Legal Shifts in the Process of Proof
Floris Bex

Bart Verheij

Argumentation Research Group
University of Dundee
Dundee, UK
florisbex@dundee.ac.uk

Department of Artificial Intelligence
University of Groningen
Groningen, The Netherlandsb.verheij@ai.rug.nl

ABSTRACTIn this paper, we continue our research on a hybrid narrativeargumentative approach to evidential reasoning in the law byshowing the interaction between factual reasoning and legal
reasoning. We therefore emphasize the role of legal story schemes(as opposed to factual story schemes that formed the heart of ourprevious proposal). Legal story schemes steer what needs to be
proven, but are also selected on the basis of what can be proven.
They provide a coherent, holistic legal perspective on a criminalcase that steers investigation and decision making. We present an
extension of our previously proposed hybrid theory of reasoning
with evidence, by making the connection with reasoning towards
legal consequences. We discuss the phenomenon of legal shiftsthat shows that the step from evidence to (proven) facts cannot be
isolated from the step from proven facts to legal consequences.
We show how legal shifts can be modelled in terms of legal story
schemes. Our model is illustrated by a discussion of the Dutch
Wamel murder case.

Keywords
Legal argumentation, Legal evidence and proof, Stories

1. INTRODUCTION
In research on legal reasoning in the field of AI & law, models of
reasoning from proven facts to legal consequences are welldeveloped (e.g., [22], [13]). Recently there is also a rise inattention for evidential reasoning (e.g. [5], [17], [25]). However,there is not much recent work that aims at modelling the fullpathway from evidence via proven facts to legal consequences(except maybe [27], see section 5). Providing a model of that fullpathway is the focus of his paper.
We will argue that the factual and legal part of legal reasoning(the steps from evidence to proven facts, and from proven facts tolegal consequences, respectively; cf. Figure 1) cannot be
separated. The phenomenon of legal shifts is a case in point: thelegal perspective on a case changes as a result of what can beproven, and at the same time determines the investigative anddecision making focus. We provide an example based on the
Dutch case of a murder in the provincial town of Wamel (ascarefully analyzed by Israëls [16]). In this case, it was impossible
to successfully charge the prime suspect for murder, but he issuccessfully charged (and convicted, after appeal andwithstanding cassation by the Supreme Court) as an accomplice toPermission to make digital or hard copies of all or part of this work forpersonal or classroom use is granted without fee provided that copies are
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the murder, while the key question of who shot the gun is notreally clarified.
We will extend our previous work on reasoning with evidence([2], [4], [6]), in which we mainly concerned ourselves with thefactual part of trials, that is, the evidence and the facts which wemight infer through evidential reasoning. As of yet we have notspecified how exactly, once the facts have been established, thereasoning towards the legal consequences proceeds. Also, theexact way in which the law might influence the reasoning 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 toevidential reasoning ([2], [4], [6]) in order to incorporate thecomplete reasoning process in a case: from evidence via facts tolegal consequences. The focus is on analytic tools for the stages ofthis process. Our proposal allows a representation of thementioned phenomenon of legal shifts, in which one legal
perspective is abandoned favouring another. For that purpose, theadditional modelling tool of legal story schemes, which can beused to establish the legal coherence (as opposed to the factual
coherence) of a case, is required.1
Factual and legal story schemes make explicit that a holistic,coherent perspective underlies all reasoning and argumentation.
Factual story schemes are important to determine which accountsof the facts are plausible, and which gaps need to be filled byfurther evidence in order to form a full picture of what happened.
Legal story schemes show which sets of (legally qualified) facts
and events are recognized as coherent wholes by the law, in thesense that a legal consequence such as a conviction can be basedon 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 theoreticalbackground used (section 2). This comprises a discussion of thetheory construction view on legal reasoning on the basis ofevidence 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). 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 ourpaper in section 6, pointing out some issues for future research.

2. FROM EVIDENCE VIA FACTS TOLEGAL CONSEQUENCES (AND BACK)
Reasoning in a criminal case is a complex process in which theavailable evidence determines which facts can be proven, andhence also which legal consequences follow. As we already

1

There exist other formal approaches to coherence , e.g. [14], [2].

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 alegal case (from evidence, via facts to legal consequences) is
gradually constructed is in place (Figure 1, adapted from Verheij
2005, p. 10). The figure not only suggests that evidence, facts andlegal consequences are gradually constructed from an imperfectinitial version, but also there is an influence both upward (fromevidence via proven facts to legal consequences) and downward(from legal consequences via proven facts to evidence).
Reasoning in a criminal case is a complex process in which theavailable evidence constrains which facts can be proven, which inturn are the grounds for legal consequences on the basis of theapplicable legal rules (Figure 1, adapted from [26], cf. also [18]).
The path of justification is from evidence via facts to legal
consequences; in the figure, this is 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 withthe discovery or exploration of new facts and evidence: the legal
perspective on a case (in the form of the legal consequences thatare 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 consequences are gradually constructed from animperfect initial version, but also that there is an influence both
upward (from evidence via facts to legal consequences) anddownward (from legal consequences via facts to evidence).

(e.g. the punishability for murder and the ensuing sentence ofimprisonment; cf. the German jurisprudential term Rechtsfolge).
In previous work ([2], [4], [6]) 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 bestmodelled 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 thecase. Arguments based on evidence can then be used to justify
these stories, as these arguments can be used to support elements
in a story with evidence or, in other words, to anchor the story in
the evidence (cf. [28]). Ultimately, the alternative stories in a caseshould be compared and the best one (i.e. the most coherent one
that best fits the evidence) should be chosen.
Another
account of
the facts

One accountof the facts
Arguments
Evidence

Figure 2: Hybrid narrative-argumentative evidential
reasoning
Figure 2 visualises the basic idea behind the hybrid theory. Thisway of hybrid reasoning with stories and arguments is particularly
close to the analytic and evaluative thinking of the professionals
that actually perform the reasoning in a criminal case, in particularcriminal investigators and judges ([18], [28], [2]).
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.

Figure 1: A theory construction perspective on legal reasoning
As for terminology, with evidence we mean the evidential data,
the primary sources of evidence the existence of which cannot besensibly denied (e.g. witness statements made in court, forensic
expert reports handed to the jury). As is usual in law, we use theterm 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”).2 By legal consequences, wemean the legal states of affairs that the law attaches to the facts

2

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).

In legal reasoning, the legal consequences are organised into
clusters of legal facts that provide legally coherent perspectives ona case. In our opinion, such a legally coherent perspective can beseen as a “legal story” about what happened in the case, a legallyqualified 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 in our case could read as follows: “On
the 5th of January 1997, Francis intentionally and with malice
aforethought killed Kevin by shooting him repeatedly with a semiautomatic weapon, which caused multiple severe injuries to
Kevin, as a result of which Kevin died”.
In any case, there are at least two legal accounts representing the“guilty” and “innocent” perspectives.3 Arguments can be used toreason from the (real-world) facts to the legal consequences, thatis, to justify the legal accounts with the facts of the case which arethemselves justified by the evidence. Ultimately, the alternative
legal accounts should be compared and the best one (i.e. the onethat best fits the proven facts) should be chosen. Figure 3 shows3

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

how legal accounts follow from the facts of the case in a similar
way as the facts follow from the evidence in the case.
Now, the combination of evidential reasoning (Figure 2) and legal
reasoning (Figure 3) gives us all the machinery we need for thereasoning in a criminal case (Figure 1). Because of the similarities
between evidential and legal reasoning, we think that thiscombination 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 on legal
consequences but also the downward, exploratory influence oflegal consequences on evidence.

3. EVIDENTIAL REASONING IN 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 whichthese facts follow. We then use arguments based on evidence toreason about these stories in order to determine which story is thebest explanation (i.e. the one that is best supported by evidence).
Thus, the formal hybrid theory is a combination of a causal theory
for building hypothetical stories about the facts, and an evidential
theory for building arguments from the evidence to the facts.
More specifically, the formal hybrid theory is a combination of aformal model of causal-abductive reasoning CT, which is basedon model-based approaches to causal-abductive inference (e.g.
[10]) and an evidential argumentation theory ET, which takes its
inspiration from standard accounts of structured and abstract
argumentation ([22], [20], [11]).

3.1 Abductive reasoning with stories andstory schemes
Figure 3: Hybrid narrative-argumentative legal reasoning

2.1 The Wamel case
Below we will briefly discuss the key concepts of stories andarguments. We will illustrate these concepts using examples
inspired by the Wamel case [16], 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 tosoft drugs and theft, but not normally associated with big
organized crime.
On January 6, 1997, Kevin's body is found some 50 kilometresfrom his home town Uden, near two barns in the village ofWamel. He has been shot dead. Later that day, Sander contacts thepolice and states that he was also at the scene of the crime,
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). Francis then walked tothe back of one of the barns. When Kevin followed him, there wasa sudden firing of shots, after which Sander fled.
Francis was ultimately convicted both in first and second instanceto 13 years imprisonment, as an accomplice to the murder of
Kevin and the attempted murder of Sander.4 This was later
confirmed by failing cassation at the Supreme Court.

4

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
and where necessary we will briefly sketch the legal context.
For example, a relevant distinction here is that the principal is
the primary actor of a crime and the accomplice an active
participant.

A criminal case usually starts when some initial evidence is foundthat points to the possibility that a crime has been committed. In
the Wamel case, the investigation started with Sander contacting
the police and telling them that Kevin had been shot near thebarns in Wamel; Kevin's body was found the same day near thebarns. On the basis of this preliminary evidence, we can formulate
one or more initial explananda, facts that have to be explained.
These explananda can be observations or they can be other facts
that are considered important (this will be further discussed in
section 4.3 when we look at the connection to the legal reasoning
layer). In the Wamel case, the most important initial explanandumis the fact that Kevin died due to multiple gunshot wounds.
Explananda can be explained by constructing stories – coherent
sequences of states and events – about what might have happened.
A coherent story (cf. [18], [25]) is causally connected in that theindividual events are connected by (sometimes implicit) causal
links. This allows us to perform abductive reasoning in order toinfer what happened to Kevin. Abductive reasoning involves“guessing” new hypotheses that explain some data (i.e. Kevin’sbody). The basic idea of such reasoning is that if we have ageneral rule ‘c is a cause for e’ and we observe e, we are allowed
to infer c as a possible hypothetical explanation of the effect e.
This cause c which is used to explain the effect can be a single
state or 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 the causal
theory CT = (RC, H, F), where RC is a set of causal rules, H is aset of hypothetical events (ground literals) and F is the set of
explananda (ground literals). Causal rules in RC are formalisedusing a connective for defeasible implication ⇒C, which only
satisfies the inference rule for (defeasible) modus ponens. A
specific causal relation between events can then be formalised as arule, e.g. Francis shot Kevin ⇒C Kevin died. As usual, a rule withvariables is a scheme standing for all its ground instances. Thus, aspecific causal link can be generalized as a causal generalization,
viz. rc1: x shoots y ⇒C y dies.
Given these causal rules and the set of hypothetical events H, wecan build a story. In CT, a story is then a finite sequence of eventsand rules expressing the explicit causal relations in the story. The
ordering of the events suggests their chronological succession.
Individual events in the story are then hypothetical events from Hor events which are causally inferred from other events in thestory by applying defeasible modus ponens to these other eventsand a rule from RC. Furthermore, as is usual in abductive-causal
models, we enforce that a story be consistent by requiring that S
CA ⊥. Stories(CT) denotes the set of all stories that can beconstructed from a theory CT. As an example, consider the story
S1:

relevant factual story schemes in CT.5 Because story schemes arein 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 thatact as schemes for all their ground instances) that denote event
types and causal rules that denote types of causal links. As withstories, the sequence represents a basic idea of chronologicalsuccession.

[Kevin was at the barns, Francis was at the barns, Francis shot
Kevin, Francis shot Kevin ⇒C Kevin died, Kevin died].

[x is at place p, y is at place p, x has motive m to kill y, x shoots y,x shoots y ⇒C y dies, y dies].

Notice that in order to provide a more holistic flavour to thecausal theory, not all causal relations in a story will be madeexplicit: the causal coherence of a story then depends on implicit
causal relations, which will be discussed below when we look atstory schemes.

Note that there is an explicit causal rule in this scheme, whichsays that x shooting has to be the cause of y dying (otherwise ywould not have been killed by x). This scheme is a concrete
version of the scheme for intentional actions (in the sense thatmurder is an intentional action). A specific story can now bematched to a story scheme by instantiating the variables in thestory scheme with constants in the story. In our example, the story
S1 is an instance of a motivated killing: both Kevin and Francis
were in the same place p (the barns) and Francis shot Kevin,which caused Kevin’s death.

In the causal theory, the “explains” relation between a story andthe explananda is defined through a notion of logicalconsequence. That is, a story S explains an explanandum f iff S ⊢Cf, where ⊢C stands for logical consequence according to the set of
all deductive inference rules extended with modus ponens for ⇒C.
This means that the explanandum is either a hypothetical event in
S or can be derived from previous events in S using causal rules.
For our initial explanandum Kevin died, we can 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 a consequence of this hypothesis. For
example, if we hypothesize that Francis shot Kevin, there shouldbe (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 [6], explicit causal rules played a larger role.
Following standard accounts of logical causal-abductive
reasoning, the explanatory stories in the previous version of thehybrid theory were represented as fully connected causal
networks. While certain explicit causal generalizations play animportant role in causal-abductive reasoning, they are atomistic inflavour. Explicit causal relations are used to link small clusters offacts and events, these clusters are considered separately and thecase 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 forparticular stories. As is argued by [24], the knowledge that is used
when thinking about stories often does not have the form ofindividual causal generalizations but is more naturally thought ofas a collection of generalized events or event types, abstract
renditions of how things generally happen in the world. One
example of such a story scheme is [18]’s story scheme forintentional actions: given some initial states of affairs, a motive
may lead to an action with certain consequences.
For our formal definition of story schemes we basically follow thedefinitions given in [2]. We assume a set FSS containing the

As an example of a story scheme, take the simple scheme formurder (in a non-legal sense):

Notice that in our example there is an element in the story scheme
which is not in 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 to some element of thescheme, not all elements of the scheme have a corresponding
event in the story. We say that a story S completes a story scheme
G iff for every element g ∈ G, there is some s ∈ S such that s is aground instance of g. In this example, the missing motive makesthat the story does not complete the scheme.
The concept of completeness can be used to determine thecoherence of a story. Recall that a coherent story is causallyconnected. In our previous work, this causal connectivity wasmodelled using individual, explicit causal links. In this paper,
however, we define coherence through the use of story schemes.
More specifically, we consider a scheme to be coherent if itcompletes a plausible story scheme. This ensures that the story“has all its parts” (e.g. no murder story with a missing motive, cf.
[30]). Furthermore, if we assume that story schemes only present
coherent views on how things generally work in the world aroundus, 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 andpredictive) causal reasoning without explicit causal rules. For
example, if we have a scheme [e1, e2, e3] and we observe e3, we
can infer [e1, e2] 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 scheme; if we
extend the murder scheme to include [...x shoots y, y bleedsheavily...], we can use this extended scheme to infer that Kevinbled heavily. Here, the abductive and predictive inference steps
are not justified by an explicit causal connection between the5Factual story schemes are schemes about real-world facts. They
are different from legal story schemes, which will be discussed
in section 4.2.

original hypothesis and the new hypothetical event, but rather by
the implicit causal connections in the story scheme.

3.2 Evidential reasoning with arguments
In the previous section, we were mainly concerned withconstructing hypotheses based on our general knowledge of theworld, encoded as either atomistic causal rules or holistic story
schemes. In reality, however, the process will also be driven byevidence. Here, arguments play an important role as they can beused to connect 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[21], which integrates [22] and [20]’s ideas on rule-based
argumentation and structured arguments within [11]‘s abstract
approach. In the theory ET = (RE, K), RE is a set of evidential
rules or generalizations and K is a consistent set of evidence, theevidential data. The evidential rules in RE are represented
similarly to the causal rules in RC, with the connective ⇒E (where
the subscript E denotes an “evidential” instead of a “causal”
inference). These evidential rules, or evidential generalizations,
are used to warrant the inferences from evidence to a conclusion.
For example, an inference from a witness testimony to someconclusion is only warranted if we accept that witnesses usually
speak the truth. This witness testimony generalization can be
represented formally as re1: witness x says “p” ⇒E p.
Now, arguments can be built by taking evidence from K and rules
from RE as premises and chaining applications of defeasible
modus ponens into tree-structured arguments, where each node in
the tree is thus an element of K, a rule from RE or the result of an
application of the defeasible modus ponens to one or more othernodes. Such a structure is very similar to the well-known
Wigmore charts from the literature [1]. As an example of a simple
argument, consider the following simple argument A1:
1. e1: Sander says ”Francis shot Kevin” (K)(RE)
2. re1: witness x says “p” ⇒E p
3. Francis shot Kevin(1, 2, DMP)
We say that Args(ET) denotes the set of all arguments that can beconstructed from a theory ET.
Arguments are a tool to deal with the contradictory evidence thatis often available in a case. In the Wamel case, for instance, themain witness Sander is unreliable. He has reported two versionsof what happened. In the first report, to his girlfriend and hermother, he says that Francis was at the crime. In the second
report, to the police, he denies Francis was there. A careful
argumentative analysis can help to find out how to handle suchconflicting information.
In our formal model, conflict between arguments is modelled as
defeat. An argument A1 can defeat another argument A2 in
essentially two ways (cf. [20]). A1 and A2 rebut each other if they
have an opposite (intermediate) conclusion. A1 undercuts A2 if
there is a conclusion ¬ri in A1 and an application of defeasible
modus ponens to ri in A2 (where ri is the name of a rule in RE).
Here, ¬ri generalises the two cases where a rule is invalid(inapplicable in all cases) and where there is an exception to therule (inapplicable in some cases), cf. [13]. For example, we mightargue that Sander is lying because he gave contradictory
statements. From Sander is lying we can then infer ¬re1 (thewitness testimony rule), as the situation in which a witness islying provides an exception to the generalization represented by
re1, that witnesses normally speak the truth. The argument about
Sander’s veracity would then undercut argument A1 for Francis
shot Kevin.
An advantage of formal models of argumentation is that they canbe used to evaluate a particular argument given a complex mass ofother evidential arguments. In other words, given a collection ofarguments and their binary defeat relations, the dialectical statusof the arguments can be determined. Following [21], we assume
that our theory for arguments instantiates one of [11]’s semantics.
For present purposes, the exact type of semantics is not important
and we simply assume that arguments can be justified, whichmeans that they are not defeated by other justified arguments,
overruled, which means that they are defeated by other justified
arguments, or defensible, which means that they are neither
justified nor overruled.

3.3 Combining stories and arguments in a
hybrid theory of IBE
An important part of our hybrid narrative-argumentative version
of Inference to the Best Explanation is the consideration ofalternative stories. Although in principle the mere contradiction of
the story proposed by the prosecution, e.g. by a solid alibi for thesuspect, 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, aserious search and consideration of alternative stories is a goodtool 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 toincriminate Francis because he himself has something to do with
Kevin’s death. Moreover, Sander gave contradictory testimonies,
first stating that Francis was the killer and later saying he does notknow who was the shooter; it could be that Sander could be lying
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]. Note that this story is almost the sameas S1, only with Sander as the shooter.
In addition to the search for alternatives, the stories themselvesalso have to be thoroughly analysed and compared. In thisanalysis, it is important to look at the extent to which thealternative stories conform to the evidence as well as theirplausibility, the extent to which the story conform to ourknowledge of the world. In the work on the hybrid theory ([2],[4]), a number of criteria are defined that determine the quality ofa particular story. These criteria are mostly defined in the hybrid
theory, that is, using a combination of ET and CT. Below, we will
discuss three criteria which are important for current purposes.
Perhaps the most important criterion to asses stories is evidential
support, which denotes the sources of evidence from K that
support a story S through a justified argument A ∈ ArgsE (i.e. e ∈K is a premise of A and some s ∈ S is a conclusion of A). Here, theelement of the story s can be either an event or a causal rule.6 In
our example, the evidence e1: Sander says ”Francis shot Kevin”
supports the story S1, as e1 supports the event in the story Francis
6This is important, as in criminal cases this sort of evidence isoften provided (e.g. a forensic report stating that “the victim’s
death was caused by a bullet”).

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”.
Related to evidential support is the concept of evidential gaps, theelements of the story (events or causal links) that are notsupported by evidence. In the formal hybrid theory, the gaps in astory S are all elements of S that are not the conclusion of ajustified argument. These elements are thus 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 hasenough evidential support (where the evidence supports otherfacts in the story), the circumstances detailed in the story make it
more plausible that the hypothesized fact happened. This is the‘gap-filling’ function of stories [1]: gaps in the evidence are filledwith 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 abasic story, we can use abduction or prediction to infer story
consequences, events which naturally 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 gaps that 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 might want to look for evidence for such a motive. Thus, thereasoning 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 lackthereof) between the story and the evidence. In a case, we also
have to consider the inherent plausibility of a story, that is,whether it conforms to our expectations and knowledge of theworld. This plausibility depends on whether a story is consistentand coherent (section 3.1). A story’s plausibility plays animportant part in guiding the investigative process; the police
would not, for example, want to pour all its resources into
pursuing a clearly implausibly hypothetical story. However, one
has to be wary of the danger of preferring a “good” story (i.e.
plausible, coherent) to a “true” story (i.e. supported by strong
evidence): [18], [28] show that in some cases, the implausible
story is actually better supported by the evidence.
The criteria of evidential support and plausibility can be used fora direct comparison of stories. For example, all other things being
equal, a story S can be considered better than a story S′ if thenumber of sources of evidence that support S is higher than S′.
Thus, we may determine the best explanation in a case. Whether
this explanation then leads to a conviction or acquittal depends onfurther (legal) factors, such as whether the story about the facts
fits the appropriate legal story (sections 2 and 3.3), who has theburden of proof and how high the proof standard is [8].

4. LEGAL REASONING IN THE
EXTENDED HYBRID THEORY
The basic hybrid theory allows for both reasoning from theevidence to the facts as well as from the facts to the evidence.
However, it does not include explicit legal reasoning, that is, thereasoning from the facts to the legal consequences and theinfluence the (desired) legal consequences may have on thevarious accounts of the facts. In this section, we extend our hybrid
theory in order to include such legal reasoning. This extension

takes the form of a legal theory LT = (LSS, R), which contains a
set of legal story schemes LSS and a set of rules R = RL ∪ RQ that
contains legal rules (RL) and qualification rules (RQ).

4.1 Legal reasoning with arguments
Whereas evidential arguments are used to establish the facts of acase, the next step is to determine the legal conclusions that canbe based on these facts. First, the real-world facts have to bequalified as legal facts or, in other words, the factual stories haveto 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 the legal rules in RL), which leads to
the relevant legal consequences.
In the legal theory LT, rules are modelled in the same way as in
the evidential and causal theories, that is, with a connective ⇒that satisfies defeasible modus ponens. We add two kinds ofgeneralizations (or rules) to our formalisms: first the legal rules in
RL that warrant the step from legally relevant operative facts to alegal conclusion. An example is the Dutch legal rule that 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 killing y was premeditated ⇒L x has murdered y.
The second additional kind of generalization is those that allow
the qualification of a fact under a legally relevant term. An
example of such a qualification rule is that if there are signs of thecareful preparation of the murder weapon, then the killing waspremeditated, viz. rq1: x prepared the murder weapon ⇒Q x killingy was premeditated. Qualification rules may be based on, forexample, linguistic conventions but they are often also warranted
by jurisprudence.
The argumentative reasoning with qualification and legal rules (inthe form of legal arguments) is modelled along the lines ofexisting work on this subject ([12], [13], [22]). We specificallybase our formal model of arguments on [21].
Legal arguments can be built by taking elements from a story S ∈Stories(CT) and rules from RL as premises and chaining
applications of defeasible modus ponens into tree-structured
arguments. As an example, take the argument A2 below, whichsays that if one person shoots another person and this causes thevictim’s death, then this counts as a killing (in the legal sense as
required by one of the conditions of rL1).
1.
2.
3.
4.
5.

Francis shot Kevinrc1: Francis shot Kevin ⇒C Kevin died
Kevin diedx shoots y ∧ rc1 ∧ y dies ⇒Q x killed yFrancis killed Kevin(story S1)(story S1)(story S1)(RQ)(1-4 DMP)

This argument can be extended to form an argument that Francis
murdered Kevin, on the basis of the rule rL1. This requires anargument for premeditation (for instance based on thequalification rule rq1) and one for intention to kill.
Like in the evidential argumentation theory, counterarguments
may be given to legal arguments. One may argue, for example,
that if the a weapon was prepared not for killing someone but
rather for a sporting activity, the preparation of the weapon does
not count as premeditation; this would then undercut any
inference based on the qualification rule rq1.

4.2 Legal story schemes
In purely argumentative approaches to legal reasoning (e.g. [1],[22]), the operative legal facts in the case are only considered asconditions of legal rules. However, we argue that they also serve
another role, namely as a legal story scheme that provides alegally coherent perspective on a case. This is analogous to factual
stories and story schemes, which provide a factually coherent
perspective on a case.
A legal story scheme is a cluster of legally qualified states andevents. In Dutch law, the definition of an offense in the criminal
code can be used to extract a legal story scheme. An example of alegal story scheme is that for murder (in the legal sense):{x killed y, x intended to kill y, x killing y was premeditated}.
Each element of the legal story scheme is one of the conditions of
the legal rule for murder rL1. In general, a legal story scheme GL isa set of literal schemes. A legal story (e.g. an indictment) is then aspecific instantiation of these literal schemes (e.g. {Francis killed
Kevin, Francis intended to kill Kevin, Francis killing Kevin waspremeditated}).
Legal story schemes are similar to factual story schemes in thatthey contain general event types, the relevant operative legal facts.
We have made a slight distinction however: whereas factual story
schemes are sequences, legal story schemes are sets, hence haveno explicit ordering. Our reason for this modelling difference isthat legal story schemes usually do not need an explicit notion ofchronology, whereas factual story schemes do. A further
difference between factual and legal stories is that legal stories do
not normally contain causal rules of the form c ⇒C e; such logicalrules are not needed in the legal theory LT, because prediction andabduction are not performed in LT (recall that in CT causal rules
can be used to predict story consequences or to abduce possible
causes). When some causal connection is an element of a legal
condition (as for instance in criminally negligent manslaughter),however, that element will have to be made explicit in the legal
story scheme.

4.3 Connecting evidential and legal reasoning
Given a legal story scheme and a story about the facts, the story
somehow has to match the scheme, that is, the events in thefactual story in some way have to correspond to the operative
legal facts in the legal story. This correspondence is defined usingarguments based on rules from RQ. Specifically, given a story S
and a legal story scheme GL, an element s ∈ S corresponds to anelement g ∈ GL iff there is a justified argument A ∈ ArgsL suchthat s is a premise of A and a ground instance of g is a conclusionof A. As an example, consider the subsequence [Francis shot
Kevin, Francis shot Kevin ⇒C Kevin died, Kevin died] from story
S1. This part of S1 corresponds to the legal story scheme formurder, because there is an argument (A2) which has these eventsas its premises and a ground instance of the legal story scheme formurder (Francis killed Kevin) as its conclusion.
Using the correspondence relation, we can define the legal
completeness of a story. We say that a story S completes a legal
story scheme GL iff for every element g ∈ G, there is some s ∈ Ssuch that s is a ground instance of g. This legal completeness issimilar to the factual completeness we defined in section 3.1: if astory completes a factual story scheme it is (causally) coherent
and if a story completes a legal story scheme it is legally coherent.
In a case, a story need not necessarily complete a factual story
scheme (i.e. it need not be causally coherent); one can besentenced for murder even if there is no clear motive. Legal story
schemes, however, need to be completed (in the end), as
otherwise we cannot say that the facts of the case (the story)
support the indictment (the legal story based on the legal story
scheme). This corresponds to the idea that a legal rule can only beapplied if all its conditions are fulfilled. In criminal law, where therole of the legality or nulla poena principle is strong, thisrequirement is especially important.
As a result of the requirement that a legal story scheme becompleted, there is a clear downward influence from the legal
layer to the factual layer: facts that correspond to the legal story
automatically become explananda. If a factual story wants to beconsidered as a serious candidate it has to be legally coherent; inorder to be legally coherent the story the facts that correspond to
the legal story scheme have to follow from the factual story.
Notice that the above definition of correspondence is similar tothat of evidential support (section 3.3). In the case ofcorrespondence, we connect the facts in the story to their legal
interpretation (i.e. the legal story based on the scheme) by
supporting the legal story with arguments based on the facts,
whereas in the case of evidential support, we connect the evidence
to their factual interpretation by supporting the factual story witharguments based on evidence. This similarity means that we canhave legal gaps, elements of the legal story which are notsupported by a fact from the factual story.
As said, in our approach factual stories may have evidential gaps.
A legal story, however, cannot have such gaps at the end of aninvestigative process – as we just argued the factual story always
needs to complete a legal story scheme. This leads to aninteresting phenomenon: since gaps cannot occur at the legal
level, gaps are pushed down from the legal level to the factuallevel. For instance, as murder requires premeditation, the legal
story about the case will certainly have to contain premeditation,as otherwise the legal consequence of punishability for murder
will not follow. The legal story will have to correspond to afactual concretisation of premeditation in the factual story, e.g., in
the form of preparatory activities. However, it can happen thatthese preparatory activities are an evidential gap, i.e., remain
unproven, and are only considered to exist as a result of the gap
filling effects of stories. This implies that formally there is nolegal gap, as the factual story does specify events corresponding topremeditation, while materially there is no direct support for thelegal element of premeditation.

4.4 Legal shifts and legal tunnel vision
The legal perspective on the facts of 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 theterm): when a small-time (and perhaps not so small-time) criminal
is found between barns, killed by bullet shots, the conclusion that
we are dealing with a murder case is quickly made. Perhaps there
is a brief consideration of the possibility of suicide, but the natureof the wounds may swiftly exclude that.
Initially the investigation will normally then be aimed at finding
the killer. This is both required by what is expected in a factual
story scheme for murder and in the corresponding legal murder
scheme. When the killer is found (or at least someone who isseriously suspected of being the killer), the legal perspective
becomes more prominent. The aim becomes to prove by evidence
that the suspect is the killer (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 perspectivethat is provided by the legal story scheme. For instance, theamount of detail of circumstances that need to be proven is
steered by what is needed to complete the case in the legal sense.
This legal perspective that is leading a process of criminal
investigation and decision making is modelled as a subset LP of
the legal story schemes LSS. LP is not a singleton but a set, as
there can be more than one type of offense that is at issue. Thereis also the possibility of an empty perspective, when as yet it isunclear what kind of crime we are dealing with.
The explication of the legal perspective on a case allows themodelling of a legal shift. Here the Wamel case can serve as anillustration. In that case, the investigative process must have beensomewhat frustrating. Already quite early Francis became a prime
suspect. But notwithstanding much efforts put into questioning
witnesses and other forms of information gathering, no clear proof
was found that pinpointed Francis to the scene of the crime, letalone as the killer.
This must have resulted in a legal shift at some point. The caseturned from a clear murder case (in the legal sense, with amurderer convicted) into one in which no murderer would be
convicted. Instead, the case became a case of accomplicity tomurder. The shift must have felt as a defeat, hard to accept. In
fact, the bullet was for long not really bitten, as shown by theprosecution's charge (first instance) that Francis was the murderer,
or else an accomplice. The murder charge was not repeated insecond instance, completing the legal shift.
In a formal model of such a legal shift, the legal perspective LPchanges to a different legal perspective LP'. Legal story schemes
can be added - when a new kind of criminal offense is becoming
part of the investigation - or removed - when some kind of offense
is no longer considered relevant.
In the Wamel case, the shift is provoked by the failure of finding
proof for a key element of the legal story scheme of murder. As aresult, an accomplicity to murder scheme becomes the legal
perspective. The legal murder scheme {x killed y, x intended to killy, x killing y was premeditated} that was an element of the legal
perspective LP is then replaced by an accomplicity to murder
scheme {y is killed, the killing of y was intentional, the killing of y
was premeditated, x participated significantly in the killing of y}.
In this scheme, it is unclear who actually killed the victim. Instead
the significant participation in a killing becomes the criminally
relevant criterion.
The Wamel case shows that the legal shift to the accomplicity
perspective is not only needed to convict people that help amurderer, but also to convict someone who may well be themurderer but cannot be proven so.
It was already mentioned that Israëls has provided a carefulanalysis of alternative stories and their relative merits, thereby
avoiding tunnel vision with respect 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 amanslaughter case, or even one of negligent homicide. In thisconnection, we propose to speak of legal tunnel vision as opposed
to factual tunnel vision. In the latter, one for instance neglects theconsideration of other wrongdoers than one's favourite suspect(here: only considering Francis, and not also Sander), whereas in
the former 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,but in the ensuing fight accidentally shooting Kevin. Indeed suchan accident might still legally count as murder, but the assumptionof malice aforethought can have led to ignoring the possibility ofan accident.

5. DISCUSSION AND RELATEDRESEARCH
Our extended hybrid model is not the first that models the fullpathway from evidence to legal consequences. [27] speaks of therule-evidence interface, with 'rule' meaning 'legal rule'. He argues
that the two sides of the rule-evidence interface have logicalsimilarities and dissimilarities. He provides visualization
techniques – akin to Wigmore charts – showing the path fromevidence via proven facts to legal consequences. A similarity isthat he uses tree structures for the representation of both the pathfrom evidence to facts ('evidence evaluation'), and from facts tolegal consequences ('rule-based deductions'). A difference is that
evidence evaluation uses plausibility schemas and plausibility
connectives, whereas rule-based deductions are modelled in termsof truth-functional connectives (with three truth values).
[1] also discuss analytic methods for reasoning with evidence inwhich the role 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 step in the process of analysing theevidence (step 2, p. 117).
In AI & Law, evidential reasoning has also been addressed tosome extent. For instance, although [13] focuses on the role oflegal rules, it also discusses the issue of proof (p. 105-106). In thisapproach, proof is based on epistemic reasons, which can derivefrom rules of evidence as they are recognized in some jurisdiction.
In [14] 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 compared on the basis of how wellthey fit the evidence is also discussed.
[22] have extensively modeled the legal part of the pathway andthey focus on the formal modeling of the assessment andresolution of conflicting arguments as they occur in the law.
While evidential reasoning plays a less important role, it is shown
how argumentation concerning the admissibility of evidence in acase with forged evidence can be formalized (p. 342). This is one
example of a “downward” influence (i.e. legal restrictions onevidence) which was not shown in this paper. However, given that
our legal theory LT is directly based on [21]’s extended version of[22], we think that the admissibility example can be rendered in
our hybrid framework fairly easily.
The above related research is all mainly argumentative in style, as
opposed to our hybrid proposal in which also the role of holistic,coherent narratives is made explicit. As is already extensively
argued in [2], a hybrid theory in which arguments are combinedwith stories is best for reasoning about the evidence and the facts.
In our opinion, including stories and (legal) story schemes also
improves the model for legal reasoning. One case in point is theway in which legal gaps may be filled using facts which arethemselves evidential gaps. Purely argumentative approaches,
which do not have stories in the factual, middle layer, have notools 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 (conditions of legal rules) and as a resultof this, any legal fact that is not supported by evidence cannot be
considered proven on the basis of the evidence.

1.

In our approach, the hybrid narrative-argumentative style ofmodeling is used for the full pathway of reasoning fromevidence via facts to legal consequences. As a result, we use
our hybrid approach for a unifying view on both evidential
and legal reasoning.

Other relevant research which models the full pathway is the morenarrative-oriented work by [18]. They show how coherent(factual) stories that explain the evidence 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. A major difference though is that the authors of[18] approach evidential and legal reasoning from a
psychological, descriptive stance whilst we also claim to havemore normative aims (in [7], for example, we propose a list of
pitfalls one should avoid when drafting a rational and intelligible
verdict in a case). Furthermore, [18] does not fully formallyspecify the connection between the evidence, the facts and the
law.

2.

In comparison with purely argumentative approaches, ouruse of story schemes (both at the evidential and at the legalstep) allows for the explicit and natural modeling of acoherent, holistic perspective on a case, as it underlies aninvestigative and decision making process.

3.

At the factual level, story schemes show evidential gaps,
showing where to strengthen investigative efforts, and point
to alternatives, thereby preventing tunnel vision. Factual
shifts occur when the perspective on the facts (in the form ofa 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 a holistic perspective that steers the processof reasoning towards legal consequences. The risk of legal
tunnel vision can be reduced by the consideration ofalternative legal story schemes. Legal shifts can be modeledin the form of the addition or removal of a legal story
scheme.

5.

But at the legal level, there is no analog of evidential gaps:
every element of a legal story needs to be covered. This
corresponds to the fact that every condition of a criminal
legal rule needs to be satisfied in order for the legal
consequence to follow (cf. the legality principle that is
dominant in criminal law).

6.

In our approach, it is made explicit that legal gaps can be
pushed down to the factual level. Every legal element that isrequired to complete a legal story is matched to an element in
the factual story. Whether all elements of the factual story are
considered to be proven, allowing the possibility of anevidential gap, is then determined at the evidential level.

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 a legal story, but abstracts from thelegal qualifications. One influential way of IBE with different
layers is [9]’s abductive model, which models a hierarchy of
causal networks. The causal networks in different layers areconnected to each other 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 birdflu). These lower-level concepts can then be abductively
explained through the usual causal rules. In theory, one could
model the legal consequences as explananda at the highest level ofabstraction and abductively infer the facts. For example, if we takethe explanandum Francis killed Kevin, we can abductively infer thefacts Francis shot Kevin, Francis shot Kevin ⇒C Kevin died, Kevindied using rq1. Thus, we could have a mainly story-based, causalabductive theory of legal reasoning.
Both [9] and [18] provide a story-based perspective on (evidential
and legal) reasoning. Again, in [2] it was already argued why ahybrid 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 aspects of both
evidential and legal reasoning.

6. CONCLUSION AND SUMMARY
In the previous sections, we have extended our hybrid narrativeargumentative approach to evidential reasoning in order to be able
to address reasoning towards 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 caseanalysis (formalized as an extended hybrid theory). The legal
perspective is relevant in a case analysis as it steers theinvestigative and decision-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 focuses on 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.

An issue with our hybrid narrative-argumentative approach is thatin 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 a counterargument toanother. In our earlier work, we have suggested that arguments
and stories are a kind of 'communicating vessels'. In the present
setting of legal story schemes, there is the related issue how thelegal 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 the holistic character of legal story
schemes, they can be used to establish the legal coherence of acase analysis.

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