‘Argumentation and evidence’
Floris Bex
Argumentation is central to legal and evidential reasoning: the prosecution argues that the suspect committed thecrime, lawyers present their closing arguments, the plaintiff argues his case by citing a relevant precedent, the court
presents concurring and dissenting arguments, and so on. There are different interpretations of the term ‘argument’:an argument can be a single reason for a conclusion but also the combination of the reasons for and against a certain
conclusion, or a dialogue between parties trying to convince each other. In the literature on reasoning with evidence,
however, a narrower definition is usually adhered to: argumentation is the construction of arguments by performing
consecutive reasoning steps, starting with an item of evidence and reasoning towards some conclusion using generalrules of inference or generalizations, where not just arguments for a conclusion but also counterarguments against a
conclusion have to be considered.
This idea of argumentation was already present in Wigmore’s Principles of Judicial Proof1, in which tree-likecharts representing inferences from evidence to a conclusion and possible weakening counterevidence are presented.
‘Neo-Wigmorians’ Anderson, Schum and Twining2 developed these argument charts, introducing the idea ofcommonsense generalizations as inference warrants. Douglas Walton has extensively discussed these different typesof commonsense generalizations in the form of argument schemes in different contexts, including legal evidence3.
Furthermore Bex, Prakken and colleagues have shown that Wigmore’s charts corresponds to logical models ofargumentation4, adding semantics for formal defeasible reasoning5. In this chapter, I will discuss argumentation in thecontext of legal evidence, presenting general ideas that draw from all of the above authors and on which there is moreor less a consensus in the academic community6.
1. The structure of evidential arguments
The basic idea of an argument is a basic syllogism, where a conclusion is inferred from premises. Evidential reasoning
with arguments involves taking the basic evidential data as premises 7 and inferring conclusions using generalizations,
usually of a conditional if-then form, which justify the inference link between premises and conclusion8. The
inferences are of an evidential nature: some evidence e and an evidential generalization ‘e is evidence for p’ allows us
to infer p. For example, a witness’ testimony ‘I saw someone who looked like John’ and the generalization ‘if a witness
says “p” then (this is evidence for) p’, where p is some state of affairs in the world, allows us to infer that the witness
saw someone who looked like John get into the car. Figure 1 shows a diagrammatic representation of this argument.
The evidence is represented by a grey box, the conclusion as a white box, the inference as an arrow and thegeneralization as a box with rounded corners.
The evidential generalization for witness testimonies can be phrased in several ways, for example, ‘witnesses
under oath usually speak the truth’, ‘if a witness testifies that p is the case then usually p is the case’ and ‘If a witness
is in a position to know whether p is true and the witness asserts p then p may plausibly be taken to be true’. The exact
generalization may be open to debate; do only witnesses under oath speak the truth? If a witness testifies to p, is thenp usually the case, or perhaps sometimes or 80% of the time? However, most people would agree that, in general,
conclusions can be drawn from witness testimonies, as in many legal systems a witness testimony is explicitly
mentioned as a legitimate item of evidence. This does not mean that witness testimonies are always true. Rather,
generalizations are often ‘default rules’, which means that if we have no reason not to believe the witness, we candraw conclusions from their testimony. But such default rules have exceptions – for example, the witness may havebad eyesight, or a reason to lie about seeing John – and evidence for such exceptions can lead to a counterargument
1 Wigmore 1931.
2 Anderson, Schum and Twining 2005.
3 Walton 2002.
4 Bex, Prakken, Reed and Walton 2003; Bex 2011; Prakken 2020.
5 Dung 1995.
6 Parts of this chapter have been adapted from chapter 3 of Bex 2011.
7 Evidential data are the primary sources of evidence which cannot be sensibly denied (e.g. that a witness statement was made incourt, that forensic expert reports were handed to the jury).
8 The generalization warrants the inference, cf. Toulmin 1958.

The witness saw someone wholooked like John

If a witness says “p” then p

Witness says “I saw someone wholooked like John”
Figure 1: A simple evidential argument
to the argument based on the witness testimony9. It should be noted that it is perfectly possible to have conclusive
generalizations. For example, ‘a person can never be at two places at the same time’ or, taking inspiration fromclassical logic ‘if witness A says p and witness B says p then always (conclusively) witness A says p’. Arguments
based on such rules are deductive and cannot be attacked on their conclusions.
It is also possible to form more complex arguments based on multiple pieces of evidence, or in which multiple
inferences are chained into arguments with intermediate conclusions. Consider Figure 2, where we have a witness
who saw someone who looked like John get into a car. In this car, the police later found a hair and shoe prints, whichis evidence for the fact that John was in the car at some point. Thus, we can conclude that John was probably the man
whom the witness saw getting into the car. In this figure, multiple smaller arguments are combined in a graph- or treelike structure, which shows many similarities to a Wigmore chart. Thus, the argument consists of several
subarguments; for example, the argument in Figure 1 is a subargument of the argument in Figure 2. Furthermore, there
are different types of (sub)arguments contained in Figure 2. Inferences are chained, where intermediate conclusions
are used to infer further conclusions (e.g. e2 → 2 → 5). In other cases, a conjunction of multiple pieces of evidence
or intermediate conclusions is needed to infer a conclusion. For example, statement 3 and 4 are both needed to inferconclusion 5, denoted by the compound arrow. Note that 5 can also be separately inferred from statement 2. So there
are essentially two arguments for conclusion 5: one based on e2, and another argument based on e3 and e4. These twoarguments corroborate: while the conclusion can be inferred from any of them, the conclusion is stronger if we haveboth arguments10.
While legal reasoning – reasoning about the legal facts and legal consequences – seems different from evidential
reasoning – reasoning about the evidence and conclusions11, the reasoning mechanisms employed are very much
related. More specifically, we can use the facts of the case, as derived from the evidence through arguments (Figure2) to further derive legal conclusions via the same kind of arguments. Figure 3 shows a legal argument which is itself
based on arguments from evidence – in the example, the bottom left proposition that John got into the car is based on
the argument in Figure 2. Here, the warrants for inferences in argumentation will be statutes and legal rules, andcounterarguments will be based on exception to legal rules12. Thus, there is no real boundary between legal andevidential reasoning in argumentation, as legal arguments are based on the conclusions of evidential arguments.

9 Counterarguments and generalizations with their exceptions are discussed in Section 1.2 and 1.3, respectively.
10 Argument strength will be briefly discussed in Section 1.2.
11 Cf. the dichotomy between a “question of fact” and a “question of law”, and Wigmore’s separation of factual proof and legal

admissibility in evidential reasoning (Wigmore 1931).
12 See Chapter 26 of Pattaro, Rottleuthner, Shiner, Peczenik and Sartor 2005.

e1: Witness says ‘I saw someone who looked like John’.
e2: Expert says that ‘the DNA profile of the hair in the car matches John’s DNA profile.
e3: Police reports that shoeprints matching ‘Runner Pro’ shoes were found in the car.
e4: Police reports that John wore Runner Pro shoes when he was apprehended.

6
gc
1
gw

e1

1:
2:
3:
4:
5:
6:

5
gd

2

gs

3

ge
e2

4
gp

gp

e3

e4

The witness saw someone like John getting into the car.
The DNA profile of the hair in the car matches John’s DNA profile.
The shoeprints found in the car were of Runner Pro shoes.
John wore Runner Pro shoes when he was apprehended.
John was in the car at some point in time.
John was the man who got into the car.

gw: If a witness says ‘p’ then p.
ge: If an expert says that ‘p’ then p.
gp: If the police reports ‘p’ then p.
gw: If a witness says ‘p’ then p.
gd: If a DNA profile of person x and a hair found at location l match, then person x was at location l.
gs: If shoe prints found at location l match the shoes of person x, then person x was at location l.
gc: If a witness saw someone looking like person x get into a car and person x was in that car at somepoint, then it was person x that the witness saw getting into the car.

Figure 2: A complex evidential argument
John murdered Bob

John killing Bob was premeditatedJohn intentionally killed Bob

After the fight, John got into the car

John purposefully drove the car into
Bob multiple times, killing Bob

Arguments based on evidence
Figure 3: Legal reasoning based on arguments from evidence

2. The dialectical nature of argumentation: attack, defeat and dialogue
In the previous section it was shown how conclusions can be supported by evidential data through arguments ofvarying complexity. Note that, however, the (intermediate) conclusions cannot be drawn conclusively, as theinferences are based on generalizations with exceptions. In other words, each inference step can be doubted andactively challenged by giving counterarguments that attack the original argument. The possibility of attack involves
the defeasibility of the inferences: an argument for a certain conclusion can be overturned by new information whichleads to, for example, an argument for the opposite conclusion or an exception to a generalization.
In the literature, two types of attack are usually distinguished13. Firstly, an argument can be rebut by giving acounterargument with as its conclusion the negation of a proposition in the original argument. For example, if John
13

Pollock 1995.

says he did not get into the car, we can infer the negation of the conclusion of the argument in Figure 2. Figure 3
shows this attack between the two conclusions as arrows with diamond heads – note that rebuttal is a symmetricalattack relation: an argument with conclusion p attacks the argument with conclusion not p and vice versa. It is also
possible to attack an intermediate conclusion of a subargument – in the example of Figure 2, by arguing that e.g. theDNA profile of the hair does not match John’s profile, or by arguing that John has never been in the car.
John was the man who
got into the car

John was not the man
who got into the car
If a suspect says ‘p’ then pargument Figure 2

John says ‘I did not get into the car’Figure 4: Two mutually rebutting arguments
Note that evidence cannot be attacked. In order to question, for example, a witness statement we can argue forthe opposite (Figure 3), or we can undercut the argument with another argument for why a particular inference is notallowed. Unlike a rebutting argument, an undercutting argument does not deny the conclusion of an argument, neither
does it deny the generalization as a whole (see section 1.3), but rather it denies the inference step by arguing for an
exception to the generalization underlying the inference. For example, say we have evidence that the expert who
analysed the DNA profiles used obsolete methods. Even though usually we would say that the opinion of experts on
DNA can be trusted, in this case we might have an exception, and the argument that the DNA profile of the hair in the
car matches John’s profile is undercut (Figure 5). Note that here it is not actively denied that the two profiles match,but that the support that the evidence gives to the conclusion is effectively ‘broken’, as the defeasible inference fromthe evidence is undercut. The undercut relation is not symmetrical: the undercutting argument attacks the original
expert testimony argument but not vice versa.
The DNA profile of the hair in the
car matches John’s DNA profile.
The expert used
obsolete methods
Expert says that ‘the DNA profile of thehair in the car matches John’s DNA profile.
Counter-expert says that theexpert used obsolete methods
Figure 5: One argument (left) undercutting another argument (right).
Attacking an argument does not guarantee the argument’s defeat: for this, the attacking argument has to bestronger than the other argument. With each specific (element of an) argument some measure of its strength orprobative force can be associated. Often, these strengths are indicated as preferences between arguments14, (e.g. anargument based on a police report is always preferred to an argument based on a citizen eyewitness) and suchpreferences can be the object of argumentation themselves (e.g. research has shown that police officers are not morereliable witnesses than citizens). There are also various ways to capture the strength of arguments precisely as, for

14 See e.g. Modgil and Prakken 2013.

example, numerical probabilities15. However, the central idea is that argumentation is a dialectical process of argument
and counterargument. Accordingly, we can determine the so-called dialectical status of arguments. Based on theformal argumentation semantics first proposed by Dung16, we can assign three different statuses to arguments: thejustified arguments (those that survive the competition with their counterarguments), the overruled arguments (thosethat lose the competition with their counterarguments) and the defensible arguments (those that are involved in a tie)17.
Consider Figure 6, in which two mutually attacking (e.g. rebutting) arguments for opposite conclusions are shown 18 for example, the argument from Figure 2 and the attacking argument from Figure 4. Now, if no preference for any
argument is defined, they are both defensible. If, however, we say we prefer the left argument for ‘John got in thecar’19, this argument is justified and the right argument is overruled.

Johnin carJohn
not incar

Figure 6: Two mutually attacking arguments

WitnessliedJohnin carJohn
not incar

Figure 7: The leftmost argument defends the rightmost argument by defeating its only attacker.
The dialectical status of an argument depends on its interactions with all other available arguments. An importantphenomenon here is defence: suppose that argument B attacks argument A but that B is itself defeated by a thirdargument C; in that case C defends A. In the example, say that we have a new argument that the witness who saw John
get into the car lied. This argument undercuts the inference e1 → 1 in the argument from Figure 2, and thus attacks
the complete argument for the conclusion that it was John who got into the car, see Figure 720. Because the newargument is itself not attacked, it is justified and defeats the argument for ‘John in car’, which is in turn overruled.
The right argument for ‘John not in car’ is now justified because its only attacker is overruled. A set of arguments that
defends itself against incoming attackers can hence be seen as a coherent and defendable position.
Note that while these semantics for determining argument acceptability are dialectical in spirit21, they do not
explicitly incorporate the dialectical process, where an argument can be accepted if it cannot be successfully
challenged in a properly conducted dialogue. Toulmin22 (2003) presents his view of ‘logic as generalized
jurisprudence’: a logic for arguments should provide the essentials of a general rational process for analysingarguments just as jurisprudence provides the essentials of the legal process. The procedural and dialogical componentof argumentation has been presented more explicitly in the literature, where various protocols or sets of rules for a

15 See e.g. Zenker 2012; Anderson et al. 2005 p. 230. For a more general account on Bayesianism and evidence, see Taroni,

Biedermann and Bozza (this volume).
16 Dung, On the acceptability of arguments.
17 See Prakken and Vreeswijk 2002.
18 Following Dung 1995, Figure 6 only shows the overall arguments and the attack relations between them – the internal structureof the arguments is abstracted away from.
19 After all, this was based on DNA evidence, shoeprints and a witness, whereas the other argument was based on just John’s
denial.
20 Note that there are really two arguments for ‘John got in the car’ in Figure 2, one based on evidence e1, e2 and another basedon evidence e1, e3, e4. Recall from the discussion of Figure 2 that there are two separate arguments for proposition 5, and each ofthese can be combined with the inference from e1 to form an argument for 6: John got in the car. Both these arguments areattacked by ‘Witness lied’, as the witness testimony is always required to conclude ‘John got in the car’, so for simplicity, Figure
6 and Figure 7 show just one argument for ‘John got in the car’.
21 Dung implicitly assumes some sort of process in which ‘The one who has the last word laughs best’ (Dung, 1995, 2).
22 Toulmin 1958.

properly conducted rational argumentative discussion are provided23. For example, van Eemeren and Grootendorst’s
obligation-to-defend rule states that ‘discussants who advance a standpoint may not refuse to defend this standpoint
when requested to do so’ and the relevance rule states that ‘standpoints may not be defended by non-argumentationor argumentation that is not relevant to the standpoint’. Such protocols serve not only an analytic function (is thediscussion rational in that it follows the rules?) but also a heuristic function (what are our options if we want to conduct
a rational discussion?). In a legal setting, dialogue protocols will be partly determined by the legal procedural rulesthat tell us, for example, which types of evidence can be brought forward by whom and at which point in theproceedings, or whose turn it is to meet the burden of proof24.
The basic idea of using a dialogue as a means of rationally analysing arguments is best explained by taking an
example of a dialogue game, where a simple game is played between two players, a proponent and an opponent. The
proponent starts by moving an argument that needs to be tested and each subsequent move (by either the proponent
or the opponent) contains an argument that attacks an argument of the other player. The rules of the game determine,for example, whether a player may repeat his earlier moves or whether a player may move only undercutters or
rebuttals. Say, for example, that we have a game in which the proponent starts by moving an argument and may notrepeat his moves, all of the arguments in the opponent’s move must defeat the proponents move and the arguments inproponent’s subsequent moves must undercut the opponent’s arguments in the previous move. The proponent starts
by moving the argument ‘John not in car’. The opponent must attack this argument and hence moves ‘John in car’.
The proponent must undercut this argument; this can be done by moving ‘witness lied’. There are now no morearguments and the opponent has no more valid moves so the proponent wins. Thus, the argument game essentiallyprovides a dialectical proof theory for arguments: the initial argument can be said to be (defeasibly) provable if the
opponent can attack (and defeat) each move the opponent makes.
3.

Generalizations and general knowledge in evidential reasoning

Generalizations play a pivotal role in reasoning with evidential arguments. They can warrant inferences from theevidential data to conclusions and can be seen as the ‘glue’ that keeps an argument together25. However,generalizations are not always true or valid, and can change over time. This is why Twining call them ‘necessary but
dangerous’26: we need generalizations in order to analyse and argue about evidence, but these generalizations can also
encode biases, stereotypes and prejudices. These dangers of generalizations can be lessened by specifying exactly
which generalizations we use, how we use these generalizations and from which sources the generalizations stem. The
more explicit the knowledge, the more it is open to analysis and criticism in the dialectical process of proof.
There are quite a few generalizations that, in one way or another, are consistently used by all kinds of reasoners
when reasoning with evidence. Looking at evidential reasoning (or indeed at reasoning in general), it can be seen thatmany arguments, as well as the attacks on them, are instances of recurring patterns, such as inferences from witness
or expert testimonies. In this sense, argumentation schemes play an important role in reasoning with evidence27.
Argumentation schemes are forms of argument that represent stereotypical patterns of human reasoning in aconditional form, just like generalizations. The idea of defining recurring patterns of reasoning through argumentation
schemes or generalizations is the subject of much study in argumentation theory, artificial intelligence and law.
As an example of an argumentation scheme, take the well-known scheme for argument from expert opinion28:
Source E is an expert in domain D.
E asserts that proposition A is known to be true (false).
A is within D.
Therefore, A may plausibly be taken to be true (false).

23 See e.g. Walton1998; Van Eemeren and Grootendorst 2004; Tuzet (this volume). For more formal approaches from artificial

intelligence, McBurney and Parsons 2005.
24 See e.g. Prakken and Sartor 2009; Bex and Walton 2012.
25 Anderson et al. 2005.
26 Twining 1999. See also Dahlman 2017; Allen and Pardo (this volume) for an in-depth discussion on generalizations and theways I which they may be dangerous or unacceptable.
27 For a discussion on argumentation schemes in the context of reasoning with evidence, see Walton 2002; Bex et al. 2003. For ageneral overview of argumentation schemes, the reader is referred to Walton, Reed and Macagno 2008.
28 Walton et al. 2008. Also see Hahn (this volume).

The notion of argumentation schemes is obviously very closely related to the notion of generalizations: argumentation
schemes are conditional rules based on world knowledge which can be used to draw inferences. The above
argumentation scheme is a slightly more general version of the DNA expert generalization given in Figure 2, where
the domain D would be ‘DNA analysis’ and it is assumed that ‘profiles a and b match’ is a statement within the domain
of DNA analysis.
Looking at Figure 2, it can be seen that each type of evidence essentially has its own associated generalization
which allows us to draw inferences from that particular type of evidence. In this way, the various types of evidence
point to generalizations that are often used in reasoning with evidence. Above we already saw the generalizations forwitness testimony and expert testimony. Another example is the generalization for inference from police reports. In
this way, we can accept stereotypical ways of reasoning about which there is a consensus, at least in the legal andphilosophical community, and thus accept that there are certain valid generalizations that can be used in rational
reasoning about evidence. Because each type of evidence has its own associated generalization, the law may also point
us to generalizations which are accepted by default; for example, in Dutch law witness testimonies are explicitly statedas a species of evidence on the grounds of which a judge can form his decision29. This means that it is highly unlikelythat the legislator believed the witness testimony generalization to be false by default. In this way, we can include thesource of the generalization in our argument – consider Figure 8, where the witness testimony generalization is(defeasibly) derived from source ‘evidence’, namely the Dutch Code of Criminal Proceedings 30.
The witness saw someone wholooked like John

If a witness says “p” then p

Witness says “I saw someone wholooked like John”

DCCP: a witness testimony is alegitimate source of evidence

Figure 8: An argument for a generalization
Ideally, a generalization comes from a clearly defined source, such as an expert, scientific literature or a legal
document, so that if we are doubtful about whether the generalization should be believed we can check the original
source. However, many generalizations that are not tied to specific types of evidence are often backed by experienceor general knowledge. Such experience-based generalizations seem to be based on a commonsense counterpart ofscientific induction and reasoning from a ‘general knowledge source’ can be formulated as a new generalization: ‘It
is general knowledge that ‘p’ is evidence for p’31. Possible undercutters of this generalization are that a piece of generalknowledge is infected by prejudice or value judgement. An example of a generalization backed by general knowledge
is shown in Figure 9. Notice that the premise from which the generalization is concluded is rendered as a white box,
which means that it is not considered to be evidential data but rather a general knowledge assumption which can itself
be called into question (i.e. attacked by an argument).

29 Article 339 paragraph 3 and article 342 Dutch Code of Criminal Proceedings.
30 Note the similarity between Figure 8 and Toulmin’s argument scheme (Toulmin 1958). The witness testimony is what Toulmin

calls the datum, which is the basis of the claim that the witness saw someone who looked like John. The generalization acts as thewarrant and the DCCP as the backing, showing why the warrant holds.
31 Bex et al. 2003.

The witness saw John

If a witness saw someone
looking like person x, thewitness saw x
It is general knowledge
that ‘p’ is evidence for p
The witness saw someone wholooked like John

It is general knowledge that ‘If awitness saw someone looking likeperson x, the witness saw x’

Figure 9: A generalization in an argument backed by general knowledge.
One of the main points of looking for stereotypical patterns of reasoning is that for each generalization, sometypical sources of doubt can be given. For example, the witness testimony generalization can be undercut witharguments questioning the witness’ veracity, objectivity and observational sensitivity 32. For example, a standard
undercutter for a generalization about perception is as follows: ‘the present circumstances are such that having apercept with content p is not a reliable indicator of p’, which can be used to question a witness’ observational
sensitivity33. In the same way, the expert testimony generalization has several typical sources of doubt. Argumentation
schemes capture these sources of doubt with a number of critical questions, which point to possible sources of doubt
in an argument based on the scheme. Critical questions fit into the dialectical view on argumentation as they can beused in a question-and-answer dialogue. The following six basic critical questions are associated with the expert
opinion scheme34:
1.
2.
3.
4.
5.
6.

Expertise Question: How credible is e as an expert source?
Field Question: Is e an expert in d?
Opinion Question: What did e assert that implies a?
Trustworthiness Question: Is e personally reliable as a source?
Consistency Question: Is a consistent with what other experts assert?
Backup Evidence Question: Is a’s assertion based on evidence?

Answers to these critical questions can lead to various types of counterarguments. For example, a negative answer tothe ‘field question’ would undercut an argument from expert opinion and a negative answer to the ‘consistency
question’ points to a possible rebutting counterargument with an opposite conclusion35. In general, there are
essentially four ways to attack a generalization36:
1.
2.

3.

Attacking the validity of the source of the generalization: it is not general knowledge that ‘If a witness saw
someone who looks like person x, then the witness saw x‘.
Attacking the defeasible derivation from the source: it is indeed general knowledge that if a witness saw
someone who looks like person x, then the witness saw x, but this particular piece of general knowledge isbased on a belief from folk psychology that people are always accurate at recognizing faces.
Attacking application of the generalization in the given circumstances: Usually it is true that ‘If a witness
saw someone who looks like person x, then the witness saw x’. However, in this case we cannot conclude
that the witness saw John as John has a very common appearance.

32 See Anderson et al. 2005, 67-70.
33 Pollock 1987.
34 Walton et al. 2008.
35 The undercutting attack in the example in Figure 5 is an answer to another critical question of the form ‘Did the expert use theright method to determine the truth of A?’.
36 Bex et al. 2003.

4.

Attacking the generalization itself: it is not the case that ‘If a witness saw someone who looks like person x,
then the witness saw person x’.

Note that the first type of attack is only possible if the source of the generalization is not evidential data but rather
general knowledge. For example, it is not possible to deny the source from Figure 8 by arguing that ‘a witness
testimony is not a legitimate source of evidence’. In this case it is possible to attack the derivation from the source.
The main difference between attacks of the third and the fourth kind is that the third kind of attack accepts thegeneralization as a general rule but denies its application in the case at hand, while the fourth kind of attack denies thegeneralization as a general rule (“it is not the case that usually...”).
4. Summary and evaluation
This chapter has introduced arguments for reasoning with evidence in legal cases. It has been shown how arguments
based on evidence to conclusions in a case can be built, how these arguments can be attacked and defended against
counterarguments, and how generalizations can be used and analysed in argumentation. The main ideas onargumentation presented in this chapter are logically and conceptually well-developed in the literature and a traditionof research on informal and formal argumentation provides the argument-based approach with the necessary academic
grounding. The argument-based approach to evidential reasoning has a number of oft-cited strong and weak points37,
which will be briefly discussed below, starting with the strong points.
Arguments allow us to explicitly link the evidence to (legal) conclusions. In this way, the relevance of theevidence for a particular conclusion can be shown, and the attack relations between arguments allow for clear
identification of points of disagreement. By reasoning with arguments and counterarguments, one explicitly takes a
so-called dialectical stance38: in argumentation, anything can be questioned: a conclusion, a generalization, the sourceof a generalization, and so on. These can all be tested in multiple ways and thus argumentation allows for a discussion
not only of the evidential data but also of the general knowledge underlying the inferences.
More formal semantics for determining argument acceptability 39 can help in determining how the various piecesof evidence interact and why a particular combination of arguments can be believed. As the example in Figure 7
shows, the status of one argument may depend on attack relations between other arguments. Thus, we can determine
which arguments need to be defeated if we want the arguments supporting some conclusion to be justified. For
example, it might be that, for example, the testimony of one witness is important because it defends a large numberof other arguments for a particular conclusion. Recent formal work also proposes algorithms for determining whethera certain conclusion is stable, meaning that no amount of new evidence will change the acceptability status of theargument40. Related to this, it can then be determined, for example, what the effect would be of finding some newpiece of evidence on the main conclusions in a case.
Argumentation is often characterized as evidential reasoning – most of the inferences and schemes used are of
the form ‘e is evidence for c’. This type of reasoning seems to be consistent with how many decision makers publicly
justify their decisions – many motivations of decisions in Dutch criminal cases include phrases of the form ‘the event
can be inferred from evidence e1’, ‘this event is based on (or supported by) evidence e1’41. Evidential reasoning also
seems to be the most natural way to think about inferring conclusions from evidence. For example, Van de Braak et
al. showed that in the case of ‘testimonial knowledge’, that is, information from testimonies and evidential documents,
people find it significantly harder to interpret causal relations like ‘John bought a weapon causes the witness to testify
that they saw John buy a weapon’ than they find it to interpret evidential relations like ‘The witness testified that theysaw John buy a weapon is evidence for the fact that John bought a weapon’42. Finally, the connection between
evidential and legal reasoning a case is best captured by reasoning from the evidence via the facts to legal conclusions.

37 Verheij, Bex, Timmer, Vlek, Meyer, Renooij and Prakken, 2016; Prakken 2020.
38

Bex and Walton 2019. A stance is the level of abstraction on which certain concepts, decisions or behaviour is judged. Cf
Dennett’s intentional stance, which views the behaviour of an entity is judged in terms of the mental properties (intentions) of theentity (Dennett 1996).
39 Dung 1995.
40 Odekerken, Borg and Bex 2020.
41
Stevens 2014; Bex and Verheij 2012.
42 Van den Braak, Oostendorp, Vreeswijk and Prakken 2008.

The above discussion leads us to the first weakness of the argumentative approach, namely that it does not allow
for reasoning with and about (explanatory) scenarios in a case. In criminal cases issues like the cause of death, butalso the relations between motives and actions, are often expressed with causal generalizations of the form ‘c is a
cause for e’. While it is perfectly possible to construct a causal argument based on a scheme from cause to effect, itcannot capture the exact causal structure of a (hypothetical) scenario in a case, and the causal relations between thevarious the elements of this scenario (e.g. the motives and actions). Furthermore, the conclusion of an evidential
argument is usually a single element of a scenario, an individual state or event (e.g. ‘John got into the car’). Thus, theoverview of the case tends to be lost in a purely argument-based approach. In a case, the various hypotheses about
what (might have) happened are usually not single conclusions but rather detailed scenarios or stories, coherent setsof events. These stories can explain the evidence and need to be compared to find the best explanation of the evidence.
Often, when faced with evidence people will start to construct stories about what might have happened, and the police
as well as decision makers such as judges increasingly employ so-called “scenario-based” reasoning43. Recognizing
the role of both stories and arguments, Bex has proposed a hybrid approach, in which stories about what (might have)
happened in a case can be constructed and compared, and arguments based on evidence can then be used to support
and attack these stories44. Figure 3 already hints at the use of scenarios or stories in a case: the two bottom claims
together essentially form a short ‘story’ about what happened – John and Bob were in a fight, which made John so
mad that he drove into Bob.
Another weak point of argumentation that is often mentioned is the lack of a systematic account of degrees of
uncertainty in argumentation45. However, one of the clear advantages of argumentation over more Bayesian
approaches – in which assumptions and generalizations are encoded as (conditional) probabilities – is that discussions
can take place in natural language. Bayesian analyses of a case are hard to understand for people less familiar withprobabilistic reasoning (e.g. judges, jurors), and the assumptions the analysis makes might not be explicitly
represented but rather included in the underlying probabilistic inference mechanisms. Recently, there has been quite
some work that has compared, integrated and discussed argument-based, story-based and probability-based accounts
to evidential reasoning46. This work shows that in many different approaches, ideas from argumentation, in particulardialectical processes, play an explicit role.
Bibliography
Allen. R. and Pardo, M. (2021). “Generalizations and Reference Classes”, this volume.
Anderson, T.J., Schum, D.A. and Twining, W.L. (2005). Analysis of Evidence, 2nd ed. Cambridge: Cambridge
University Press.
Taroni, F., Biedermann, A. and Bozza, S. (2021). “The Bayesian Approach to Legal Evidence”, this volume.
Bex, F.J. (2011). Arguments, Stories and Criminal Evidence: A Formal Hybrid Theory, Springer.
Bex, F.J., Prakken, H., Reed, C. and Walton, D.N. (2003). “Towards a formal account of reasoning about evidence:argumentation schemes and generalisations”. Artificial Intelligence and Law, 11: 125 – 165.
Bex, F.J. and Walton, D.N. (2012). “Burdens and Standards of Proof for Inference to the Best Explanation: Three
Case Studies”. Law, Probability and Risk 11 (2-3):113-133.

43 See a.o. Pennington and Hastie 1992; Wagenaar, Van Koppen and Crombag 1993 for psychological evidence that a scenario-

based approach is often used. More recent work that further develops scenario- or narrative-based accounts is Pardo and Allen
2007; Pardo and Allen (this volume); Mackor and Van Koppen (this volume).
44 Bex 2011.
45 Though there has recently been work on integrating probabilistic, Bayesian approaches with argumentation, see e.g. Zenker
2012; Hahn and Hornikx 2016.
46 See Verheij et al. 2016; Prakken, Bex and Mackor 2020.

Bex, F.J. and Walton, D.N. (2019). Taking the Dialectical Stance in Reasoning with Evidence and Proof, a comment
on R.J. Allen & M.S. Pardo, Relative Plausibility and Its Critics, International Journal of Evidence and Proof, 23(1–2): 90–99, Sage Publications.
Bex, F.J. and Verheij, B. (2012). Solving a Murder Case by Asking Critical Questions: An Approach to Fact-Findingin Terms of Argumentation and Story Schemes” Argumentation, 26:3, 325-353.
Dahlman, C. (2017). “Unacceptable Generalizations in Arguments on Legal Evidence”, Argumentation, 31:83-99.
Dennett, D.C. (1996). The Intentional Stance. Cambridge, MA: MIT Press.
Dung, P.M. (1995). “On the acceptability of arguments and its fundamental role in nonmonotonic reasoning, logic
programming and n–person games” Artificial Intelligence 77:2, 321 – 357.
Hahn, U. (2021). “Source Reliability and Appeal to Expert Opinion”, this volume.
Hahn, U. and Hornikx, J. (2016). “A normative framework for argument quality: argumentation schemes with a
Bayesian foundation”. Synthese 193.6:1833-1873.
Mackor, A.R. and Van Koppen, P.J. (2021). “Scenario Theory and Anchored Narratives”, this volume.
McBurney, P. and Parsons, S. (2005). “Dialogue games for agent argumentation” in I. Rahwan and G. Simari (eds),
Argumentation in Artificial Intelligence, Springer.
Modgil, S.J. and Prakken, H. (2013). ‘A general account of argumentation with preferences’. Artificial Intelligence
195: 361-397.
Odekerken, D., Borg, A. and Bex, F. (2020) “Estimating Stability for Efficient Argument-based Inquiry”,
Computational Models of Argument. Proceedings of COMMA 2020, Frontiers in Artificial Intelligence andApplications 326:307-318, IOS Press.
Pardo, M.S. and Allen, R.J. (2007). “Juridical Proof and the Best Explanation”. Law and Philosophy, 27: 223 – 268.
Pardo, M.S. and Allen, R.J. (2021). “Reasoning to the Best Explanation” [2021], this volume.
Pattaro, E., Rottleuthner, H., Shiner, R.A., Peczenik, A. and Sartor, G. (2005). A Treatise of Legal Philosophy andGeneral Jurisprudence, Springer.
Pennington, N. and Hastie, R. (1992). “Explaining the evidence: Tests of the story model for juror decision making”.
Journal of Personality and Social Psychology 62:2, 189 – 206.
Pollock, J.L. (1987). “Defeasible reasoning”. Cognitive Science 11:4, 481 – 518.
Pollock, J.L. (1995). Cognitive Carpentry: A Blueprint for How to Build a Person. MIT Press.
Prakken, H. (2020). “An argumentation-based analysis of the Simonshaven case”, Topics in Cognitive Science, 12:4,
1068-1091.
Prakken, H., Bex, F.J. and Mackor, A.R. (2020) Models of Rational Proof in Criminal Law, special issue of Topics in
Cognitive Science 12:4, Wiley.
Prakken, H. and Sartor, G. (2009). ‘A logical analysis of burdens of proof’. In H. Kaptein, H. Prakken, B. Verheij(Eds.) Legal Evidence and Proof: Statistics, Stories, Logic, p. 223-253, Ashgate Publishing.

Prakken, H. and G Vreeswijk (2002). “Logics for defeasible argumentation”. In R. Goebel and F Guenthner,
Handbook of Philosophical Logic, 219 – 318, Kluwer Academic Publishers.
Stevens, L. (2014). “Bewijs waarderen. Hoe doen strafrechters dat?” Nederlands Juristenblad, 89(40): 2842–2850. In
Dutch (Evaluating evidence: how do judges in criminal cases do this?).
Toulmin, S.E. (1958). The Uses of Argument, Cambridge University Press.
Tuzet, G. (2021). “Pragmatic Aspects of Evidence Discourse”, this volume.
Wining, W.L. (1999). “Necessary but Dangerous? Generalizations and Narrative in Argumentation about Facts in
Criminal Process” In J.F. Nijboer and M. Malsch (Eds.), Complex Cases: Perspectives on the Netherlands Criminal
Justice System, p. 69 – 98, Thela Thesis.
Van den Braak, S.W., Oostendorp, H. Vreeswijk, G. and Prakken, H. (2008). “Representing Narrative and Testimonial
Knowledge in Sense–making Software for Crime Analysis” Proceedings of JURIX 2008: The 21st Annual Conference,
160 – 169, IOS Press.
Van Eemeren, F.H. and Grootendorst, R. (2004). A Systematic Theory of Argumentation. The Pragma–dialectical
Approach. Cambridge University Press.
Verheij, B., Bex, F.J., Timmer, S.T., Vlek, C., Meyer, J.J.-Ch, Renooij, S. and Prakken, H. (2016) “Arguments,
Scenarios and Probabilities: Connections Between Three Normative Frameworks for Evidential Reasoning”. Law,
Probability & Risk, 15, 35-70.
Wagenaar, W.A., Van Koppen, P.J. and Crombag, H.F.M. (1993). Anchored Narratives: The Psychology of Criminal
Evidence, St. Martin”s Press.
Walton, D.N. (1998). The New Dialectic: Conversational Contexts of Argument, University of Toronto Press.
Walton, D.N. (2002). Legal Argumentation and Evidence, Penn State University Press.
Walton, D.N., Reed, C. and Macagno, F. (2008). Argumentation Schemes, Cambridge University Press.
Wigmore, J.H. (1931). The Principles of Judicial Proof or the Process of Proof as Given by Logic, Psychology, andGeneral Experience, and Illustrated in Judicial Trials, 2nd ed. Little, Brown and Company.
Zenker, F. (Ed.) (2012). Bayesian Argumentation: The Practical Side of Probability, Springer.