Some theorists on deliberative democracy distinguish it from negotiation in that participants need to give reasons for their positions. The reasons don’t need to be held by everyone else involved, but everyone else should be able to accept them. There are a few reasons for this:

to help find common ground

In a negotiation you may concede certain issues, either to conserve strength or in the hopes that your opponent will reciprocate. But if you establish that a position is mutually preferred, not just conceded, that will bring parties closer together.

to educate participants

In class, I’m continually criticising civic engagements that just act to educate people without giving them power, but I’ll accept that education about the diversity of viewpoints in a community is a great secondary effect of engagement.

to make the outcome satisfactory

In a negotiation, parties walk away from the table saying “oh well, that’s the best we could do with the cards we had”. That’s going to lead to hard feelings and attempts at reversing the decision down the road. Deliberative democracy should leave people saying “that’s the best of all possible solutions”.

Deliberative democracy is also supposed to be better at incorporating diversity than representative democracy. But what if your participants are so diverse that they use completely different methods of reasoning? Examples:

• scientific evidence versus anecdotal evidence
• oral history versus ownership-by-cartography
• evidence gathered while dreaming or hallucinating

I think the most we can require is that each participant’s system of reasoning be internally consistent: all proclamations of the machine elves are given equal standing. But I’m skeptical of the ability to assess the internal consistency of other peoples’ systems of reasoning. It appears that deliberative democracy requires us all to become social relativists?