Dialogical Models of Explanation
ExaCt Vancouver July 21-22, 2007
Douglas Walton
Example of a Hamblin Dialogue
Each member in the sequence is defined by Hamblin (1971, p. 130) as a triple, n, p,l .
n represents the length of the dialogue (the number of moves so far). p is a participant.
And l is a what Hamblin calls a locution. Using Hamblin’s notation, a small dialogue
with three moves for far could be represented as follows.
Small Dialogue:
0, P0 , L4 ,1, P1, L3 ,2,P0, L2 
In the simplest case, there are two participants, called the proponent and the
respondent. When either party makes any move (speech act), the rules determine which
statements are inserted into, or deleted from that participant’s commitment set.
Rules define what kinds of moves can be made and what response move needs to be
made just after the other party’s last move. Rules define when a sequence of dialogue
successfully realizes the communal goal of the dialogue. Each party has a goal, and the
dialogue as a whole has what can be called a communal goal.
Dialogue Typology
Dialogue
Persuasion
Critical
Discussion
Information
Seeking
Interview
Negotiation
Advice
Solicitation
Inquiry
Scientific
Inquiry
Expert
Consultation
Deliberation
Public
Inquiry
Eristic
Quarrel
Locutions and Speech Acts
•
•
•
•
Statements and questions are locutions.
Making an assertion is a speech act.
Asking a question is a speech act.
Asking for an explanation is an even more
specific speech act.
• Putting forward an argument is a speech act.
• Offering an explanation is a speech act.
Speech Act Moves in a Dialogue
Goal of Dialogue
Sequence of Moves
Turn-taking
Respondent's Move
Speech Act
Post-condition
Proponent's Move
Pre-condition
Initial Situation
Speech Act
Evaluating Argumentation
• Take the text of discourse as your evidence.
• Is the selected speech act an argument, a
report or an explanation?
• If an argument, what are the premises and
conclusions?
• Does it fit an argumentation scheme?
• Apply the scheme to the argument
Reasoning, Argument and Explanation
Reasoning can be used for differing purposes, for
example in explanations and arguments. Reasoning is a
process of inference in passing from certain
propositions known or assumed to be true to other
propositions in a sequence (Walton, 1990). Abductive
reasoning is inference to the best explanation
(Josephsons, 1994). Practical reasoning seeks out a
prudential line of conduct for an agent in a particular
situation, while theoretical reasoning seeks evidence
that counts for or against the truth of a proposition
(Walton, 1990).
What is an Argument?
An argument is a social and verbal means of
trying to resolve, or at least contend with, a
conflict or difference that has arisen between
two parties engaged in a dialogue (Walton
1990, p. 411). According to this definition, an
argument necessarily involves a claim that is
advanced by one of the parties, typically an
opinion that the one party has put forward as
true, and that the other party questions.
Asking Questions
• The speech act of asking a question is
different from the speech act of putting
forward an argument.
• Questions don’t make assertions.
• But questions can be loaded.
• So asking a question may not be entirely
harmless or free from assertive content.
What is an Explanation?
The new dialectical theory (Walton, 2004) models
an explanation as a dialogue between two agents in
which one agent is presumed by a second agent to
understand something, and the second agent asks a
question meant to enable him to come to understand
it as well. The model articulates the view of Scriven
(2002, p. 49): “Explanation is literally and logically
the process of filling in gaps in understanding, and
to do this we must start out with some
understanding of something.”
How to Tell the Difference
Test to judge whether a given text of discourse contains an
argument or an explanation.
Take the statement that is the thing to be proved or explained,
and ask yourself the following question. Is it taken as an
accepted fact, or something that is in doubt? If the former, it’s
an explanation. If the latter, it’s an argument.
The Goal of Dialogue is Different
The purpose of an argument is to get the hearer to come to
accept something that is doubtful or unsettled. The purpose of
an explanation is to get him to understand something that he
already accepts as a fact.
Dialogue Model of Explanation
• Dialogue Conditions: explainee asks
question of a specific form asking about
what is assumed to be a known fact S.
• Understanding Conditions: explainee does
not understand S, but assumes that explainer
understands S.
• Success Conditions: explainer by what she
says brings the explainee to understand S.
Explanation in a Sequence of Dialogue
Event Taken
as Factual
by Both
Parties
Attempt
Judged to be
Successful
or not by
Respondent
Something
Perplexing
to
Respondent
about Event
Not Successful
Explanation
Dialogue
Concluded
Respondent
asks
Proponent for
Help in
Understanding
Successful
Proponent
Offers
Explanation
Attempt
Rules for CE Dialogue System
• Opening: when explainee makes an explanation
request for S (accepted fact).
• Locution Rules: defines different speech acts
(kinds of moves) that are allowed.
• Dialogue Rules: show which move must follow
each previous kind of move.
• Success Rules: show when transfer of
understanding has been achieved.
• Closing: when explainee says ‘In understand it’ or
explainer says ‘I can’t explain it’.
Typical Profile of Explanation Dialogue
Locution
Speaker
Content
U(XE)
U(XR)
ExplanRequest(S)
XE
S
Not-S
S
ExplanResponse(T)
XR
T
?
T
Understand S
XE
S
S,T
Dialogue Closes
Problems for Future Work
• How can we test whether understanding has
successfully been transferred?
• How can we evaluate whether one given
explanation is better than another?
• What is the structure of explanations of
human (and artificial agent) actions?
• What tools do we have for visualizing the
logical structure of an explanation?
What is the test whether understanding has
been successfully transferred?
• Scriven (1972, p. 32) Suggested an answer to this question
in his remark quoted below.1]
• How is it that we test comprehension or understanding of a
theory? We ask the subject questions about it, questions of
a particular kind. They must not merely request recovery
of information that has been explicitly presented (that
would test mere knowledge, as in knowing the time or
knowing the age of the universe). They must instead test
the capacity to answer new questions.
• This remark suggests that the test is the explainee’s
capacity to answer new questions, shown in a dialogue.
• But what kind of dialogue is it?
Examination Dialogue
• The examiner puts questions to the examinee, keeps track
of the examinee’s answers, and probes into them critically.
• Examination dialogue is classified by Dunne, Doutre and
Bench-Capon (2004), and Walton (2006) as a species of
information-seeking type of dialog that can often shift to a
persuasion dialog in which the questioner critically probes
into the tenability of the respondent’s collective replies
(Dunne, Doutre and Bench-Capon, 2004, p. 1560).
• In this way, the formal structure of examination as a
dialogue model can be applied to central features of the
kind of cases of examination commonly found in trials in
law.
Shift from Explanation to Examination
• We can test for the success (failure) of an
explanation by asking the explainee
questions about new situations that are
similar to S or are extrapolated from S.
• For example, if the explainee can draw a
new inference from S that is reasonable,
that is evidence he has understood S
correctly.
Example of a Dialectical Shift
• Two agents have a joint intention to hang a
picture. One has the picture and a hammer,
and knows where the other can get a nail.
They have a deliberation dialogue but can’t
agree on who should do which task. They
then shift to a negotiation dialogue in which
the one agent proposes that he will hang the
picture if the other agent will go and get the
nail (Parsons and Jennings, 1997).
Evaluating Competing Explanations
• Car crash where passenger claimed driver lost
control, and driver claimed passenger suddenly
pulled handbrake (Dutch Supreme Court Case
cited by Prakken and Renooij, 2001).
• Evidence: skid marks, crashed car, handbrake
found in pulled position, expert witness says
pulling handbrakes can cause wheels to lock.
• Analysis of Prakken and Renooij: the driver’s
account explains the factual evidence and
contradicts less of it than the passenger’s account.
• For summary, see (Walton, 2004a, 170-175)
Action Explanations
• Explanations of actions, of the kind
especially common in history and law, is
based on goal-directed reasoning.
• Goal-directed or means-end reasoning is
called practical reasoning.
• Practical reasoning has a special
argumentation scheme. Indeed, it has two of
them.
Instrumental Scheme for Practical
Reasoning
• I have a goal G.
• Bringing about A is necessary (or sufficient)
for me to bring about G.
• Therefore, I should (practically ought to)
bring about A.
Scheme for Value-based Practical
Reasoning
• I have a goal G.
• G is supported by my set of values, V.
• Bringing about A is necessary (or sufficient)
for me to bring about G.
• Therefore, I should (practically ought to)
bring about A.
The Scalpicin Example
Araucaria
Araucaria is a software tool for analyzing arguments.
It aids a user in reconstructing and diagramming an
argument using a simple point-and-click interface.
The software also supports argumentation schemes,
and provides a user-customizable set of schemes
with which to analyze arguments.
Once arguments have been analyzed they can be
saved in a portable format called "AML", the
Argument Markup Language, which is based on
XML.
http://www.computing.dundee.ac.uk/staff/creed/araucaria/
Some References
P.E. Dunne, S. Doutre, and T.J.M. Bench-Capon, ‘Discovering Inconsistency through
Examination Dialogues’, Proceedings IJCAI-05, Edinburgh, 2005, 1560-1561.
S. Parsons and N. R. Jennings, ‘Negotiation through Argumentation: A Preliminary
Report’, Proceedings of the Second International Conference on Multi-Agents
Systems, ed. Mario Tokoro, AAAI Press, Menlo Park, California, 1997, 267-274.
H. Prakken and S. Renooij, ‘Reconstructing Causal Reasoning about Evidence: A
Case Study’, Legal Knowledge and Information Systems, ed. B. Verheij et al.,
Amsterdam, IOS Press, 131-142.
M. Scriven, ‘The Concept of Comprehension: from Semantics to Software’,
Language Comprehension and the Acquisition of Knowledge, ed. J.B. Carroll and
R.O. Freedle, Washington, W. H. Winston & Sons, 1972, 31-39.
M. Scriven, The Limits of Explication’, Argumentation, 16, 2002, 47-57.
D. Walton, ‘A New Dialectical Theory of Explanation’, Philosophical Explorations,
7, 2004, 71-89.
D. Walton, Abductive Reasoning, University of Alabama Press, 2004a.
D. Walton, ‘Examination Dialogue: An Argumentation Framework for Critically
Questioning an Expert Opinion’, Journal of Pragmatics, 38, 2006, 745-777.