Information Technology Reference
In-Depth Information
Wilma and Bert wish to establish the truth of some factual proposition, they will use a
dialogue as described there.
In contrast, persuasion can concern matters with both directions of fit, although prob-
ably evaluative propositions are more usually the topic than factual ones. This is because
if the persuader is correct (and honest), for factual topics an inquiry dialogue will serve
to achieve the goals of a persuasion dialogue. It may be, however, that the persuader has
some interest in establishing the proposition, and this interest will persist even if it be-
comes aware of information suggesting that the proposition is in fact false. If one of the
agents represents a salesperson, for example, it may act in this way. Since persuasion
may have this adversarial element we distinguish
open persuasion
, where the persuader
is expected to tell the truth, the whole truth and nothing but the truth, and
partial
(i.e
not
impartial
)
persuasion
where the persuader must tell only the truth and nothing but
the truth, but need not tell the whole truth if that would damage its cause. Open persua-
sion about a fact is simply an inquiry dialogue where the persuader initially believes the
proposition under consideration, so that these dialogues can also be characterised by
I1 and I2 above. We will henceforward confine ourselves to persuasion dialogues that
concern matters of preference, so that there will be subjective elements dependent on
tastes and preferences as well as facts.
Open Persuasion
OP1: Wilma believes that Bert does not believe that
p
B
:
KB
B
0
p
B
OP2: Both wish that at the end of the dialogue Bert believes that
p
B
if and only if
p
B
is a consequence of their joint knowledge bases and Bert's preferences:
KB
B
t
KB
W
0
F
KB
B
0
p
B
↔
∪
p
B
, where the dialogue terminates in
t
steps.
Note that at the end of an open dispute, Bert and Wilma may differ as to whether
p
or
p
, since their beliefs reflect their own individual preferences applied to the shared
information. Again the dialogue will always terminate because either the agent is per-
suaded, or all factual knowledge has been exchanged.
For partial persuasion we include the desire to, as it were, win the dialogue, irrespec-
tive of the truth of the matter. Although partial persuasion can be conducted regarding
a matter of fact, we will consider here only persuasion relating to matters involving el-
ements of preference. The initial goal remains OP1, and Bert's final goal remains OP2,
but Wilma has a different goal, PP3. PP4 represents the condition under which Wilma
can legitimately satisfy her goal. Again the dialogue terminates in
t
steps.
¬
Partial Persuasion using Preferences
PP3: Wilma's goal is that Bert should believe that
p
:
KB
B
t
p
B
PP4: Wilma can succeed if she has information to enable Bert to believe
p
:
KB
B
t
KB
W
0
F
KB
B
0
p
B
↔
(
∃
S
)
⊆
such that
S
∪
p
B
.
Note that open persuasion begins with a conflict, but has the same goals for both partic-
ipants, whereas in partial persuasion they have different views as to what constitutes a
successful termination. Both agents can realise their individual goals if
p
B
does follow
from their collective knowledge and Bert's preferences. If not, strategic considerations
may affect the outcome: it may be that there is a subset of Wilma's KB which could be
used to persuade Bert, but that she reveals too much, so that Bert is unpersuaded. Here
