The missing link revisited: The role of teleology in representing legal argument

T. J. M. BENCH-CAPON

Department of Computer Science, The University of Liverpool, Liverpool, UK

E-mail: tbc@csc.liv.ac.uk

Abstract. In this paper I recapitulate the ideas of Berman and Hafner (1993) regarding the role of

teleology in legal argument. I show how these ideas can be used to address some issues arising from

more recent work on legal argument, and how this relates to ideas associated with the “New Rhetoric”

of Perelman. I illustrate the points with a discussion of the classic problem of which vehicles should

be allowed in parks.

1. Introduction

The first morning of ICAIL 1993 in Amsterdam concerned argument. The first two

papers presented, Henry Prakken’s logical framework for modelling legal argument

(Prakken 1993) and Tom Gordon’s paper on using dialogue games to model legal

argument (Gordon 1993), have been enormously influential and there has followed

a great volume of work articulating, developing and combining these approaches.

Just before lunch on that morning a no less interesting paper with an entirely

different approach was presented, Don Berman and Carole Hafner’s Representing

Teleological Structure in Case Based Legal Reasoning: The Missing Link (Berman

and Hafner 1993). Unfortunately this has not produced anything like the same

degree of subsequent research. In this paper I want to recapitulate the ideas in that

paper and to re-examine them in the light of what we have learnt about modelling

legal argument since 1993. In doing so I hope to establish that the time is ripe to

pay some very serious attention to their ideas.

_ This paper was originally written in December 1999. Since then it has received responses from

Henry Prakken and Giovanni Sartor (in this volume), and has been developed in on-going work, both

by Henry Prakken and by myself in collaboration with Giovanni Sartor. The most recent expression

of my views can be found in Bench-Capon and Sartor (2001). In preparing this paper for publication

I have attempted to remain faithful to my original views, and not to anticipate too much later

developments, although I have taken the opportunity to correct some mistakes in the original version.

80 T. J. M. BENCH-CAPON

2. Hunting, shooting and fishing

The paper presented in Amsterdam (Berman and Hafner 1993) was based on three

cases, commonly used in teaching American students law. In the first, Pierson v

Post, the plaintiff was hunting a fox, on open land, in the traditional manner using

horse and hound when the defendant killed and carried off the fox. The plaintiff

was held to have no right to the fox because he had gained no possession of it. In

the second case, Keeble v Hickeringill, the plaintiff owned a pond and made his

living by luring wild ducks to the pond with decoys, shooting them and selling

them. Out of malice the defendant used guns to scare the ducks away from the

pond. Here the plaintiff won. In a third case, Young v Hitchens, both parties were

commercial fisherman. The plaintiff spread a net, some half a mile in length, and

began to close it. When the opening was no more than a few dozen feet wide, the

defendant sped into the gap, spread his own net and caught the fish which had been

trapped by the plaintiff as he closed his net. In this case the defendant won.

Berman and Hafner then constructed an argument for the defendant in Young,

against the background of Pierson and Keeble. They say that they are following

the approach used in HYPO (Ashley 1990). They do indeed use the three-ply style

of argument developed in HYPO, in which a party to the case cites a precedent,

the opponent responds and the original party attempts to rebut the response. Their

representation of the cases, however, differs somewhat from the original conception

of HYPO (e.g., Ashley and Rissland 1988). Berman and Hafner use factors, which

are features of the case which may be present or absent and which, if present, favour

either the plaintiff (pro-plaintiff factor) or the defendant (pro-defendant factor).

HYPO in contrast used dimensions, which are features of the case which can take

a range of possible values, ordered according as to the extent to which they favour

a particular side. Consider the question of whether the hunter had possession of

the animal. Seen as a factor, we simply ask whether the animal was caught or

not. Seen as a dimension, we can have a range of possibilities progressively more

favourable to the defendant, running from caught to no contact at all, and passing

through some intermediate positions such as mortal wounding, wounding, hot pursuit,

started, and seen. Using dimensions permits a richer representation of the case

situation, and allows us to avoid some awkwardness in choosing factors, such as

whether the factor should be caught (pro-plaintiff), or not caught (pro-defendant),

or perhaps both, as well as not requiring us to make “all or nothing” decisions.

Using factors, on the other hand, does make a useful simplification. In fact the use

of factors has in recent years become rather more common than dimensions: the

description of cases in CATO (Aleven 1997) and the reconstruction of case based

reasoning of Prakken and Sartor (1998) both use factors rather than dimensions.

In the remainder of this paper I shall use factors in this way, although I think

dimensions remain important and interesting, and I hope to explore the difference

that using them makes in some future work.

THE MISSING LINK REVISITED 81

Berman and Hafner can be seen as identifying five factors. Two are proplaintiff:

that the plaintiff was following his livelihood (LIVELIHOOD) and that

the land was owned by the plaintiff (OWNLAND). Three are pro-defendant: that

the animal was not caught (NOTCAUGHT), that the land was open (OPEN)

and that the defendant was in competition with the plaintiff (COMPETE). Pierson

contains NOTCAUGHT and OPEN, Keeble OWNLAND, LIVELIHOOD and

NOTCAUGHT and Young NOTCAUGHT, OPEN and COMPETE. Actually Berman

and Hafner speak of four factors, one of which, the status of the land, takes two

values. This makes it look rather like a dimension (although if it were a dimension

we might expect more than these two values, and include, for example, the possibility

of the defendant owning the land). I think it is more consistent to see five

factors, but to bear in mind that OWNLAND and OPEN are mutually exclusive.

With these five factors, Pierson looks rather clear: the plaintiff does not own

the land, did not catch the beast and was looking for pleasure rather than business,

so only pro-defendant factors are present. Keeble, although the plaintiff was not in

possession of the ducks, had the pro-plaintiff factors that the land was owned and

he was engaged in a commercial pursuit, and we know that these were sufficient to

overcome the pro-defendant factor NOTCAUGHT.

If we wish to make an argument for the defendant in Young, we can propose

that Pierson is followed. The plaintiff can reply by distinguishing on the grounds

that the plaintiff is making his living, and cite Keeble to show that not having

captured the prey is not fatal to the plaintiff’s case. The defendant can now give a

rebuttal, since he can distinguish Keeble, on the grounds that in Young the water

is not owned by the plaintiff, and further add that the motive of the defendant was

not malice but business competition. So the issues are identified, but the question

remains as to whether are persuaded (or are able to persuade a judge) that the extra

pro-defendant factor and the missing pro-plaintiff factor in Young are sufficient to

cause us to reject Keeble.

And this is where the reasoning in this model runs out. Although we have

identified some candidate cases, the question remains as to which should govern

Young, and why it should do so. To find clues as to whether we can give reasons for

following Pierson rather than Keeble we need to examine the texts of the decisions.

Importantly these texts refer to the purposes that the judges saw as being promoted

by their decisions. Pierson was found in favour of the defendant

For the sake of certainty, and preserving peace and order in society. If first

seeing, starting or pursuing such animals . . . should afford the basis of actions

. . . itwould provide a fertile source of quarrels and actions. (Quoted in Berman

and Hafner 1993, italics mine).

One judge dissented: for him the pursuit and destruction of foxes was of suf-

ficient social value to be encouraged and protected by law. Two points should be

noted: first that the reason why capturing the animal matters is because only that

is considered sufficiently clear evidence of a right to the animal, and second that

what seemed to be a clear case containing only pro-defendant factors was in fact

82 T. J. M. BENCH-CAPON

disputed. Perhaps we should have included in our analysis an extra, pro-plaintiff,

factor, relating to the social value of the plaintiff’s activity, to reflect that the case

was in fact decided by weighing competing social values.1 In the second case,

Keeble, the social utility is greater, and the evidence for this is that the plaintiff

could earn a living from hunting ducks. Although the right to make one’s living

undisturbed is alluded to, the crucial point is that:

When decoys have been used . . . in order to take a profit for the owner of the

pond . . . and whereby the markets of the nation may be furnished; there is

great reason to give encouragement thereunto (Quoted in Berman and Hafner

1993, italics mine).

In other words here (unlike in Pierson) we can be sure that the plaintiff’s

activity is valuable because we know he can make a living from it, and so people

are prepared to pay for his activity. We can assuage our doubts with respect to

certainty because we have a clear criterion for saying that the activity is one to be

encouraged. When we come to Young, the social benefit is neutral – the same fish

furnish the markets of the nation whether they are delivered by Young or Hitchens.

Having removed this reason, the appeal to the need for certainty can prevail, just

as it did in Pierson. Arguably, in addition in this case the decision can also be

seen as encouraging vigorous competition, which may have even greater economic

benefits.

Seen from this teleological perspective, and informed by the reasons for the

rules as well as the rules themselves we can see two things:

• That we can come to a rational2 decision as to the case to follow;

• That apparent similarities and differences (the open land in Pierson and the

owned land in Keeble, and the engagement in making a living in both Keeble

and Young) may be more or less useful. Distinguishing on the ownership of the

land weakens the effect of Keeble for the plaintiff in Young, but does little to

positively promote a decision for the defendant, unless we wish to argue that

potential presence of ducks on a pond confers possession of the ducks on the

pond owner.

Berman and Hafner then proceed to an analysis of an example of reasoning

performed by Branting’s GREBE system (Branting 1991). Here they clearly show

how relying on rules manifested in cases without reference to the purposes of these

rules leads the reasoner astray, through pursuing false similarities and differences

between the cases.

The last section of the paper gives some suggestions for augmenting a representation

of cases in terms of factors with the legal purposes which explain why each

of the factors favours the plaintiff or the defendant. Now we can judge competing

arguments not only on the importance of the factors themselves, but on the value

we accord to the purposes from which they arise. This both makes the arguments

more realistic, and the choice between competing arguments less arbitrary.

THE MISSING LINK REVISITED 83

3. Theory construction and theory coherence

I have recapitulated Berman and Hafner (1993) at some length, both because it is

an excellent paper, and because it provides a strong argument that working from

decisions without their reasons will often leave us with no reason to prefer one

precedent to another, and can even lead us into error. In this section I shall consider

one of the leading approaches to modelling legal argument that has been developed

since 1993, and suggest that it also is unable to resolve disputes because it ignores

the purpose of the rules it employs.

In a series of papers, of which we can take Prakken and Sartor (1998) as representative,

Henry Prakken and Giovanni Sartor have articulated a model of legal

reasoning based on a logical formalisation, and the notion of a dialogue game.

Their main aim is to allow conflicting norms to be reconciled, and the essential

idea is that to win a case one must put forward an argument which can be defended

against any attack. Attacks may either be undercutting, attacking a premise in

the original argument, or defeating, establishing the negation of the conclusion of

the original argument. An attack can be defended against either by attacking the

attacking argument, or, in the case of a defeater, claiming a higher priority for the

rule grounding the original argument than that grounding the putative defeater. As

the debate proceeds, arguments introduce new rules, and their coherence with other

rules is tested. What is happening here is that we are constructing a theory (in the

logical sense), which is considered coherent if its sentences are able to withstand

attack from within the theory. This is excellent as an ex post reconstruction of the

reasoning, because here we can use the decision itself to reveal priorities. It, is

however, less useful ex ante, since it is unclear where these priorities come from.

In Prakken and Sartor (1998) they make use of their account to reconstruct a

style of factor based reasoning, such as we have seen above. Here each case gives

rise to three rules:

• A rule of the form if conjunction of all pro-plaintiff factors present then

plaintiff

• A rule of the form if conjunction of all pro-defendant factors present then

defendant

• A rule expressing that one of these rules has a higher priority that the other,

depending on the way the case was decided.

In Bench-Capon (1999) I showed how we could express these rules diagrammatically

as a partial order of factor combinations. The idea is that we represent

all combinations of pro-plaintiff factors and all combinations of pro-defendant

arguments. Together these represent all possible pro-plaintiff and pro- defendant

arguments. The ordering will express priorities between the arguments. We now

order these arguments on the assumption that an argument with more factors is

stronger than an argument with fewer factors. When we have a case we are able

to order the pro-plaintiff and the pro-defendant arguments in that case, according

to the preference expressed in the decision. These connections allow us to say

84 T. J. M. BENCH-CAPON

something about the relative order on pro-plaintiff and pro-defendant arguments.

The theory is coherent if there are no cycles in the resulting directed graph. Additionally,

we can say that the theory is complete if for every pro-plaintiff argument

and every pro-defendant argument we can see which is preferred.

Let us look at Pierson, Keeble and Young in this way, based on factors adapted

from Berman and Hafner (1993).3

The pro-plaintiff factors I shall use are:

(A) – plaintiff was pursuing his livelihood

(B) – the plaintiff was on his own land

The pro-defendant factors I shall use are:

(C) – plaintiff was not in possession of the animal

(D) – defendant was pursuing his livelihood

(E) – the land was “open”

We now use Prakken and Sartor’s method decribed above to identify the rules used

in each of the three cases.

Pierson yields the rules:

(R1) – plaintiff (no factors in Pierson favour the plaintiff)

(R2) – if C and E then defendant

(R3) – R2 > R1

Keeble yields the rules

(R4) – if A and B then plaintiff

(R5) – if C then defendant

(R6) – R4 > R5

In Young we have:

(R7) – if A then plaintiff

(R8) – if C and D and E then defendant

And the point is to decide which of R7 and R8 has priority.

The diagram of the resulting partial order including the preferences R3 and R6 is

shown in Figure 1.

As we can see the priorities gleaned from the previous cases are not helpful, or

at any rate not decisive, in the case of Young since we cannot deduce the ordering on

the pro-plaintiff and pro-defendant arguments in that case. The plaintiff must argue,

on the basis of Pierson and Keeble, that his pursuit of his livelihood is sufficient

to overcome the additional weight that the defendant’s case gets from the unowned

land and the fact that the defendant was also pursuing his livelihood. As we know,

the plaintiff’s case did not convince, but the partial order does not allow us to

predict this. The problem is that the theory remains coherent whether we add R7 >

R8 or R8 > R7. No cycle appears whichever way we direct the Young arc in Figure

1.

THE MISSING LINK REVISITED 85

Figure 1. Partial Order for Pierson, Keeble and Young.

But could we not broaden our notion of coherence here to allow us to give a

rational underpinning to the preference of one or other of these priorities? The

idea is to restore the missing link of teleology by requiring theories not only to be

coherent logically, but also to be coherent from the perspective of some ordering

of the desired values promoted by the decisions. This idea also has jurisprudential

foundations in the New Rhetoric (Perelman and Olbrechts-Tyteca 1969; Perelman

1980).

4. Coherence and teleology

Let us start with a quotation from Perelman (1980).

Since Descartes, however, only mathematical demonstration, the compelling

proof, imposed by its evidence on every reasonable human being, has been

judged worthy of attention. . . . Arguments which justify our options, choices,

and decisions, are never as compelling as demonstrative proofs; they are more

or less strong, relevant, or convincing. . . . in argumentation it is always possible

to plead for or against, because arguments which support one thesis do

not entirely exclude the opposite one; this in no way means that all arguments

are of the same value. (p 150)

What Perelman is arguing here is that while logic is important – violation of

logical coherence requires a position to be abandoned because it is simply untenable

– it is not the only ground for rational preference. Thus we can prefer an

argument for good reasons even when those reasons are not coercive. Applied to

86 T. J. M. BENCH-CAPON

our situation we may say that logical considerations should not be our only criterion

of coherence; we also need to consider coherence from the perspective of purpose

and values.4

Let us now consider the animal cases in this light,

We have 5 factors:

(A) – plaintiff was pursuing his livelihood

(B) – the plaintiff was on his own land

(C) – plaintiff was not in possession of the animal

(D) – defendant was pursuing his livelihood in competition with the plaintiff

(E) – the land was “open” –

We also find from the decisions three values:

V1: certainty – the need to have clear law to discourage speculative litigation;

V2: promotion of a larger Gross National Product – to improve economic wellbeing;

and

V3: the sanctity of property – to allow people full enjoyment of what is rightly

theirs.

The last is implicit, but underlies all the reasoning. In all three cases, only

because the plaintiff was not in possession of the animal does the defendant have a

case at all. Now we can say that values relate to factors as follows:

• V1: relates to C

• V2: relates to A and D

• V3: relates to C and putatively relates to B and E.

The reason why I say at this stage that V3 only putatively relates to B and E. is

that wild animals of their nature move around and do not respect ownership rights.

Thus the presence of a wild animal on one’s own land is perhaps not sufficient

to confer ownership, although it probably does confer rights of (possibly not exclusive)

pursuit. Remember that in Keeble the defendant did not trespass, since the

duck scaring was done from his own land. I am not sure of the law here: Section

4(4) of the United Kingdom Theft Act 1968 states that “Wild creatures, tamed or

untamed, shall be regarded as property; but a person cannot steal a wild creature”,

but this does not entirely clarify the matter for me. I do not think the issue is settled

from the three cases: I address it later in the paper through the use of a hypothetical

case.

Now Pierson contains factors C and E. From this we can see that in Pierson we

can only be concerned with the values V1 and V3. Both these values are served

by finding for the defendant. In Keeble, however, the factor A is present and so we

need to consider another value, V2. From the text of the decision, this appears to

be sufficient to win, and the presence of B and absence of E is not relied on. The

relation of B and E to V3 is thus not clarified by this case. These two decisions

suggest a possible ordering of values: V3, V2, V1. Possession of the animal would

THE MISSING LINK REVISITED 87

Figure 2. Factor preferences based on values.

be decisive because it promotes V3, and does no harm to V1. Keeble shows V2 to

be more important that V1, since although the facts considered alone might suggest

that B was the crucial factor, with the decision relying on the preference of V3 to

V1, the text of the decision makes very clear that V2 is the deciding issue. Other

orderings are possible, but this is consistent with the decisions.

When we now turn to Young, we see that facts are neutral with respect to both

V2, since D now applies, and V3 since B is absent and C is present, and so we can

revert to a decision on the grounds of V1, and follow Pierson. The decision for the

defendant in Young, can therefore be explained.

If we take these values, and the preference revealed in Keeble, into account we

can get ordering pictured in Figure 2.

Four lines have been inserted to represent these value judgements:

• We first put a line from []�¨p to D&E�¨d, to indicate that in the absence of

C, the defendant has no case: where the plaintiff is in possession, no problems

of certainty arise, GNP is unaffected, and so V3, the sanctity of property, is

unchallenged. This is assumed to be implicit in the ruling of Pierson, which

states that the defendant had not gained possession of the fox because he had

neither captured not mortally wounded it.

• Next we put a line from A�¨p to C&E�¨d. If the plaintiff’s livelihood is in

question and the defendant’s is not, V2, GNP, holds sway. Thus A has priority

over anything not containing D

• Third we put a line from C �¨ d to B �¨ p. If GNP is unaffected, we say that

V1, certainty, rules, so that C wins any case without A,

88 T. J. M. BENCH-CAPON

• The fourth line, from C&D �¨ d to A&B �¨ p, is to indicate C also wins any

case with both A and D, since where the case is neutral with respect to V2, V1

should govern.

This is one suggested interpretation, one which downplays the relevance of B

and E to V3. This theory is complete and enables any case (involving these factors)

to be decided. Moreover, we can see that Pierson is effectively decided by (C�¨d)

> ([]�¨p): E is unnecessary for the defendant’s case. Keeble is effectively decided

by A�¨p > C�¨d: neither the presence of B nor the absence of E is necessary to

the plaintiff’s case; and we could predict that Young will be decided by C&D�¨d

> A�¨p: again we may say that E is irrelevant.

Now consider a hypothetical case. Suppose, for example, that a person owned

a duck pond and a professional hunter killed ducks on it and sent them to market.

Suppose the pond owner sues. The factors in this case are thus B,C and D. The

above theory would suggest that the pond owner should lose. This is because in

the above theory I am assuming that B and E do not concern V3 with sufficient

certainty to override the promotion of V2. Were, however, the case to be decided

in favour of the pond owner, since B is the only pro-plaintiff factor, the doubts as

to whether or not B promoted our highest value, V3, would be removed. Now that

we know that B promotes V3, we can say that, since V3 is our highest value, B is

to be preferred to C and D. Adding this preference gives the theory shown in figure

3, the modification being that B can now be given the same effect as the absence

of C, that owning the land is as good as being in possession of the animal. Note

that nodes containing B are incomparable to nodes containing E, since the factors

cannot co-occur. Figure 3 thus also represents a coherent (and complete) theory.

Both Figures 2 and 3 offer complete and coherent theories: the difference between

them is whether we want to say that B promotes V3 or not. This requires a case like

our hypothetical to supply an answer: a decision for PondOwner in the hypothetical

case would render the theory of Figure 2 incoherent.

The key point here is that the cases in the example do not give us a decision as

to whether ownership of the land confers possession of the animal, since that issue

favoured the winner in each of our three cases anyway. The cases are thus neutral

between the theories in Figures 2 and 3, although both suggest a decision for the

defendant in Young. However, if we have a case like Pond-Owner, it is precisely this

point that we need to argue. Note that we do not argue by starting from the rule of

Keeble and arguing that that neither the fact that Pond-Owner was not pursuing his

livelihood and Duck-Hunter was is sufficient to distinguish the case, but we must

argue that ownership of the land confers possession of the animal and so promotes

V3. If this is accepted victory for Pond-Owner will flow from our hierarchy of

values.

I shall now apply this thinking to the classic example of open texture: the

problem of vehicles in the park first raised by Hart.

THE MISSING LINK REVISITED 89

Figure 3. Theory on the assumption that ownership of the land confers possession of the

animal.

5. Vehicles in the park

Before turning to vehicles in the park I shall refer to a case told of by Recasens-

Siche and quoted in Perelman (1980), which apparently took place in Poland at

the beginning of the century. In a railway station a sign prohibited the use of the

stairway to people with dogs. A peasant with a bear on a leash was annoyed to be

refused entry, since no one could mistake his bear for a dog. The station master

was, however, adamant in his refusal.

This is an example of an a fortiori argument: whatever reasons we have for

excluding dogs we have also for excluding bears. Some might regard this as an

argument from analogy: a bear is sufficiently like a dog to be excluded. But a

bear is also unlike a dog – it is bigger, fiercer and generally more threatening. The

point is these differences are all such as to give stronger reasons for excluding the

bear. If we construe the argument as analogical, we need to recognise that what

makes the similarities and differences relevant is an appeal to a value which the

rule is intended to promote, in this case the comfort and peace of mind of other

passengers.

Now we turn to Hart’s example of the vehicle in the park. A local park has

a by-law prohibiting vehicles. The by-law poses two problems: what is to count

as a vehicle? For example are roller-skates, skateboards, cycles, and lawnmowers

vehicles? And can we make exceptions? Should we allow ambulances in if there

is an emergency, or a taxi in exceptional circumstances, or a tank designed as a

memorial to local soldiers?

90 T. J. M. BENCH-CAPON

If we are going to use a teleological perspective to answer these questions we

first need to construct a model of parks which links parks and their activities to

values. I shall only sketch a model here, and some of my modelling may well be

susceptible to (rational) disagreement.

Let us suppose that the City Fathers provide their parks with two main aims: to

provide a place for citizens to relax in the fresh air, and to take exercise. I suppose

that their picture is of their citizens sitting in the sunshine, or strolling through

pleasant surroundings. Certain things are essential to achieve this: the park must be

a safe, clean place, and must be an open space. Certain other things are conducive

to their aims: attractive surroundings will encourage people to enter the park, and a

quiet atmosphere aids relaxation. Other things are hostile to these aims: fast moving

objects make the park dangerous, noise hinders relaxation and so forth. Anything

which is essential to the values must be included; anything which entirely prevents

the realisation of the values must be excluded. Other things can be considered on

their merits as to whether they are more or less conducive or otherwise to the values.

Note that the relationship is propagated: something conducive to a conducive

thing is itself conducive, and something conducive to a hostile thing is hostile, and

the like.

When fitting out the park, the City Fathers therefore provide lawns, benches,

paths, flower borders, some statues and a lake. Also they provide a park keeper to

keep the place safe and clean.

We can now consider some by-laws. What will guide us is the desire to provide

a coherent ordering of the values. Should people be allowed on the grass? There is a

conflict between our values here: allowing people on the grass promotes relaxation

since it provides more sitting space and encourages sunbathing and dozing, but is

hostile in that it makes the park less attractive, both because walking on the grass

is bad for lawns, and because people lying around on them is generally untidy. The

decision here depends on the view of the park and its clientele that the City Fathers

take: is it essentially to be a “green lung” or a city showpiece? Let us introduce

a third value “civic pride”, and suppose that if this is given pre-eminence, then

people will be kept off the grass.

Next consider ball games. Ball games are strongly conducive to exercise, but

create noise and disturbance, are harmful to lawns, and potentially dangerous to

both flowers and people. If people are excluded from the grass altogether, ball

games can be banned on an a fortiori argument. Otherwise we have a conflict

between the two values of exercise and relaxation: and on how these values are

rated for the particular park in question our decision will depend.

Already we can see three different models of park emerging according to how

the values are rated relative to each other. We can have a “recreation ground” style

park where exercise is most highly valued, a standard park where relaxation is

paramount, and a formal “garden” where civic pride is most important.

Now consider dogs. Dogs promote exercise, by encouraging their owners to

walk, but can be harmful to lawns and flowers, can create noise and mess, and – in

THE MISSING LINK REVISITED 91

the case of some dogs – can compromise safety. In the case of a formal garden we

might want to exclude them altogether, but in the other cases dogs might be permitted,

although we might wish to mitigate their most harmful effects by imposing

restrictions on their access by insisting that they are kept on leads, and that their

owners are liable to remove their fouling.

Now, having established some context, we can turn to vehicles. Although today

we see cars as the paradigmatic vehicle, recall that many of our parks (and their bylaws)

predate the internal combustion engine. Probably therefore the correct central

case is a horse drawn vehicle. Such vehicles promote none of our three values, and

are harmful to them, as a source of noise, mess, and potential accidents. All of

these apply a fortiori to motor cars. But what of the problem cases?

• Roller skates, skate boards and cycles: These can be seen as promoting exercise,

and are less polluting than horse drawn or motor vehicles, but still

present the safety hazards, and are disruptive of relaxation. My view is the

above argument suggests that it would be coherent to class them as vehicles in

parks where civic pride and relaxation are accorded sufficient weight as against

exercise, but not in the recreation ground style park. So if the grass is out of

bounds, ball games are prohibited and dogs must be kept on a lead, we would

expect roller skates and skateboards to go also.

• Lawnmowers: These vehicles are as noisy, polluting and unsafe as any considered

so far. However, they can be regarded as essential to the upkeep of

lawns, whether for display or for ball games, and lawns are an important

contributor to all three of our values. We would therefore expect them not

be banned as vehicles, although we would expect their use to be restricted

to authorised park staff. This also probably allows us to expect other vehicles

used for maintenance, even quite large lorries, to be exempt from the ban.

• Ambulances in an emergency: Here we have something which clearly is a

vehicle, but one which banning would compromise the safety of the park users,

an essential precondition for achieving all of our values. Thus we would expect

our by-law to be waived here.

• Taxis, in exceptional circumstances: Again these would probably be permitted,

but the question as to what constitute exceptional circumstances would depend

on the values governing the particular park. A mayor might be driven to an

official ceremony in a showcase park to promote civic pride, but would be

considered overbearing if he was driven through a recreation ground. Taxis

might be permitted to give disabled access to less formal parks, etc.

• A Tank as Memorial: This will not exhibit any of the harmful aspects of

vehicles, being stationary, other than its intrinsic unsightliness. If we want to

ban it, we would be better advised to argue on aesthetic grounds rather than

because it is a vehicle.

The above is intended to suggest is that the questions look more difficult when

they are asked in isolation, divorced from the context in which they might arise.

Consider roller skates: if people have different conceptions of a “park” they might

92 T. J. M. BENCH-CAPON

well have different intuitions about whether roller skates should be allowed. If,

however, we recognise that that are different styles of park, shaped by the values

that they are intended to promote, we can explain these different intuitions. The

style of park, and the values it is intended to promote, is in practice revealed by the

context: particular features of the park, and other regulations and decisions made to

organise the park. What we are trying to do is to develop a coherent theory which

will explain the various aspects of the park and its regulations, not in terms of

logical coherence – there is no logical contradiction between allowing ball games

and banning roller skates – but in terms of the various elements tending towards

the same ends. The last case, the tank as a memorial, also illustrates another way

in which values can help: if we know why a thing is banned we can see what

features of that thing cause it to be banned. If those features are removed, as the

harmful features of vehicles are absent in a static and disabled memorial tank, the

application of the rule in that case becomes pointless pedantry.

6. Conclusion

In this paper I have tried to revive the idea from Berman and Hafner (1993) that

teleology indeed provides a missing link necessary to make sense of a body of

law. This aspect has been neglected in recent years in favour of a purely logical

account of legal argument. Useful as this is, it cannot tell the whole story: we have

to recognise that arguments may have different value, even when either side of a

case can be argued and neither side has a logically decisive argument.

Logic underwent a brilliant development during the last century when, abandoning

the old formaulas, it set out to analyze the methods of proof used

effectively bymathematicians. . . . One result of this development is to limit its

domain, since everything ignored bymathematicians is foreign to it. Logicians

owe it to themselves to complete the theory of demonstration obtained in this

way by a theory of argumentation. (Perelman and Olbrechts-Tyteca 1969, p.

10)

Note that logic is not challenged – within its own domain – but is seen as failing

to provide guidance in many areas that we can find important. This guidance can

come from teleology, from notions of value, from consequences: in short from

the New Rhetoric. These ideas have already been shown to be effective in the

domain of health education (Grasso et al. 2000). I think we understand the logic

of legal argument quite well now, and we need to recognise that we “owe it to

ourselves” to complete this understanding, by adding in the purposes that our rules

are intended to promote. The need was apparent in Berman and Hafner (1993), but

the programme is still to be carried out.

THE MISSING LINK REVISITED 93

Acknowledgements

I hope I may be permitted to make a short acknowledgement of the contribution of

Don Berman. I first encountered him as an encouraging and supportive reviewer of

some of my very early work in AI and Law. When I later met him I found him to

be open, friendly and always excellent company. Don was always most helpful and

supportive to new researchers, and a pertinent and constructive critic of the work

of others. His own work was always insightful. Many people in the AI and Law

community owe much to Don, and he is sorely missed.

I would also like to thank Edwina Rissland and an anonymous referee for their

helpful comments on a previous version of this paper.

Notes

1 If we were using dimensions instead of factors, we might propose a dimension of motive ranging

from earning a living, through social altruism and pleasure to malice. Alternatively, or additionally,

using a dimension which recognised hot pursuit as a step towards possession would provide some

case for the plaintiff. Such a dimension would also help the plaintiff in Young, since the strict test

used here, which would require the fish to have been landed on the boat, could be softened to reflect

that the fish were under his control in that they were trapped in an almost closed net.

2 By rational, I mean only that reasons can be given, rather than that the decision is determined. The

social purposes recognised, and the relative values ascribed to them can change over time, and vary

from one jurisdiction to another. Moreover, the choice of factors has a very significant effect on the

outcome predicted by the model.

3 Here I use five factors, making OWNLAND and OPEN distinct factors. I have also replaced

COMPETE by a factor true if the defendant is pursuing his livelihood. I believe that this subsumes

COMPETE, and can be used as well if two people are engaged in earning their livelihoods in

incompatible but not competitive ways, as for example if one was a duck hunter and the other a

professional wildfowl painter. It will also cover cases where the defendant is earning a living and the

plaintiff is not.

4 For a fuller discussion of Perelman’s ideas, see Bench-Capon (2001).

References

Ashley, K. D. and Rissland, E. L. (1988). A Case-Based Approach to Modelling Legal Expertise.

IEEE Expert, pp. 70–77.

Ashley, K. D. (1990). Modeling Legal Reasoning. MIT Press: Cambridge.

Bench-Capon, T. J. M. (1999). Some Observations on Modelling Case Based Reasoning with Formal

Argument Models. In Proceedings of the Sixth International Conference on AI and Law, 36–42.

ACM Press: New York.

Bench-Capon, T. J. M. (2001). George C. Christie, The Notion of an Ideal Audience in Legal

Argument. Artificial Intelligence and Law 9(1): 59–71.

Berman, D. H. and Hafner, C. D. (1993). Representing Teleological Structure in Case-Based Reasoning:

The Missing Link. In Proceedings of the Fourth International Conference on AI and Law,

50–59. ACM Press: New York.

Branting, L. K. (1991). Reasoning with Portions of Precedent. In Proceedings of the Third

International Conference on AI and Law, 145–154. ACM Press: New York.

94 T. J. M. BENCH-CAPON

Gordon, T. F. (1993). The Pleadings Game: Formalizing Procedural Justice. In Proceedings of the

Fourth International Conference on AI and Law, 10–19. ACM Press: New York.

Grasso, F., Cawsey, A. and Jones, R. (2000). Dialectical Argumentation to Solve Conflicts in Advice

Giving: A Case Study in the Promotion of Healthy Nutrition. International Journal of Human-

Computer Studies 53: 1077–1115.

Perelman, Ch. (1980). Justice, Law and Argument. Reidel: Dordrecht.

Perelman, Ch. and Olbrechts-Tyteca, L. (1969). The New Rhetoric: A Treatise on Argumentation.

University of Notre Dame Press: Notre Dame.

Prakken, H. (1993). A Logical Framework for Modelling Legal Argument. In Proceedings of the

Fourth International Conference on AI and Law, 1–9. ACM Press, New York.

Prakken, H. and Sartor, G. (1998).Modelling Legal ReasoningWith Precedents in a Formal Dialogue

Game. Artificial Intelligence and Law 6(2–4): 231–287.

Retirado de: http://www.kluweronline.com