Combining Explanation and Argumentation in Dialogue
Douglas Walton1 and Floris Bex2
Abstract.2 In the hybrid theory, explanation and argumentation
are used together in such a way that evidence, in the form ofarguments, can be used to support an explanation. But theinterlocking of argument and explanation in a hybrid systemcompounds the problem of how to differentiate between them inreal cases. The distinction is imperative if we want to avoid themistake of treating something as fallacious while it is not.
Furthermore, the two forms of reasoning may influence dialogue
protocol and strategy. 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 argument from explanation.

1

INTRODUCTION

The hybrid model of [1][4] combines arguments and explanations
in such a way that an argument can support an explanation. The
idea of argumentation and explanation being combined is alsofamiliar in the notion of inference to the best explanation. But ingeneral, there is a difference between argument and explanation,
and as we will show in this paper, it would be a fundamental error
to criticize an argument as falling short of standards for theacceptability of a rational argument, when what was put forward
was meant to be 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?’ canbe interpreted as either asking for a reason that supports someclaim of the speaker or as asking for an explanation for someobserved anomaly. So here we have a pervasive problem, which
can only be solved if we can find some clear and useful method of
distinguishing between explanations and arguments. It is not only aproblem for logic and discourse analysis, but also for explanation
systems in computing [7], and particularly for hybrid models thatcombine argument with explanation [4][15].
Our solution to the problem of distinguishing argument andexplanation lies in dialogue, more specifically, in speech act theory[23]. According to this view, it is the illocutionary force of the
speech act in a dialogue that determines whether reasoning isargumentation or explanation [5]. Illocutionary force can be seenas the intention of uttering some locution: one can say p with anintention of explaining p, arguing for p, 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 of making 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
22Centre for Research in Reasoning, Argumentation and Rhetoric(CRRAR), University of Windsor, Canada.
Argumentation Research Group, University of Dundee, United Kingdom.

some assertion is meant to explain a proposition or argue for it?
The solution lies in the different purposes of explanation andargumentation. Where 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 distinguishbetween argumentation and explanation. For example, we mightwant to be able to handle situations in which argumentation is
fallacious whilst explanation is not. Furthermore, confusion ofargumentation and explanation this may lead to undesirable
misunderstandings and unwanted behaviour in multi-agent
dialogue, as the use of either argumentative or explanatory
techniques may influence dialogue protocol and strategy. Finally,
the distinction is important in the analysis of natural language texts.
In this paper, we briefly discuss argumentation and explanationand how we can distinguishing between them. We also discuss an
example of the fallacy of begging the question, which in case of anargument is a fallacy but for explanation is not. In section 3 wethen show how argument and explanation can be combined in a
dialogical setting and how the rules for arguing differ from therules for explaining.

2

ARGUMENTATION AND
EXPLANATIONIn the context of argumentation, premises are offered as proof of aconclusion or a claim, often in order to persuade someone or settle
an issue. A number of computational models of argumentation
have emerged and matured in the past twenty-or-so years [17] andthe computational aspects of the dialectics of argument and of thestructure of argument are well understood (see e.g. [16]).
In the context of explanation, the explananda (facts to be
explained) are explained by a coherent set of explanans (facts that
explain). The usual purpose of explanation is not necessarily toconvince 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 the context of medical andsystem diagnosis [9]; other examples of computational explanation
are [8], which models explanatory dialogues, and [22], which uses
explanations for natural language understanding.
Despite the important role explanations can play inargumentative dialogue, there have not been many attempts tocombine argumentation and explanation into one formal model.
Perhaps the most thorough work thus far is [1][4], in whicharguments in the framework of [16] are combined with abductivecausal reasoning based on standard models of explanation [9] in
one hybrid theory. The basic idea of this hybrid approach is asfollows. A logical model of abductive-causal reasoning takes asinput a causal theory (a set of causal rules) and a set ofobservations that has to be explained, the explananda, and produces
as output a set of hypotheses that explain the explananda in termsof the causal theory. Arguments can be used to support and attack
stories, and these arguments can themselves be attacked anddefeated. Thus, it is possible to reason about, for example, theextent to which an explanation conforms to the evidence. This isimportant when comparing explanations: the explanation that isbest 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 theparticipants. As a simple example of a dialogue, take the following
exchange between Allen and Beth, which is taken from [18].
(1) Allen: The Evanston City Council should make it illegal totear 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 (implicitly) construct andnavigate an underlying reasoning structure [21], a static renditionof 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 is explained inspeech act theory [23]. A speech act can be analyzed as alocutionary act (the actual utterance, e.g. ‘What’s the justification
for preserving them?’), but also as an illocutionary act which
consists of the illocutionary force (the intention of uttering a
locution: one may say p with an intention of asserting p, asking p,
challenging p, promising p and so on) and the propositional
content, the proposition(s) the act refers to. In our example, speechacts (1) and (2) have the same propositional content, namely ‘The
Evanston City Council should make it illegal to tear down thecity’s old warehouses’. The illocutionary force, however, differs
between (1) and (2): where (1) is uttered with the intention ofasserting ‘The Evanston City Council should make it illegal to teardialogue

Beth:
Why?

Allen: The
warehouses
should bepreserved.

assertingreasoning
structure

The warehouses
should be preserved.

2.2

The problem of distinguishingargumentation and explanation

The very first problem in attempting to analyze the concept of an
explanation is to attempt to provide criteria to determine whensome piece of discourse that looks like it could be either an
explanation or an argument should be taken to fit into one categoryor the other. One possible way of distinguishing between
argumentation and explanation might be to look at the product ofour reasoning, that is, the underlying reasoning structure. At firstsight, 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 generalrule p  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  q, where this rule need notnecessarily be causal. However, as it turns out it is also possible togive abductive or causal arguments (see e.g. [27]'s causal
argument). Similarly, one may perform explanatory reasoning by
taking a rule q  p, meaning q is evidence for p (see [4] for a
discussion on evidential and causal reasoning).
As was previously argued in [5], argument and explanation can
only be properly distinguished by looking at the dialogical context

Allen:
They should be reserved
because they are
valuable architecturally.

requestargument

illocutionary
relations

down the city’s old warehouses’, (2) can be seen as an instance ofrequesting an argument for this sentence. Figure 1 shows theexample dialogue at the top, which is connected to the underlying
reasoning structure via illocutionary relations.
There are different types of dialogue [26], each with a different
goal. In persuasion dialogues, for example, one of the players
makes a claim which he had to defend, while the other player’s
goal is to dispute this claim. Another example of a dialogue type isinquiry dialogue [26], the aim of which is to increase knowledge.
The participants in such a dialogue collectively gather, organize
and assess hypothetical explanations and evidence for and against
these explanations. Hence, Walton [24] identifies both explanation
and argumentation as functions of an inquiry dialogue. [1] havedefined an inquiry dialogue based on the hybrid theory in which
the participants build explanations and then support and criticallyanalyze these explanations using arguments. In this type of
dialogue, the participants collectively build a hybrid theory of
explanations and arguments.

arguing

Arg

Beth:
Why?

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

requestargument or
explanation?

The warehouses
are valuable
architecturally.

Figure 1. Argumentation and explanation in dialogue.

arguing or
explaining?

Arg/
Expl

The olderbuildings lend thetown its distinctive
character.

of reasoning. In order to determine this context, we need not justlook at the original intention of the speaker (i.e. the illocutionary
force of a speech act) but also at the broader dialogical context,
such as the utterance that was replied to by the speaker and theintentions of the other participants. Consider our example in Figure
1. Allen makes his first move by asserting that the old warehouses
should be preserved, and then at her first move Beth asks for ajustification for this claim. Here it is clear that Beth is requesting
an argument to justify Allen’s claim. Allen provides this at his next
move, 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 an argument but Allen’s
second reply is ambiguous.

2.2.1

Circular Arguments and Explanations

The distinction between argumentation and explanation is vitally
important, as it would be a fundamental error to criticize a text as
falling short of standards for acceptability or validity of a rational
argument, when in fact the text that was put forward was meant as
an explanation, and not an argument. A case in point is the fallacy
of begging the question.
The fallacy of arguing in a circle, or begging the question, iscommitted by an instance of circular reasoning that fails to work as
an argument supposed to prove the conclusion that is in doubt. A
standard textbook example is provided by the following shortdialogue between a man, Smith, and his bank manager.
Manager: Can you give me a credit reference?
Smith: My friend Jones will vouch for me.
Manager: How do we know he can be trusted?
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 of Jones depends on thetestimony of his friend Smith. This obviously won’t work becauseof the circularity in the procedure of providing evidence to support
a claim in an argument. If Jones’s trustworthiness can be vouched
for by some source independent of Smith, then the argument would
work, and would no longer commit the fallacy of begging thequestion.
To extend the example a bit further, suppose that a third-party
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.

Figure 2. Circular Reasoning in the Credit Reference Example.

could vouch for Jones, and that the trustworthiness of this third
party is not dependent on the trustworthiness of either Smith orJones. Then there would still be a circle in the argumentation
structure, as shown in figure 2, but the two text boxes on the rightfunction as premises in a linked argument supporting thetrustworthiness 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 problem with real cases where the fallacy of begging thequestion is a serious danger is that the circle is embedded in a text
where it may be mixed in with much other discourse. This danger
becomes even more serious when the discourse combines
argumentation with explanation. But if you can find such a circle inan argument, it represents quite a serious criticism of thatargument. A rational argument used to persuade a respondent toaccept its conclusion must not be based on premises that 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 theargument is useless to prove the conclusion. It lacks what has beencalled a probative function.
The situation is different for explanations. An explanation canbe circular, but still be useful as an explanation. The reason is that
there are feedback processes in nature, and to explain what ishappening, the account given needs to go in a circle. For example,
the more overweight a diabetic gets, the more insulin is producedin his blood, but the more insulin there is in his blood, the more heeats, and the more he becomes overweight. In this vicious circle,
the problem becomes worse and worse by a continual process of
feedback that escalates it.
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 thatcreates an argument the older buildings lend the town its distinctive
character so the warehouses are valuable architecturally (figure3). Now extend the dialogue as follows:(6) Beth:

OK agreed. But why do the older buildings lend thetown its distinctive character?
(7) Allen: The warehouses are valuable architecturally.
When examining this dialogue we might be suspicious about thepossibility that it contains the fallacy of begging the question. For
after all, Alan, when asked by Beth what is the justification forpreserving the old warehouses (4) replies that the warehouses arevaluable architecturally (5). But then later, at his last move in the
dialogue (7), reverts back to making the same statement again. It
definitely appears that the dialogue is circular. The question then iswhether the circularity is benign or vicious.
Let’s interpret Beth’s question (6) as a request for explanation.
Now the reasoning in the dialogue is no longer a sequence purelyof argumentation, but a mixture of argumentation and explanation(figure 3). In order to prove his claim that the warehouses arevaluable 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 thelatter. 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 to her, and so there is nointerdependency in the sequence of argumentation of the kindrequired for the committing of the fallacy of begging the question.

Arg

The
warehouses
should bepreserved.

Arg

The
warehouses
are valuable
architecturally

The olderbuildings lend
the town its
distinctive
character.

ExplanFigure 3. Mixed Version of the Warehouse Example

The circularity could help Beth to understand the situation. There iscircular reasoning, but no circular argumentation.

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
already mentioned at the start of section 2: an argument is a speech
act used to convince the hearer of some unsettled claim and an
explanation is a speech act used to help the hearer to understandsomething. This distinction can be drawn as one of a difference of
purpose of discourse. Since the distinction is drawn this way it canbe seen to be based on a dialogue model of communication inwhich two parties take turns in putting forward speech acts. As
argued above, in order to then determine whether something is anargument 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 aimof transferring understanding from an explainer to an explainee
raises further questions. What is understanding, and how can it betransferred from one party to another? Research in AI andcognitive science shows that communicative agents understand theactions of other agents 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 bemodeled as explanation schemes or scripts [22]. An explanation
scheme is an generic scenario, an abstract rendering of a sequence

Explainee
asks whyquestion.

Explainer
presents
story.

Explaineefinds anomaly
in story.

of actions or events of a kind. For example, the restaurant-script
contains information about the standard sequence(s) of events thattake place when somebody goes to dine in a restaurant.
Explanation schemes can be instantiated by particularexplanations and thus the scheme provides the conditions for the
explanation’s coherence [1]. Take, for example, a man who entersa restaurant, orders a hamburger and then removes his pants andoffers the waiter his pants. This particular story is incoherent,
because it does not adhere 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 insuch a way that it hangs together as a coherent script about what
happens when someone spills hot liquid on one’s clothes. Thus, anexplanation may be causal, motivational, teleological, and so on.
A dialogue model of explanation can then be constructed bybuilding it around the notion of the mutual comprehensibility of astory, 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 insituations they are both familiar with. This is the route taken by
Schank and his colleagues in cognitive science (see e.g. [22]).
According to them, explanation is a transfer of understanding fromone party to another in a dialogue, where understanding is clarified
scripts, “frozen inference chains stored in memory”. On Schank’s
theory, failures of understanding of kinds that trigger a need for an
explanation occur because of an anomaly, a gap in a story that
contains a part where it fails to make sense, or even where thewhole 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 betaken from script libraries.

3.1

A Dialogue System for Argument andExplanation

We now propose an example of a dialogue system forargumentation and explanation, based on the protocols presented
by [6][25]. Our dialogue system consists of a communication
language that defines the possible speech acts in a dialogue, aprotocol that specifies the allowed moves at any point in the
dialogue, commitment rules, which specify the effects of a speech
act on the propositional commitments of the dialogue participants.

EXPLANATIONDIALOGUE

The story
holds up oris refuted.
Explanation
evaluated.

STOP

Explainee
accepts
explanation.

Explainer
explains
anomaly.

Examination
dialoguesuccessful.

Sequence of
examination
moves byboth parties.

EXAMINATIONDIALOGUE

Figure 4. Explanation and examination dialogues combined.

STOP

Explaineeprobesdeeper: notsatisfied.

Furthermore, we assume that both players have their own separate
knowledge bases containing argumentation schemes andexplanation schemes, which form the basis of arguments andexplanations proposed in the dialogue [20].
In a dialogue game for argumentation and explanation,
essentially two types of dialogue are combined, namely
explanation dialogue [25][14][8] and examination dialogue [10]. Ina pure explanation dialogue in which the explainer is trying totransfer understanding to the explainee; an examination dialogue
can be used to test (evaluate) an explanation. Examination dialogue
is more adversarial than explanation dialogue. For example, theanswerer’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 andexamination dialogues as a process.
The speech acts of a game for explanation and argumentation
are presented in the typical format F p, 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 (anymore) to .
These speech acts are standard in systems for argumentative
dialogue (see e.g. [13]). Now, for explanation we need otherspeech acts, as defined by [6][25].
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 notunderstand an explanation.
Note the with explanation, the issue is not whether a player s
convinced (i.e. wants to be committed to a propositions) but rather
whether he understands a proposition.
Commitment rules specify the effect of moving 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 retract speech act.
The following standard protocol rules are part of the dialoguesystem (see e.g. [24]).
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 theircommitments 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 is committed and they are not.
6. A challenge  move may only follow either a claim  move oran argue  because  move.

7. A challenge  move can only be responded to by either anargue  because  move or a retract  move.
8. Players are only allowed to challenge propositions to which theother player is committed and they are not.
9. Players can only concede to propositions to which the otherplayer is committed.
10. Players can only retract propositions to which they arecommitted.
The above rules capture the basics of argumentative dialogue. The
rules encapsulate the idea that argumentation is an activity aimed atproving (or disproving) some claim: once both parties arecommitted 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 aclaim, but one of the two may not fully understand it.
11. Players are only allowed to request explanations ofpropositions to which both players are committed.
12. Players are only allowed to request explanations ofpropositions 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 bothplayers are committed.
15. Players are only allowed to explain propositions for which they
have an explanation scheme in their knowledge base and theother 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 adifferent aim, namely making someone understand a proposition
instead of committing them to it.

4

RELATED RESEARCH

In addition to the dialogue systems that combine argumentationand explanation as proposed in [6][25], there are numerous
explanations systems that incorporate the ideas about transferring
understanding through explanations. For example, ACCEPTER[12] 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 processed by ACCEPTER along thelines of the dialogue sequence above, include the death of a race
horse, the explosion of the space shuttle Challenger, the recall ofAudi 5000 cars for transmission problems, and an airliner thatleaves from the wrong departure gate ([12], 38). Cawsey’s work
[8] on computational generation of explanatory dialogue andMoore’s dialogue-based analysis of explanation for advice-givingin expert systems [14] 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 canthen be argued with using the argumentative moves of CATO [1],which were originally developed for reasoning with legal cases.
What this means is that [3] have a skeleton dialogue system thatuses scripts to perform argumentation instead of explanation. Thisconforms with our findings: it is not the logical structure of thereasoning or the schemes used in reasoning that determines
whether something is explanation or argumentation but the context
of the dialogue in which the reasoning is performed and theschemes are used.

5

CONCLUSION

In this paper, we have discussed the problem of distinguishing
between argumentation and 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 thereasoning 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 arequest for argumentation, this may lead to undesirable
misunderstandings and unwanted behaviour by agents. Finally, thedistinction is important for the connection between argumentation,
story-based explanation and discourse analysis, as argumentation
schemes and explanation schemes can play important roles in theanalysis of natural language texts [19][11].
Our solution involves looking at the context of dialogue todetermine whether reasoning is argumentation or explanation.
Whether something is argumentation or explanation is determinedby the intention of uttering a locution, and this intention can beinferred from the context of the dialogue, such as the speech act
that was replied to and the knowledge and intentions of the otherplayers. This context of dialogue can be modeled as a dialoguesystem (section 3). In this sense, our dialogue system forargumentation and explanation does not only provide normative
rules for coherent dialogue (as is usual), but it also helps us
describe the difference between argumentation and explanation in
dialogue.

ACKNOWLEDGEMENTS
We gratefully acknowledge the support of EPSRC under grant
EP/G060347/1 for Floris Bex and the support of the Social
Sciences and Humanities Research Council of Canada for Insight
Grant 435-2012-0101 for Douglas Walton.

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