Legal Stories and the Process of Proof
Floris J. Bexa – School of Computing (University of Dundee)
Humanities Computing Group (University of Groningen)Bart Verheij – Artificial Intelligence Department (University of Groningen)aCorresponding author: florisbex@gmail.com

11 INTRODUCTION
In research on legal reasoning in the field of AI & law, models of reasoning fromproven facts to legal consequences are well developed [26][16]. Recently there isalso a rise in attention for evidential reasoning [7][8][20][30]. However, there is
not much recent work that aims at modelling the full pathway from evidence via
proven facts to legal consequences (except maybe [32], see section 5). Providing amodel of that full pathway is the focus of his paper.1
We will argue that the factual and legal part of a case (the steps from evidence
to proven facts, and from proven facts to legal consequences, respectively; Figure1) cannot be separated. The phenomenon of legal shifts is a case in point: the legal
perspective on a case changes as a result of what can be proven, but at the sametime this perspective also determines exactly what needs to be proven. We
provide an example based on a murder case set in the provincial Dutch town ofWamel (as carefully analyzed by Israëls [19]). In this case it was impossible tosuccessfully convict the suspect for murder, as the key question of ‘who shot the
gun?’ is never clarified. However, the suspect was convicted (after appeal andwithstanding cassation by the Supreme Court) as an accomplice to murder.
We extend our previous work on reasoning with evidence [5][7], in which we
mainly concerned ourselves with the factual part of trials, the evidence and thefacts that can be inferred from it. In this work it was not specified how exactly,
once the facts have been established, the reasoning towards the legal
consequences proceeds. Also, the exact way in which the law might influence thereasoning about the facts and the evidence is an open question.
The contribution of the paper is as follows. We propose an extension of our
hybrid narrative-argumentative approach to evidential reasoning [5][7] in order toincorporate the complete reasoning process in a case: from evidence via facts tolegal consequences. In this extended hybrid theory we introduce the idea of legal
stories and legal story schemes, which can be used to establish the legal coherence(as opposed to the factual coherence) of a case, is required.2 These legal stories
steer what needs to be proven, but are also selected on the basis of what can beproven and can thus be used to model shifts in legal perspectives. Furthermore,
we will argue that a combination of legal stories and factual stories allows for anatural modelling of reasoning with circumstantial evidence. This is especially
useful in cases where there is no direct evidence for the “guilty act” that has to be
proven (e.g. the suspect shot the victim), and for proving motive which is often
hard to find reliable direct evidence.
Factual and legal story schemes make explicit that a holistic, coherent
perspective underlies all reasoning and argumentation. Factual story schemes areimportant to determine which accounts of the facts are plausible, and which gaps
12This paper adapts and extends our [10].
There exist other formal approaches to coherence, e.g. [17][4][30].

2need to be filled by further evidence in order to form a full picture of what
happened. Legal story schemes show which sets of (legally qualified) facts andevents are recognized as coherent wholes by the law, in the sense that a legal
consequence such as a conviction can be based on them. We will show how both
factual and legal story schemes are a tool to reduce the risk of tunnel vision.
In the following, we start with a discussion of the theoretical background used
(Section 2). This comprises a discussion of the theory construction view on legal
reasoning on the basis of evidence via facts to legal consequences. We also
provide a brief overview of the Wamel murder case that we use as an illustration.
Then follows a review of the evidential part of our hybrid theory (Section 3). This
review also contains a discussion of the story schemes which were previously
discussed in [5]. In Section 4, the hybrid theory is extended to include the legal
step in the pathway from evidence via facts to legal consequences. In Section 5,
we put our approach in perspective by a discussion in the light of related research.
We conclude our paper in Section 6, pointing out some issues for future research.

2 FROM
EVIDENCE
VIA
FACTS
CONSEQUENCES (AND BACK)

TO

LEGAL

Reasoning in a criminal case is a complex process in which the available evidence
determines which facts can be proven, and hence also which legal consequences
follow. As we already indicated above, this also works the other way: the law
often regulates which facts have to be proven, which in turn determines which of
the evidence is relevant. As a result, a theory construction perspective, in which
the overall reasoning about a legal case (from evidence, via facts to legal
consequences) is gradually constructed is in place (Figure 1, adapted from [31], p.
10). The figure not only suggests that evidence, facts and legal consequences aregradually constructed from an imperfect initial version, but also there is an
influence both upward (from evidence via proven facts to legal consequences) anddownward (from legal consequences via proven facts to evidence).
Reasoning in a criminal case is a complex process in which the available
evidence constrains which facts can be proven, which in turn are the grounds forlegal consequences on the basis of the applicable legal rules (Figure 1, adaptedfrom [31], cf. also [27]’s legal-theoretic and [21]’s AI & Law take on theory
construction). The path of justification is from evidence via facts to legal
consequences (visualised as the white upward arrows). However, there is also an
influence in the other direction. This influence is not about justification but rather
has to do with the discovery or exploration of new facts and evidence: the legal
perspective on a case (in the form of the legal consequences that are at issue)
steers which facts need to be proven for the legal consequences to actually follow,
while the facts that have to be proven guide the search for evidence.
To sum up, we view legal (evidential) reasoning from a theory construction
perspective. Figure 1 not only suggests that evidence, facts and legal
3

consequences are gradually constructed from an imperfect initial version, but alsothat there is an influence both upward (from evidence via facts to legal
consequences) and downward (from legal consequences via facts to evidence).

Figure 1: A theory construction perspective on legal reasoning

As for terminology, with evidence we mean the evidential data, the primarysources of evidence the existence of which are not an issue (e.g. witness
statements made in court, forensic expert reports handed to the jury). As is usual
in law, we use the term fact to denote descriptions of states or events, the truth ofwhich are currently unknown and have to be proven (cf. the terms “fact-finder”,“question of fact”).3 By legal consequences, we mean the legal states of affairs
that the law attaches to the facts (e.g. the punishability for murder and the ensuingsentence of imprisonment; cf. the German jurisprudential term Rechtsfolge).
In previous work [5][7] we focused on the bottom part of Figure 1, that is,evidential reasoning about the evidence and the (real-world) facts. We argue that
this evidential reasoning is best modelled in a hybrid theory that uses both stories
and arguments. In the hybrid theory, facts are organised into multiple hypotheticalstories, coherent accounts of what (might have) happened in the case. Arguments
based on evidence can then be used to justify these stories, as these arguments canbe used to support elements in a story with evidence or, in other words, to anchor
the story in the evidence (cf. [33]). Ultimately, the alternative stories in a caseshould be compared and the best one (i.e. the most coherent one that best fits theevidence) should be chosen.
Figure 2 visualises the basic idea behind the hybrid theory. This way of hybrid
reasoning with stories and arguments is particularly close to the analytic andevaluative thinking of the professionals that actually perform the reasoning in acriminal case, in particular criminal investigators and judges ([21], [33], [5]).

3

We assume a rough distinction between “real-world” facts, which tell us something about the(physical) reality (e.g. Francis was angry with Kevin, Francis shot Kevin) and legal facts, facts
which tell us something about the legal reality (e.g. Francis' killing of Kevin was premeditated,
Francis is punishable for murder).

4One accountof the facts

Another accountof the facts
Arguments
Evidence

Figure 2: Hybrid narrative-argumentative evidential reasoning

At first view, legal reasoning – reasoning about the (legal) facts and legal
consequences (the top part of Figure 1) – seems quite different from evidential
reasoning (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). Whilst the content and context of evidential reasoning are different
from those of legal reasoning, the reasoning mechanisms employed are related.
In legal reasoning, the legal consequences are organised into clusters of legal
facts that provide legally coherent perspectives on a case. In our opinion, such alegally coherent perspective can be seen as a “legal story” about what happened in
the case, a legally qualified account of what happened. This is particularly
apparent in Dutch cases, where the indictment is usually phrased as a small legal
story (intermixed with their legal qualification). For example, a murder charge inour case could read as follows: “On the 5th of January 1997, Francis intentionallyand with malice aforethought killed Kevin by shooting him repeatedly with asemi-automatic weapon, which caused multiple severe injuries to Kevin, as aresult of which Kevin died”.
In every case, there are at least two legal accounts representing the “guilty”
and “innocent” perspectives.4 Here the “guilty” perspective will normally be very
detailed (as per the requirements for the prosecution's indictment), whereas the"innocent" perspective sometimes is not much more than a denial of the "guilty"
perspective. Arguments can be used to reason from the (real-world) facts to thelegal consequences, that is, to justify the legal accounts with the facts of the casewhich are themselves justified by the evidence. Ultimately, the alternative legal
accounts should be compared and the best one (i.e. the one that best fits theproven facts) should be chosen. Figure 3 shows how legal accounts follow fromthe facts of the case in a similar way as the facts follow from the evidence in thecase.
Now, the combination of evidential reasoning (Figure 2) and legal reasoning(Figure 3) gives us all the machinery we need for the reasoning in a criminal case
(Figure 1). Because of the similarities between evidential and legal reasoning, we
think that this combination can be modelled without introducing too much newconceptual and logical machinery. However, the exact connection and similarities
between the evidential and the legal layer will have to be made more clear,particularly if we not only consider the upward, justificatory influence of evidence
4

In practice, there might be more alternative legal accounts in a case and the alternatives will be
more specific.

5

on legal consequences but also the downward, exploratory influence of legal
consequences on evidence.
One legal
account of thecase

Another legal
account of the case
Arguments
Facts

Figure 3: Hybrid narrative-argumentative legal reasoning

2.1 The Wamel case
Below we will briefly discuss the key concepts of stories and arguments. We will
illustrate these concepts using examples inspired by the Wamel case [19], which
also serves as a running example throughout the paper. In the Wamel case, there
are three key actors: Kevin Moyson, the victim, Sander Mornie, the main witness
and friend of Kevin’s, and Francis Liebrand, the prime suspect and an
acquaintance of Kevin’s. All three are members of a loosely connected
community of petty criminals often related to soft drugs and theft, but notnormally associated with big organized crime.
On January 6, 1997, Kevin's body is found some 50 kilometres from his home
town Uden, near two barns in the village of Wamel. He has been shot dead. Laterthat day, Sander contacts the police and states that he was also at the scene of thecrime, allegedly trying to escape. According to Sander's initial, later denied,statements, Francis was also at the barns and an argument developed between
Kevin and Francis (allegedly over a 5000 guilders debt that Francis owed Kevin).
Kevin then walked to the back of one of the barns. When Francis followed him,
there was a sudden firing of shots, after which Sander fled.
Francis was ultimately convicted both in first and second instance to 13 years
imprisonment, as an accomplice to the murder of Kevin and the attempted murderof Sander.5 This was later confirmed at the Supreme Court.

3 REASONING WITH THE HYBRID THEORY
The hybrid theory is essentially a theory of Inference to the Best Explanation(IBE). Given a set of facts that have to be explained, we hypothesize various
causally connected stories from which these facts follow. We then use arguments
based on evidence to reason about these stories in order to determine which storyis the best explanation (i.e. the one that is best supported by evidence). Thus, theformal hybrid theory is a combination of a causal theory for building hypothetical5

In this paper, we generally assume a Dutch legal framework. Even though the use of legal terms
in different jurisdictions has many pitfalls, such terms will be translated more or less literally andwhere necessary we will briefly sketch the legal context. For example, a relevant distinction here isthat the principal is the primary actor of a crime and the accomplice an active participant.

6

stories about the facts, and an evidential theory for building arguments from theevidence to the facts. More specifically, the formal hybrid theory is a combinationof a formal model of causal-abductive reasoning CT, which is inspired by modelbased approaches to causal-abductive inference (e.g. [13]) and an evidential
argumentation theory ET, which takes its inspiration from standard accounts ofstructured and abstract argumentation ([26], [23], [14]).
The hybrid theory combines reasoning with causal and evidential rules
formalised with a connective for defeasible implication , which only satisfies
the defeasible modus ponens inference rule.6 A causal rule e1 C e2 stands for ‘e1(presumably) caused e2’; a specific causal relation between events can then beformalised as a rule, e.g. Francis shot Kevin
C Kevin died. Similarly, anevidential rule e1 E e2 means that ‘e1 (presumably) is evidence for e2’, andspecific evidential relations can be formalised as rules, e.g. Sander says ”Francis
shot Kevin” E Francis shot Kevin. As usual, a rule with (meta)variables is ascheme standing for all its ground instances. Thus, for instance, a specific causal
link can be generalized as a causal generalization (e.g. x shoots y C y dies,
which means so much as “if you shoot someone, this may cause them to die”) anda specific evidential link can be generalized as an evidential generalization (e.g.
witness x says “p” E p, interpreted as “witnesses usually speak the truth”).

3.1 Abductive reasoning with stories and story schemes
A criminal case usually starts when some initial evidence is found that points tothe possibility that a crime has been committed. In the Wamel case, theinvestigation started with Sander contacting the police and telling them that Kevinhad been shot near the barns in Wamel; Kevin's body was found the same daynear the barns. On the basis of this preliminary evidence, we can formulate one ormore initial explananda, facts that have to be explained. These explananda can beobservations or they can be other facts that are considered important (this will befurther discussed in section 4.3 when we look at the connection to the legal
reasoning layer). In the Wamel case, the most important initial explanandum is thefact that Kevin died due to multiple gunshot wounds.
Explananda can be explained by constructing stories – coherent sequences ofstates and events – about what might have happened. A coherent story (cf. [21],[30]) is causally connected in that the individual events are connected by(sometimes implicit) causal links. This allows us to perform abductive reasoning
in order to infer what happened to Kevin. Abductive reasoning involves“guessing” new hypotheses that explain some data (i.e. Kevin’s body). The basic
idea of such reasoning is that if we have a general rule ‘c is a cause for e’ and we
observe e, we are allowed to infer c as a possible hypothetical explanation of theeffect e. This cause c which is used to explain the effect can be a single state or
6

See also David Poole’s work (e.g. [24]) for a combination of causal and evidential reasoning.

7

event, but it can also be a causally connected chain of events, a story. One
explanation for Kevin’s death is that Sander and Kevin went to the barns in
Wamel to meet Francis and that Francis shot Kevin, which caused Kevin’s death.
In our formal model, abductive reasoning is done using a causal theory CT.
Definition 2 [Causal Theory] A causal theory is a tuple CT = (RC, H, F, FSS)
where
RC is a set of causal rules of the form φ1, …, φn C ψ;
H, the hypotheticals or hypothetical events, is a set of ground literals;
F, the explananda which have to be explained, is a consistent set of groundfirst-order literals.
FSS is a set of factual story schemes (Definition 5).
The causal rules RC are the generalizations we discussed above. Given thesecausal rules and the set of hypothetical events H, we can build a story, a finite
sequence of events and rules expressing the causal relations between these events.
Definition 3 [Story] A story S based on a causal theory CT is a finite sequence[φ1,…,φn], where n > 0, such that for all φi (1 i n):φ1 H; andφi H RC; or
φi follows from ψ1, …, ψn {φ1, …,φi-1} by application of defeasible modus
ponens.
The reason we model a story as a sequence is that many stories have achronological structure that give it a sequential character of some kind. Note that,
however, the sequentiality of a story is not its prime characteristic, it is not whatmakes a story coherent; rather, coherence is governed by whether a story “has all
its parts” (definition 6). More specific issues pertaining to, for example, temporalreasoning and the fact as to whether causal relations can be pinned down to one
specific point in a sequence are hence left implicit in our model.
Thus, a story starts with an event and further events in the story are either
events from H or events which are causally inferred from the rest of the story.
Stories(CT) denotes the set of all stories that can be constructed from a theory CT.
As an example, consider the story S1:[Kevin was at the barns, Francis was at the barns, Francis shot Kevin, Francis shotKevin

C Kevin died, Kevin died].

Notice that in order to provide a more holistic flavour to the causal theory, not all
causal relations in a story will be made explicit: the causal coherence of a story
then depends on implicit causal relations, which will be discussed below when we
look at story schemes.
In the causal theory, the “explains” relation between a story and the
explananda is defined through a notion of logical consequence ⊢C, where ⊢Cstands for logical consequence according to the set of all deductive inference rules
extended with modus ponens for C.
8

Definition 4 [Explanation] A story S is an explanation for a set of explananda F
iff for all f F:
S ⊢C f; andS is consistent.
As is usual in model-based reasoning, we consider only subset-minimal
explanations. For our initial explanandum Kevin died, we can thus abductively
infer S1 as an explanation, as Kevin died follows from S1.
Note that using causal rules, we can also perform predictive reasoning, where
one assumes a hypothesis and tries to predict what will be the case as aconsequence of this hypothesis. For example, if we hypothesize that Francis shot
Kevin, there should be (Kevin’s) blood at the scene of the crime, as we would
normally expect that being shot causes one to bleed quite heavily. This predictive
reasoning can then be used in the search for new evidence (Section 3.3).
In our earlier work [7], explicit causal rules played a larger role. Following
standard accounts of logical causal-abductive reasoning, the explanatory stories in
the previous version of the hybrid theory were represented as fully connectedcausal networks. While certain explicit causal generalizations play an importantrole in causal-abductive reasoning, they are atomistic in flavour. Explicit causal
relations are used to link small clusters of facts and events; these clusters are
considered separately and the case is not considered ‘as a whole’.
In contrast, a holistic perspective on story coherence is provided by story
schemes, abstract scenarios that can serve as a scheme for particular stories. As isargued by [28], the knowledge that is used when thinking about stories often does
not have the form of individual causal generalizations but is more naturally
thought of as a collection of generalized events or event types, abstract renditionsof how things generally happen in the world. One example of such a story schemeis [22]’s story scheme for intentional actions: given some initial states of affairs, amotive may lead to an action with certain consequences.
For our formal definition of story schemes we basically follow the definitions
given in [5]. We assume a set FSS containing the relevant factual story schemes in
CT.7 Because story schemes are in effect abstract stories, the structure of story
schemes is very close to that of specific stories. Basically, a story scheme G is asequence containing literal schemes (literals with variables that act as schemes for
all their ground instances) that denote event types and causal rules that denote
types of causal links.
Definition 5 [Factual Story Scheme] A factual story scheme G FSS is a finite
sequence of literal schemes and causal generalizations (i.e. causal rule schemes).

7

Factual story schemes are schemes about real-world facts. They are different from legal story
schemes, which will be discussed in section 4.2.

9

As with stories, the sequence represents a basic idea of chronological succession.
As an example of a story scheme, take the simple scheme for murder (in a nonlegal sense):[x is at place p, y is at place p, x has motive m to kill y, x shoots y, x shoots ydies, y dies].

Cy

Note that there is an explicit causal generalization in this scheme, which saysthat x shooting has to be the cause of y dying (otherwise y would not have been
killed by x). This scheme is a concrete version of the scheme for intentional
actions (in the sense that murder is an intentional action). A specific story can
now be matched to a story scheme by instantiating the variables in the story
scheme with constants in the story. In our example, the story S1 is an instance of amotivated killing: both Kevin and Francis were in the same place p (the barns)
and Francis shot Kevin, which caused Kevin’s death.
Notice that in our example there is an element in the story scheme which is notin the story, namely x has motive m to kill y (which would be Francis has motive
m to kill Kevin in the story). Even though the events in the story correspond tosome element of the scheme, not all elements of the scheme have a corresponding
event in the story. This leads us to the notion of a complete story.
Definition 6 [Complete Story] A story S = [ 1,..., n] is complete w.r.t. a story
scheme G = [ 1,..., n] iff every i is a ground instance of i.
In the above example, the missing motive makes the story incomplete (w.r.t. themurder scheme). Note that here, we define only one measure of completeness: astory either fully instantiates a story scheme or it does not. In [5], other measuresof completeness (e.g. whether a story has extra elements that are not in thescheme) are defined.
The concept of completeness can be used to determine the coherence of astory. Recall that a coherent story is causally connected. In our previous work, thiscausal connectivity was modelled using individual, explicit causal links. In thispaper, however, we define coherence through the use of story schemes. Morespecifically, we consider a scheme to be coherent if it is complete w.r.t. someplausible story scheme. This ensures that the story “has all its parts” (e.g. nomurder story with a missing motive, cf. [35]). Furthermore, if we assume thatstory schemes only present coherent views on how things generally work in theworld around us, we accept that by completing a scheme the story adheres to thescheme’s implicit causal coherence.
Matching a part of a story to a scheme allows for (abductive and predictive)
causal reasoning without explicit causal rules. For example, if we have a scheme[e1, e2, e3] and we observe (a ground instance of) e3, we can infer a story instanceof [e1, e2, e3] as a possible abductive explanation of e3; in our example, Francis
has motive m to kill Kevin can thus be abduced from story S1 using the story
scheme for murder. Similarly, we may perform predictive reasoning using a story
10scheme; if we extend the murder scheme to include [...x shoots y, y bleedsheavily...], we can use this extended scheme to infer that Kevin bled heavily. Here,the abductive and predictive inference steps are not justified by an explicit causal
connection between the original hypothesis and the new hypothetical event, butrather by the implicit causal connections in the story scheme.

3.2 Evidential reasoning with arguments
In the previous section, we were mainly concerned with constructing hypotheses
based on our general knowledge of the world, encoded as either atomistic causal
rules or holistic story schemes. In reality, however, the process will also be driven
by evidence. Here, arguments play an important role as they can be used toconnect the evidence to a story: given some evidence, we can infer conclusions
through defeasible argumentative inferences until we arrive at some event in our
hypothesised story. Thus, we can support a story with evidence.
Our evidential argumentation theory ET takes its inspiration from the ASPIC+
framework [25], which integrates [26] and [23]’s ideas on rule-based
argumentation and structured arguments within [14]‘s abstract approach.
Definition 7 [Evidential Theory] An evidential theory is a tuple ET = (RE, K)
where
RE is a set of evidential rules of the form φ1, …, φn E ψ;K, the evidence, is a set of ground literals.
Arguments can be built by taking evidence from K and rules from RE as
premises and chaining applications of defeasible modus ponens into treestructured arguments (similar to the well-known Wigmore charts from theliterature [2]).
Definition 8 [Argument] An argument based on an evidential theory ET is a
finite sequence [φ1, …, φn], where n > 0, such that for all φi (1 i n):φi K RC ; orφi follows from ψ1, …, ψn {φ1, …,φi-1} by application of defeasible modus
ponens.
As an example of a simple argument, consider the following simple argument A1:
1. e1: Sander says ”Francis shot Kevin”
2. re1: witness x says “p” E p
3. Francis shot Kevin

(K)
(RE)
(1, 2, DMP)

We say that Args(ET) denotes the set of all arguments that can be constructedfrom a theory ET.
Arguments are a tool to deal with the contradictory evidence that is often
available in a case. In the Wamel case, for instance, the main witness Sander isunreliable. He has reported two versions of what happened. In the first report, to
his girlfriend and her mother, he says that Francis was at the crime. In the second

11report, to the police, he denies Francis was there. A careful argumentative analysis
can help to find out how to handle such conflicting information.
In our formal model, conflict between arguments is modelled as defeat. Here,
we use the common notation φ̄ for the complement of a formula φ (thecomplement of φ is ψ if φ = ψ and ψ if φ = ψ).
Definition 9 [Defeat] Given two arguments A and B:
A rebuts B iff φ A and ψ B such that φ ψ̄ and ψ K.
A undercuts B iff φ A and r RE such thatφ r̄ ; andthere is an application of defeasible modus ponens to r in B.
A defeats B iff A either rebuts or undercuts B.
So an argument rebuts another argument if they have an opposite (intermediate)conclusion, and an argument undercuts another argument if the application of
defeasible modus ponens to a rule in the second argument. Here, r generalises
the two cases where a rule is invalid (inapplicable in all cases) and where there isan exception to the rule (inapplicable in some cases), cf. [16]. As an example, takethe following argument:
1. e2: Sander gave contradictory statements
2. re2: witness x gives contradictory statements
3. re1

(K)
(RE)
E re1
(1, 2, DMP)

Here, it is argued that a situation where a witness gives contradictory statements is
an exception to the generalization that witnesses normally speak the truth (rulere1). This argument undercuts argument A1 for Francis shot Kevin.
An advantage of formal models of argumentation is that they can be used toevaluate a particular argument given a complex mass of other evidential
arguments. In other words, given a collection of arguments and their binary defeat
relations, the dialectical status of the arguments can be determined. Following[25], we assume that our theory for arguments instantiates one of [14]’s
semantics. For present purposes, the exact type of semantics is not important andwe simply assume that, depending on the semantics chosen, arguments can bejustified, overruled, or defensible.

3.3 Combining stories and arguments in a hybrid theory of IBE
In [5][7], it is argued that arguments and stories need to be combined into one
hybrid theory. In this hybrid theory, explanatory stories are used to explain the
explananda, and arguments based on evidence are used to support and attack thesestories. In this way, the evidence is used prove or disprove different stories about
the facts in a case.
Now, the formal hybrid theory is a combination of an evidential theory and acausal theory.
12Definition 10 [Hybrid Theory] A hybrid argumentative-narrative theory is atuple HT = (ET, CT), where
ET is an evidential theory
CT is a causal theory such that every f F is the conclusion of a justified
argument A in Args(ET) based on evidence.
An important part of the hybrid narrative-argumentative theory is theconsideration of alternative stories. Although in principle the mere contradictionof the story proposed by the prosecution, e.g. by a solid alibi for the suspect,suffices for the preclusion of a conviction, in most cases there are alternative
stories, for each of which there is some support (but not conclusively justifying)and for each of which there is some attack (but not conclusively defeating).
Moreover, a serious search and consideration of alternative stories is a good tool
to lessen the danger of too narrow tunnel vision.
In the Wamel case, a natural suspect (in addition to Francis) might be Sander.
Sander was also at the barns and he could have tried to incriminate Francis
because he himself has something to do with Kevin’s death. Moreover, Sandergave contradictory testimonies, first stating that Francis was the killer and later
saying he does not know who was the shooter; it could be that Sander could belying because he himself is the killer, viz. [Kevin was at the barns, Sander was at
the barns, Sander shot Kevin, Sander shot Kevin C Kevin died, Kevin died]. Notethat this story is almost the same as S1, only with Sander as the shooter.
In addition to the search for alternatives, the stories themselves also have to bethoroughly analysed and compared. In this analysis, it is important to look at theextent to which the alternative stories conform to the evidence as well as theircoherence, the extent to which the story conform to our knowledge of the world.
In the work on the hybrid theory [5][7] a number of criteria are defined that
determine the quality of a particular story. These criteria are mostly defined using
a combination of arguments based on evidence and stories. Two importantconcepts are evidential support and the evidential contradiction, that is, howevidence supports or contradicts stories via arguments.
Definition 11 [Evidential Support] Evidence φ
K supports a story S
Stories(CT) iff there is a justified argument A Args(ET) such that φ is a premiseof A and ψ S is a conclusion of A.
Here, the element of the story can be either an event or a causal rule.8 In our
example, the evidence e1: Sander says ”Francis shot Kevin” supports the story S1,
as e1 supports the event in the story Francis shot Kevin through the evidential
argument. Note that evidence only supports a story through a justified argument:
if the argument is defeated, the evidence does not support the explanation as thelink between the evidence and the story is effectively “cut”.
8This is important, as in criminal cases this sort of evidence is often provided (e.g. a forensic
report stating that “the victim’s death was caused by a bullet”).

13Given the evidential support, we can determine what the evidential coverageof a story [22] is, namely all pieces of evidence in K hat support the story. The
higher this coverage, the better the story. However, for each story we must also
consider falsifying evidence; a story may cover a lot of the evidence but if there is
one important piece of evidence that contradicts it or if the story is contradicted on
an important element we must be careful not to accept the story too readily.
Definition 12 [Evidential Contradiction] Evidence φ K contradicts a story S
Stories(CT) iff there is an argument A Args(ET) such that φ is a premise of Aand ψ,¯ is a conclusion of A, whereS.
So, for example, if Francis denies shooting Kevin in his testimony, thiscontradicts the story S1.
Related to evidential support and contradiction is the concept of evidential
gaps, elements of a story for which there is no evidence.
Definition 13 [Evidential gaps] An evidential gap in a story S is some ψwhich is not supported or contradicted by evidence
K.

S

Evidential gaps are hypothesised events for which there is no direct evidence.
Even without direct evidence we may still believe some fact if we consider it inconjunction with other facts. If a fact fits a coherent story that has enoughevidential support (where the evidence supports other facts in the story), thecircumstances detailed in the story make it more plausible that the hypothesizedfact happened. This is the ‘gap-filling’ function of stories [2]: gaps in the evidence
are filled with events that fit the total picture painted by the story.
Evidential gaps also play an important role in the investigative phase, as they
point to new avenues of investigation. Given a basic story, we can use abduction
or prediction to infer story consequences, events which follow from the story. In
section 3.1, we already showed two examples of such story consequences, namely
Francis has motive m to kill Kevin and Kevin bled heavily. Now, evidential gapsthat have been inferred as story consequences are relevant as they guide the search
for new evidence; after inferring that Francis should have a motive, we mightwant to look for evidence for such a motive. Thus, the reasoning about the facts
acts out its influence on the (search for) evidence in the case (i.e. the “downward”
influence in Figure 1).
Evidential support and gaps concern the connection (or lack thereof) between
the story and the evidence. In a case, however, we often also have to consider theinherent coherence of a story, that is, whether it conforms to our expectations andknowledge of the world (see definition 6 and below in section 3.1). In previous
work, the causal coherence of stories was often explicitly represented by requiring
a story to be fully causally connected. The causal links could then be questioned
with arguments based on general knowledge (cf. [8]) and thus the coherence of astory could be supported or contradicted (e.g. by asserting that ‘it is generalknowledge that x shoots y C y dies’). In this paper, however, we use the14modelling technique of story schemes to gauge coherence, that is, a story iscoherent if it completes a story scheme (definition 6).
A story’s coherence plays an important part in guiding the investigative
process; the police would not, for example, want to pour all its resources into
pursuing a clearly implausible and incoherent hypothetical story. However, one
has to be wary of the danger of preferring a “good” story (i.e. plausible) to a“true” story (i.e. supported by strong evidence): [21][33] show that in some cases,
the incoherent story is actually better supported by the evidence.
Criteria like coherence, the total evidential support and the number of
evidential gaps can be used to judge the quality of explanatory stories. Thus, they
allow for the comparison of explanations in the overarching process of Inference
to the Best Explanation. For example, [7] rank stories according to their total
evidential coverage (i.e. the more evidence supports a story, the better the story).
[11] have further shown how standards and burdens of proof influence thecomparison of explanations. For example, the ‘beyond a reasonable doubt’
standard requires that for a story to be accepted, there is no coherent alternative
available (where this coherent alternative then represents the reasonable doubt).
In addition to the ranking of stories, there are of course other factors that
influence the legal decision-making process. For example, it may be a perfectly
valid strategy for the defense to simply deny the prosecution’s allegations without
presenting a story. If the judge or jury then accepts the defense’s denial andacquits, they have not performed inference to the Best Explanation. However, we
think that in general a coherent story can provide a stronger case against the otherside’s story than a simple denial or an imperfect story, and that providing the best
explanation is the most sound strategy available.

4 LEGAL REASONING IN THE EXTENDED HYBRIDTHEORYThe basic hybrid theory allows for both reasoning from the evidence to the facts
as well as from the facts to the evidence. However, it does not include explicit
legal reasoning, that is, the reasoning from the facts to the legal consequences andthe influence the (desired) legal consequences may have on the various accountsof the facts. In this section, we extend our hybrid theory in order to include such
legal reasoning. We introduce two new types of rules, namely legal rules andqualification rules.
One type of legal rules (cf. [16][26][32]) warrant the step from legally
relevant operative facts to a legal conclusion. An example is the Dutch legal rulethat someone can be sentenced for murder, when he has killed someone,
intentionally and with premeditation: rL1: x killed y x intended to kill y x killingy was premeditated L x murdered y. Another type of legal rules, which we willcall qualification rules, allow for the qualification of a fact under a legally
relevant term. An example of such a rule is that if there are signs that the murder15

weapon was prepared, then the killing was premeditated rq1: x prepared themurder weapon Q x killing y was premeditated. Note that both types of legal
rules are what Searle XX calls constitutive rules, rules of the form “X counts as Y
in context C”. From a continental legal perspective it makes sense to distinguishqualification rules In a continental legal system, non-qualification legal rules areusually given by law (e.g. murder is rule 289 in the Dutch Criminal Code),
whereas qualification rules are often based on, for example, linguistic conventions
or jurisprudence, as it does not make sense for the lawgiver to explicitly
enumerate all the possible ways of killing (e.g. “stabbing which causes death iskilling, shooting which causes death is killing, etcetera”) .
These new rules are part of a legal theory (cf. the causal, evidential and hybrid
theories of definitions 2, 7 and 10), which also contains the legal story schemes.
Combining these rules and legal story schemes with an existing hybrid theory
provides us with all the tools necessary to reason from evidence to legal
conclusions as in Figure 1.
Definition 14 [Legal Hybrid Theory] A legal hybrid theory is a tuple LHT =(HT, R, LSS), where
HT is a hybrid theory (definition 10);
R = RL RQ is a set of rules that contains legal rules (RL) and qualification
rules (RQ) of the form φ1, …, φn L ψ and φ1, …, φn Q ψ, respectively;
LSS is a set of legal story schemes.

4.1 Legal reasoning with arguments
Whereas evidential arguments are used to establish the facts of a case, the next
step is to determine the legal conclusions that can be based on these facts. First,
the real-world facts have to be qualified as legal facts or, in other words, thefactual stories have to be interpreted as legal stories on which a conviction can bebased. Here the qualification rules of a legal theory LT (specified in RQ) are
guiding. Then these legal stories lead to a legal conclusion (on the basis of thelegal rules in RL), which leads to the relevant legal consequences.
The argumentative reasoning with qualification and legal rules (in the form oflegal arguments) is modelled along the lines of existing work on this subject ([15][16][26]). We specifically base our formal model of arguments on [25]. Legalarguments can be built by taking elements from a story S in the relevant hybrid
theory and rules from RL and RQ as premises and chaining applications ofdefeasible modus ponens into tree-structured arguments.
Definition 15 [Legal Argument] A legal argument based on a story S is a finite
sequence [φ1, …, φn], where n > 0, such that for all φi (1 i n):
φi S RL RQ ; orφi follows from ψ1, …, ψn {φ1, …,φi-1} by application of defeasible modus
ponens.

16

The set of all legal arguments that can be constructed from a legal hybrid theory
LHT is denoted as Args(LHT). As an example, take the argument A2 below, whichsays that if one person shoots another person and this causes the victim’s death,then this counts as a killing (in the legal sense as required by one of the conditionsof rL1).
1. Francis shot Kevin(story S1)
2. rc1: Francis shot Kevin C Kevin died(story S1)
3. Kevin died(story S1)
4. x shoots y rc1 y dies Q x killed y(RQ)
5. Francis killed Kevin(1-4 DMP)
This argument can be extended to form an argument A3 that Francis murdered
Kevin, on the basis of the rule rL1.
1. Francis killed Kevin
2. Francis intended to kill Kevin3. Francis’ killing of Kevin was premeditated
4. x killed y x intended to kill y x killing y waspremeditated L x murdered y
5. Francis has murdered Kevin(argument A2)(argument ?)(argument ?)(RL)(1-4 DMP)

Note, however, that this argument requires separate arguments for premeditation(item 3 on the list) (based on, e.g., rule rq1) and for intention to kill (item 2), bothof which should also be based on the same story S1.
Like in the evidential argumentation theory, counterarguments may be given
to legal arguments. One may argue, for example, that if the weapon was prepared
not for killing someone but rather for a sporting activity, the preparation of theweapon does not count as premeditation; this would then undercut any inference
based on the qualification rule rq1.

4.2 Legal stories and legal story schemes
In purely argumentative approaches to legal reasoning (e.g. [26]), the operative
legal facts in the case are considered as conditions of legal rules (e.g. in argument
A3). We argue that these conditions provide a legally coherent perspective on acase. In this sense, they can be thought of as a legal stories, analogous to factual
stories, which provide a factually coherent perspective on a case.
A legal story scheme is a cluster of legally qualified, generic states and events.
Definition 16 [Legal Story Scheme] A legal story scheme GL
literal schemes.

LSS is a set of

In Dutch law, the definition of an offense in the criminal code can be used to
extract a legal story scheme. An example of a legal story scheme is that for
murder (in the legal sense): {x killed y, x intended to kill y, x killing y waspremeditated}. Each element of the legal story scheme is one of the conditions of
the legal rule for murder rL1. Note that when rules contain disjunctions as
17

antecedents, there will be multiple legal story schemes, each containing one or
multiple of these disjuncts.
A legal story (e.g. an indictment) is then a specific instantiation of a legal
story scheme.
Definition 17 [Legal Story] A legal story LS is a set of literals {φ1,…,φn} suchthat every element i LS is a ground instance of someGL, where GL is alegal story scheme in LSS.
So an example of a legal story is LS1 = {Francis killing Kevin was premeditated,
Francis intended to kill Kevin, Francis killed Kevin}, an instantiation of the legal
story scheme proposed above. As discussed above, it is possible to present
multiple legal stories, for example when dealing with a rule that has disjunctive
premises. A similar situation is when the prosecution performs reasoning in thealternative, that is, they argue that either the accused killed the victim or,alternatively, he helped someone else kill the victim. With such reasoning theprosecution pre-emptively performs a legal shift: consider this factual and legal
story first, but if that is not convincing enough consider a different interpretationof the case. We further discuss legal shifts in section 4.3.
Legal story schemes are similar to factual story schemes in that they containgeneral event types, the relevant operative legal facts. However, a majordifference is that in the particular context of criminal law the set of legal story
schemes will be finite and knowable (because they are the conditions of legal
rules; cf. the legality principle in criminal law), whereas factual story schemes arepart of our implicit and potentially infinite ‘stock of commonsense knowledge’.
Further formal distinctions are that factual story schemes are sequences and legal
story schemes are sets (legal stories usually do not need an explicit notion ofchronology (sequence), whereas factual stories do), and that legal story schemes
and stories do not contain causal rules (when a causal connection is an element ofa legal condition, as for instance in criminally negligent manslaughter, thatelement will have to be made explicit as a proposition in the legal story scheme).
The idea of legally coherent perspectives on a case is not new, and otherapproaches to formalising legal coherence have been proposed [17][4].
Furthermore, as we showed in [6], legal story schemes are very similar to thecases – coherent clusters of legally relevant facts – in the AI and Law literature on
case-based reasoning (e.g. [3]) and, as we discussed above, these clusters of legal
facts serve as the conditions to legal rules. The reason we use the terms “legal
stories and story schemes” is that this emphasizes the similarities between
reasoning at the factual level and reasoning at the legal level.
Similar to factual stories, legal stories can complete legal story schemes.
Definition 18 [Complete Legal Story] A legal story S is complete w.r.t. a legal
story scheme G iff every i LS is a ground instance of some
G L.

18

Factual stories have varying degrees of coherence depending on how well they
complete a story scheme: a story with a missing motive is slightly incoherent, astory with a missing motive and action and consequence in the wrong order ismore incoherent, and so on. Furthermore, it is possible to make a decision (e.g. toconvict) on the basis of an incomplete story as it is possible to, for example,
convict for murder even if there is no clear motive.
For legal stories, it is not so much a question of a gradual scale of coherence
but rather a question of whether the story meets the required conditions forapplication of a legal rule or not; it is not possible to make a decision on the basisof an incomplete legal story, as one cannot, for example, convict for murder if
intention has not been proven. So in the decision-making stage, legal stories
always have to be complete. Incomplete legal stories, however, are very wellpossible at various points in an investigation. For example, a legal story that
contains Francis killed Kevin but no other information fits various legal story
schemes (for murder, manslaughter etcetera), but does not complete any of them.
The investigation may then be steered by this incomplete legal story as theinvestigators look for ways to prove, for example, premeditation or intention (cf.
the phenomenon of legal shifts in section 4.5).

4.3 Connecting evidential and legal reasoning
If a valid and acceptable conclusion is to be drawn on the basis of a legal story,
the individual elements of that legal story need to be proven. This, in turn, can bedone by showing that there is a factual story based on the evidence that meets thestandard of proof, and that this factual story qualifies as a commonsenseinterpretation of the legal story. In other words, the factual account of the case has
to support the legal account of the case.
Definition 19 [Supporting a Legal Story] Elements 1,..., n of a factual story S
support an elementof a legal story LS iff there is a justified argument A
Args(LHT) such that 1,..., n are premises of A and ψ is a conclusion of A.
Notice that this definition is similar to definition 11 for evidential support: theevidence supports events in the factual story, and these facts in turn support theelements of the legal story. As an example, consider the subsequence [Francis
shot Kevin, Francis shot Kevin C Kevin died, Kevin died] from story S1. This partof S1 supports the element Francis killed Kevin of legal story LS1, because there isan argument (A2) which has these events as its premises and Francis killed Kevin as
its conclusion.
Figure 4 shows the complete reasoning from evidence to legal conclusions via
facts. Notice that there are four separate levels: evidence, factual story, legal story
and legal conclusion. Each of these levels depends on the level directly below it:legal conclusions are inferred from legal stories, legal stories are inferred fromfactual stories and factual stories are inferred from evidence.
19

legalconclusion

Francismurdered
Kevin

legal
argument

legal
story

Francis’ killingof Kevin waspremeditatedFrancisintended tokill Kevin

Franciskilled Kevinlegal (qualification)arguments
Francis and Kevin
had an argument
at the barns

factualstory

Kevin walked
away and Kevinfollowed him

Francisshot Kevin

Kevin
died

evidential
arguments

evidence

Sander’s
testimony

Sander’s
testimony

Coroner’sreportFigure 4: Reasoning from evidence to legal conclusions via stories

4.3.1 Pushing down gaps
The similarity between evidential support (definition 11) and supporting a legal
story (definition 19) means that there is also such a thing as legal gaps, elementsof the legal story which are not supported by a fact from the factual story.
However, whilst factual stories may have evidential gaps a legal story cannot havesuch gaps at the end of a successful investigative process that can lead to aconviction.
Definition 20 [Supported Legal Story] A legal story LS is fully supported by afactual story S iff every element ψ LS is supported by elements 1,..., n S.
This leads to an interesting phenomenon: since gaps cannot occur at the legal
level, gaps can be pushed down from the legal level to the factual level. For
instance, as murder requires that one person killed another, the legal story about
the Wamel case will have to contain Francis killed Kevin, as otherwise the legal
conclusion ‘murder’ will not follow. This element of the legal story has to besupported by a factual concretisation of ‘killing’, as set out in argument A2.
Notice, however, that the facts that qualify as ‘killing’ (i.e. [Francis shot Kevin,Francis shot Kevin C Kevin died, Kevin died]) do not necessarily have to be
directly supported by evidence, that is, they can remain an evidential gap(rendered in Figure 4 as dotted boxes). Formally there is no legal gap, as thefactual story does specify events supporting Francis killed Kevin, but materiallythere is no direct evidential support for Francis killed Kevin, that is, there is no
chain of argumentative reasoning from the evidence to Francis killed Kevin.
This is an example of the ‘gap-filling’ effect of stories, where evidential gaps
can still be believed when considered as part of a coherent story that has a lot ofevidential support. In general, it is a matter of good judgment which elements of a20

story must be directly supported by evidence and which can be assumed inconjunction with the other facts; it is not unusual that a murder conviction does
not specify direct evidence for the killing (see [11] for examples of murderconvictions in cases where there was no evidence for the killing).
Pushing down gaps to the factual level shows why it is important to connect
legal reasoning and factual reasoning with stories. In a purely rule-based
approach, Francis shot Kevin and Francis shot Kevin C Kevin died would have to
be assumed, as they are here. However, in a story-based approach the assumption
is made plausible by having it as an element in a plausible, evidentially supported
story.

4.3.2 Legal shifts and legal tunnel vision
If we compare Figure 4 to Figure 1 it becomes clear how the different levels caninfluence each other. The legal perspective on a case drives not only what happens
in court but also what occurs in the pre-trial investigative phase. In the Wamel
case, it was quite clear that the factual perspective was murder (in the everyday,
non-legal sense of the term): when a criminal is found killed by pistol shots, theconclusion that we are dealing with a murder case is quickly made. Perhaps there
is a brief consideration of the possibility of suicide, but the nature of the wounds
may swiftly exclude that.
Initially the investigation will then be aimed at finding the killer. This isrequired by both the factual story scheme for murder and in the corresponding
legal murder scheme. When a suitable suspect is found the legal perspective
becomes more prominent. The aim then becomes to prove that the suspect is thekiller; x killed y in the legal story scheme for murder. The factual story scheme(which can include the killer, the circumstances of the killing, the murder weapon,
the motive, and perhaps several other more factually oriented elements) remains
relevant, but it becomes coloured by the legal perspective that is provided by thelegal story scheme. For instance, the amount of detail of circumstances that need
to be proven is steered by what is needed to complete the case in the legal sense.
For example, intention is in this case quite easily proven: the fact that Francis shot
Kevin several times is enough to show that Francis did not intend to merely
incapacitate Kevin out of self-defence. This means that the factual story does notneed to be further extended in order to show intention.
The explication of the legal perspective on a case allows the modelling of alegal shift. If during a case it becomes clear that it is not possible to fully support
the legal story that represents the current perspective with a factual story that canbe accepted according to the current proof standard, other legal stories and story
schemes that can be supported by the factual story will come into view. In the
Wamel case, for example, no clear evidence was found that pinpointed Francis as
the one who actually shot Kevin (notice in Figure 4 that Francis shot Kevin is anevidential gap). While it is sometimes possible to convict even in the absence of
direct evidence for the killing (as discussed in the previous subsection), in the21

Wamel case there were too many doubts regarding, among other things, Francis’
motive and the reliability of Sander’s testimonies. The case hence turned from amurder case (in the legal sense) into a case of accomplicity to murder, in which it
is not required to prove ‘who pulled the trigger’. The legal murder story {Francis
killing Kevin was premeditated, Francis intended to kill Kevin, Francis killed
Kevin} was replaced by an accomplicity to murder story {Kevin is killed, the killingof Kevin was intentional, the killing of Kevin was premeditated, Francis
participated significantly in the killing of Kevin}. In this scheme, it is unclear who
actually killed the victim. Instead the significant participation in a killing becomesthe criminally relevant criterion.
The fact that after a legal shift a new factual story is needed (and hence new
evidence to support this story is sufficient) is a clear example of a “downward”
influence (Figure 1): what happens at the legal level influences the reasoning in
the factual level. Another example of such a downward influence is when thelegal level – that is, the current legal perspective – determines the coherence of thefactual story. At the moment, the factual story in Figure 4 is perfectly coherent.
However, say that it needs to be established how long ago the murder took place
to deal with a statutory limitation for prosecution. A new element is then added to
the legal story, namely the fact that the crime took place within the period ofprescription (the maximum time after a crime that legal proceedings based on thecrime may be initiated). In order to have a coherent factual story that supports thislegal story, a new element should also be added to this factual story; for example,
that the killing took place 2 months ago, which is well within the period ofprescription.
It was already mentioned that Israëls has provided a careful analysis ofalternative stories and their relative merits, thereby avoiding tunnel vision withrespect to the facts. Our modelling of the legal perspective in a case shows that
there can be a second kind of tunnel vision, namely by neglecting legal story
schemes. For instance, an apparent murder case may in fact be a manslaughter
case, or even one of negligent homicide. In this connection, we propose to speakof legal tunnel vision as opposed to factual tunnel vision. In factual tunnel vision,
one for instance neglects the consideration of other wrongdoers than one's
favourite suspect (here: only considering Francis, and not also Sander). Instead in
legal tunnel vision, one focuses too much on finding proof for malice
aforethought, whereas in fact it could be true that Francis wanted to frighten
Kevin in order to become Uden's criminal alpha male, and in the ensuing fightaccidentally shooting Kevin. Indeed such an accident might still legally count as
murder, but the assumption of malice aforethought can have led to ignoring thepossibility of an accident.

22

5 DISCUSSION AND RELATED RESEARCH
Our extended hybrid model is not the first formalized proposal that models thefull pathway from evidence to legal consequences. A recent proposal is [32] by
Walker who speaks of the rule-evidence interface, with 'rule' meaning 'legal rule'.
He argues that the two sides of the rule-evidence interface have logical similarities
and dissimilarities. He provides visualization techniques – akin to Wigmore charts– showing the path from evidence via proven facts to legal consequences. A
similarity is that he uses tree structures for the representation of both the pathfrom evidence to facts ('evidence evaluation'), and from facts to legal
consequences ('rule-based deductions'). A difference is that evidence evaluation
uses plausibility schemas and plausibility connectives, whereas rule-based
deductions are modelled in terms of truth-functional connectives (with three truth
values).
[2] also discuss analytic methods for reasoning with evidence in which therole of law is made explicit. They emphasise that the (potential) ultimate
probandum (i.e., the legal consequence) needs to be made explicit at an early stepin the process of analysing the evidence (step 2, p. 117).
In AI & Law, evidential reasoning has also been addressed to some extent. For
instance, although [16] focuses on the role of legal rules, it also discusses the issue
of proof (p. 105-106). In this approach, proof is based on epistemic reasons,which can derive from rules of evidence as they are recognized in somejurisdiction. In [17] the model of rules is extended to a theory of qualitative,
reason-based comparison of alternatives. In light of this theory, the connection
with evidence and proof, and how different accounts of the facts can be comparedon the basis of how well they fit the evidence is also discussed. The coherence
theory associated with this model is developed in [18] making connections withlegal theory (e.g., [1]).
[26] have extensively modeled the legal part of the pathway and they focus on
the formal modeling of the assessment and resolution of conflicting arguments asthey occur in the law. While evidential reasoning plays a less important role, it isshown how argumentation concerning the admissibility of evidence in a case with
forged evidence can be formalized (p. 342). This is one example of a “downward”
influence (i.e. legal restrictions on evidence), not discussed in this paper.
However, given that our legal theory LT is directly based on [25]’s extended
version of [26], we think that the admissibility example can be rendered in our
hybrid framework.
The above related research is all mainly argumentative in style, as opposed toour hybrid proposal in which also the role of holistic, coherent narratives is madeexplicit. As is already extensively argued in [5], a hybrid theory in whicharguments are combined with stories is best for reasoning about the evidence andthe facts. In our opinion, including stories and (legal) story schemes also improves
the model for legal reasoning. One case in point is the way in which legal gaps
23

may be filled using facts which are themselves evidential gaps. Purely
argumentative approaches, which do not have stories in the factual, middle layer,
have no tools for filling such evidential gaps, that is, they miss the gap-filling
function stories fulfil. In such argumentative approaches, the line of reasoning
would go from the evidence all the way up to the operative legal facts (conditionsof legal rules) and as a result of this, any legal fact that is not supported byevidence cannot be considered proven on the basis of the evidence.
Other relevant research which models the full pathway is the more narrativeoriented work by [22]. They show how coherent (factual) stories that explain theevidence can be matched to “verdict categories”, which are essentially legal story
schemes. The ideas provided in this work have been a great influence on the
hybrid theory (also indirectly via [33]). A major difference though is that theauthors of [22] approach evidential and legal reasoning from a psychological,
descriptive stance whilst we also claim to have more normative aims (in [9], forexample, we propose a list of pitfalls one should avoid when drafting a rational
and intelligible verdict in a case). Furthermore, [22] does not fully formallyspecify the connection between the evidence, the facts and the law.
In our extended hybrid theory of inference to the best legal explanation, we
reason at different layers of abstraction: a factual story is essentially the same as alegal story, but abstracts from the legal qualifications. One influential way of IBE
with different layers is [12]’s abductive model, which models a hierarchy of
causal networks. The causal networks in different layers are connected to eachother using abstraction axioms (e.g. “swine flu is a type of influenza”). High-level
concepts are then abductively explained by concepts lower in the hierarchy
through abstraction axioms (e.g. if we observe influenza this can be swine flu or
bird flu). These lower-level concepts can then be abductively explained throughthe usual causal rules. In theory, one could model the legal consequences as
explananda at the highest level of abstraction and abductively infer the facts. For
example, if we take the explanandum Francis killed Kevin, we can abductively
infer the facts Francis shot Kevin, Francis shot Kevin C Kevin died, Kevin diedusing rq1. Thus, we could have a mainly story-based, causal-abductive theory oflegal reasoning.
Both [12] and [22] provide a story-based perspective on (evidential and legal)reasoning. Again, in [5] it was already argued why a hybrid theory which
incorporates arguments is preferred to such purely narrative approaches. Briefly,
the argumentative machinery (e.g. arguments and counterarguments,
argumentation schemes and critical questions) provide a natural model of aspectsof both evidential and legal reasoning.

6 CONCLUSION AND SUMMARY
In the previous sections, we have extended our hybrid narrative-argumentative
approach to evidential reasoning in order to be able to address reasoning towards
24the legal consequences that can be attached to a case. Whereas before the hybrid
theory was limited to evidential reasoning and stopped at the facts, we now cancomplete a line of legal reasoning up until the legal decision. We have introduced
the notion of a legal story scheme, thereby allowing the explication of the legal
perspective taken in a case analysis (formalized as an extended hybrid theory).
The legal perspective is relevant in a case analysis as it steers the investigative anddecision-making process. In fact, there is a legal analogue of the familiar factual
tunnel vision that we dubbed legal tunnel vision: when one too strongly focuseson the evidential needs to complete a case in terms of one kind of legal
perspective, better alternatives may be pushed out.
Our proposal can be summarized as follows.
1. In our approach, the hybrid narrative-argumentative style of modeling is used
for the full pathway of reasoning from evidence via facts to legal
consequences. As a result, we use our hybrid approach for a unifying view onboth evidential and legal reasoning.
2. Our use of story schemes at the factual as well as the legal level allows for the
explicit and natural modeling of a coherent, holistic perspective on a case, as it
underlies an investigative and decision making process.
3. At the factual level, story schemes show evidential gaps, emphasising whereto strengthen investigative efforts, and point to alternatives, thereby preventing
tunnel vision. Factual shifts occur when the perspective on the facts (in theform of a favorite factual story scheme) is changed, by adding and/or
removing story schemes that steer the evidence marshaling process.
4. At the legal level, something similar occurs. A legal story scheme provides aholistic perspective that steers the process of reasoning towards legal
consequences. The risk of what we have called legal tunnel vision can be
reduced by the consideration of alternative legal story schemes. Legal shifts
can be modeled in the form of the addition or removal of a legal story scheme.
5. But at the legal level, there is no analogue of evidential gaps: every element ofa legal story needs to be covered to allow for a successful conviction. This
corresponds to the fact that every condition of a criminal legal rule needs to besatisfied in order for the legal consequence to follow (cf. the legality principlethat is dominant in criminal law).
6. In our approach, it is made explicit that legal gaps can be pushed down to thefactual level. Every legal element that is required to complete a legal story ismatched to an element in the factual story. Whether all elements of the factual
story are considered to be proven, allowing the possibility of an evidential
gap, is then determined at the evidential level.
An issue with our hybrid narrative-argumentative approach is that in its present
form we do not provide a deep connection between stories and arguments whereas
there seems to be one. For instance, one reasonable story provides a25

counterargument to another. In our earlier work, we have suggested thatarguments and stories are a kind of ‘communicating vessels’: a change in anargumentative analysis implies a change in an narrative analysis, and vice versa(cf., e.g., [9]). In the present setting of legal story schemes, there is the related
issue how the legal conditions of a valid rule are connected to a legal story
scheme. One perspective (underlying this paper) is that the legal conditions
provide the atomistic building blocks for a legal story scheme. As a result of theholistic character of legal story schemes, they can be used to establish the legal
coherence of a case analysis.

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