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about the local eateries, and so they will pool their knowledge to get a more complete
picture of the situation before deciding. Thus one agent may solicit recommendations,
and another agent may attempt to persuade that agent of its own favourite venue. We
will use this illustration throughout this paper.
In [9], dialogue types are characterised by an initial situation, a collective goal, and
individual goals, all stated informally. For inquiry dialogues the initial situation is that
both agents are not certain of some proposition
p
. Both individual goals and the collec-
tive goal are the same: to determine whether or not
p
. In persuasion one agent will argue
that
p
, or that some action
φ
should be done hoping that the other agent will come to
agreement. The collective goal is to resolve whether
p
is true or
φ
should be done. With
regard to individual goals, persuasion is asymmetric: the persuader wishes to convince
the persuadee, whereas the persuadee wishes to explore the possibility that its current
opinion should be revised in the light of information known to the persuader: the per-
suadee is interested in what is true, whether it be
p
or
p
. A different case of persuasion
is what Walton terms a
dispute
[8]. In this case the persuadee also wishes to convince
the other agent that its own original position is correct, so that its individual goal is
now that the other should believe
¬
p
or that
φ
should not be done: we will not consider
disputes further in this paper. Deliberation is generally held to concern actions: initially
both agents are unsure whether or not to
φ
, and individually
and collectively
they wish
to come to agreement as to whether or not to
φ
. In the next section we will explore
the distinctions further, with a view to precisely characterising persuasion dialogues in
particular.
¬
2
Distinguishing the Dialogue Types
Although some have suggested that persuasion cannot be applied to actions, this is con-
trary to common usage and we believe that the correct distinction is related to
directions
of fit
, a distinction made by e.g. Searle [7]. Searle distinguishes theoretical reasoning,
reasoning about what is the case, from practical reasoning, reasoning about what it is
desired to be the case, and what should be done to realise those desires. In the first
case it is necessary to fit one's beliefs to the world, whereas in the second the idea is
to make the world fit one's desires, in so far as one has the capacity to do so. In these
terms, inquiry represents an attempt to better fit the beliefs of the agents to the world,
and deliberation how best to make the world fit the collective desires of the agents.
Persuasion can be about either. Note, however, that when we have two (or more) par-
ticipating agents, we have two (or more), probably different, sets of desires to consider.
In deliberation no set of desires should be given pre-eminence, but rather the group as a
whole needs to come to an agreement on what desires they will adopt collectively (e.g.
[5]). In contrast, as discussed in [1], in persuasion it is the desires of the
persuadee
that
matter: a persuadee is fully entitled to use its own preferences to assess any proposition
or proposal, without any need to consider what the persuader desires. The construction
of a set of collective desires introduces an additional order of complication, and puts
deliberation beyond the scope of this paper. Therefore in what follows we will focus
exclusively on persuasion.
