Combining Explanation and Argumentation in Dialogue
Floris Bex1 and Douglas Walton2
1

University of Groningen. The Netherlands
CRRAR, University of Windsor, Canada

2

Abstract. Explanation and argumentation can be used together in such a waythat evidence, in the form of arguments, is used to support explanations. In ahybrid system, the interlocking of argument and explanation compounds the
problem of how to differentiate between them. The distinction is imperative if
we want to avoid the mistake of treating something as fallacious while it is not.
Furthermore, the two forms of reasoning may influence dialogue protocol andstrategy. In this paper a basis for solving the problem is proposed using a dialogue model where the context of the dialogue is used to distinguish argumentfrom explanation.
Keywords: Argumentation, Explanation, Dialogue

1

Introduction

The hybrid model of [2][4] combines arguments and explanations in such a way thatan argument can support an explanation. The idea of argumentation and explanation
being combined is also familiar in the notion of inference to the best explanation. But
in general, there is a difference between argument and explanation, and as we willshow in this paper, it would be a fundamental error to criticize an argument as fallingshort of standards for a rational argument, when what was put forward was actually an
explanation.
A problem is that in many cases of natural language discourse, the same piece of
discourse can reasonably be interpreted as either an explanation or an argument. Similarly, a question ‘Why?’ can be interpreted as either asking for a reason that supports
some claim of the speaker or as asking for an explanation for some observed anomaly.
So here we have a pervasive problem, which can only be solved if we can find someclear and useful method of distinguishing between explanations and arguments. It is
not only a problem for logic and discourse analysis, but also for explanation systems
in computing [7], and particularly for hybrid models that combine argument with
explanation [4][18].
Our solution to the problem of distinguishing argument and explanation lies in dialogue, more specifically, in speech act theory [26]. According to this view, it is theillocutionary force of the speech act in a dialogue that determines whether reasoning
is argumentation or explanation [5]. Illocutionary force can be seen as the intention ofuttering some locution: one can say p with an intention of explaining p, arguing for p,© Springer-Verlag Berlin Heidelberg 2011

challenging p, promising p and so on. We thus argue that the distinction between
argument and explanation is not a logical one but rather that the only correct way ofmaking this distinction is to look at the dialogical context.
The question is then how to determine the purpose or intention of uttering a locution. In other words, how do we know whether some assertion is meant to explain aproposition or argue for it? The solution lies in the different purposes of explanation
and argumentation. Argumentation is meant to convince someone else, explanation is
aimed at helping them understand. Hence, the rules for argumentation and explanation
are different.
There are various reasons for wanting to properly distinguish between argumentation and explanation. For example, we might want to be able to handle situations inwhich argumentation is fallacious whilst explanation is not. Furthermore, confusionof argumentation and explanation may lead to undesirable misunderstandings andunwanted behaviour in multi-agent dialogue, as the use of either argumentative or
explanatory techniques may influence dialogue protocol and strategy. Finally, thedistinction is important in the analysis of natural language texts.
In this paper, we discuss argumentation and explanation and how to distinguish between them. We also discuss an example of the fallacy of begging the question, which
in a case of an argument is a fallacy but for explanation it may not be. In section 3 wethen show how argument and explanation can be combined in a dialogical setting andhow the rules for arguing differ from the rules for explaining.

2

Argumentation and Explanation

How can one determine, in a given text of discourse where it is said that one event
occurred because of another event, the text should be taken as representing an argument or an explanation? The problem is that cases where a given text of discourse
could be interpreted as expressing either an argument or an explanation are fairly
common, as an instructor of an informal logic course can tell you. Another factor isthat in artificial intelligence, something called a justification explanation been recognized [7], suggesting that argument and explanation are often combined and work
together. Suffice it to say that abductive reasoning, also commonly called inference tothe best explanation, is just such a species of argument. There is also a tendency
among students who are learning to use argumentation techniques in introductory
logic courses, once they have learned some tools to analyze and evaluate arguments,
to see any text of discourse they are given as expressing an argument. This can be a
problem. The student who treats an explanation as an erroneous argument committing
a fallacy, for example the fallacy of arguing in a circle, when the argument is really an
explanation, has committed an error by misapplying logic.
Logic textbooks attempt to solve this problem by offering a pragmatic test to
determine, in a given case, whether a passage expresses an argument or an explanation, namely by looking at how the discourse is being used in the given case. If it isbeing used to prove something that is in doubt, it is an argument. If it is being used toconvey understanding of something that does not make sense or is incomprehensible,

it is an explanation. The focus of this way of drawing the distinction is on the proposition or event that is to be explained or proved. If it is not subject to doubt (e.g. it isgenerally accepted as true, or can be taken for granted as true), the bit of text in question should be taken as an explanation. If it is subject to doubt, that is, if it is unsettled
whether it is true or not, then the bit of text in question should be taken as an argument.
Let’s look at two examples of explanations cited in the most widely used logic
textbook [14, p. 19]. Here is the first one: the Challenger spacecraft exploded after
liftoff because an O-ring failed in one of the booster rockets. Classifying this assertion
as an argument or an explanation depends on whether the statement that the Challenger spacecraft exploded after liftoff should be taken as a statement that is accepted as
factual or whether it should be taken to be a statement that is subject to doubt and that
requires proof, or at least some supporting evidence, before it is accepted. The statement that the O-ring failed is not being used to prove the statement that the spacecraft
exploded. That the spacecraft exploded is not in doubt. Most of us graphically remember seeing the exploding spacecraft on TV. The passage quoted above is nottrying to prove that statement by providing evidence or reasons that support or imply
it. The passage assumes that it is an accepted matter of fact that the spacecraft exploded, and is trying to show why it exploded. So the passage contains an explanation, as
opposed to an argument. Because it is generally taken as common knowledge that the
Challenger spacecraft exploded after liftoff, the whole causal statement is taken as an
explanation.
The same principle applies to the second example: cows can digest grass, while
humans cannot, because their digestive systems contain enzymes not found in humans. Should we take it as an accepted fact that cows can digest grass while humans
cannot, or should we take this statement as subject to doubt and something that needs
to be proved before it can be accepted? Again, it seems fairly plausible that the statement that cows can digest grass while humans cannot is generally accepted as part ofcommon knowledge. If so it doesn’t need to be proved, and the compound statement
joined by the causal ‘because’ connective should be taken as an explanation.
We need to be aware, however, that this distinction based on common knowledge
is not the only criterion required to distinguish arguments from explanations in a natural language text of discourse. Another part of the evidence or the so-called indicatorwords, like ‘therefore’, ‘since’, ‘accordingly’, and so forth. The problem is that thesame indicator words are often used with respect to both arguments and explanations.
Hence in any individual case one has to look carefully at the details of the actual text
of discourse in the given case.
In the context of argumentation, premises are offered as proof of a conclusion
or a claim, often in order to persuade someone or settle an issue that is subject todoubt or disputation. A number of computational models of argumentation haveemerged and matured in the past twenty-or-so years [20] and the computational aspects of the dialectics of argument and of the structure of argument are well understood (cf. [19]).
In the context of explanation, the explananda (facts to be explained) are explainedby a coherent set of explanans (facts that explain). The usual purpose of explanation

is not necessarily to convince someone but rather to help someone understand why the
explananda are the case. Computational models for explanation are mainly based on
the technique of abductive (model-based) reasoning, which has been studied in thecontext of medical and system diagnosis [9]; other examples of computational explanation are [8], which models explanatory dialogues, and [25], which uses explanations for natural language understanding.
Despite the interest in dialogue treatments of explanation, the formal dialecticalsystems deriving from the early work of Hamblin treat only arguments. In Hamblin’s‘Why-Because System with Questions’ [12, pp. 265-276], there are two participants
who take turns making moves following syntactical rules (protocols). For example,
when one party asks the question ‘Why A?’, the other party must reply with one ofthree speech acts: Assertion A; No commitment A; Statements B, B → A (where →represents the material conditional of propositional calculus). The language is that ofpropositional calculus, but it could be any other logical system with a finite set of
atomic statements [12. p. 265]. As each party moves, statements are either inserted
into or retracted from its commitment set of the party who made the move. A recordof each party’s commitments is kept and updated at each next move. On Hamblin’s
account, “a speaker is committed to a statement when he makes it himself, or agrees
to it as made by someone else, or if he makes or agrees to other statements fromwhich it clearly follows” [13, p. 136]. Interestingly, a why-question can only be arequest for the other to present an argument, never an explanation.
Despite the important role explanations can play in argumentative dialogue, there
have not been many attempts to combine argumentation and explanation into one
formal model. Perhaps the most thorough work thus far is [2][4], in which argumentsin the framework of [19] are combined with abductive-causal reasoning based onstandard models of explanation [9] in one hybrid theory. The basic idea of this hybrid
approach is as follows. A logical model of abductive-causal reasoning takes as input acausal theory (a set of causal rules) and a set of observations that has to be explained,
the explananda, and produces as output a set of hypotheses that explain the explananda in terms of the causal theory. Arguments can be used to support and attack stories,
and these arguments can themselves be attacked and defeated. Thus, it is possible toreason about, for example, the extent to which an explanation conforms to the evidence. This is important when comparing explanations: the explanation that is best
supported and least falsified by arguments is, ceteris paribus, the best explanation.
2.1

Argumentation and explanation in dialogue

Dialogues consist of a series of locutions or utterances made by the participants. As asimple example of a dialogue, take the following exchange between Allen and Beth.
1. Allen: The Evanston City Council should make it illegal to tear down the city’s old
warehouses.
2. Beth: What’s the justification for preserving them?
3. Allen: The warehouses are valuable architecturally.
4. Beth: Why are they so valuable?

5. Allen: The older buildings lend the town its distinctive character.
During a dialogue, the participants construct and navigate an underlying reasoning
structure [23], a static rendition of the claims, arguments and explanations proposed.
For example, in the above dialogue one of the arguments made is ‘The warehouses
are architecturally valuable therefore the Evanston city council should make it illegal
to tear them down’. The link between a dialogue and this underlying structure can be
explained by combining speech act theory [26] with Hamblin-style dialogue theory. A
speech act can be analyzed as a locutionary act (the actual utterance, e.g. ‘What’s thejustification for preserving them?’), but also as an illocutionary act which consists of
the illocutionary force, meaning that it functions a kind of move in a dialogue. For
example, one may include p in different kinds of moves like asserting p, asking p,
challenging p, promising p and so on. In our example, speech acts (1) and (2) have thesame propositional content, namely ‘The Evanston City Council should make it illegal to tear down the city’s old warehouses’. The illocutionary force, however, differs
between (1) and (2): where (1) is uttered with the intention of asserting ‘The Evanston City Council should make it illegal to tear down the city’s old warehouses’, (2)can be seen as an instance of requesting an argument for this sentence. Figure 1
shows the example dialogue at the top, which is connected to the underlying reasoning structure via illocutionary relations.
Allen: The
warehouses
dialogue should bepreserved.

Beth:
Why?

Allen:
They should bereservedbecause they are
valuablearchitecturally.

Beth:
Why?

Allen: they are valuable
architecturally because
The older buildings
lend the town its
distinctive character.

assertingillocutionary
relationsrequestargumentThe
reasoning warehouses
should be
structurepreserved.

arguing

Arg

requestargument or
explanation?

The
warehouses
are valuable
architecturally

arguing or
explaining?

Arg/
Expl

The olderbuildings
lend thetown its
distinctive
character.

Fig. 1. Argumentation and explanation in dialogue

There are different types of dialogue [30], each with a different goal. In persuasion
dialogues, for example, one of the players makes a claim which he has to defend,
while the other player’s goal is to dispute this claim. Another example of a dialogue
type is inquiry dialogue, the aim of which is to increase knowledge. The participantsin such a dialogue collectively gather, organize and assess hypothetical explanations
and evidence for and against these explanations. Hence, Walton [28] identifies bothexplanation and argumentation as functions of an inquiry dialogue. Aleven [1] hasdefined an inquiry dialogue based on the hybrid theory in which the participants build
explanations and then support and critically analyze these explanations using arguments. In this type of dialogue, the participants collectively build a hybrid theory of
explanations and arguments.
2.2

The problem of distinguishing argumentation and explanation

The very first problem in attempting to analyze the concept of an explanation is toattempt to provide criteria to determine when some piece of discourse that looks likeit could be either an explanation or an argument should be taken to fit into one category or the other. One possible way of distinguishing between argumentation and explanation might be to look at the product of our reasoning, that is, the underlying reasoning structure. At first sight, it often seems an explanation is abductive and causal
whilst an argument is modus-ponens style, non-causal reasoning. The basic idea of
causal abductive inference is that if we have a general rule p c q, meaning p causes
q, and we observe q, we are allowed to infer p as a possible explanation of q. In contrast, argumentation is often seen as reasoning from a premise p to a conclusion q
through an inference rule p c q, where this rule need not necessarily be causal.
However, as it turns out it is also possible to give abductive or causal arguments (cf.
[31]; causal argument). Similarly, one may perform explanatory reasoning by taking arule q c p, meaning q is evidence for p (see [4] for a discussion on evidential andcausal reasoning).
As was previously argued in [5], argument and explanation can only be properly
distinguished by looking at the dialogical context of reasoning. In order to determine
this context, we need not just look at the original intention of the speaker (i.e. theillocutionary force of a speech act) but also at the broader dialogical context, such as
the utterance that was replied to by the speaker and the intentions of the other participants. Consider the example in Figure 1. Allen makes his first move by asserting thatthe old warehouses should be preserved, and then Beth asks for a justification for thisclaim. Here it is clear that Beth is requesting an argument to justify Allen’s claim.
Allen then provides this, but then Beth asks him the why-question: why are they sovaluable? The speech act could be interpreted as requesting either an argument (challenging) or an explanation (Figure 1). Allen’s first reply to a challenge constitutes anargument but Allen’s second reply is ambiguous.
Circular Arguments and Explanations. Circular reasoning has long been a concern
in logic. The fallacy of arguing in a circle has been included under the heading of
informal fallacies in logic textbooks since the time of Aristotle [12]. But circularity is
not been concerned exclusively with respect to arguments. Circular explanations areoften condemned by the logic textbooks as unhelpful and confusing. But the reasonsfor condemning circular explanations are different from those for condemning circular argumentation [27].

The fallacy of arguing in a circle, or begging the question, is committed by an instance of circular reasoning that fails to work as an argument supposed to prove theconclusion that is in doubt. A standard textbook example is provided by the following
short dialogue between a man, Smith, and his bank manager.
1. Manager: Can you give me a credit reference?
2. Smith: My friend Jones will vouch for me.
3. Manager: How do we know he can be trusted?
4. Smith: Oh, I assure you he can.
Here we can detect a sequence of circular reasoning. The trustworthiness of Smith is
supposed to depend on the testimony of his friend Jones, but the trustworthiness ofJones depends on the testimony of his friend Smith. This obviously won’t work because of the circularity in the procedure of providing evidence to support a claim in anargument. If Jones’s trustworthiness can be vouched for by some source independentof Smith, then the argument would work, and would no longer commit the fallacy of
begging the question. In this kind of case, we cannot prove claim q by relying on
premise p and then try prove p by backing it up by using q as a premise. It does notfollow, however, that all circular arguments are fallacious as we now indicate.
Jones will
vouch for
Smith.

Smith
can betrusted.

A third party
can vouchfor Jones.
Jones
can betrusted.

Smith will
vouch for
Jones.

The trustworthiness of
this third party does
not depend on thetrustworthiness ofeither Smith or Jones.

Fig. 2. Circular reasoning in the credit reference example

To extend the example a bit further, suppose that a third-party could vouch for Jones,
and that the trustworthiness of this third party is not dependent on the trustworthinessof either Smith or Jones. Then there would still be a circle in the argumentation structure, as shown in Figure 2, but the two text boxes on the right function as premises ina linked argument supporting the trustworthiness of Jones. This new argument gives
us a way of breaking out of the circle that we were locked into in the previous argument represented by the dialogue above. The argumentation as a whole shown in
Figure 2 has a circle in it, but when evaluated a whole it does not commit the fallacy
of begging the question.

The problem with real cases where the fallacy of begging the question is a serious
danger is that the circle is embedded in a text where it may be mixed in with muchother discourse. This danger becomes even more serious when the discourse combines argumentation with explanation. But if you can find such a circle in an argument, it represents quite a serious criticism of that argument. A rational argumentused to persuade a respondent to accept its conclusion must not be based on premisesthat can only be accepted if part of the evidence for one of these premises depends on
the prior acceptance of the conclusion itself. If, so the argument is useless to prove theconclusion. The argument lacks what has been called a probative function [27].
The situation is different for explanations. They need to be evaluated in a different
way. When a circular explanation is fallacious it is because it is uninformative or
useless in transferring understanding. As with arguments, however, an explanation
can be circular, but still be useful as an explanation. One reason is that there are feedback processes in nature, and to explain what is happening, the account given needs to
go in a circle. For example, the more overweight a diabetic gets, the more insulin is
produced in his blood, but the more insulin there is in his blood, the more he eats, andthe more he becomes overweight. In this vicious circle, the problem becomes worse
and worse by a continual process of feedback that escalates it. To understand that theprocess is circular helps to explain the whole picture of what is going on.
Let us return to our warehouse dialogue from section 2.1. First, let us assume that
Allen’s reply (5) is a speech act of arguing that creates an argument ‘the older buildings lend the town its distinctive character so the warehouses are valuable architecturally’ (Figure 3). Now extend the dialogue as follows:
6. Beth: OK agreed. But why do the older buildings lend the town its distinctive character?
7. Allen: The warehouses are valuable architecturally.
When examining this dialogue we might be suspicious about the possibility that it
contains the fallacy of begging the question. After all, when Allen is asked by Bethabout the justification for preserving the old warehouses (4), Allen replies that thewarehouses are valuable architecturally (5). But then later, at his last move in the
dialogue (7), he reverts back to making the same statement again. It definitely appears
that the dialogue is circular. The question then is whether the circularity is benign orvicious.
Let’s interpret Beth’s question (6) as a request for explanation. Now the reasoning
in the dialogue is no longer just a sequence of argumentation, but a mixture of argumentation and explanation (Figure 3). In order to prove his claim that the warehouses
are valuable architecturally, Allen has used the premise that the older buildings lend
the town its distinctive character. But then he has used the former as an explanation to
help Beth understand the latter. The sequence of replies is then circular but not fallacious. Allen is merely explaining why the older buildings lend the town its distinctive
character. Since Beth has agreed to this proposition, Allen does not need to prove it,and so there is no interdependency in the sequence of argumentation of the kind required for the committing of the fallacy of begging the question. There is no failure tofulfill the probative function of the kind that signals circular reasoning of a kind asso-

ciated with committing the fallacy of begging the question. Allen is not using premisep to prove conclusion q and then using q as a premise required to prove p.
This is an unusually subtle case to disentangle. There is a circularity there, but it isbenign one where the explanation fits into the argumentation in a way that is not an
obstruction to the dialogue. The circularity could help Beth to understand the situation. So it does have a legitimate function. There is circular reasoning, but no circularargumentation.
Arg

The
warehouses
should bepreserved.

Arg

The
warehouses
are valuable
architecturally

The olderbuildings lend
the town its
distinctive
character.

ExplanFig. 3. Mixed Version of the Warehouse Example

3

Defining Explanation in Dialogue

How then, given the text of discourse, are we to determine whether the text is better
taken to represent an argument or an explanation? The test widely adopted in logic
textbooks uses the distinction between an accepted fact and a disputed claim wasdiscussed in section 2. But we need to go even beyond that and look more broadly at
how arguments and explanations function as different kinds of moves in a dialogue.
An argument is a speech act used to convince the hearer of some unsettled claim andan explanation is a speech act used to help the hearer to understand something. Thisdistinction can be drawn as one of a difference of purpose of discourse. Since thedistinction is drawn this way, it can be seen to be based on a dialogue model of communication in which two parties take turns in putting forward speech acts. As argued
above, in order to then determine whether something is an argument or an explanation, we need not just look at the original intention of the speaker (i.e. the illocutionary force of a speech act) but also at the broader dialogical context.
Defining explanation as a speech act put forward with the aim of transferring understanding from an explainer to an explainee raises further questions. What is understanding, and how can it be transferred from one party to another? Research in AI andcognitive science shows that communicative agents understand the actions of otheragents because they share “common knowledge” of the way things can normally be
expected to proceed in familiar situations in everyday life. This common knowledge
can be modeled as explanation schemes or scripts [25]. An explanation scheme is a
generic scenario, an abstract rendering of a sequence of actions or events of a kind.
For example, the restaurant-script contains information about the standard sequence(s) of events that take place when somebody goes to dine in a restaurant.

Explanation schemes can be instantiated by particular explanations and thus thescheme provides the conditions for the explanation’s coherence [2]. Take, for example, a man who enters a restaurant, orders a hamburger and then removes his pants
and offers the waiter his pants. This particular story is incoherent, because it does notadhere to the typical restaurant scheme. But if this story fits another explanation
scheme it can still be coherent. Suppose information is added that the waiter spilled
hot soup on the man’s legs. This new information would fill out the story in such a
way that it hangs together as a coherent script about what happens when someone
spills hot liquid on one’s clothes. Thus, an explanation may be causal, motivational,
teleological, and so on.
A dialogue model of explanation can then be constructed by building it around thenotion of the mutual comprehensibility of a story, or connected sequence of events or
actions that both parties can at least partially grasp in virtue of their common
knowledge about the ways things can be generally expected to happen in situations
they are both familiar with. This is the route taken by Schank and his colleagues incognitive science (cf. [25]). According to them, explanation is a transfer of understanding from one party to another in a dialogue, where understanding is clarified
scripts, “frozen inference chains stored in memory”. On Schank’s theory, failures ofunderstanding of kinds that trigger a need for an explanation occur because of ananomaly, a gap in a story that contains a part where it fails to make sense, or even
where the whole story fails to make sense because it does not “add up”. An explanation, on this approach, is a repair process used to help someone account for the anomaly by using scripts that could be taken from script libraries.
3.1

A Dialogue System for Argument and Explanation

We now propose an example of a dialogue system for argumentation and explanation,
based on the protocols presented by [6][29]. Our dialogue system consists of a communication language that defines the possible speech acts in a dialogue, a protocolthat specifies the allowed moves at any point in the dialogue and commitment rules,
which specify the effects of a speech act on the propositional commitments of the
dialogue participants. Furthermore, we assume that both players have their own separate knowledge bases containing argumentation schemes and explanation schemes,
which form the basis of arguments and explanations proposed in the dialogue [22].
In a game for argumentation and explanation, essentially two types of dialogue are
combined: explanation dialogue [8][17][29] and examination dialogue [10]. In a pureexplanation dialogue the explainer is trying to transfer understanding to the explainee;
an examination dialogue can be used to test (evaluate) an explanation. Examination
dialogues are more adversarial. For example, the answerer’s inconsistency in previous
replies can be attacked using probing counter-arguments to test his trustworthiness(for example, as a witness). Figure 4 shows the combination of explanation and examination dialogues as a process.

STOP

Explainee
asks whyquestion.
EXPLANATIONDIALOGUE

Explanation
evaluated.

Explainer
presents
story.

The story
holds up oris refuted.

STOP

Explainee
finds
anomaly instory.

Explainer
explains
anomaly.

Examination
dialoguesuccessful.

Sequence of
examination
moves by bothparties.

Explainee
accepts
explanation.

Explaineeprobesdeeper: notsatisfied.

EXAMINATIONDIALOGUE

Fig. 4. Explanation and examination dialogues combined

The speech acts of a game for explanation and argumentation are presented in the
typical format Fp, where F is the illocutionary force and p is the propositional content.
1. claim . The player claims a proposition .
2. argue because . The player states an argument because based on an argumentation scheme SA from the player’s knowledge base.
3. challenge . The player asks for an argument for .
4. concede . The player admits that proposition is the case.
5. retract . The player declares that he is not committed (any more) to .
These speech acts are standard in systems for argumentative dialogue (cf. [16]). Now,
for explanation we need other speech acts, as defined by [6][29].
6. explain because . The player provides an explanation because based on an
explanation scheme SE from the player’s knowledge base.
7. explanation request . The player asks for an explanation of .
8. inability to explain . The player indicates that he cannot explain .
9. positive response: The player indicates that he understands an explanation.
10. negative response: The player indicates that he does not understand an explanation.
Note that with explanation, the issue is not whether a player is convinced (i.e.
wants to be committed to a proposition) but rather whether he understands a proposition.
Commitment rules specify the effect of moving with one of the speech acts. A
player becomes committed to any claim, argument or explanation he puts forward,and also to any claim he concedes to. Commitments can be retracted by the retractspeech act.
The following standard protocol rules are part of the dialogue system (cf. [28]).
1. The players each take their turn.
2. The players cannot move the exact same speech act twice.
3. Players cannot commit to propositions which would make their commitments inconsistent.
4. Players are only allowed to argue for propositions to which they are committed but
the other player is not.
5. Players are only allowed to argue against propositions to which the other player iscommitted and they are not.
6. A challenge move may only follow either a claim move or an argue becausemove.
7. A challenge move can only be responded to by either an argue because
move or a retract move.
8. Players are only allowed to challenge propositions to which the other player iscommitted and they are not.
9. Players can only concede to propositions to which the other player is committed.
10. Players can only retract propositions to which they are committed.
The above rules capture the basics of argumentative dialogue. The rules encapsulate
the idea that argumentation is an activity aimed at proving (or disproving) someclaim: once both parties are committed to a claim, there is no point in arguing any
further.
For explanation the rules are different, as explanation is aimed at improving understanding. Both parties can be committed to a claim, but one of the two may not fully
understand it.
11. Players are only allowed to request explanations of propositions to which bothplayers are committed.
12. Players are only allowed to request explanations of propositions for which they
themselves do not have an explanation scheme in their knowledge base.
13. A request explanation move can only be responded to by an explain because
move or an inability to explain move.
14. Players are only allowed to explain propositions to which both players are committed.
15. Players are only allowed to explain propositions for which they have an explanation scheme in their knowledge base and the other party does not.
16. An explain move is always followed by either a positive response or a negative response.
Note how explaining is in a sense analogous to arguing but with a different aim,
namely making someone understand a proposition instead of committing them to it.
The system can be applied to the two examples taken from the logic textbook [14],the Challenger spacecraft example and the example about the digestive system of a

cow. These are classified as explanations because of the rules stating that players are
only allowed to argue for or against propositions to which the other player is notcommitted. In the one example it is taken as common knowledge that the Challenger
spacecraft exploded after liftoff. In the other example, it is taken to be common
knowledge that cows can digest grass while humans cannot. Therefore both parties
can be taken to be committed to both these propositions. Hence in both examples, itwould be inappropriate for either party to argue either for or against these propositions. However it would be appropriate for either party to offer an explanation.
Briefly, it can be shown how a script is involved in the spacecraft example as follows. To make the explanation successful the party to whom it was directed musthave enough general knowledge about how rockets work, how a rocket can explode,and to connect an O-ring failure to a leakage of fuel. There must also be knowledge
about what might normally be expected to happen when a fuel leak occurs during theoperation of the rocket motor. The receiver of the explanation must also know that the
booster rockets are attached to the spacecraft in such a way that if the booster rocket
explodes, the whole spacecraft that is attached to it will also explode. To connect allthese events into a coherent script that explains how the spacecraft exploded after
liftoff the receiver of the explanation must already have the common knowledge required to understand how this series of events and objects is connected up into a coherent story.
How the system applies to the example dialogue about the warehouses is indicated in Figure 1 in the account given of the illocutionary relations in that figure. The
evidence for classifying moves as arguments or explanations is indecisive in the instance where Beth asks Allen the question ‘Why are the warehouses so valuable?’ As
noted, the speech act could be interpreted as requesting either an argument or an explanation. There was another ambiguous speech act when Beth asks Allen why thewarehouses are so valuable. This speech act could be interpreted as requesting either
an argument or an explanation, as noted in the discussion of the case in section 2.2.
The system manages these cases by analyzing them as instances where the evidence
given in the dialogue exchange is insufficient to classify the speech act as either anargument or an explanation. The system needs to then follow up by shifting to an
examination dialogue where the dialogue participant who asked the question needs tobe examined and must indicate whether he or she is putting forward the speech act as
an argument on explanation. In many instances, especially the short ones like thosefound in the logic textbooks, the text of the case is merely given, and there is no possibility of examining the questioner. In such cases we need to make a determination
based on the given textual and contextual evidence. It is our contention that this determination needs to be made in the framework provided by our hybrid system of
dialogue for argument and explanation.

4

Related Research

We have presented only relatively simple examples, or at any rate short ones, that can
fit the space confines of this paper. However, we would suggest as a project for fur-ther research applying the dialogue system comprising both arguments and explanations to longer examples of dialogues of the kind that can already be found in theliterature. This literature is about explanation systems, but it could be helpful to reexamine the examples used in them, as well as other longer texts containing explanations, using this new system. In some instances of applying our system to problematiccases where there are ambiguous instances of questions that could be requests for
either explanations or arguments, participants will need to extend the dialogue by
having a clarification dialogue used to deal with ambiguity.
In addition to the dialogue systems that combine argumentation and explanation
as proposed in [6][29], there are numerous explanations systems that incorporate theideas about transferring understanding through explanations. For example,
ACCEPTER [15] is a computational system for story understanding, anomaly detection and explanation evaluation. In this system, explanations are directed towards
filling knowledge gaps revealed by anomalies. Examples of explanations processedby ACCEPTER along the lines of the dialogue sequence above, include the death of arace horse, the explosion of the space shuttle Challenger, the recall of Audi 5000 cars
for transmission problems, and an airliner that leaves from the wrong departure gate([15], p38).
The schemas in ACCEPTER’s memory are represented as MOPS (memory organization packages) representing stereotyped sequences of events. MOPS help anagent understand by providing expectations on how things can normally be expected
to go in a familiar situation. MOPS are comparable to the stories used in the hybrid
theory. A simplified version of the explanation of the explosion of the space shuttle
Challenger modeled by Leake [15, 39-53] can be used to show how this example fits
nicely into the way of treating explanations in the hybrid theory.
This version of the explanation [15, 39] can be summed up as follows. The
boosters burned through, allowing flames to reach the main fuel tank, causing an explosion. According to the engineers, the explosion was caused by the booster seals
being brittle and the cold weather. The explanation given is that the Challenger’s
explosion was caused by the flame in the booster rockets, and prior to that by the cold
weather which was the cause of the brittleness of the O-rings which enabled theflames to leak out through the seals. This causal sequence can be displayed in the
hybrid theory as shown in figure 5. The arrows with filled heads represent causal
relations, while the arrows with white heads represent arguments.
Coldweather

Brittlenessof the Orings

Boosters
burnedthrough

Enabled theflames to leakout of theboosters throughthe seals

The engineers gave this information
Fig. 5. Explanation supported by evidence

Allowedflames toreach main
fuel tank.

Challenger’s
explosion

The explanation given in the example in section 2 explained the Challenger explosion by presenting the story that the spacecraft exploded because the O-ring failed in
one of the booster rockets. This story leaves out intervening causal steps made explicit in the fuller story represented in figure 5. Also, we see at the bottom left of figure 5,
there was additional information given by testimony of the engineers. This testimony
can be seen as an argument supporting the two initial items in the causal story sequence along the top and right. This supplemented explanation expands the story ofwhat happened, yielding better understanding of why the Challenger explosion happened. It does this by filling further information in the causal sequence in the story
and by adding in evidence supporting part of the story.
Cawsey’s work [8] on computational generation of explanatory dialogue andMoore’s dialogue-based analysis of explanation for advice-giving in expert systems[17] also took a dialogue approach. Moore defines explanation as an inherently incremental and interactive process that requires a dialogue between an explanation
presenter who is trying to explain something and a questioner who has asked for an
explanation.
An interesting piece of related research is [3], which uses scripts or story schemes
to model cases about the facts. These cases can then be argued with using the argumentative moves of CATO [1], which were originally developed for reasoning withlegal cases. What this means is that [3] have a skeleton dialogue system that uses
scripts to perform argumentation instead of explanation. This conforms with our findings: it is not the logical structure of the reasoning or the schemes used in reasoningthat determines whether something is explanation or argumentation but the context ofthe dialogue in which the reasoning is performed and the schemes are used.

5

Conclusion

In this paper, we have discussed the problem of distinguishing between argumentationand explanation. In many cases, the same piece of discourse can reasonably be interpreted as either an explanation or an argument, and the logical structure of the reasoning proposed also does not conclusively distinguish between the two. The distinction
is important for several reasons. First, there are situations in which argumentation
may be fallacious whilst explanation is not, as illustrated by our examples of circularreasoning in section 2.2.1. Second, explanation and argumentation serve different
aims and it is important that there is no confusion in multi-agent dialogue; if a request
for explanation is interpreted as a request for argumentation, this may lead to undesirable misunderstandings and unwanted behaviour by agents. We have shown that such
confusions can easily lead to the committing of logical fallacies. The illustration we
have used to make this point is the specific fallacy of begging the question, also
known as arguing in a circle. Finally, the distinction is important for the connection
between argumentation, story-based explanation and discourse analysis, as argumentation schemes and explanation schemes can play important roles in the analysis ofnatural language texts [11][21].

Our solution involves looking at the context of dialogue to determine whether reasoning is argumentation or explanation. Whether something is argumentation or explanation is determined by the intention of uttering a locution, and this intention canbe inferred from the context of the dialogue, such as the speech act that was replied toand the knowledge and intentions of the other players. This context of dialogue can bemodeled as a dialogue system (section 3). In this sense, our dialogue system for argumentation and explanation does not only provide normative rules for coherent dialogue (as is usual), but it also helps us describe the difference between argumentationand explanation in dialogue.

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