TELEOLOGICAL
REASC~NING
Jaiip
Unhwdty
Dq)artment
IN REASON-BASED
of Limburg
of Metitjuridicii
P.O.
Box 616
6200 MD
Maastricht
+31 43883053
email:
r.ruliml)u
changes,
describes
has special
facilities
is specljied
by model-theoretic
a version
for
means of an extended
legal
and goals
details
of Remon-llased
teleological
example.
Logic
reasoning.
means,
how RBL can be used to wodel
between
/ 3020
jiiiip.hilg@n)~ti]ju
AEWTRACT
This paper
that
This example
the logical
rg, nl
they define
extensions
The logic
and is illustrated
theory.
b-v
while
dif~erence
with
[Vcrheij
used to model
on the other
the phenotnenon
hand.
The appendices
presuppositions
of ‘deontic
give more
of RllL
2.
and OM
collapse’.
RBL
Reason-Based
Logic,
characterisation
reasoning
with
goals. Iogieal
of rules vs. goals and principles
INTRODUCTION
arguments
important
reasoning.
and interests
[Summers
[McCarty
1978].
In the field
and Kracht
1991, and %ndcrs
a short introduction
an extended
of RBL
of RBL
example
I will
difference
between
and goals on the other hand.
and more examples
found
[Hage and Verhcij
with
goals, however,
0
1995 ACM
the
reasoning
with
Moreover.
about the
is that the application
of a rulel
pleads for the rule’s
the ‘application’
of a goal leads to a
of a state that
is based on weighing
an action
derivation
that
of a
all the reasons that plead
this conclusion.
is a two step-procedure.
As a consequence,
The first
step consists
of all reasons that plead for or against
conclusion;
the second step consists
of
lveighi ng these reasons.
can bc
in
2.1
Weighing
ttiiscms
Suppose we have the following
next to some minor
rule and goal:
Rule theft: If somebody
is a thief, he ought to be
imprisoned.
Goal youth-protection:
Young persons are to be protected
from harmful environments.
all or part of this material is grnnted provided
dkdbuted
for direct commercial
advantage, the
title of the publication
and its date appear, and
by permission
of the Association
for Computing
or to republish, requires a fee andlor specific
1
and reasoning
conclusion
the possible
characterisa(ion.
by typical
rule
of rules.
to the goal. The actual
derivation
These papers do not deal
0-89791-758-8/95/0005/001
was inspired
to that goal, or for performing
of the determination
of RBL
RBL
such as analogous
contributes
for or a~~inst
analysis
legal rules and legal principles
reasons,
Similarly
of Naess on
contributes
either
the logical
199-i] and (especially)
to appear],
Permission
to copywithoutfee
that the copies nre not made or
ACM copyright
notice and the
notice is given that copying is
Machinery.
To copy otherwise.
permission.
an RBL-thcmy.
illustrate
an informal
of the applications
in [Hage and Verheij
weighing
Toulmin’s
rules
1966] and Dworkin’s
reason w41ich pleads for the presence
rules on the. one hand. and Icgal
description,
between
and the application
conclusion.
and inference
[Naess
for
are the work
[e.g. Raz 1975],
1958], the work
1978]. Moreover,
vididity
of the
tcIcological
principles
A more elaborate
[Touhnin
application,
in
this paper
that also deals with
legal
(warrants)
legal rules and
bc draw’n from
concerning
statements
only leads to a reason which
characterisation
that can validly
reasoning
between
The basic idea of RBL
goals. Moreo\cr.
a model-theoretic
is a topic
was especially
sources of influence
of Reason-Based
a version
that not only deals \vith
but also with
which
of Raz on practical
theory
TO REASON-
rules and in particular
legal forn~s of reasoning
of Law and AI,
1980, Kocrs
possibilities
1993],
can be
with
distinction
[Dworkin
or another
conclusions
After
goals.
in one form
(RBL)
contains
in which
reasoning
principles,
the
is wage
logic
Its main
of the distinction
play a role, is also very
199 1]. This paper describes
Logic
emphasises
reasoning
INTRODUCTION
for reasoning
argumentation
are not only based on cases, legal rules or
Teleological
rights
teleological
which
rule application.
is a nonmonotonic
legal reasoning.
principles.
than by means of model
1994] shows how RBL
analogous
AN INFORMAL
BASED LOGIC
developed
policies,
in RBL by means of
rather
case-based
and Hage
Kevwords
Legal
conclusions
An early description
interconnection
illustrates
valid
of RBL-theories,
rules on the one hand and legal principles
on the ontological
1.
LOGIC
Hug~
If }ve want to infer
should
collect
imprisonment.
$1.50
1
The nolion
Iqyl
11
~vbethcr John should
be imprisoned,
all the reasons that plead for and against
If John is a thief.
of a ‘nlle’
principles.
application
is used here in a broad
of the rule
sense, that also includes
we
his
tkeJt makes this fact into a reason why John ought
imprisoned.
youth
If John is still young,
makes the fact that imprisonment
in a harmful
environment
imprisoning
whether
To determine
information.
premise.
which
reason wins.
for instance
a young
2.3
persons
outweighs
imprisonment
a rule is applied
that the reason that imprisonment
places him in a harmful
is involved.
it is possible
Given
Similarly,
of
protects
environment
weight
to infer
important
anything.
case in which
knowledge.
namely
conclusion,
instance,
There
is, however.
we need no explicit
or only reasons against
imprisoning
him.
infer that John ought
is a thief
If. for
wc only
without
Similarly,
“
Teleological
performing
reasoning
some action
contributes
to the achievement
logical
terminology
action
ought
to be performed.
of a rent contract
contributes
- for the truth
with
to the protection
same example
of
Clearly.
or - in
if continuation
3.
is continued
are intricate
describing
relations
the situation,
in terms of a
to the state tvhcre
is based on first
RBL
the
Teleological
achieve
reasoning
does not only’ deal with
a goal, but also with
a negative
Actions
intlttence
avoiding
on the achievement
and states that detract
avoided,
situations
and consequently
from
such actions
and having
prohibition
of racist propaganda
obtain.
obtain;
A reason
For instance,
the state of tiairs
is a state of affairs
False sentences
states of
is that part of
that
that is denoted
by
express states of affairs
facts are states of tiairs
that
is a fact that has a particular
significance
for a conclusion,
in that it either pleads for or
against it. From a Iogical point of view, all states of affairs,
means to
including
that have
facts and reasons,
In RBL-theories
of the goal.
are individuals.
it is both necessary
refer to states of affairs
(facts,
to use sentences
reasons)
and to
that are expressed
a goal are to bc
there is a reason against
performing
actions2,
A state of affairs
expresses
A fact
in the
of FOPL,
are all true in RBL.
that includes
by a closed sentence.
that do not actually
and slales
(FOPL)
is the language
of FOPL
Thief(john)
John is a thief.
describe
of RBL
real i ty that is expressed
actually
I will
LOGIC
logic
the sentence
teleological
bo~h actions
that reason.
PREDICATE
order predicate
facts, and reasons.3
a ~rue sentence,
a mechanism
that can deal with
that contribute
to goals.
a
the issue of weighing
AND
uses a rich ontology,
affairs.
of which falls
and for that purpose
does not generate
OF REASON-BASED
outside the scope of this paper. My purpose here is to
demonstrate the facilities \vllich RBL offers to deal with
reasoning,
case do not
imprisoned.
FUNCTION
and that the theorems
bct~vccn these two ways of
the discussion
if there
the goal youth-
for a particular
if a reason is not generated,
sense that the language
lessees are protected.
There
is not relevant
can be stated in
that case. So if there is an
John’s being
SPECIAL
RBL
state. The state that the
contributes
a reason why John ought to
the goal -vouth-protection
SYMBOLS
of the Iessces. this is a reason
to another
of
that this
of a hoLIsc
can also be described
the
the fact that John
reasons does not even arise concerning
is to be continued.
state that contributes
rent contract
For instance.
the acw owner
why the rent contract
This
of the sentence
This
are not relevant
reason against
that action.
As a consequence,
reasons concerning
emergency,
is that if
a goal, this is a reason for performing
premise),
by the applicability
the goal youth-protection
Goals which
reasoning
if his crime
over rule thejt (this
Rule emergency
In cases of emergency,
protection
is not relevant.
to
the need
knowledge.
The basic idea of teleological
prevails
does not even become
generate
2.2
is to be imprisoned
of rule [heft is excluded
is a state of emergency.
In such a case it is possible
if some act
be imprisoned.
John. and no reasons
to be imprisoned.
is relevant
environment.
stated in an additional
the rule prescription.
~vcighiag
a conclusion.
Nobody
be explicitly
application
one
theft
would bc applied.
only the rule
for weighing
it is not
when there are only reasons for a
have a reason for imprisoning
against
a conclusion.
should
means
if John is a thief.
of a rule can be excluded.
Since the rule prescription
about the relative
Normally
This
that we have the rule
Rule prescription:
is prescribed,
not to be
was relevant.
is applied
a harmful
the application
of goals
are satisfied.
the goal youth-protection
Suppose
dud John ought
of the reasons for and against
possible
such
that the rule theft was applied
if its conditions
John from
However,
the issue of
imprisoned.
If we do not have any information
and the relevancy
that the rule theft normally
this ‘weighing
to derive
reasons
now we have assumed
and that the goal youth-protection
by an additional
the reason that hc is a thief where
knowledge’
to
we need more
is supplied
Exclusionary
Until
to be imprisoucd.
Such information
having
of John places him
into a reason against
John ought
reason against
a prohibition.
the
John. These reasons have to bc weighed
determine
speech. this is a (non-decisive)
to be
the goal to protect
2
those states. If a
infringes
the right
,Actiolls
are ~ction.types.
concretely
of free
telcologiwl
- imprisoning
znd deontic
.Lich as this pmlicular
3
12
S,,lllc
~tltologicn]
such as imprisoning
John.
A more
reasoning
should
case of imprisoning
presuppositions
of
somebody,
comprehensive
also deal with
Or - more
theory
action
of
tokens
John.
RBL are exposed
in Appendx
1.
by these same sentences.
between
Moreover,
these sentences
express should
be maintained.
to argue that John is a thief.
John is a thief
predicates
simple
For instance.
connection
the states of affairs
For this purpose,
of characters
firnction
that begin
symbols
beginning
expressed
predicate
with
corresponds
with
him.
(including
to a sentence,
each predicate
symbol
as strings
in the senlcnce
Mter
is replaced
For example.
The term goal(gid)
of
goal(gid,
of the
that is to be obtained:
that denotes a
goal(protectionjohn,
is used as an abbreviation
of the term
stafe).
by the
●
the states of affairs
{
.. .
.}/n(forn=Ol
These symbols
by the senlences
1,2,
...)
are used to refer to sets of states of tiairs,
most often reasons.
Thief(john)
Guilty (john)
●
& Ought(imprison(john))
are respectively
thief(john)
guilty(john)
referred
to by the (erms
reasons_ pro(atom)
reasons_con(atom)
The function
& ought(imprison(john)).
such as steal. or
●
doll
number
of special
rule/35,
goal/2,
reasons_pro/1.
is that of FOPL.
and predicate
., . . ..
}/n (for n = 1.2.
reasons_con/1,
Accepted/l,
Relevant/2.
symbols.
a
do(actior))
that is
0/1.
Ought/l.
●
from
action.
with
0/1 is a deontic
applied
Reason/3.
and
the sets of all
against
that operate
the doing
used in combination
Applicable/3,
Applies/3,
are functions
denotes
the refraining
...).
do/1. -do/l.
Excluded/3,
Contributes_to/2,
but contains
function
{.,
reasons_pro(atorrr)
Atom.
and -doll
do/1 and -do/l
of RBL
atom, pro)
atom, con)
have as their values
reasons that plead for respectively
by functions,
imprison(john).
The language
= {r I Reason(r,
= {r I Reason(r,
symbols
reason s_con(atorn)
are denoted
Valid/l,
The parameters
identifier
protcctcd_from_harmful_environment(john)).
the term that
(uppercase)
by terms.
the unique
by means of an RBL-term
state of atTairs. for instance
of characters
To obtain
the first
same letter in lowercase.4
expressed
letter.
respectively
s(ate is described
and
of a
(and goal/1)
goal and the state (of affairs)
goal(gicf, state)
and back,
of the term
the identifier
this does not lead to confusion.
of a goal specify
as strings
Icttcr,
goal/2
Because
Just like rules. goals are denoted
wc need a
are wri[(cn
terms)
a lowercase
●
Since
by these scntenccs.
an uppercase
conclusion).
condition,
rule is unique,
into terms that denote
symbols
is used as an abbreviation
rule(rid,
~ve want both
can only have terms m argumenls,
scntenccs
The term rule(rid)
that they
and to refer to the fact that
as a reason for imprisoning
means to translate
Actions
the logical
and the states of affairs
of action.
on action
-do(action)
do/1 and -do/l
types.
denotes
are normally
the Ought/l-predicate,
predicate
for ought-to-be.
It can be
iteratedly.’
and
O(sfate)
Outweighs/3.
means tha~ the state of affairs
state ought to be
the case.
●
rule/3 (and rule/1)
In RBL
●
ndcs (and principles)
language.
arc denoted
In this way it is possible
reason about them.
Ought
by /erm.Y of the
a rule or principle
performed,
has
condition,
.
corJc/usion)
Here condition
is a sentence
literal
We assume that conditiorr
of RBL.
of conjunctions
condition
The first
of RBL
and com/Ll.$ion
of one or more Iitemls,
is a possible
argument
Each disjunct
of
●
reason for conclmim.
Valid( rule(rid))
Accepted/l
The scnhmce
the idcnt ificr
is accepted.
of
that each rule has a unique
Accepted(goal(gid))
Acceptance
function
sentences
of ~OpL,
symbols.
to terms
The number
e.g. +
By ovcrhmding
is as simple
following/
:IIICI &
are Irealed
the mxmion.
m dtscrihcd
irsdicotcs
the arity
as if lhev
tlw tr:msl;~lim]
in k
ofllw
is for
Excluded/3
Excluded(rule(rid),
/conds,
are :11S0
the rule with identiticr
id is excluded,
~f
/cone/ are respecti\cly
the instantiated
conclusion
tcxl.
Iilnction
means that the goal gid
is for goals what validity
fulcs.
●
~Ollne~tives
means that the rule with
id is valid.
The scntencc
3
to be
means that an action ought
Valid/l
idcn[ificr
identifier.
~le
for ought-to-do.
Ought(-do(action))
The sentence
a
is a disjunction
of a rule, Yid, is called
the rule. It is assumed
4
predicate
means that an action ought
not to be performed.
the form:6
rule(rid,
is a deontic
Ought(do(action))
to refer to them and to
A term denoting
Ought/l
or predicate
●
/cone/) means that
where
/conds and
conditions
and
of the rule.
Applicable/3
symbol.
6
Metavariables
characters
for sentences will be dmowd
hv strings of i!:,lic
.
with WI upper case ch:mwter,
e.g.. ..1101 )1.
Applicable(rule(
rid), facts,
cone/usjon)
means
begmnmg
Mcta\ariables
characters.
The scntencc
for tcnm.
e.g.. d[ow.
such as Atot}t
will
be dcm)tcd
m strings
I usc the ~vmvmliou
am{ CIIOIII. rcprmmt
a xntemx
of ilalic
(lint mutclling
lower
c:tw
7
mcl Jv:Ir Itd Ilcs.
and iw contspondinx
\ppet]dix
I conlait)s
dconl IC prc(iimtcs,
I cInn
13
SOII)C additional
remarks
on the meaning
of the
that the rule with
facts denoted
idcntiticr
for the conclusion
.
by the
reasons2
(as reasons concerning
a reason
reasonsf
and reasons2
rid is made applicable
by the term facts and may generate
denoted
fackz,
by the term conclusion.
..,, facts”},
an action
Contributes_to(
action,
state)
of the type action contributes
the goal state is accepted
and relevant,
or a remon
to be performed:
The sentence
state statef
state2
Contributes_to(
contributes
is accepted
the truth
obtain:
theory.
state2)
to the goal state2,
means that the
action
If the goal
statel.
that expresses that it ought
Contributes_to(
-state)
action,
1
an action.
that no action
which
substitution
expresses
ought
of statel
stafe7,
dclrncts
state2
-state2)
from
is acccptcd
the goal state2,
and relevant.
2
If (Iw
ought
or for the truth
not to obtain:
of the scntcncc
0(-state7
that expresses
gid is relevant
Relevancy
for the performance
Relevant(goal(gid),
for the prcscncc
only generate
of the
of affairs
StiltC
is to ndcs,
state.
instantiated
to thief(john),
o(punished(john)).
8
its conditions
and its conclusion
denoted
by the term
IO
found
that the reasons in the set denoted
atom)
by the term reasons
the reasons in the set denoted
Dossihle
who
conclusions
means
state2),
Contributes_to(
action)
action,
action,
are true,
-state),
Contributes_to(
values
the truth
state7,
A&B
is true,
discussed
with
speci~
logically
possible
nre assumed
possible
A and
are constraints
worlds.
might
are accessible.
as sentences
possible
constraint
on logically
in this section
worlds
that we tie
want
to
Valid
in =1]
worlds.
it is assume d that Atom
free varizhles
sentence
parts as a
an accessibility-relation
which
can e.g.
if and orzl y if the sentences
a subset of logically
10 work
worlds
of a compound
elementary
E.g. it is a constraint
are then to he dctined
In the following,
possible
1.25.
value
of its more
worlds.
~vorlds.
prefer
logically
definition
The constraints
accessible
Nloreover.
7
(predicate)
in which
say that the comtrainls
atom.
9
outweigh
the way
preferred
reasons2,
state)),
1990,
that tbe sentence
Readers
Reason(facts,
on mere
on tbe truth
on RBI.-possible
arc a reason for the conclusion
0utweighs(reasons7,
statel,
are true,
pro) is true.
in Lukaszmvicz
B are both true.
Outweighs/3
The sentence
state7,
and Relevant(goal(gid),
Such constrain~
I consider
pro) means that the facts
atom, The sentence
stafel)
stafe2)),
lx
instantiated
atom, con) means that facts arc a reason against
Contributes_to(
d) If Accepted(goal(gid,
on Iogic:dly
by the tcrln~ac(s
state2)),
)), pro) is true.
worlds
denoted
acfion,
are true, then
pro)) is true.
ought(-do(action
depends
atom,
action)
state),
pro) is true.
o(-statel),
ReasonJ3
The sentence Reason(facts,
.s4ate)), Contributes_to(
-state 2), and Relevant(goal(gid),
statel) are true,
then Reason(contributes_to(
sfatel,
-sfate2),
o(punished(john)))
with
is true, then
pro) is also true. 10
then Reason(contributes_to(
Goals
The sentence Applies(rule(rid),
facts, conclusion)
means
that the rule with identifier rid applies on the basis of the
facts denoted by the term facts and generates a reason for
the conclusion
denoted by the term conclusion.
E.g.
thief(john),
is false,
atom),
and Relevant(goal(gid),
-state),
reasons if they are rclcvarrt.
means that the rule thefi applies
atom),
c) If Accepted(goal(gid,
Applies/3
Applies(rule(theft),
facts,
o(sfatef),
means dull the goal
is to goals what non-exclusion
atom)
then Reason(contributes_to(
means that the
of an action.
state)
and Facfs are
facts, iconcfl
facts,
ought(do(action),
state2).
goal gid is relevant
The sentence
conclusion)),
rule(rid),jacfs,
b) If Accepted(goal(gid,
action)
of one of
some
that it
),
Relevant(goal(gid),
under
o.
.sfata). and Relevant(goal(gid),
Reason(contributes_to(
action,
Relevanff2
The sentence
Condition
under
a) If Accepted(goal(gid,
this means
and
rid), facts, icorrc/) is true.
Reason(applicable(
means tha~
of FOPL8
hold for RBL9:
Facts is an instance
condition,
applics(rde(rid),
Contributes_to(
to the usual constraints
especially
If Applicable(ntle(rid),
to be
T is an RBL-
u, and that the term iconc/ is the instance
then Applicable(rule(
or for the truth
if
of that
of T come out true.
semantics
of the sentence
If Valid( rule(rid,
that there is a reason against the prcscncc of state of affairs
statel,
is subject
theoretical
true. and if Excluded(rule(rid),
Ought(-do(acfion)).
goal to achieve
world
that the sentence
to
this means that
of the sentence
the presence
Assume
an RBL-theory
REtL-models
all sentences
ones which
the disjuncts
means that the
there is a reason not to perform
from
of an RBL-theory
in which
or for
the goal state. If the goal to
from
achieve state is accepted and relclant,
The sentence
be drawn
of the term conchsion
action detracts
performed:
world
the following
this means that there is a
of (he sta[e of affairs
of the sentence
can validly
An RBL-possible
statel,
and relevant.
CONCLUSIONS
that hold for model
O(statel).
The sentence
.
{ factsj,
n >0.
An RBL-model
possible
ought
Ought(do(action)).
reason for the presence
.
with
and only if it is true in all preferred
for the
an action.
expresses that an action
which
VALID
A conclusion
If
this means that
there is a reason to perform
of the sentence
-t.
means that the
to the goal state.
truth
*
The terms
Contributes_to/2
The sentence
●
atom).
must both have the form
denotes
an RBbatom,
to be bound
under
universal
quantification.
Io
by the term
“[his
definition
;U dwwilwd
14
contains
a minor
in [1 [age and Verheij
deviation
1994,
from
earlier
and to appear]
versions
of RBL
3
a) If Applies(rule(rid),
facts, atom)
Reason(fact.s,
atom,
b) If Applies(rule(rid),
Reason(facts,
4
pro)
is true, then
bc dealt with
is also true.
facts, -atom)
the relative
OrdiIlary
is true. then
a) If Outweighs(reasons_pro(
reasons_con(afom),
atom),
atom)
is true. then Atom is
reasons_pro(atorn),
can deal with
is
than any other Rt3L-model.
is less preferred
that are not
An RBL-model
than an RBL-model
M2 if either
one
is the case:
is false in M 1 and wue in M2.
any sentcncc
of the form Excluded(rule(rid),
and fdsc
of the form Reason(facts,
is true in Ml
and false in M2. 11
maximises
goals, and minimises
the number
atom, pro/con)
SOME
special
the number
of rclcvimt
of reasons and exciudcd
CHARACTERISTICS
is an extension
facilities
it allows
in FOPL.
to rcm.on defensibly
all
In addition
with
both rules andl
irrelevant
1994: Gordon
corresponds
rebutters,
the work
wilh
more powerful
use the full
arguments,
11
RBL has a mode] theoretic
lacks constructive
Notice
of RBL
preferred
However,
it
AN APPLICATION
or arguments
conference-paper.
Therefore
example
rules and their
that both
with
is a polished,
part of Du{ch
law that deals with
of
difference
understandable.
have in mind
in a
rules and with
reasons makes the logical
Colliding
There
between
The example
but realistic
representation
the transfer
I
of a
of property
reasons
is a legal principle
that deals with
by non-owners.
a right
namely
the transfer
the principle
of
that nobody
that he does not have. Let us translate
into the language
of RBL
Valid(rule(nemo_plus,
transfers(x,
y, z) & -owner(x,
-o(owner(y,
z)) ))
12
For instance.
10 dctivc
it is not possible
that smncbody
II is possible
tvitll
as follows
13:
z),
13
(rccursi~’e)
1Iwe
to adci rules
rather
reasons.
conflicts
than
that) tbot he ough[
to collide
third
oughI
party
dw third
ncw owner
,\ppendix
Ican
h12. and h12
mode].
would
make
Cf. Hage
that has not yet been solved.
party
one or
and
the principle,
In o~her worda,
the new owner
in Dutch
Ye\
the goal,
haa as its consequence
to be the new owmer.
par(yis
The actual
/s not tfre new owner,
nof 10 be the new owner.
with
and whether
law.
I discuss
whkh
that the
the questions
be ought
to be the
this phenomenon
in
2.
the resulting
p]-incip]e
in its fommliscd
case dl;it
the dlird
parry
problems
we ‘solved’
prtnciple,
This
ok’ (I1c rule
15
which
possible.
is that the third
seem to collapse
‘1’o overcome
h 11 nor h 12 is a
are punishable
Ihat he is not punishable.
theory,
of inferences
a difficulty
of the principle
is assunwd
wbethw
on tllc
10 a domain
kinds
from
ro appear.
wc cncountcr
consequence
can all
to usc the rule that thieves
is not a thief
of dw mentioned
\“mbcij
poinl
that holds for other
hi 1 is ICSSprefcmxl
of RBL
only give one extended
how the phenomenon
legal rules and principles
more
These arguments
thnn h{ 1. In such a case. neither
all possibilities
I will
that combi ncs reasoning
exclusionary
in other
from a logical
for dealing
mechanism
OF RBL
reasons is
a conflict
to argue about rule exclusion
that it is possible
is less preferred
12
semantics.
rules of inference.
to illustrate
and applicability
and their application,
conflict
backward
of rules in the
Syllogism.
It is not possible
SCISof thcm.
exclusion
basis of the same logical
nor does it allow
of a Hypothetical
this principle
to argue about their \alidity
Because it is possible
priorities,
as a default
[Pollock
that tvcighing
potential
and
to lhc effect of
only deal with
their
RBL
[1992].
rules. or the derivation
Finally,
can transfer
and that goals arc
because it cannot
it is possible
(relevancy).
in
the understanding
but also bctwccn
(acceptability),
dcscribcd
to the usc of undcrcutters
Since rules and goals arc individuals
of view,
is
reasons can bc compared
a pair of reasons (defaults
theories),
RBL
1994].
that rules are excluded
Weighing
between
others,
1993; Sartor
The possibility
1987].
logic for legal reasoning.
to, amongst
and Pearl
fashion
6.1
it has
goals.
comparable
[Verheij
obey the rules designated
with
property
As a nonmonotouic
of a
are satisfied,
rule application
or
1995].
by non-owners,
OF RBL
of FOPL:
that are possible
[Prakken
analogous
goals. and that illustrates
rules.
Since RBL
1994; Prakken
to have reasons for the application
has no built-in
reasoning
6.
bonds,
in M2.
any sentence
inferences
[Brewka
are
of defaults
Relevant(goai(gid),
acfion/state)
This preference-rc]ation
5.
to argue about this
about the ordering
core in Gcffncr
presently
any sentence of the form
about
in
1994].
rcasoniug
RBL
are those RBL-models
icorrc/)) is true in Ml
c.
in other logics
Hagc
.. .. factsn }, 0, atom) }vith n >0.
RBL-models
of the following
b.
arguments
RBL-conclusions
Outweighs({factsl,
less preferred
a.
to arguments
is true, then Atom is
true.
Ml
comparable
atom),
atom)
false.
Preferred
it is possible
rule other than that the rule conditions
b) If Outweighs(reasons_con(
5
since the information
in the same way too. Such arguments
Since it is possible
true.
Moreover,
of sets of reasons is contained
sentences.
knowicdge
atom, con) is also true.
easily.
weights
logical
version
becomes
by cheating
snme nmmxver
in!nsfe~
of_)tlutobles
ditliculties,
1 have giverr the legal
the conclusion
that it ought
the new owner.
In this way
a bit in the formalisation
not be the
the Iotical
oftbe
is later on also used in the formalisation
(If x transfers
should
Moreover,
third
z to .v, and x was not the owner
not become
in Dutch
parties
6.2
of z. thco v
the owmcr ofz. )
civil
To increase
law. the goal is acccp[ed
in good faith
following
that
facts:
(If somebody.
Since there is no reason to conclude
obtain
is excluded,
Moreover.
)
is to bc applied.
casey, joyce, book) &
book), o(owner(joyce,
book)),
and we
since this rule is meant
and the goal to protect
the following
will
plLN principle
a reason
not bc the case that Joyce bccomcs
owner
the book.)
irrelevant.
in good faith
arc to bc protcc[cd
Reason(contributes_to(
owner(joyce),
in_good_faith(joy
ce)) + protected(joyce)
o(owner(joyce,
book)), pro)
contributes
to the protection
reason why it ought
owner
the owner
),
also hold:
rule(nemo_plus))
To decide whether
Joyce becomes
weighing
of the book. this
Outweighs(
{contributes_to(
owner(joyce),
the owner
knowledge,
the
that Joyce becomes
of the book.
the protection
the owner
of parties
whether
of the book.
of the book.
in good faith.
reason that Casey transfers
Casey was not the owner
actually
principle,
that govern
that Joyce should
knowledge
legal security
whe[hcr
in particular
bccomc
judges
\rill
with
as pointed
extent
depends
is more or less in
between
out by Dworkin.
legal rules
[Dworkin
1978,
is only more or [ess, because to
a rule applies
in an all-or-nothing
those principles
fashion,
and goals are discarded
ndc. For example,
rule only discards
This
difference
on how many principles
by an applicable
of rules
the rule only
it seems as if the rule
fashion.
the logical
it can be argued
and goals which
that a
were
this situation.
14
llese
proper.
16
rwlcs are pm
in
the same issue. As a
In this way, although
in an all-or-nothing
it is
the generation
reasons.
}vliich
usc
and prevents
a reason for its conclusion,
p, 24], The accordance
the
the case to which
a reason why the party
against
other
the goal
the rule
the one reason needs not to be weighed
and principles
cases, is uncertain.
asks for the introduction
monopolises
the owner
and making
irrelevant,
reasons that deal with
applies
in good
a goal, this
consequence
accordance
of parties
principle
is. it generates
becomes
generates
the book to Joyce and that
of the book. Howc~’er,
this weighing
to
the
the reason based on the ncmo-plus
it can be derived
new owner
Therefore,
outweighs
of other
of the book.)
If the reason based on the protection
faith
good faith
to a case, replaces
in good faith
oj” mutables
applicable.-That
to be
this contribu[cs
some other
in that case.)
for that case.)
the nemo-phrs
parties
tron.sfer
the reason that
oot~vcighs
to a case, replaces
rule is excluded
goal is not relevant
it ought
not be
to that case. The
take care for that14:
(If a rule that is applicable
such as:
to protect
is conccrncd
the owner
by a rule, it should
replaces(rule(rid),
goal(gid),
-relevant(goal(
gid), cone/) ))
By excluding
(As far as the question
both the nemo-
Valid(rule(goal_replacement,
applicable(rule(
rid), corrals, cone/) &
is a
in_good_faith(joy
ce)) + protected(joyce)
)},
{transfers(casey,
joyce, book) & -owner(casey,
book)},
o(owner(joyce,
book)))
if Joyce becomes
RBL-rules
rule. the latter
to bc the case that Joyce becomes
replaces
or goal is replaced
(If a rule that is applicable
of the book. )
we need additional
in good faith,
Valid(rule(rule_replacement,
applicable(rule(
ridl), condsl,
corrc/7) &
replaces(rule(ridl),
rule(rid2),
excluded(rule(rid2
),conds2, cone/2) ))
is
of pm-tics in good failh.
the nemo-
parties
to a case if the rule is applicable
following
thal the acccplcd
we also have
(The fact that if Joyce bccomcs
of the
and the goal protecfion~ood~aith.)
If a principle
of
applied
goal that parties
it ought to
the owner
Replaces(rule(transfer_of_mutables),
goal(protection_good_faith))
Ihc book 10 Joyce and thal
Since there is also no reason to conclude
a mutable
to replace
plus principle
Replaces(rule(transfer_of_mutables),
con)
Casey was not the owmcr of the book arc together
why it ought
z) &
transfers
party becomes
(The rule tralT.~fer_o~~/tutables
(The facts that Casey transfers
adopt the
good.)
the reason:
Reason(transfers(
-owner(casey,
might
else who acts in good faith,
be the case that the latter
that the nemo-plus
the principle
the legislator
who is not the owner,
good to somebody
Transfers(casey,
joyce, book)
-Owner(casey,
book)
ln_good_faith(joyce))
Contributes_to(
owner(joyce),
in_good_faith(joy
ce)) + protected(joyce)
principle
Icgal security.
rule:
Valid(rule(transfer_of_
mutables,
mutable(z)
& transfers(x,
y, z) & -owner(x,
in_good_faith(y),
o(owner(y, z)) ))
are to bc protcctcd:
Accepted(goal(p
rotection_900d_fa
ith,
in_good-faith(y)
+ protected(y)))
Suppose we have the following
and principles
Rules
of Ihe legal
domain
knowledge,
and not of RBL
taken into account
in making
[Anscombe
that rule [Hage
forthcoming],
1956],
rude [Foot
obligation
7.
RBL
is a logic for dcfcasiblc
quite different
conceptualisation
shares the important
addition
with
differences
And finally,
weighing
[Hagc
connected
calling
cxplicilt.
1993].
BEHIND
‘derived’
RBL
That
Introduction
of domains
systems that operate
Breuker
1994].
for intelligent
in these domains
[cf. Valcntc
In this appendix
of the ontological
which
arc important
assumptions
they influenced
short and is consequently
controversial.
have strong
my position
described
merely
It cannot
different
rather
opinions,
RBL
apodic(ic,
peculiarities
facts can only be established
theory
was rude must be ‘derived’
up to deal with
of rudeness.
is established
( a promise.
phenomenon.
manifests
modal
itself
some
action
the result of a
My starting
point
mind.
The world
into categories
which
consists
that are products
nevertheless
products
indcpendcnt
world
without
the human
property
rights,
bad luck.
world
mind,
world
are a product
the ontology
[Lorenz
is only forbidden
there \vould
nature
Not products
it has certain
physical
~vith a mind-
[White
E.g. a picture
is only
it belongs
all
an
to a particular
consequences;
the brutality
the murderer
of the murdeq
he bought
stocks. estuaries.
mind
shuns Oceam’s
existcncc
not have been
it from
is the reason wby
I introduced
prescncc
of entities.
prcscncc
indicate
for those facts which
I ~vould call reason-based.
of facts is most conspicuous
such as the fact that the seas arc filled
\\’itll
some
amounts
to its being
rude. Second,
other facts because in some non-
a promise
of the other facts.
‘causes’ the coming
into
of an obligation.
Constitution
razor and Iibcrall)
of human
First,
or
of the
nature
indcpcndcnt
comes in two kinds.
sense, they ‘cause’ the existence
E.g. my making
The mind-dcpcndcnt
almost
epistemic
to some other fact. E.g. the specific
of my behavior
adopts a prolifcrntion
seem to obtain
all value judgments,
of his house because
some facts constitute
1977]. but
that the constitutcnts
of the human
of RBL
because
to
1952, p. 80f.],
dcontic,
must be insane, given
facts can amount
1976]. For example.
championships,
This assumption
the
and - of course - a set
[Hare
with
(anankastic,
other facts. Constitution
of the human
of the mind,
that are not given
[cf. Putnam
by the facts that generated
for instance),
the
of an
In all of these cases. we can say that some facts consti~ute
make up of the
the work
of objects and facts Jvhich fill
have been made up at will
employs
the existence
the builder.
is that the ontological
we live in is to a large extent
the
10 some of its other characteristics;
type or bemuse
in
construction
world
code which
most notably,
in connection
thanks
of Smith
as mental
from
that some facts can only exist thanks
scntcnccs
beautiful
thinking.
world
must be
the door in someone
1975 l). and many classifications.
is not
about the role of ndcs and rcasom
And
obligation
John is the owner
The
(slamming
other facts. their supcrvenience
in the logic
but is rather
they are somehow
the fact that the ball passed the goal line.
obligation
This
it is
those I,VIIO
it makes clear how RBL
thought
from
which
of norms.
but it can. 1 hope. clarify
of legal reasoning,
philosophical
way in
must Ibc
even where
to comince
to those \Yho are intcrcstcd
dcvicc.
and the
is taken
not to stick
a goal in a soccer match
of the behavior
notion
and
This exposition
bc cxpcctcd
above. Moreover,
a technical
(legal)
behind
I propose
CISC’Sface) and a given behavioral
1 give a short exposition
the logic.
For instance,
my behavior
nature
Ontologies
of an institution
facts seem to be
Therefore
The presence of reason-based
ONTOLOGY
facts
Constitution
with
‘derived’.
1: THE
Some
and Weinberger
unless the notion
by means of other facts from
APPENDIX
them insrirutional
not all reason-based
to institutions.
1969].
to that name.
and a way [o make the
way be integrated
[Searle
is
an
facts to social
1974 and McCormick
very broadly.
it provides
rules and principles
somctinles
19871. However,
in
five dollars
these reason-based
[McCormick
sets of reasons. and
can in a natural
reasoning
institutions,
its
i(
such Iogics.
Moreover,
reasoning,
between
RBL
case-based
of odwr
about priorities.
for teleological
logical
Despite
of legal reasoning.
facilities
it can deal with
reasoning
facilities
legal reasoning.
behavior
and the fact that Jones is under
to pay Smith
lUNC conncclcd
CONCLUSION
the fact some particular
1958],
Some [acts
bct\vccn
wat cr. that
derivation
the notion
of constitution
by showing
of some facts had to bc ‘derived’
from
satisfaclo~.
derivation
constitution.
this usc of the word
‘derived’
is not
la fact. I now want to distinguish
and constitution.
the vcv
that the
the
of some other facts. The quotes around
that in my opinion
completely
inftucncc.
and
existence
In the case of
of the constituted
facts is
Earth turns around the Sun. etc. Olher facts canno( cxisl
independent
of human culture. such as the facts that
based on the constituting
facts. For example,
soccer only exists thanks
to the fact that the ball passed the
Michael
goal line. And I only have an obligation
Jordan
the grocer
money
is a basketball-player.
for the potatoes
the fact thal 1 OJVC
1 bought
from
him
17
the goal in
thanks
to the
promise
from
I made. The ‘derivation’
the constituting
of constitution
of the constiiutcd
facts is the rc-thinking
assignments
facts
(but cf. Httgc et a/. 1994 on the proccctural
It is, however.
nature of legal conclusions).
Often.
however,
not constitute
presence.
we derive
them,
This
occasion.
other facts which
gi\fc c~’idcncc
bccausc hc had a molivc
epistemic
modal
The occasion
committed
that
that hc might
fact that John is probab(v
The distinction
to existence,
bc the
(hc
actually
constitution
of reasons. The reasons involved
reasons w~v something
derivation
are reasons
something
I/7r7/
Bccausc
can
in constitalion
arc
in
distinction
legal issues and issues of fact. The Dutch
is the
can only judge
the factual
statements.
cannot
application
Only
if they are
reasons.
In this respect,
If a universal
is a non-issue
statements.
reasoning
dcfcasible.
A statement
with
guarantees
the truth
If reasoning
issues.
cannot
be
false and cannot
(in case of a valid
is considered
defensible,
this goes
like a rule (or a principle
statements
be used
or it is true and
of the conclusion
in the argument.
with
inference
is
in the case of
true conclusions,
argument).
arguments
about the ]cgal issues of a case. not about
statement
it refers. The issue
statements
is either
to infer
was involved
Court
or validity)
even arise.
to sho}v that something
bct]vccn
Supreme
acceptance
brute facts into reasons. Next
they generate
from
in arguments
case.
In the law, there is a corresponding
of rules (their
true. it is tntc for all the cases to which
bct}tccn
is the case. The reasons in\ol\cd
tobe/ie\e
of
for instance,
create obligations.
they need application.
rttlcs differ
that John
and dcrilation
by means of a dis[inclion
the assignment
happens,
In such cases, there is a reason
to transform
applied,
of application
bctwccn
from
rcases. This
was forced.
does not suflice
the murder.)
also be approached
to refrain
the rule that promises
The mere existence
the murderer.
make if probable
of the rule that promises
Cases Iikc this make it clear that rtdes need to be applied.
and the
these same facts constitute
and the motive
not to apply
do not make John in(o
they are oaly indications
(However,
possible
einparlicula
if the promise
do
for their
if wc concltrclc
and an occasion
murderer.
kinds
facts from
occurs, for instance.
A motive
a murderer:
significanc
but which
John is the murderer
are applications
create obligations.
of the relation
Seeming
or goal)
cases of defensible
are cases where
material
as statements
[Tottlmin
rules are disguised
19581.
Rules
and
principles
If a fact A is a reason for the prcscncc
exists primarily
secondarily
general
between
relation
for which
(from
bctwccn
kinds
reason-giving
certain
instance.
this
they express it.
Acceptance
(or validity)
kinds
hindsight,
when
some facts arc recognized
is the case when case la~v is ‘restated’
Some other times
as in the case of statutory
facts into legal
in the form
the ndc is there before
of mlcs.
Icgal rules which
Reasons are facts that are significant
other facts. Tlleyderive
byhumans,
certain
instance,
Inusingrttlcs.
kinds
toothcr
promises
to do what one has promised.
types of facts has a dispositional
occurrences
of promises
for the existence
nature.
arc usua]ly
of an obligation.
facts. For
connection
correspond
to
respect to
to the contents
ought
thieves
characteristic
of the rule. For example,
to be punished
ought
rules as a kind
Not evcry~hing
Baptising.
the
makes it the case
usually
of rules maybe
to be punished.
the cause of the error
of imperatives
[e.g. Ross 1968,
that makes the world
for instance,
fit itself
is an
also makes the world
(although
rules depends
Therefore,
Ivhicll
on the world).
can be described
cxprcsscs
significance
this relation
rttlcs) or va/id
These concrctc
saying
18
of the rule depend
what is the case in the world
or false. If a reason-giving
bet\\’ccn
Concrctc
assigned
can be made with
It is not the case that the contents
as reasons why onc ought
This
to
fit the speech act. )
of
frolllassigtllllcllt
l~ull~:llls assigl~sigl~ific:lllccto
of facts inrclation
they consider
for the exislcncc
tl~issigl~ificallcc
For
the
hand have a different
correspond
imperative.
oftit.
aim to correspond
and rules. Rules aim to make the world
p. -Mf.].
Rules as instruments
is from
fit
of fit,
of the imperative.
distinction
to consider
means of legislation.
direction
statements
(This
by
aim to tit
direction
of fit: they aim to make the world
that in the world
only make
reasons after the rule has been crcatcd
Statements
on the other
Imperatives,
rule that thieves
the reasons. such
to word
of tit of statements
the world.
A similar
lvith
as reasons, This
to world
speech act to the world.
the content
to bc reasons for other
the rule can only bc reconstructed
have the word
the direction
direction
of a rttlc comes down to it that
of facts arc considered
facts. Sometimes
speech acts which
speech acts that aim to make the world
while the Iattcr have the world
or a rule. Ru]cs
do not dcscribc
from
t hc act. The former
of the
f:]cts and the facts
principles)
of tit
[ 1975] distinguished
the world
fac(s. The expression
they arc reasons is a principle
now on subsuming
relation;
Scarlc
relation
of facls. and only
individual
bctwccn
Directions
of fact B. facts Iikc
A are reasons for facts like B. The reason-giving
connection
by saying
is accepted
on
of
rules are not true
exists,
this is a fact
that the rule which
(in the case of social
(in the case of institutional
that rtdcs are accepted
the existence
or valid
rules).
Sentences
are true or false; the
rules that occur in them have no truth
properly
considered
as logical
spcci[kr the meaning
value and arc
othcnvise
individuals.
of sentences
than by rc-using
by truth
conditions,
the same sentence
needs
rcconsidcration,
The truth
conditions
The distinction
dcontic
of deontic
bctwccn
modalities
nrlcs and statements
as WC1l as in the non-deonlic
statements,
norms,
as opposed
express dcontic
affairs
obtain,
values
values
of dcontic
that obtain
such its contents
If these stales of
not. This
statements.
just Iikc
depends
What
in the world,
statement
answer
Smith
for instance.
five dollars.
Dcontic
corresponds
is not amenable
should
bc noticed,
connection
and mcflning
of the logical
the dcontic
to have verifiable
Such truth
statement.
why this particular
truth
conditions
by pointing
Clcarly
circumstances
under which
statements.
all facts which
(all reason-based
These truth
Actually
obtain
The author
mistake
p:IIy
reasons which
this paper.
in an earlier
to thank
arc that a sentence
conditions
which
holvcvcr.
all responsibility
in (I]c field
of know]cdge
the transfer
of knowledge
the reasons againsl
hmc been elaborated
they do not spcci&
the meaning
but in my opinion
the cntcrprisc
RBL,
1978])
.
who played
of the semantics.
to a draft
an
and who pointed
out a
The author
referees of ICAIL
’95
of this paper He takes,
for the errors that possibly
and business
F.
in
of
to
19
companies.
financed
Based Systems
the level of expertise
hold for
S }vhicll
Clearly
about
that legal reasoning
[Alex~
for this paper was partly
for Knowlcdgc
reasons
facts.
statements,
version
useful comments
seeks to improve
F is true if and only if the
plead for F oul~vcigh
about the
conclusion
Bart Verheij,
the anonymous
for their
The research
for
conditions
argument
to have a
be called
have
rema i ncd.
Jvc hold the
and not only for dcontic
expresses a state of affairs
It is these truth
these truth
to thank
role in formalizing
also wants
but they
conditions
It appears
that might
to do. (Cf. A1ex@s view
wishes
important
conditions
because of their constituting
facts),
conditions
truth
conclusions.
of deon[ic
deontic
ACKNOWLEDGEMENTS
Foundation
to give general
that sometimes
reasoning
is
normative
causes the phenomenon
)vhcre a factual
which
conclusion
is ‘the law’.
of the law leads to a normative
is a spccics of practical
to be true.
It is also possible
correct,
in the phenomenon
injla/io/7,
of such an
in
For
statement.
The actual
leads to factual
out that Jones
such truth
of the dcontic
conclusion
reasoning
ill
to
is Icgally
interpretation
is to be preferred,
counterpart
truth
obtains.
The ‘proper’
interpretation
is to be chosen.
we
of that interpretation
“Ilc
by the reasons
that Jones ought
of a particular
the phenomenon
for
the vcritiablc
arc given
state of athirs
five dollars.
do not give the meaning
do indicate
concrete,
is shown
conditions
can be given
ihe fact cxprcsscd
of the sentence
five dollars
Smith
More
statements
deontic
the truth
promised
is which
what we ought
of dcontic
instance,
the consequences
co//apse.
dcmfic
Yet
must be w’hat the law is. For instance,
interpretation
contents
what we
deontic/practical.
It
1950].
of the facts that constitute
conditions
do; it is essentially
II is this daal nawrre of the law (and other
tradition
and
legal
1978].
systems) ~vhich. I think,
appears to
[contra:
the question
ti~c
in the
empirist
[McCormick
answers
lhc
vcritication.
in semantics.
separated
of interpretation
ought
which
to pay Smith
that this diffcrcncc
be entirely
reasoning
argument
of this dual
of legal rules is concerned,
[AICXT 1978. p. 297].
the
aims to
what the law is and what
in matters
is consequcntialist
argue from
which
As a consequence
Conscquentialist
to (should)
and as
On the other
As such it is the
of a legal text to the (incorrectness
of oughl -
by inspecting
empirical
verification
statements.
sentence
bc vcriticd
that Jones ought
remnant
It seems attractive
the form
‘The table
The sentence that
is not a diffcrcncc
bctwccn
me as an outdated
[cf. Hernpel
diffcrcncc,
however.
the application
the conclusion
that the table is
from
be cannot
interpretation
to direct
of vcritication
deontic
To (I1c sentence
can directly
the sentence
dollars
deontic
reasoning
to pay
thinking.
1958]. In particular
to the
The
[Fuller
of the law, the questions
where
arc in this respect
1967]. The semantics
is of course another
method
1969].
behavior
the Ialv should
of other statements.
the table is round
deontic
statements
dots in this respect not differ
table, while
enterprise
human
statcmcn(s?
five dollars?
the state of affairs
[cf. Davidson
semantics
Smith
corresponds
to pay Smith
to all other statements.
statements
There
to dcontic
is: The state of aft%irs that Jones ought
similar
round
correspond
that Jones ought
is round’
hand. the law is a teleological
Hart
states of affairs
phenomenon,
matter.
guide
nalurc
some ideal world.
Which
COLLAPSE
are an empirical
result of practical
on [he
actua/
\vorld. and not in
in the
2: DEONTIC
The law is on the one hand a social
rules or
are true, othcnvisc
of all other statements.
states of affairs
Dconlic
of dcontic
states of affairs.
the statements
means that the truth
the truth
sphere.
to formulations
APPENDIX
holds in the
which
in the Netherlands
based systems,
in this field
by the
(SKBS),
and to promote
between
universities
MacConnick,
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