which the characters move. And to me, good dialogue always involves conflict. Take this example, from James Lee Burke's Sunset Limited. Our hero, Dave Robicheaux, is a cop in Louisiana, and he's about to take delivery of a suspect. This portion of dialogue could have been omitted or it could have been a straightforward exchange where Dave takes the suspect from the deputy and says thanks. Instead, Burke uses it to characterise Dave and the deputy, and the deputy's attitude towards Dave:

A uniformed deputy picked up Cool Breeze in front of a pawnshop on the south side of New Iberia and brought him into my office.
'Why the cuffs?' I said.
'Ask him what he called me when I told him to get in the cruiser,' the deputy replied.
'Take them off, please.'
'By all means. Glad to be of service. You want anything else?' the deputy said, and turned a tiny key in the lock on the cuffs.
'Thanks for bringing him in.'
'Oh, yeah, anytime. I always had aspirations to be a bus driver,' he said, and went out the door, his eyes flat.

Notice how when Dave asks the question, 'Why the cuffs?', Burke doesn't have the deputy answer it - instead, he says what's on his mind. This adds more conflict immediately and the passage begins to hum with concealed tension. Compare it with this section from Patricia Cornwell's Unnatural Exposure, where the tension is given to us overtly. Our heroine, Kay Scarpetta, is talking to her police contact, Marino:

'I can't believe this.' I was only getting angrier. 'I have to release information to correct misinformation. I can't be put in this position, Marino.'
'Don't worry, I'm going to take care of this and a whole lot more,' he promised. 'I don't guess you know.'
'Know what?'
'Rumor has it that Ring's been seeing Patty Denver.'
'I thought she was married,' I said as I envisioned her from a few moments earlier.
'She is,' he said.

This is a simple exchange of information. Scarpetta does her usual thing of getting angry at the flimsiest excuse (this is how Cornwell characterises her, in general), and then we learn about 'Ring' and 'Patty Denver' in a very mundane dialogue predicated on the fact that Marino knows something and Scarpetta doesn't:

'I guess you don't know.'
'Know what?'

... or that Marino is confirming something that she's unsure of:

'I thought she was married' [ ... ]
'She is.'

It's much easier to write dialogue like this, persuading yourself that you're filling the reader in on useful information - and to be fair, a crime or mystery novel sometimes has to do this to fill in back story. But it's not dramatic, it's not much fun to read, and it leaves your characters speaking like robots. Just look at The Da Vinci Code to see what I mean.

So what can we learn? The lessons seem to be:

1. Resist the temptation to create 'Call and Response' dialogue: 'Who's that?' 'It's me.' It might seem to flow, but it's dull.
2. Similarly, if you have a character ask a question, don't let your next speaker answer it directly.
3. To prevent your dialogue being functional, add in a phrase or sentence that helps characterise your speaker - like 'I always had aspirations to be a bus driver' above.
4. Edit and keep the sentence-length short. Like this.
5. Never have someone tell someone else something they already know, just to fill in the reader.

Oh, and in the words of George Orwell, break these rules rather than say anything outright barbarous!