A COMPUTATIONAL FRAMEWORK FOR USING
BOTH RULES AND PREVIOUSLY-DECIDED CASES IN
A LEGAL DECISION MAKING PROCESS
UCL
KAMALENDU PAL
Department of Computer Science
University College London
Gower Street, London WCIE 6BT
A thesis submitted for the degree of Master of Philosophy
in the University of London
June 1997
/ B I b L . (l o n o i k.]
ProQuest Number: U642047
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A b s tr a c t
A h y b rid know ledge-based sy ste m , A dvisory S u p p o rt for H om e S e ttle m e n t in D ivorce
(A S H S D ), w hich ex p lo its b o th g en e ral legal rules (for ru le-b ased re a so n in g or R B R ) an d
specific in fo rm a tio n ta k e n from p reviously-decided sim ilar cases (for ca se-b a se d reaso n in g
or C B R ), is d esc rib ed . Legal know ledge in th e sy ste m covers th re e a sp e c ts o f m a trim o n ia l
hom e s e ttle m e n t in divorce in E nglish law , n am ely ow ned hom e s e ttle m e n t, tra n s f e r of
ten an cy , an d in ju n c tio n s to p ro te c t a spo u se, o r a fam ily m e m b e r in th e c u sto d y o f a
spouse. T h e user ca n select e ith e r re aso n in g m e th o d (R B R o r C B R ), o r in d ic a te no
preference. A S H S D ’s rule b ase co n sists o f tw o ty p e s o f rule. T h e first ty p e of rules
d e te rm in e s w hich o p tio n s a re legally applicab le. T h e second ty p e in d ic a te s how th e c o u rts
are likely to a c t w ith in th e ra n g e o f o p tio n s available, w hich is d e te rm in e d by th e first
ty p e of rules.
W h en C B R is selected , th e sy stem uses th e fe a tu re s o f p rev io u sly -d ecid ed cases to
select th e m o st sim ilar cases to th e s itu a tio n t h a t is d esc rib ed in th e in p u t a n d disp lay s
th e ir d e ta ils o f decisions.
W h e n no p reference is in d ic a te d , th e sy stem applies each m e th o d se p a ra te ly , an d th e n
p re se n ts re su lts b ased on an a u to m a te d re la tiv e ra tin g o f th e q u a litie s o f th e R B R (based
A C K N O W L E D G E M E N T
It is a g re a t p leasu re to acknow ledge m y d e b t to m an y people involved, d ire c tly o r
indirectly, in th e co m p letio n o f th is th esis. I am p a rtic u la rly g ra te fu l to m y su p e rv iso rs,
P ro fe sso r J o h n C am p b ell an d D r M ark Levene, for e n c o u rag in g m e in th is w ork, offering
su g g estio n s an d p ru n in g m an y u n fru itfu l b ra n c h e s of research . I am g ra te fu l to J o h n for
his g u id an ce an d especially for th e tim e a n d effort he sp e n t r e s tr u c tu rin g a n d m ak in g
c o n stru c tiv e su g g estio n s on ea rly d ra fts o f th is thesis.
I am g ra te fu l to D r S te p h e n G u e st o f th e Law F aculty, U n iv ersity C ollege L o n d o n , for
ta k in g tim e from his b usy schedule in th e v alid atio n s tu d y o f th e im p le m e n te d sy ste m . I
am also th a n k fu l to D r D a n H u n te r o f th e Law School, U n iv ersity o f M e lb o u rn e , A u s tra lia ,
for p ro v id in g useful c o m m e n ts on th e im p le m e n ted softw are.
It is now m y p leasu rab le d u ty to reco rd m y in d e b te d n e ss to som e of m y frie n d s for th e
help th e y have given m e in p ro d u c in g th is th esis. F o rm o st a m o n g st th e m is S u k h d ev K heb-
bal w ho, over la s t th re e y ears, h a s given m e valu ab le in fo rm a tio n on so ftw a re. T ony B al-
lardie, S an ja y K a d a m , W illiam L an g d o n , J e n s D zikow ski, R afael S o rd in i, E liseo R e a te g u i,
W ilfred Ng, A rif Iq b a l and J o n a th a n P oo le have p rovided m e w ith th e ir e x p e rt o pinions
an d help.
C ontents
1 In tr o d u ctio n 1
1.1 B a c k g r o u n d ... 1
1.2 A rtificial Intelligence in C o n te x t o f L a w ... 2
1.3 T h e Legal T h e o re tic a l C o n c e p t s ... 3
1.3.1 T h e Legal P o s i t i v i s t s ... 4
1.3.2 Legal R e a l i s m ... 8
1.4 T h e Legal D ecision-M aking P r o c e s s ... 11
1.5 M odel fo r th e P re s e n t R e s e a r c h ... 18
1.5.1 Id e n tific atio n a n d A cqu isitio n of K n o w l e d g e ...20
1.5.2 R e p re se n ta tio n o f th e C ollected K n o w l e d g e ...23
1.5.3 R easo n in g on th e R ep re sen ted K n o w l e d g e ... 24
1.5.4 N o tio n o f R ule-B ased R e a s o n i n g ... 25
1.5.5 N otion o f C ase-B ased R e a s o n i n g ... 29
C o n te n ts iii
1.6.1 P r o je c t O rie n ta tio n ... 31
1.6.2 W h y a H y b rid S y stem ?... 32
1.6.3 O verview o f A S H S D ... 33
1.7 S tr u c tu re o f th e T h e s i s ... 37
2 P r e v io u s R ela ted R esea rch 39 2.1 I n t r o d u c t i o n ... 39
2.2 R u le-B ased R easo n in g S y s t e m s ... 40
2.2.1 T A X M A N I P r o j e c t ... 40
2.2.2 B ritish N a tio n a lity A c t ...41
2.2.3 T h e O xford P ro je c t ... 45
2.2.4 LDS an d SAL S y s te m s ... 46
2.2.5 T A X A D V I S O R ... 47
2.2.6 L a te n t D a m a g e S y stem ... ...47
2.2.7 T h e Use o f M e ta -ru le s in R ule-B ased Legal C o m p u te r S y ste m s . . . 48
2.2.8 C o m m e n ta ry on R B R S y s t e m s ... 48
2.3 C ase-B ased R easo n in g S y s t e m s ... 49
2.3.1 J U D G E ...49
2.3.2 H Y P O ... 51
C o n te n ts iv
2.3.4 C H A S E R ... 53
2.3.5 C o m m e n ta ry on C B R S y s t e m s ...54
2.4 H y b rid Legal K now ledge-B ased S y s t e m s ... 55
2.4.1 T A X M A N I I ... 55
2.4.2 G a r d n e r ’s S y s te m ... 56
2.4.3 G R E B E ... 57
2.4.4 C A B A R E T ...58
2.4.5 P R O L E X S ... 60
2.4.6 IK B A L S I I ... 61
2.4.7 H E L IC I I ...61
2.4.8 C o n c l u s io n s ... 62
3 F ram ew ork o f th e S y ste m 64 3.1 I n t r o d u c ti o n ... 64
3.2 C o n c e p ts b eh in d A SH SD ... 65
3.2.1 C h a r a c t e r i s a t i o n ... 65
3.2.2 O b je c tiv e s for th e S y s t e m ... 65
3.3 A S H S D ’s K now ledge B ase D e v e l o p m e n t ... 66
3.4 T h e D o m ain ; M a trim o n ia l-H o m e -R e la te d O r d e r s ... 66
C o n te n ts v
3.5.1 M odel B u i l d i n g ... 70
3.5.2 K now ledge A c q u is itio n ... 72
3.5.3 In c re m e n ta l D ev elo p m e n t o f Full S y s t e m ... 80
3.5.4 T estin g an d U ser T r i a l s ...82
3.6 T h e A S H S D H y b rid R easo n in g M o d e l ... 83
3.6.1 S y stem C o n tro l M e c h a n i s m ...83
4 K n o w led g e R ep resen ta tio n and O rganisation 86 4.1 I n t r o d u c ti o n ...86
4.1.1 Legal K now ledge in R ule F o r m ... 86
4.2 Legal K now ledge in C ase F o r m ... 88
4.2.1 A SH SD - C ase K now ledge R e p re se n ta tio n an d O r g a n i s a t i o n ...91
4.3 E x am p le: M a rtin (B .H .) v M a rtin ( D . ) ...95
4.3.1 Ju d ic ia l O pinion for M a rtin v M a r tin ... 96
4.3.2 K now ledge R e p re se n ta tio n an d O rg a n isa tio n for M a r tin v M a r tin case 99 4.3.3 M a trim o n ia l-H o m e H y p e rn o d e S tr u c tu r e a n d C o n t e n t s ... 102
4.3 .4 A p p e al H y p e rn o d e o f th e M a rtin v M a rtin c a s e ...103
4.3.5 D ecision H y p e rn o d e o f th e M a rtin v M a rtin c a s e ... 103
4.3.6 S u m m a r y ...104
C o n te n ts vi
5.1 K now ledge-B ased S y ste m an d F u z z i n e s s ... 105
5.1.1 O verview of F uzzy S et T h e o ry ... 106
5.1.2 W h a t is F uzziness ? ... 106
5.2 F uzzy S e ts - N o ta tio n , T erm in o lo g y an d B asic P r o p e r t i e s : ...108
5.2.1 C lassical S et o r C risp S e t ...108
5.2.2 C h a ra c te ris tic F u n c tio n of a C risp S e t ... 108
5.2.3 Fuzzy S et an d its C h a ra c te ris tic F u n c t i o n ... 109
5.2.4 F o rm al Fuzzy S et R e p r e s e n t a t i o n ... I l l 5.2.5 H edges o f F uzzy S e t s ...113
5.3 Fuzzy K now ledge R e p re se n ta tio n in A S H S D ... 115
6 O rganisation o f K n o w led g e B a se 119 6.1 I n t r o d u c t i o n ... 119
6.2 R ule B ase S t r u c t u r e ... 120
6.2.1 C o m p reh en siv e A d v i c e ... 122
6.3 C ase B ase M a n a g e m e n t an d C ase R e t r i e v a l ... 127
6.3.1 E x a m p le : E xclusion O rd e r F ro m a R e n te d M a trim o n ia l H om e . . . 130
6.3.2 Selection of S im ilar C ases for a New C a s e ...135
6.3.3 P a r tia l A dvice M e c h a n is m ... 141
C o n te n ts vii
6.3.5 S election of S im ilar C ases for a New C a s e ... 149
6.3.6 No R ule-B ased A d v i c e ...157
6.3.7 No S uggestion from R ule B ase a n d C ase B a s e ...157
6.4 A u to m a te d D ecision on th e Q u a litie s of th e R easo n in g M e t h o d s ...157
7 E m p irical O b servations and V a lid ation o f A S H S D 159 7.1 I n t r o d u c ti o n ...159
7.2 W h y E m p irical O b serv atio n ? ...160
7.2.1 E m p irical O b se rv a tio n s ... 160
7.2.2 E x am p le: T h e O verall S u ita b ility o f an y P a r tic u la r R easo n in g M e th o d 160 7.3 C o n c l u s i o n s ...174
7.4 O verview o f th e P ro je c t V a l i d a t i o n ... 175
7.4.1 V a lid atio n o f A S H S D ...175
7.4.2 S econd S te p of V a l i d a t i o n ...181
7.5 K now ledge B ase M a in te n a n c e A sp e c ts of A S H S D ... 182
8 C o n clu sion s 186 8.1 I n t r o d u c t i o n ...186
8.2 M o tiv a tio n ...186
8.3 S u m m a ry o f R e s u l t s ...187
C o n te n ts viii
8.5 L im ita tio n an d F u tu re R e s e a r c h ... 192
8.5.1 In te g ra tio n of A SH SD w ith a D a ta B ase M a n a g e m e n t S y ste m . . . . 192
8.5.2 In c o rp o ra tio n o f a B e tte r U ser I n t e r f a c e ...193
8.5.3 Inclusion o f a C ritic M o d u l e ... 193
8.5.4 E x te n sio n o f th e Scope of A SH SD ... ... 194
8.6 C o n clu d in g R e m a rk ... 194
A P r e v i o u s l y D e c i d e d C a s e s 1 9 5 B Q u e s t i o n n a i r e U s e d in t h e V a l i d a t i o n P r o c e s s 2 1 5 C Q u e s t i o n n a i r e U s e d in t h e C r i t i c a l I n s p e c t i o n o f A S H S D 2 1 8 C .l B ack g ro u n d In fo rm a tio n a b o u t th e S y stem ...219
C .2 D ifferen t R ule-B ased A d v i c e ... 223
C .2.1 C ase-B ased A d v i c e ... 223
C .2 .2 Q u e stio n n a ire for th e te s t c a s e s ...224
C .3 E x tr a Q u e stio n s ...227
List o f Figures
1.1 T h e c o m p u ta tio n a l f r a m e w o r k ... 33
1.2 D ifferen t ty p e s o f b e h a v io u r leading to ru le-b ased o u tp u t ... 36
3.1 D e co m p o sitio n o f legal an a ly sis b l o c k ... 71
3.2 D e co m p o sitio n o f ow ned m a trim o n ia l hom e b l o c k ... 72
3.3 D e co m p o sitio n o f offending b e h a v io u r ...74
3.4 A n ‘a v a ila b le -a c tio n (s)’ rule for an in ju n c tio n -re la te d c a s e ... 76
3.5 A n ^available-action(s)^ rule for an ow ned ho m e s e ttle m e n t c a s e ... 77
3.6 R u le-b ased ‘p re d ic tio n ’ in an exclusion o rd e r for p ro te c tin g a sp o u se . . . . 78
3.7 R u le-b ased ‘p re d ic tio n ’ in an exclusion o rd e r for p ro te c tin g a c h i l d ... 79
3.8 S y ste m l a y o u t ... 84
4.1 T h e g en e ral rule s tr u c tu r e a n d a te n a n c y tra n s f e r r u l e ...87
4.2 H y p e rn o d e c a s e b a s e ...91
4.3 A p o rtio n of th e ‘p a r tic ip a n ts ’ h y p e rn o d e ... 92
L ist o f F ig u r e s x
4.4 D ifferent ty p e s of re la tio n sh ip h y p e rn o d e s ... 93
4.5 D ifferent ty p e s o f m a trim o n ia l h o m e ... 94
4.6 D ifferent ty p e s o f m a trim o n ia l hom e h y p e rn o d e s ...95
4.7 T h e m ain case h y p e rn o d e for th e M a rtin v M a rtin c a s e ...96
4.8 In d ex h y p e rn o d e s for th e M a rtin v M a rtin c a s e ... 97
4.9 P a r tic ip a n ts a n d re la tio n h y p e rn o d e s for th e M a r tin v M a rtin c a s e ... 97
4.10 P a rtic ip a n t h y p e rn o d e s for th e M a rtin v M a rtin c a s e ... 98
4.11 A d u lt a n d children p a r tic ip a n t h y p e rn o d e s for th e M a rtin v M a rtin case . . 100
4.12 Legal an d g ro u p p a r tic ip a n ts for th e M a rtin v M a rtin c a s e ... 101
4.13 R e la tio n s am o n g th e p a rtic ip a n ts for th e M a rtin v M a rtin c a s e ... 101
4.14 F a c ts h y p e rn o d e for th e M a rtin v M a rtin c a s e ...102
4.15 D ifferen t c o u rt h y p e rn o d e s for th e M a rtin v M a rtin c a s e ... 102
4.16 M a trim o n ia l-h o m e h y p e rn o d e for th e M a rtin v M a rtin c a s e ...102
4.17 A p p e a l h y p e rn o d e fo r th e M a rtin v M a rtin c a s e ... 103
4.18 D ecision h y p e rn o d e for th e M a rtin v M a rtin c a s e ... 103
5.1 C h a ra c te ris tic fu n c tio n o f A ...109
5.2 A c h a ra c te ris tic fu n c tio n for fuzzy se t G O O D ...109
5.3 F uzzy se ts on len g th o f m a rria g e w ith ‘v e ry ’ h e d g e ...114
L ist o f F ig u r e s xi
5.5 T h e advice an d th e p re c o n d itio n s of B R U L E 1 9 ...118
6.1 rule bcLse s t r u c t u r e ...120
6.2 R e p re se n ta tio n of s te p s in th e sim ila rity c isse ssm e n t...128
6.3 D ia g ra m m a tic re p re s e n ta tio n of th e re la tiv e d ista n c e s b etw een cases . . . . 134
6.4 C lassification of p re co n d itio n s o f B R U L E 2 2 ... 144
7.1 T h e c o m p ariso n of R B R an d C B R effectiveness on te s t cases ...172
7.2 T h e d ifferen t decision ca te g o rie s in g ra p h ic a l fo rm ...173
C .l T h e c o m p u ta tio n a l fr a m e w o r k ...220
C .2 D ifferent ty p e s o f p re c o n d itio n s o f B R U L E 1 1 2 ... 221
List o f Tables
5.1 F uzzy te rm ‘g o o d ’ ...107
6.1 S om e o f th e p rev io u sly -d ecid ed in ju n c tio n -re la te d cases sto re d in th e case b a s e ...130
6.2 T h e re la tiv e sim ila rity d ista n c e for in ju n c tio n c a s e s ...132
6.3 T h e m u tu a l sim ilarity coefficients of th e abo v e in ju n c tio n -re la te d cases . . . 136
6.4 S om e o f th e p rev iously-decided ow ned hom e s e ttle m e n t cases s to re d in th e case b ase ...150
6.5 T h e re la tiv e sim ila rity d ista n c e for ow ned hom e s e ttle m e n t c a s e s ... 151
6.6 T h e m u tu a l sim ila rity coefficients fo r th e ab ove c a s e s ... 152
7.1 R eal te s t cases used in th e em p irical o b s e r v a t i o n s ...162
7.2 D erived (h y p o th e tic a l) te s t cases used in th e em p irical o b s e r v a tio n s ... 163
7.3 T h e scores an d th e a p p ro p ria te n e s s of ca te g o ries for som e te s t ca ses . . . .1 7 0 7.4 T h e re su lts of th e case base v a l i d a t i o n ... 179
7.5 G ra d in g s tr u c tu r e to assess th e case base v a li d a ti o n ... 180
L ist o f T a b le s 0
C hapter 1
In trod u ction
1.1
Background
C o m p u te r science, an d in p a rtic u la r A rtificial Intelligence (A I), is now m a k in g a n o ticea b le
im p ressio n on law - as w itn ess th e grow ing n u m b e r of jo u rn a ls a n d p u b lic a tio n s dealin g
w ith A I a n d law to g e th e r. F u rth e rm o re , th e legal d o m a in h a s becom e an a r e a in w hich
a p p lic a tio n s o f A I have grow n su b sta n tia lly . H ow ever, th e m a jo rity o f th e re searc h on
a p p lic a tio n s o f A I fo r th e legal profession an d th e c o n se q u en t tra c k reco rd o f re searc h on
legal re aso n in g have n o t y e t p ro d u c ed eflfective s u p p o rt sy ste m s a t a high level of legal
co m p e te n c e . A ty p ical opinion of th e s ta te of th e a r t is:
T hough co m p u te rs are used e x te n siv e ly by law yers f o r legal data storage a n d re trieva l purposes, th ey have n o t y e t been sa tisfa c to rily p rogram m ed to in te rp re t th is raw m a te ria l or to provide a ssista n c e in reasoning w ith, draw ing in fe r en ces fro m , a n d o fferin g advice on the basis of, the fo r m a l sources o f the law.
[(S usskind, 1987a), p p .3]
Chapter 1. Introduction 2
M an y a sp e c ts o f legal re aso n in g re q u ire fu r th e r s tu d y before th e s itu a tio n can b e im proved
q u a lita tiv e ly . In th is th esis, o u r p rim a ry concern is c o m p u te r science an d n o t law . B u t
even w ith o u t d e ta ile d or specialised know ledge of legal p ra c tic e s, we can id en tify one
a sp e c t o f legal re aso n in g w hich is also p re se n t fo r m an y o th e r k in d s o f ex p e rtise : rules
an d cases are used, an d so m etim e s to g e th e r. In research on k n ow ledge-based sy ste m s in
g en eral, using rules an d cases to g e th e r in tr e a tin g som e p ro b lem needs to be u n d e rsto o d
b e tte r . W e ex am in e one specific an d new a p p ro a c h to th is use o f know ledge in tw o different
re p re se n ta tio n s, w ith ex a m p les o f know ledge d ra w n from a specialised a r e a o f law .
1.2
A rtificial Intelligence in C ontext o f Law
T h e ad v a n ce o f in fo rm a tio n tech n o lo g y (IT ) an d its im p a c t on o u r d aily life c a n n o t be u n
d e re s tim a te d . H ow ever, legal professionals have been slow to ex p lo it th e im m en se p o te n tia l
of IT . In ste a d o f using IT to m axim ise p ro d u c tiv ity an d fee-earn in g cap acity , c o m p u te r
sy ste m s have been used m ainly for w ord p rocessing and ac c o u n tin g w ith in th e legal p ro
fession. IT hcLS y e t to be ex p lo ited as an effective tool by law yers.
T h e m o st v alu ab le reso u rces o f legal firm s are th e know ledge a n d e x p e rtise o f law yers.
B u t th e know ledge o f sen io r legal p ra c titio n e rs is n o t easily available to less ex p erien ced
law yers, s tu d e n ts , an d clients. C learly, re le v an t technologies in th is a re a are know ledge-
based sy ste m (K B S ): in p a rtic u la r, e x p e rt sy ste m s w hich w ould allow sca rce e x p e rtise and
know ledge to be m ore w idely available an d easily accessible. F o r law yers a n d clien ts to
have access to v aluable e x p e rtise a t th e to u c h o f a few keys could im p ro v e p ro d u c tiv ity ,
qu ality , an d p e rfo rm a n c e . In a d d itio n , th e use of th e se techn o lo g ies could give legal firm s
a c o m p e titiv e a d v a n ta g e over o th e rs t h a t a re slow er to a d o p t th e technology. T h e re fo re
th e c o n s tru c tio n o f a u to m a te d legal d é c isio n -su p p o rt sy ste m s is a v alu ab le exercise, from
th e p o in t o f view o f d e te rm in in g w h a t is feasible, d esira b le a n d /o r efficient. T h is view is
n o t u n u su al to find a m o n g th o se involved in research an d in th e p a r ts o f legal p ra c tic e
w here a s y m p a th e tic view of research exists.
In a u to m a tin g th e legal d é c isio n -su p p o rt sy ste m s, o ne h as to u n d e r s ta n d en o u g h of th e
Chapter 1. Introduction 3
w h a t is delivered p ro d u c es o u tp u t t h a t a legal sp ec ia list w ould re g a rd as helpful an d n o t
irre le v a n t o r m isleading. T h is u n d e rs ta n d in g includes th e o rie s a n d view s a b o u t w h a t law
is, w h a t are ty p ic a l legal p ro b lem s a n d how th e y are solved, w h a t are th e uses for legal
k now led g e-b ased sy ste m s, an d so fo rth . Since m o st o f th e se a s p e c ts refer in so m e way,
even in d ire c t, to th e th e o re tic a l fo u n d a tio n s of law a s a discipline, legal th e o ry should
be consid ered for its relevance to th e a u to m a tio n of a n y legal d é c isio n -su p p o rt sy stem .
In th e n e x t sec tio n , th ere fo re , we discuss several id eas from classical a u th o rs in legal
th e o ry fo r th e ir p o te n tia l relevance to o u r w ork. H ow ever, th is th e sis is n o t in te n d e d as a
c o n trib u tio n to legal th eo rie s; its significance is in c o m p u te r science, in co n n e c tio n w ith a
specific a u to m a te d d é c isio n -su p p o rt sy ste m t h a t uses m u ltip le know ledge re p re s e n ta tio n s .
1.3
T h e Legal T heoretical C oncepts
D ifferent re se a rc h e rs [e.g. (S usskind, 1987a), (G a rd n e r, 1987), (Zeleznikow & H u n te r,
1994)] of AI a n d law have arg u ed for th e relevance of ju risp ru d e n c e ^ to th e a u to m a tio n of
legal d ec isio n -m a k in g processes. S usskind w rites:
It is beyond a rgum ent, how ever, th a t all expert s y s te m s m u s t co n fo rm to so m e ju r isp r u d e n tia l theory because all expert sy s te m s in law n ecessa rily m a k e a s s u m p tio n s about the nature o f the law a n d legal reasoning. To be m ore specific, all expert s y s te m s m u st em body a theory o f stru ctu re a n d in d iv id u a tio n o f laws, a theory o f legal n o rm s, a theory o f d escrip tive legal science, a theory o f legal reasoning, a theory o f logic an d the law, a n d a th eo ry o f legal sy ste m s, as w ell as e le m e n ts o f a s e m a n tic theory, a sociology a n d a p sychology o f law (th eo ries th a t m u s t all th em se lv es rest on m ore basic p hilosophical fu n c tio n s ) . I f th is is so, it w ould see m p ru d e n t th a t the general th eo ry o f law im p lic it in expert sy s te m s should be explicitly articu la ted ... [(S usskind, 1987a), p p .20]
' Jurisprudence m eans legal philosophy (or legal theory). A m ong the topics included in legal philosophy
are theories o f law; the concepts o f law and legal institutions; legal reasoning and adjudication; and m any
Chapter 1. Introduction 4
T h e ab ove sp ecification m ak es som e d e m a n d s t h a t are u n ique to legal k n ow ledge-based
s y ste m s. In o th e r a re a s (e.g. engineering, m edical science, etc.) for w hich one w ould wish
to design a know ledge-based sy stem th e re is m uch m ore of a consen su s a b o u t th e n a tu r e of
th e th e o ry t h a t d escrib es th e discipline. A n en gineering or m edical school w ould g en erally
n o t c o n d u c t co u rses on th e n a tu r e o f en g in eerin g o r m edicine b e c au se th e p ra c tic e o f th e se
p rofessions h a rd ly ever raises th e kind o f fo u n d a tio n a l q u e stio n s t h a t d riv e o ne b ac k to
b asic th e o ry a b o u t th e discipline. Such concerns, how ever, o ften arise in legal p ra ctice;
hence, th e se are th e kinds of q u estio n t h a t a course in ju risp ru d e n c e ask s a b o u t law . In
law th e re is no single a g re e m e n t a b o u t w h a t law is, n o r a b o u t th e tr u e n a tu r e o f legal
reaso n in g , b u t som e a g re e m e n t is n ev e rth eless needed if legal ra tio n a lity is to b e self-
conscious. M oreover, legal p ra c titio n e rs have no b o d y o f scientific know ledge lying a t th e
h e a r t o f th e ir discipline, unlike e x p e rts in th e fields w here o th e r k now ledge-based sy ste m s
hav e been c re a te d successfully. In s te a d , law re sts u p o n se ts o f fu n d a m e n ta l values a b o u t
w hich th e re is a g re a t deal of d e b a te .
To clarify th e s itu a tio n , we shall in tro d u c e som e b ack g ro u n d to ju ris p ru d e n c e t h a t is
re le v an t to o u r re searc h . W e focus on w h a t is im p o r ta n t to u n d e rs ta n d w hen we discuss
‘m o d e llin g ’ law in th e sense t h a t is re le v an t for o u r ow n ap p lic a tio n . T h is in clu d es a p p re c ia tio n o f th e tw o m o st in flu en tial c a m p s in ju risp ru d e n c e : th e legal p o s itiv is ts an d th e legal realists. T h ese tw o c a m p s d is p u te over one highly re le v an t q u e stio n : is legal d ec isio n -m a k in g c o n stra in e d by rules ? W e look first a t th e a p p ro a c h of legal p o sitiv ists,
befo re e x a m in in g th e ap p ro a c h e s of th e legal re alists.
1 .3 .1 T h e L e g a l P o s it i v is t s
L egal p o sitiv ism em erged in its m o d e rn d re ss in th e w ork of J e re m y B e n th a m (H a rt,
1982) a n d his follow er J o h n A u stin (M orison, 1982). T h e c e n tra l claim o f legal p o sitiv ism
is t h a t law is s e p a ra te an d d is tin c t from m orality . P o sitiv ists claim t h a t law is b ase d u p o n
ex p licit rules an d w h e th e r som e rules are legal rules d ep e n d upo n w h e th e r th e y hav e been laid dow n in som e so u rce such as leg islatio n , codes, p rev iously-decided case re p o rts or
Chapter 1. Introduction 5
H ow ever, legal p o sitiv ists do n o t deny t h a t ju d g e s so m etim e s decide cases by reference
to m o ral values or social policy co n sid eratio n s. It is necessary for th e d ec isio n -m a k er to do
th is, ac co rd in g to th e p o sitiv ists, w henever th e ex istin g rules of law fail to give a clearly-
d e te rm in e d an sw er in a specific case. In claim in g t h a t law is s e p a ra te fro m m o rality , th e
p o sitiv ists are den y in g t h a t m o ral ju d g m e n ts are n ec essary to discover w h a t th e ex istin g
law is; b u t discovering th e ex istin g law is n o t alw ays en o u g h in itse lf t o decid e a case.
W h e re th e law d o es n o t give an answ er, th e d ec isio n -m ak er m u st e sta b lish , by his or her
decision, a new legal rule^ a n d th is will be done on th e basis of e x tra -le g a l c o n sid e ra tio n s of m o ra lity an d social policy. T h u s, th e legal p o sitiv ists seek to find a series o f legal rules
w hich ex p lain th e v arious laws.
T h e m ain th e m e of rule-b ased ju risp ru d e n c e is n o t a new one, th o u g h it h a s been
ac cep ted an d a c c o m m o d a te d freely d u rin g th is ce n tu ry . In th e ea rly p a r t o f th is c e n tu ry
th e re w as a school t h a t p re se n ts an ap p e a lin g e x a m p le to th o se in te re ste d in th e a p p lic a tio n
of c o m p u te r m e th o d s to law . A te rm ‘m echanical ju r is p r u d e n c e ’^ w hich gives a p ic tu re sq u e d e sc rip tio n of it, a p p e a re d a t le a st as early as 1908 w ith th e p u b lic a tio n of D e an R oscoe
P o u n d ’s a rtic le (P o u n d , 1908).
T h e m odel o f legal re aso n in g by P o u n d , w hich is b ase d on a logical d e d u c tio n , needs
to sa tisfy tw o s e p a ra te c rite ria for th is m odel to fu n c tio n . F ir s t, legal c o n c e p ts m u st
be specific, w ell-founded, clear an d inclusive o f all cases. Secondly, th e se legal c o n c e p ts
m u st be s u ita b le for re p re s e n ta tio n as e ith e r logical sta te m e n ts^ o r p ro d u ctio n rules^ w hich w ould ty p ically be o f th e form : I F < c o n d itio n (s)> T H E N < c o n c lu sio n > . T h e n logical d e d u c tio n is th e only form o f re aso n in g needed, if th e law can indeed be re p re se n te d in such
a sim ple way. H ow ever, for p ro p o n e n ts o f such an a p p ro a c h , w hich we can call m e chanical
^Form al logic \s used to represent th e know ledge cuid p r e p o s itio n a l calculus is usually th e representation schem e. For exam ple: p & q ^ r (mecining th at p and q togeth er im ply r) where p stan d s for ‘Tony is drunk’, q m eans ‘Tony is driving his car’, and r indicates that ‘T on y’s driving licence m ust be revoked by th e transport au th ority’. Therefore this exam ple represent the drink-driving legal rule in prepositional
calculus.
^Production rules, i.e. rules o f the sam e logical form but which are used to produce new inform ation.
T his involves basically a deductive reasoning process. For exam ple, if the know ledge base o f a system
Chapter 1. Introduction 6
jurisprudence^ law is n o t so sim ple. In ste a d th e m o d ern legal th e o ris ts hav e p ro p o se d w ays in w hich we can a d a p t th e p o sitiv ist th e o ry to c o n te m p la te th e real w orld m o re accu ra te ly .
T h e s ta rtin g -p o in t for th e m o d ern legal p o sitiv ists is th e w ork of H .L .A . H a rt. His
th e sis [e.g. (H a rt, 1961), (H a rt, 1983)] is t h a t law c o n sists o f ru les only. T h e se ru les can
be classified in to th e p r im a r y rules an d th e secondary rules. P rim a ry rules a re ru les a b o u t c o n d u c t, of th e kind w ith w hich we are all fam iliar: ‘do n o t bully \ ‘do n o t s te a l’, ‘alw ays obey y o u r p a ren ts etc. S eco n d a ry rules are rules a b o u t o th e r rules: a b o u t how to a lte r o th e r rules, how to in te rp re t th e m , how to e n a c t th e m , a n d how to recognise th e m as valid
rules. W h e n th e m ean in g of th e w ords of a rule m akes it ap p lica b le to a given fa c tu a l
s itu a tio n , he ag rees to a p p ly logical d e d u c tio n . B u t each rule hets a ‘p en u m b ra o f d o u b t’,
w here it is n o t know n w h e th e r th e rule applies o r n o t. T h is lead s to th e n o tio n s o f ‘easy case ’ an d ‘hard case ’.
T h e d istin c tio n betw een hard a n d easy cases is u su al in th e ja rg o n o f ju risp ru d e n c e . An easy case is one w here th e legal decision for th e issue is clear a n d basically u n d isp u te d .
O ne g en erally ta k e s in to c o n sid e ra tio n t h a t easy cases a re s e ttle d w h en ev er th e fa c ts are
clear. E a sy cases t h a t com e th e p o in t of litig a tio n do so only in o rd e r t h a t q u e stio n s of
fa c t ca n b e resolved ac co rd in g to th e legal ru les of proof. O nce th e c o u rt h a s esta b lish e d
th e fa c ts, th e legal decision sh o u ld th e n b e sim ple a n d easily achieved by th e use o f th e
law on th e fa c ts ac co rd in g to s ta n d a r d ty p e s of inference. Since easy cases by d efinition
do n o t raise difficult legal issues, th e y are h a rd ly ever ap p e a le d .
H a rd cases a re an u n av o id ab le fe a tu re of th e law . A h a rd case is one t h a t d o es n o t fall
u n d e r a s e ttle d ru le of law , or t h a t a p p e a rs to fall u n d e r tw o rules, th e use of w hich w ould
p ro d u c e differing o r o p p o sin g so lu tio n s, or is a case t h a t falls clearly u n d e r o n e legal rule,
b u t w here th e o u tc o m e w ould be an irra tio n a l re su lt. Since th e p o ssib ilities fo r h u m a n
in te ra c tio n a re so varied an d since we can never fully p re d ic t th e fu tu re , it is im p o ssib le to
fo re c a st a n d c re a te a useful rule w hich w ould a n tic ip a te a n d resolve every useful a sp e c t of
h u m an in te ra c tio n . W h e n th e v a ria tio n s o f life th ro w in to th e c e n tre o f th e legal sy stem
a u n iq u e kind o f d isp u te , arisin g from a new kind of ac tiv ity , a new technology, o r a new
p ersp ectiv e w hich c re a te s a case t h a t fails to fall c o m fo rta b ly u n d e r th e p rev ailin g rules,
Chapter 1. Introduction 7
we have a h a rd case for th e law.
F o r a easy case th e decision can be m a d e d eductively. B u t for cases b elo n g in g in th e
p e n u m b ra , i.e. h a rd cases, w hich c a n n o t be decided in a d e d u c tiv e way. H a r t believes t h a t
th e d ec isio n -m ak er m ay well decide th e case a t his ow n d isc re tio n . A s H a r t says:
W here the rules are vague, all we can do is to p redict w hat the ju d g e s w ill say
[(H a rt, 1983), p p .168].
W h en the area o f open texture"^ is reached very o fte n all we can pro fita b ly o ffe r in a n sw e r to the q uestion: ‘W h a t is the law o f the m a tte r ? ’ is a guarded p red ictio n o f w hat the courts w ill do. [(H a rt, 1961), pp. 143].
O ne o f th e c o n te m p o ra ry d efen d ers of legal positiv ism is R ic h a rd S u ssk in d , w ho h as
a d v o c a te d th e use o f legal know ledge so u rc es t h a t m ay red u ce th e vag u en ess o f th e original
la w -s ta te m e n t w hen one is co n sid erin g h a rd cases. S usskind claim s:
R u le s do a n d should p la y a cen tra l role in legal science, legal know ledge rep re se n ta tio n a n d legal reasoning. O v erw helm ing a u th o rity f o r th is p ro p o sitio n can be fo u n d in legal theory, a n d even a p h ilo so p h er such as D w orkin, who has q u estio n ed the su ffic ie n c y o f rules fo r legal d ecisio n -m a kin g , does n e v e rth e le ss h im s e lf seem to presuppose a p re d o m in a n t place f o r them , as M a c C o rm ic k has show n. I f this is so, an d rules have, as M a c C o rm ic k alleges, ‘logical p r im a c y ’, th e n surely it should be sought, in the fir s t in sta n ce, to rep resen t legal know ledge in rule fo r m . [(S usskind, 1987a), p p .78-79]
N ev erth eless, ac co rd in g to S u ssk in d ’s ow n an a ly sis (S usskind, 1987) th e re is a larg e
d iv ersity o f o pinions am o n g legal th e o ris ts a b o u t w h a t rules a c tu a lly a re . W h ile th e y
seem to ag ree t h a t rules have a n te c e d e n ts a n d co n se q u en ts, th e re are m a n y view s a b o u t
Chapter 1. Introduction 8
w h a t th e se are m ad e of. To follow th e m u p in d e ta il w ould be bey o n d th e sco p e of th is
th esis even if it w ere p rim arily a b o u t law an d n o t a b o u t c o m p u te r science. W e confine
o urselves to p re se n tin g th e ex a m p le w hich H a rt gave t h a t is used o ften in discu ssio n s of
ju risp ru d e n c e : th e rule t h a t p ro h ib its an yone from b rin g in g a n y vehicle in to a p a rk . His
an a ly sis is:
A law m ig h t say, ‘vehicles p rohibited in the p a r k ’. T h e c o n c e p ts o f ‘v ehicles’ m ig h t have h ad a clea r m ean in g w hen th e law was w ritte n , an d th e re fo re no d o u b t ap p lied to tr a n s p o r t
such cLS th e h orse an d c a r t o r ca rriag e . B u t new in v en tio n s in la te r tim e s m ay w iden th is
c o n c e p t to in clu d e such vehicles such as snow m obiles. Sim ilarly, in la y m a n ’s lan g u ag e , a
p e r a m b u la to r is a ‘vehicle’; how ever, a c o u rt case will n o t define it as a vehicle a p p r o p ria te
to th e p u rp o se s o f th is law. Legal d e b a te co n tin u es as to w h e th e r o p en te x tu r e sh o u ld be
h an d led as an a p p e a l to th e tr u e in te n t o f th e s t a t u t e o r by som e a lte r n a te m ean s. T h is
ex am p le th e n falls w ith in th e c a te g o ry of ‘hard c a s e ’, a n d c a n n o t be d e te rm in e d w ith o u t reference to som e e x te rn a l m a te ria l.
A case such as th is m ay effectively be a h a rd case, a n d like all h a rd cases p re se n ts
c o m p lic a tio n s for legal p o sitiv ists. P o sitiv ism can be seen to be a m ild fo rm o f rule
sce p tic ism . R ules fu n c tio n in easy cases, b u t n o t in th e h a rd cases. If th e p o sitiv ist view
o f legal re a so n in g is c o rre c t, th e n know ledge-based sy ste m s can only be b u ilt to h an d le
easy cases. If so, th e n know ledge-based sy ste m s have a so m e w h a t lim ited u tility in law
since it is h a rd cases t h a t are litig a te d an d re q u ire legal re searc h by th e p ra c titio n e r . As a
co nsequence o f th e se kinds of co n cern s a new ca m p of legal th e o ry arose. T h is new ca m p
a tte m p te d to an sw er a ra n g e of concerns a b o u t legal p o sitiv ism an d o th e r schools. Its
schem e o f th e o ry is know n as legal realism .
1 .3 .2 L e g a l R e a lis m
T h e tw o m o st im p o r ta n t fa cets of th e re a lists ’ id ea seem to be th e ir rule sc e p tic ism and th e ir c o n c e n tra tio n on the c o u r ts ’ role is s e ttlin g d isp u te s. R ealism a tte m p t s to b e b o th p ra c tic a l a n d p ra g m a tic . T h e essence o f th e a p p ro a c h is t h a t th e re is m o re to law th a n th e
Chapter 1. Introduction 9
value in th e logical ap p lica tio n of legal rules to fa c tu a l s itu a tio n s . T h e re a lis ts ’ a ttitu d e
prefers ru le an a ly sis plus a sociological a p p ro a c h . T h u s ac co rd in g to th e m : ‘Law is as law
d o e s’. A science o f law should be b u ilt u p o n a s tu d y o f th e law in a c tio n . T ru e id eas are
th o se t h a t w ork in p ra c tic e . Law is, essentially, ^W hat legal d e c isio n -m a k e rs d o \ It is n o t to be discovered j u s t in m ere rules. T h u s, a n o th e r n a m e for legal re a lists is th e te rm ‘rule
sc e p tic s’.
P e rh a p s th e m o st a u th o rita tiv e school of rule scep tics h as been th e A m eric an legal
realism m o v em en t. O liver W endell H olm es is one of th e em in en t figures in th is m o v em en t,
w ith his fa m o u s s ta te m e n t:
T h e life o f the law has n o t been logic: it has been experience. [ (H olm es, 1881), p p .l]
T h e A m eric an legal re alists have criticised legal positiv ism by p lead in g t h a t it:
1. F ails to co n sid er t h a t no tw o caaes can ever be iden tical;
2. F ails to assu m e t h a t th e id en tificatio n o f c o n c e p ts an d s itu a tio n s is n o n -d e d u ctiv e;
an d
3. F ails to recognise t h a t th e re c a n n o t be a n te c e d e n t legal ru les b in d in g on a ju d g e
(W a sse rstro m , 1961).
T h e legal re a lists p lead t h a t legal d ecisio n -m ak ers m ake decisions fo r a ra n g e of re aso n s
w hich c a n n o t b e ex p ressed o r a t le a st a re n o t clear on th e face of th e ju d g m e n t given. T h u s,
ac co rd in g to th e re a lists, it is p o in tle ss to claim t h a t a legal decision is re ach e d v ia th e
ex istin g rules; r a th e r, th e decision is m o re a reflection of th e d e c isio n -m a k e r’s biases. O nce
th e d ec isio n -m ak er h as reach ed a decision b ased on th e se biases, th e n he o r she is q u ite
likely to find a legal rule on w hich to ju stify th e decision.
O ne p o p u la r c o n te m p o ra ry an d m ore s o p h istic a te d view is t h a t o f R o n ald D w orkin,
Chapter 1. Introduction 10
T h e d ifference betw een legal p rin c ip le s an d legal rules is a logical d istin c tio n . B o th se ts p o in t to p a rticu la r d ec isio n s about legal obligation in p a rtic u la r c ir cu m sta n c es, but th ey d iffe r in the character o f the directio n th ey give. R u le s are applicable in an a ll-o r-n o th in g fa sh io n . I f the fa c ts a rule stip u la te s are given, th e n e ith e r the rule is valid, in w hich case the a n sw er it su p p lies m u s t be accepted, or it is not, in which case it co n trib u tes n o th in g to the d ecision.
[(D w orkin, 1967), p p .25]
He also a rg u es t h a t p rinciples an d policies, w hich (unlike rules) do n o t fu n c tio n in an
a ll-o r-n o th in g fash io n , m u st be w eighed an d b alan ced :
W h en p rin c ip le s in te rse c t ... o ne who m u s t resolve the c o n flic t has to take in to account the relative w eight o f each. T h is c a n n o t be, o f course, an exa ct m e a su re m en t, a n d the ju d g m e n t th a t a p a rtic u la r p rin c ip le o r p o licy is m ore im p o rta n t th a n a n o th er w ill o ften be a con tro versia l one. N eve rth e less, it is an integral p a rt o f the concept o f a p rin cip le th a t it has th is d im e n sio n , th a t it m a k es se n se to ask how im p o rta n t or how w eighty it is ... [(D w orkin, 1967), pp.27]
D w orkin believes t h a t every case h as a rig h t an sw er an d it is n o t alw ays n re ach e d by th e
ap p lic a tio n of rules. He also em p h asises t h a t in h a rd cases th e d ec isio n -m a k er sh o u ld weigh
an d b alan c e th e conflicting in te re sts t h a t are a t sta k e . B alan c in g o r w eighing in te re sts,
how ever, is an u n fo r tu n a te an d m isleading m e ta p h o r as it su g g ests th e ex isten c e o f an
o b je c tiv e scale o r c rite ria w here in p ra c tic e none m ay be fo u n d .
A s a m a tte r o f fa c t, th e d ev e lo p m e n t of a u to m a te d know ledge-based sy s te m s in law
could n o t be m o re d elica te . If we su p p o se t h a t th e legal p o sitiv ists are rig h t, th e n we have a
se ttle d b o d y o f rules. In fo rm a tio n tech n o lo g y h as long h a d th e to o ls to d e d u c e conclusions
based on th e se rules. If m ech an ical ju risp ru d e n c e w ere th e one an d only th e o ry to ta k e in to
a c c o u n t, th e n we could ap p ly lo g ic-p ro g ram m in g m e th o d s m ech an ically to th e exercise of m ak in g legal decisions.
Chapter 1. Introduction 11
we c a n n o t h ope to build legal know ledge-based sy stem s. Since each legal decision is m ad e
c o n siste n t w ith a series of fa c to rs n o t describ ed in th e ju d g m e n ts an d p e rh a p s n o t even
a c c o u n ta b le to m odelling, th e n we can never h ope to design a u to m a te d know ledge-based
sy stem s.
I t a p p e a rs t h a t in ju risp ru d e n c e th e re alistic an sw er lies b etw een th e tw o th e o re tic a l
e x tre m e s. Few w ould go along w ith th e su g g estio n in tro d u c e d by m ech an ical ju r is p r u
d ence t h a t all legal sy ste m s can be e n c a p su la te d in p ro d u c tio n rules. D e d u c tio n alone is
in a d e q u a te to describ e all a sp e c ts of legal decisio n -m ak in g . T h u s any sy ste m b ase d upon
d e d u c tiv e re a so n in g processes will be in co m p lete for ex p ressin g th e co m p lex ities p re se n t
in all legal d éc isio n -su p p o rt sy stem s.
Few w ould also a sse n t to th e id e a t h a t all decisions a re b ased on to ta lly in c o n siste n t
o r inaccessible c o n sid e ra tio n s an d b iases of legal d ec isio n -m ak ers. S urely so m e o f th e
decisions m ay b e am b ig u o u s, co m plex or illogical. B u t all of th e m ? T h is is a d o u b tfu l
o u tco m e, an d o ne t h a t m o st people w ould n o t ac cep t.
T h e e x tre m e view s are: [1] N o th in g in legal know ledge is rule-like (i,e, a ru le-scep tic
view ), a n d [2] E v e ry th in g re le v an t in legal know ledge is rule-like (i,e. a ru le-b ia sed view ).
B u t in te rm e d ia te view s re g a rd in g th is m a tte r seem to b e fa r m o re co m m o n . A c co rd in g to
c u rre n t th o u g h ts , rules a re c e n tra l in law b u t a re n o t th e exclusive m ed iu m for re p re se n tin g
legal know ledge. P e rh a p s th e n th e m a jo rity of cases sh o u ld be decided by so m e th in g n e a r
to a p o sitiv ist a p p ro a c h . B u t th is is a co n tro v e rsial an d difficult issue in th e a u to m a tio n o f
legal d éc isio n -su p p o rt sy stem s. T h is th esis ta k e s a m ore sim p le-m in d ed a p p ro a c h to th e
difficulties in bu ild in g legal d é c isio n -su p p o rt sy ste m s, as we sh all see la te r , b u t o ne t h a t
is te n a b le . I t p ay s a t le a st as m uch a tte n tio n to A I as to legal th e o re tic a l s ta n d p o in ts .
1.4
T he Legal D ecision-M aking P rocess
A fte r discu ssin g th e n a tu re o f law in th e lig h t o f th e tw o im p o r ta n t conflicting legal
th e o rie s, we com e to a n o th e r q u estio n o f ju risp ru d e n c e . T h e p re se n t q u e stio n is ‘How
Chapter 1. Introduction 12
It is n o t a t all u n u su al for th e law in ac tio n to ex h ib it little likeness to th e s tr u c tu r e
of rules fo u n d in p u blished p re se n ta tio n of s t a t u t e s a n d p rev io u sly -d ecid ed case re p o rts,
b u t w h a t is th e e x a c t n a tu r e o f th e p rocess t h a t gives rise to th is difference? It is in th e
ev e ry d ay b e h a v io u r o f legal p ra c titio n e rs t h a t th e legal sy ste m ta k e s s h a p e a n d g e ts th in g s
done. T h e a b s tr a c t an d o ften s h o rt s ta te m e n ts of le g isla tu re s are given fo rm an d p u rp o se
in th e choices legal p ra c titio n e rs m ake a b o u t th e reach a n d m e an in g o f th e ir id e a of th e
law.
T h e re is a s u b s ta n tia l a m o u n t o f lite ra tu re [e.g. (C ard o zo , 1921), (W ilson, 1982), (D yer
& F low ers, 1985), (W ah lg ren , 1990), (B ing, 1990), (W ah lg ren , 1992)] available on th e legal
d ec isio n -m ak in g process. T h e w rite rs o f th e se w orks have h ig h lig h ted a sig n ifican t n u m b er
o f elem e n ts gov ern in g th e legal decisio n -m ak in g process. F or ex a m p le , legal decision
m ak in g is to a g re a t e x te n t a d o m a in -d e p e n d e n t ta s k . T h a t is to say, th e legal decision
m ak in g pro cess an d its c o n s titu e n ts are influenced by th e s tr u c tu r e of th e a p p r o p ria te
su b s ta n tiv e law an d by th e m eth o d o lo g ical rules t h a t h av e evolved in its in te rp re ta tio n
an d use. T h u s, th e re is no u n ique legal d ecisio n -m ak in g m odel available fo r all a re a s of
law.
D e sp ite th is o b se rv a tio n , it is com m o n ly found t h a t a p r a c titio n e r ’s legal decision
m ak in g (reaso n in g ) process esta b lish e s a se t of fa c ts re p re se n tin g an a c tu a l case, an d
d e te rm in e s th e ca te g o ries w ith in th e fram ew o rk o f law in to w hich each o f th e fa c ts fits.
D ifferent k in d s o f a c tio n s m ay follow from th is c a te g o risa tio n . F o r exam ple:
• A clien t m ay be advised to ta k e a specific course o f ac tio n to ben efit fro m som e legal
rig h ts.
• S om e a rg u m e n t m ay be p u t fo rw ard before a c o u rt.
• A client m ay be advised to n e g o tia te a g reem en ts.
I t is n o t y e t clear in gen eral how a legal p ra c titio n e r a c tu a lly acco m p lish es th e processes
o f b rin g in g to g e th e r th e re le v an t se t o f fa c ts, a n d th e n selec tin g a re le v an t legal ca te g o ry ,
th o u g h som e p a s t stu d ie s have been m ad e to in v e stig a te th e se processes. O n e such s tu d y
Chapter 1. Introduction 13
Law School. S everal tech n iq u e s w ere used to ex a m in e his reaso n in g , including a protocol a nalysis^ in w hich th e p rofessor w as asked to solve p rev io u sly unseen cases a n d d escrib e a t each s te p th e fa c ts he w as con sid erin g an d th e goals to be fulfilled. T h e re searc h er
reco rd ed t h a t th e categorisation o f th e legal ac tio n a n d fa c t collection is a ‘relatively flu id p ro c e ss’. T h is p rocess n ev e rth eless allow s th e legal professio n al t o find th o s e rules an d fa c ts t h a t w ould help fram e th e d isp u te ac co rd in g to a co n v e n ie n t in te rp re ta tio n of th e
c lie n t’s story.
T h e re searc h er su m s u p t h a t an a u to m a te d ‘in te llig e n t’s y s te m for th is kind of a c tiv ity w ould need to form a d ju s ta b le m odels an d th eo rie s to clarify all know n fe a tu re s of th e
b e h a v io u r of th e p a rtie s, n o tice d iscrep an cies a n d g a p s in th e m odel for a d d itio n a l clarifi
c a tio n , a n d th e n find an d reason by a n a lo g y from sim ilar prev io u sly -d ecid ed case re p o rts.
In a n u tsh ell, th e se look like a sp ecificatio n s for th e a c tio n s o f a highly skilled h u m a n . B u t
th is e x p e rim e n t seem s to fail to pro v id e an y cle a r-c u t u n d e rs ta n d in g of th e finer d e ta ils of
how a legal p ra c titio n e r reasons.
N evertheless, th is is unlikely to u p se t A I re searc h ers excessively, becau se over larg e
n u m b e rs of o th e r specialised d o m ain s cog n itiv e sc ie n tists a n d p sy ch o lo g ists hav e n o t been
ab le to clarify ev e ry th in g a b o u t how e x p e rts reason a n d solve p ro b lem s. In fa c t, no
desig n ers o f know ledge-based sy ste m s d e m a n d o f th em selv es t h a t th e y sh o u ld re p lic a te
h u m an reaso n in g , w ith ev e ry th in g or a n y th in g t h a t it m ig h t be. All t h a t is d e m a n d e d is
t h a t som e a sp e c ts o f h u m an reaso n in g should be m odelled using sym bolic c o m p u ta tio n .
In ste a d of d e ta ile d re p lic atio n of h u m a n reaso n in g , th e aim is to e m b o d y in a c o m p u te r
sy ste m , w ith th e aid of sym bolic c o m p u ta tio n , th e co m p eten cies:
[a] to accom plish som e defined ta s k s to th e sam e level o f a d e q u a c y as an e x p e rt;
[b] to a c c o m m o d a te ju stific a tio n s for decisions m ad e.
D ifferent m e th o d s prevail by which a know ledge engineer^ can ex a m in e th e a c tio n o f an
technique for isolating the procedures used by a hum an problem -solver on the basis o f a record of
selected aspects o f his or her problem -solving behaviour for given specific problem s,
Chapter 1. Introduction 14
e x p e rt d u rin g th e ach iev em en t o f his ta sk s an d g e t him to g e n e ra te som e kind o f d e sc rip tio n
o f ex p e rt-lev el ac tiv ities. It m ay be im possible to ex a m in e d ire c tly th e p ro b lem -so lv in g
pro cess t h a t goes on in th e h ea d of an e x p e rt, b u t, by e x a m in a tio n of e x p e rt b e h a v io u r
w hen he o r she ask s q u estio n s a b o u t th e p ro b lem an d re ach e s co nclusions, it is possible
to c o n s tru c t a m odel o f th e reaso n in g process t h a t will d isp lay th e d esired b e h a v io u r
(W ielin g a & S chreiber, 1989).
M oreover, fo rm u la tio n an d a p p lic a tio n of law is a flexible p a r tn e rs h ip b etw e en legis
la to rs an d decisio n -m ak ers (e.g. ju d g e s, m a g is tra te s , re g is tra rs e tc .). In so m e cases, th e
leg islato rs play th e d o m in a n t role in th e p a r tn e rs h ip by sp ecify in g m o st o r all o f th e d e ta il
re le v an t to th e a p p lic a tio n o f th e law . In o th e r cases, th e leg islato rs specify a lim ited
a m o u n t o f d e ta il an d d eleg a te th e resp o n sib ility for th e re m a in in g d e ta il to th e decision
m ak ers. T h e se allow for a sign ifican t a m o u n t of ju d ic ia l d isc re tio n a ry behaviour on th e p a r t of legal d ecisio n -m ak ers in th e pro cess a t each decision p o in t.
Ju d ic ia l d iscre tio n is, for th e m o st p a r t, a m y ste ry - to th e g en e ral public, to th e com m u n ity o f law yers, to te a c h e rs o f law , an d to ju d g e s th em selv es (M iller, 1978). A m erican
J u d g e H a rry E d w a rd s referred to th is p h en o m en o n in th e follow ing te rm s :
O ne m ig h t expect th a t today, m ore than a h a lf-c e n tu ry a fte r the Legal R ea list m o v e m e n t, the p h e n o m e n o n o f the exercise o f ‘ju d ic ia l d isc r e tio n ’ w ould have been so ex h a u stiv ely stu d ied as to m e rit no m ore th a n a p a ssin g reference in prepa ra tio n fo r the e x a m in a tio n o f m ore co n tro ve rsia l m a tte rs. T h a t tu rn s ou t n o t to be true. N o t o n ly does the a c tiv ity o f ju d ic ia l law m a kin g rem a in m y ste rio u s, but a su rp risin g ly large n u m b e r o f people, both w ith in a n d w ith o u t the legal c o m m u n ity , q u estio n its leg itim a cy in a n y fo r m . [(E d w a rd s, 1984), p p .388]
W h ile d iscre tio n h as been th e s u b je c t o f th o ro u g h d iscu ssio n , th e re is really an in
significant a m o u n t o f research com bining th e A I an d law p o in ts of view c o n c ern in g how
d iscre tio n is a c tu a lly exercised by legal decisio n -m ak ers. T h e s tu d y o f th e n a tu r e of j u
dicial d isc re tio n , in th is p ersp ectiv e, m u st begin w ith its d e fin itio n . T h is is by no m ean s
C hapter 1. Introduction 15
d iffe ren t th in g s in different c o n te x ts. G allig an illu s tra te s th e difficulty by saying:
[T]he e x te n t to w hich officials, w h eth er th ey be ju d ic ia l or a d m in istra tiv e , m ake d ec isio n s in the absence o f p rev io u sly fixed, relatively clear, a n d b in d in g legal standards. F requently it appears th a t decisio n s are m ade a n d so p ow er exer cised according to co n sid era tio n s which vary fr o m one area o f sta te a c tiv ity to another, fr o m one type o f in s titu tio n to another, a n d even fr o m one se t o f c ir c u m sta n c e s to another, in the absence o f th a t p a tte rn o f n o rm a tiv e sta n d a rd s a n d p rin c ip le s w hich g en e ra lly is thought to be so central to the very n o tio n o f legal order. [(G alligan, 1986), p p .l]
T h e re fo re , ju d ic ia l d isc re tio n m ean s th e pow er th e law gives th e d ec isio n -m a k er to
choose a m o n g several a lte rn a tiv e s , each o f th e m being law ful. T h is defin itio n assum es,
o f course, t h a t th e d ec isio n -m a k er will n o t a c t m echanically, b u t will w eigh, reflect, gain
im p ressio n s, te s t, an d stu d y . H ow ever, th is self-conscious use of th e pow er o f th o u g h t
does n o t say w h a t th e re su lt o f ju d ic ia l d iscre tio n will be. It o nly p re scrib es how th e
d ec isio n -m a k er m u st a c t w ith in th e fram ew o rk o f his o r h er d isc re tio n . M oreover, ju d ic ia l
d isc re tio n , by d efin itio n , is n e ith e r an e m o tio n a l n o r a m e n ta l s ta te . It is, r a th e r, a legal
s itu a tio n in w hich th e d ec isio n -m a k er h a s th e lib e rty to choose a m o n g a n u m b e r o f o p tio n s.
T h u s, d iscre tio n assu m es a zone o f p ossibilities r a th e r th a n j u s t one p o in t. T h e zone of
law ful o p tio n s m ay be n a rro w , as w hen th e d ecisio n -m ak er is free to choose betw een only
tw o law ful a lte rn a tiv e s. O r th e ra n g e o f law ful o p tio n s m ay be co n sid erab le, as w hen th e
d ec isio n -m a k er faces m an y law ful a lte rn a tiv e s an d c o m b in a tio n s o f a lte rn a tiv e s . In th is
sense, legal so u rces d istin g u ish b etw een narrow an d broad d iscre tio n .
F u r th e r , as we know , legal d ec isio n -m a k ers c a n n o t m ak e law o u t o f a ir a n d th e y have
to ab id e by legal n o rm s. T h u s th e n a tu r a l q u estio n arises: W hat are the sources o f ju d ic ia l d isc re tio n ! T h e m ain so u rc es o f ju d ic ia l d iscre tio n are; s ta tu to ry n o rm s, p rin c ip le s and
case law (i.e. p reviously d ecided case d ecisions).
E v e ry s t a tu t o r y n o rm h a s a lin g u istic elem en t w hich is ex pressed in w ords. A s t a t u t e
m ay hav e a co m p lex s tr u c tu r e w ith n u m ero u s in te rtw in e d c o n d itio n a l clauses an d cross-
Chapter 1. Introduction 16
t h a t p a r t of th e leg islatio n . G iven a p a rtic u la r case, th e legal d ec isio n -m ak er in te rp re ts t h a t
case in th e lig h t o f th e s t a tu t e s in th e p a r tic u la r a r e a a n d uses th e freed o m in c o n s tru c tin g
ju s tific a tio n s fo r p o ssible decisions specific to t h a t case. In case law also, previously-
decided case decisions a re th e evidence o f th e law an d a p a r tic u la r o u tc o m e o f a d ju d ic a tio n .
T h e re aso n s fo r th e ex isten ce of ju d ic ia l d iscre tio n in case law are for th e m o st p a r t, and in
th e ir g en e ral sense, th e sa m e reaso n s t h a t p ro d u c e d iscre tio n in s ta t u to r y law - nam ely, th e
lack of c la rity in th e te rm s . T h e p roblem of p re c e d e n ts (i.e. previo u sly -d ecid ed cases) is
n o t ju s t in th e w o rd s th em selv es, b u t also th e co n c ep ts t h a t th e d ec isio n -m a k er w a n ts th e
w ords to c o m m u n ic a te to th e re ad er. T h e se co n c ep ts have clear im p lic a tio n s in o n e ty p e of
case, y e t th e y m a y lead to d o u b ts a b o u t th e ir im p lica tio n in a n o th e r ty p e o f case. Indeed,
case law , like s ta t u t o r y law , reflects principles, policies, a n d s ta n d a r d s . T h e u n c e rta in ty
t h a t ex ists in th e s t a tu to r y law also ex ists in case law , an d w ith g re a te r force, precisely
b ecau se th e re is no b in d in g te x t to guide th e d elin ea tio n o f th e b o rd e rs o f th e co n c ep ts.
P rin cip les a re rules o f b eh a v io u r t h a t are b ased on eth ica l values such as fairness,
ju stic e , a n d m o rals. P rin c ip le s serve v ario u s fu n c tio n s in th e law; th e d e te rm in a tio n as to
th e s itu a tio n s to w hich th e p rinciples will ap p ly is in th e h a n d s of th e d ecisio n -m ak er.
W e can say t h a t in som e sense d iscre tio n is a m a n ife sta tio n o f a m b ig u ity o r c o n te x t-
d ep e n d en ce o f w ords. A h u m a n e x p e rt can d e te rm in e w h e th e r a w ord h a s a n u m b e r of
m ean in g s. T h e re fo re it is re aso n ab le to a rg u e t h a t th e know ledge en g in eer sh o u ld ta k e
ac c o u n t o f th e se v ary in g m ean in g s in th e know ledge base design. T h is can be d o n e by
fra m in g a lte r n a tiv e rules from w hich th e user can choose, d e p e n d in g on th e u s e r’s opinion
re g a rd in g th e c o n te x t o f th e s itu a tio n .
T h is is n o t to say t h a t m odelling legal d ec isio n -m a k in g is so easy, n o r indeed to a rg u e
t h a t legal know led g e-b ased sy ste m s are ap p licab le in all cases. A t th e sam e tim e , ju d icial
d iscre tio n is an issue lu rk in g b eh in d th e design o f any legal d éc isio n -su p p o rt s y ste m . Even
if one ign o res it, o ne is in effect m ak in g a choice a b o u t how th e re su ltin g sy ste m s h an d le
discre tio n .
It is o fte n b o th difficult an d u n d esira b le to m ak e a legal ru le precise to th e e x te n t
Chapter 1. Introduction 17
are so clear t h a t th e y can be used like an on-ofF sw itch . T h e p erso n using th e rule c a n n o t
alw ays say w ith c e rta in ty ^yes, it a p p lie s’or Ht does n o t apply h e r e ’. T h is m e a n s t h a t legal p ra c titio n e rs m u st o ften re s o rt to th e ir own ju d g m e n t in d eciding w h e th e r a ru le ap p lies or
n o t. In a d d itio n , legal decisio n -m ak ers are a s su sce p tib le as an y o n e else to new or ch a n g in g
social a ttitu d e s to w a rd th e a u th o rity of rules. B ecause o f th e se co n sid e ra tio n s, n o b o d y
h a s given an y convincing sim ple s tra ig h tfo rw a rd m e th o d o f d e te rm in in g u n d e r a r b itr a r y
c o n d itio n s w h e th e r o r n o t a rule sho u ld apply.
In th in k in g a b o u t how th e law can b e st serve its p u rp o se s, legal d éc isio n -su p p o rt
s y ste m s desig n ers fre q u e n tly ru n in to w h a t m ay be d esc rib ed ro u g h ly as a conflict b etw een
p re ssu re to t r e a t rules as in a sim ple e x p e rt sy ste m , w here th e re is no c o n te x t in which
th e rules are in te rp re te d (i.e. th e rules th em selv es are th e c o n te x t), a n d p re ssu re to give
so m eone d iscre tio n in in te rp re ta tio n . In d esigning a ty p ic a l legal d é c isio n -su p p o rt sy stem
one h a s to give c e rta in a m o u n t o f d isc re tio n a ry pow er to its user. T h e w ay in w hich we do th is in th e sy stem A SH SD m ay look a little artificial or re s tric te d by c o m p a riso n w ith
th e free-ran g in g discussion above, b u t we tr y to com ply w ith as m uch of th e s p irit o f th e
discussion as is allow ed by th e k n o w led g e -re p resen ta tio n fo rm a ts (rules a n d cases) and
th e ir s ta n d a r d to o ls o f re aso n in g t h a t are available fro m c u rre n t c o m p u te r science. In
o u r ru le-b ase, for ex am p le, th e rules w ork in th e u su al sense of c o m p u te r science o r logic.
‘D is c re tio n ’ is so m e th in g for th e user to consider a t ju s t tw o sta g e s. F irstly , w h en A SH SD
en q u ire s for re le v an t fa c ts, th e user decides w h a t is re lev an t o r tru e , a n d p re se n ts th is
as in p u t. Secondly, a fte r A S H S D p ro d u c es o u tp u t from its ru le-b ased se c tio n , th e user
is free to decide if a su g g ested conclusion is a c c e p ta b le o r if som e e x te rn a l c o n sid e ra tio n
re q u ires it to be s e t aside. T h e sam e in te rp re ta tio n applies to A S H S D ’s ca se-b a se d side.
T h e sy ste m selects th e m o st sim ilar cases w ith re sp e c t to th e new case by a s ta n d a r d AI
a p p ro a c h , a n d th e n it is u p to th e user to in te rp re t th e decision p a r ts of th o s e cases in th e
lig h t o f th e p re se n t case.
W e do n o t believe t h a t ju d ic ia l d isc re tio n a ry pow er can be a u to m a te d . T h e m ain re aso n s are: [1] It is difficult to re p lic ate to ta lly a m u ltite x tu re d p ro cess such as legal
d ec isio n -m a k in g , an d [2] Legal decisio n -m ak in g is h u m a n istic r a th e r th a n m ech a n istic.
T h erefo re, m echanised d isc re tio n a ry pow er seem s possible only w ith in re s tric te d lim its.
