CLASSIFICATION OF MODALITY FUNCTION AND ITS APPLICATION 
TO JAPANESE LANGUAGE ANALYSIS 
Shozo NArro, Akira SHIMAZU, and Hirosato NOMURA 
Musashino Electrical Communication Laboratories, N.T.T. 
3-9-11, Midori-cho, Musashino-shi, Tokyo, 180, Japan 
Abstract 
This paper proposes an analysis method for 
Japanese modality. In this purpose, meaning of 
Japanese modality is classified into four semantic 
categories and the role of it is formalized into five 
modality functions. Based on these formalizations, 
information and constraints to be applied to the 
modality analysis procedure are specified. Then by 
combining these investigations with case analysis, the 
analysis method is proposed. This analysis method has 
been applied to Japanese analysis for machine 
translation. 
1. Introduction 
Since the meaning of a sentence consists of both 
proposition and rnodality, TM analysis of modality is as 
indispensable as that of proposition for natural 
language understanding and machine translation. 
However studies on natural language analysis have 
mainly concerned with the propositional part, and 
algorithms for analyzing rnodality have not yet been 
sufficiently developed. The aim of this paper is to 
clarify the function of modality and to propose a method 
for analyzing the modality in Japanese sentences. 
Structure of a Japanese complex sentence can be 
formalized roughly by iterative concatenation of simple 
sentences. The simple sentence consists of cases and a 
predicate. The cases have surface representations of 
noun phrases or adverb phrases while the predicate has 
that of verb or adjective or adjective verb. A noun 
phrase is defined as the recursive concatenation of noun 
phrase or that of embedded sentence. We have 
employed '.he case structure as a basic meaning 
structure for a simple sentence, and extended it to 
retain the construction of complex sentences 
mentioned. Modaiity is additive information 
represented by auxiliary words such as modal particles, 
ending particles, and auxiliary verbs and sentence 
adverbs. The modal particle is attached to a noun 
phrase or a sentence element while the ending particle 
is attached to the enci position of a sentence. The 
auxiliary verb !mmediately follows a verb phrase. 
Modality represented in such grammatically different 
context is incorporated into the case structure, and the 
result construction is named as an extended case 
structure Ivl which enable us to propose a uniform 
framework for analyzing both proposition and modality. 
In this paper, we first classify modality into four 
semantic categories. Second, we define five modality 
functions using the logical representation of the 
meaning and then characterize the roles of each 
function. Third, we specify hard problems to be 
resolved in modality analysis. Fourth, we list the 
information and constraints to be considered in 
establishing the procedure of modality analysis. Then, 
we propose a method for analyzing modality based on 
these investigations. Finally, we exemplify the 
analysis by showing translations from Japanese into 
English. The method has been used to analyze 
Japanese sentences in a machine translation system. 17~ 
2, Classification of modality 
Traditionally, modality has been classified into 
three categories, i.e. tense, aspect and modal. :0-! This 
classification is not sufficient for the deep analysis of 
the meaning structure of a sentence, however, because 
it does not account for the role of Japanese modal 
particles. Adding this role, we expand this 
classification into four categories, namely tense, aspect, 
modal and implicature shown in Table 1. Each category 
can be further classified into subcategories, and those 
are shown in Table 2 through Table 5 (Each table gives 
both examples of Japanese expressions and their 
English equivalents). Our classification of modality 
features two characteristics concerning the assignment 
of adverbs and modal particles : 
(1) Among the two kinds of adverbs, namely 
sentence adverbs and case adverbs, we assign 
sentence adverbs to modality while case 
adverbs to case relations. Sentence adverbs are 
classified into three subcategories in the modal 
Table I. Four categories of Modalitv 
Categories Meaning 
Tense i temporal view of a event relative to the speaking 
time 
state of events viewed from time progress at a Aspect sl:ecifled time point 
Modal speaker's or agent's attitude or judgement to the occurrence of events 
implicative meaning represented by modal I mplicature particles 
27 
category : \[evaluation\], \[judgement\] and 
\[statement-manner\]. (Traditionally, all 
adverbs are assigned to modality.) 
(2) Modal particles are assigned to modality and 
are classified into a distinct category, 
implicature (They have been usually discussed 
separately from modality) ~41. 
3. Modality functions and their roles 
By employing logical expression as the 
representation of the meaning structure, we can define 
modality functions as operations on logical expressions 
in strict terms. In the past, studies on modality 
analysis in logical framework treated each type of 
modality individually. IsH6\] Here, we deal with it, 
however, as a whole and combine it with the 
propositional structure so that we can provide a 
uniform framework for the representation and the 
analysis of the meaning structure. In this purpose we 
employ the higher order modal logic formalism. It1 
In this regard, we introduce the five types of 
modality functions, which add or modify modality : 
{I) addition of the modality operator. 
{2) surface modification of the case structure. 
(3) semantic modification of the case structure. 
(4) determination of the scope of negation, 
(5) addition of the implicative meaning. 
We will now discuss the roles of each type of 
modality function respectively by indicating their 
logical representations. 
3.1 Addition of the modality operator 
This is the most fundamental function and it simply 
adds the modality meaning to the propositional 
meaning. In the following two sentences, (sl) has no 
modality while (s2) has modality : 
(sl) Hiroko ga hashiru. (Hiroko runs.) 
Run(Hiroko), 
"~ In the ~'ollowing. each example sentence is succeeded by an English translation and a logical representation .f the meaning 
Table 3. Tense 
Japanese Meaning ,expression 
Past ta 
Non-past ru 
English expression 
-ed (past tense) 
present tense, or future tense 
(S2) Hiroko ga hashit teiru. (Hiroko is runnzng.) 
\[durative\] Run(Hiroko). 
(s2) is obtained by adding the durative aspect operator 
"teiru (progressive)" to (sl) c'~. 
3.2 Surface modification of the case structure 
This does not change the logical meaning structure 
even when the surface structure is modified. However 
higher level information such as focus and attention is 
sometimes added. 
The passive auxiliary verb "reru" or "rareru" can 
modify the surface case structure without changing the 
logical meaning structure. The focus is usually placed 
on the ~ubject part of the passive sentence, as follows : 
(s3) Hiroko ga yasai we taberu. 
(Hzroko eats vegetables.}, 
3x(Vegetable(x)AEat(Hiroko,x)), 
(s4) Yasai ga Hiroko ni tabe rareru. 
(Vegetables are eaten by Hzroko.), 
3x((Vegetable(x)AEat(Hiroko,x))A{Focus(x)}), 
where the predicate Focus(x) signifies that the focus is 
placed on the argument x. 
3.3 Semantic modification of the case structure 
This results in one of the two alternatives : 
(a) one argument is added to the original predicate, 
(b:, a higher order predicate is introduced. 
Both changes are equivalent in meaning but the way of 
representing the change is different. 
The following fragments of modality cause the 
semantic modification of the case structure : 
I) causative Cseru" or "saseru"), 
2J affected-passive Creru" or "rareru"), 
3) hope Ctehoshii'" and "temoraitai"), 
4~ request ,~"temorau"), 
5) benefit ("tekureru .... teageru", and "teyaru"). 
Tabie 2. Aspect ( tdou means concatenation, and d~ mtans empty character.) 
Meaning Japanese expressi.n ~ Er~glish expression 
Inchoative 
• \] ust-bei'or e- incJ'd~a tive 
haji mf~ru, - kakeru. ~dasu 
I .... 
(-hajimeru, *-kakc:u ~dasuJ (tokoro, bakari;, u~.osuru, tokoro, bakari 
\[inchoa=ive verhl begin, commence, start: 'set about -. -ing'. fai to. 
c~me to, take to 
I be go ng to. be go=ng to-*-\[inchoative verbl 
just have \[inchoative verbi-en Just-afterdnchoative i--ha'line. ~kake. ~dashi#. ta - (tokoro, hakari) 
Durative ~teiru, ~ e.ru, ~tsuLukert:, ~tesrutokoro, 11dut-:ttive verb~ go on, "keep (onJ *- -ing'. continue, remain, teik 
u. ~ t~utsuaru I ver.h + on and on, over and over, (repetition of verb) 
Iterative -teiru, ~teoru, -tsuzukeru t verb reDresnntin~ repetition of action (durative verbl 
Terminative 
J ust-before-termin:, te 
--owaru, --oeru, -teshimau 
(-owaru, -oeru, -teshimau) - (tokoro, bakarD 
(-owat, -oe, ~teshimat, d#). ta- (tokoro, bakari) 
! ~owat, -oe, --te.~himat, ~b) • telru 
J ust-after-terminative 
Terminative- qtate 
g r {, I I 
{affected verbl cease, finish, leave off, discontinue, 'stop d- -ing' 
be going t.o -¢- { affected verbl 
\[ just have {affected verbl-en 
i huve-,~..en 
28 
For an example, the causative auxiliary verb "seru" 
or %aseru" results in (a) the addition of the causative 
agent, or (b) the introduction of a second-order 
predicate CAUSE(x,y) in which argument x represents 
the causative agent and argument y represents a 
predicate, as follows : 
(s5) Taro ga Hiroko ni yasai wo tabe saseru. 
(Taro makes Hiroko eat vegetables.) 
(a)3x(Vegetable(x)/',Eat'(Hiroko,x,Taro)), or 
(b)3x(Vegetable(x)ACAUSE(Taro, 
Eat(Hiroko,x))), 
where the predicate Eat'(x, y, z) is obtained by adding 
the argument z corresponding to the causative agent to 
the predicate Eat{x, y) in (s3). 
For another example, though the auxiliary verb 
"reru" or "rareru" has five meanings, namely, 
"passive", "affected-passive", "ability", "respective" and 
"spontaneity", "passive" meaning among them falls 
into type (2) above while "affected-passive" meaning 
falls into this type and the affected-agent is added : 
Is6) Taro ga Hiroko ai yasai wo tabe rareru. 
(Taro was'adversely) affected 
by Hiroko's eating vegetables.) 
(a) 3x(Vegetable( x }/xEat"(Hiroko.x.Ta ro)), or 
(b)3x(Vegetable(x)AAFFECTED-PASSIVE 
(Taro,Eat(Hiroko,x))). 
3.4 Determination of the scope of negation 
Table 5. Implicature 
Meaning 
Limitation 
Degree 
Extreme-example 
Japanese expression 
shika, kin, dake, bakari, 
made, kurai 
dake, bakari, hodo, kurai 
sac, demo, datte, made 
English 
expression 
only 
as, about 
even 
Stress sae, ha, too, koso even 
Example demo, nado, nari for example 
Parallel yara, ya, mo and 
Addition I sae, made also 
Selection earl, ka or 
Uncertainty ~ara, ka some 
Distinction ha us for 
The modal particle "wa" determines the role of the 
auxiliary verb "nai" as a partial negation while the case 
particle "ga" determines it as total negation. In the 
following sentences, (s9) is partially negated while (s8) 
is totally negated : 
(s7)Zen'in ga kuru. \[Everybody comes.) 
vx(S(x)3Come(x)), 
(s8)Zen'in ga ko nai. (Nobody comes.) 
vx(S(x) ~ ~ Come(x)), 
(sg)Zen'in wa ko nai. (Not everybody comes.) 
-- vx(S(x~ ~Come(x)), 
where the predicate S(x) denotes "zen'in \[all the 
persons)". 
Table4 Medal 
Meaning I .Japanese expression English expression Meaning .Japanese expression 
Negation nai, zu not. never temiru 
Ability dekiru, uru, reru. rareru can. he able to. be possible 
Spontaneity ~ reru, rareru heccme to 
nakerebanaranai, must. should, Obligatoriness m~banaranai, bekida have to 
Necessity ! hitsuyougaaru he necessary 
lnevitabdity canno! help ...ing zaruwoenai, hokanai 
hougayoi. 
I nikoshitakotohana 
I saesurebavoi. " 
Try 
!Command 
Question 
nasal, \[imperative 
form of verbl 
ka 
English expression 
try 
\[imperative form of verbl 
\[ interrogative 
transformationl 
Request tekure, retai please ... (to 2nd personl 
Permission teyoi may. can 
Invitation Let's, Shall we U 
I sere. saseru 
Preference may well Causation 
Sufficiency bajuubunda, bayoi he enough Request " (to 3rd personl temorau 
Stress noda, nodearu do Passive reru. rareru 
Certain-presumption !hazuda. nichigainai must 
1-ncertain-conclusion vouda, souda he likely 
:'resumption rashii ~eem 
Guess u, you. darou, think toom(~wareru 
Uncertain-guess kameshirenai may 
Hearsay soucta I l hear that ! I'. is said that ... 
int.ention , u, :sumortda. utoshiteiru be going to. will. 
Plan voteidearu, have a plan to kotonishiteiru 
tai. tehoshii, hope, want Hope temoraitai I 
make (a person, ',, do 
get (a person~ to do. have 
{passive 
transformationl 
\[affected-passive • ~.ffected-pass~ve reru. rareru transformationr 
13enefit tekureru ! have la person~ to do 
desu, masu Politeness 
Respect 
Evaluationl 
reru. rareru 
saiwalnimo, 
zannennakotoni. 
odoroitakotoni .... 
\[Judgement\] osoraku, kanarazu, akirakani, omouni .... 
genmitsuniitte, 
(Statement-mannerJ yousuruni, 
hontounotokoro .... 
fortunately, 
regretably, 
to our surprise .... 
perhaps, surely, 
evidently, 
in my opinion .... 
in short. 
strictly speaking, 
in all fairness .... 
29 
3.5 Addition of the implicative meaning 
An extra logical formula corresponding to the 
implicative meaning is added by modal particles such 
as %hika (onlyf and ~dake (only)" as in : 
(sl0) Hiroko wa yasai shika tabe nai. 
(Hiroko eats nothing but vegetables.) 
~x(Vegetable(x)AEat(Hiroko,x)) 
Avx( -~Vegetable(x)~ -, Eat(Hiroko,x)). 
4, Problems in modality analysis 
4.1 Ambiguity of the modality meaning 
(I) Ambiguity due to multiple meaning 
The aspect expression "teiru" has three different 
kinds of meanings, that is, the "durative", "iterative" or 
"terminative-state" aspects. For example, 
(sll)Hiroko ga yasai wo tabe teiru. 
(Hiroko {is eating, eats and eats. has eatenl 
vegetables.) 
3x(Vegetable(x) 
/x{\[durative\],\[iterative\],\[ termina tire-state\]} 
Eat(Hiroko, x)). 
(21 Ambiguity concerned with case structure 
As stated in Section 3.3 above, the auxiliary verb 
"reru" or "rareru" has five meanings, and, among them, 
the "passive" and "affected-passive" meanings result in 
modification to the case structure. Therefore, 
disambiguation of the meaning of ~reru" or "rareru" 
has a close relationship to analysis of the propositional 
meaning. 
Moreover the auxiliary verb "rareru" in the 
following {s12) means "respect", and that in (s13) 
means "passive", respectively. Whereas, both 
expressions are same except the additional meaning of 
respect and focus, as follows : 
(sl2)Sensei ga yasai wo tabe rareru. 
(The teacher eats vegetables.) 
3x(Vegetable(x)/kEat{the-Teacher,x)) 
ARespect(Speaker,the-Teacher), 
(sl3)Yasai ga sensei ni tabe rareru. 
(Vegetables are eaten by the Teacher.; 
3x((Vegetable(x)/xEat(the-Teacher,x)) 
/x{Focus(x)}), 
where the predicate Respect{x,y) means that x respects 
y. 
4.2 Scope of modality 
Even if',he main clause has a negative expression, it 
does not always mean that the main clause is negated. 
Sometimes the subordinate clause is negated. We call 
this phenomenon the transfer of negation. 
Furthermore even if rnodality involved is not negation, 
it sometimes affects the subordinate clause. 
Although the main clause in the following (s14) is 
not usually negated, the subordinate clause is. 
Nevertheless, the tense information in the main clause 
has an effect on the subordinate clause. (s14) is 
constructed from (s14-1) and (s14-2) by a simple 
coordinate conjunction, however the corresponding 
logical expression is not a simple concatenation of each 
logical expression : 
(sl4)Taro wa hige wo sot be kaisha e ika nakat ta. 
(Taro went to the company without shaving.) 
\[past\] -- Shave(Taro,beard) 
A{past\]Go(Taro,Company), 
(sl4-1)Taro wa hige wo soru. (Taro shaves beard. 
Shave(Taro, beard), 
(sl4-2)Taro wa kaisha e ika nakat ta. 
(Taro did not go to the company.) 
\[past\]-- Go(Taro, Company). 
(sS) and (s9) also exemplify the problem for determining 
the scope of negation. 
4.3 Treatment of implicative meaning 
Modal particles such as "shika (only)" and "sae 
(even)" convey individual implicative meaning. In 
order to obtain the logical representation of the 
implicative meaning, we are forced to provide different 
formulae expressive of the each meaning of each modal 
particle. For example, if we assign the formula (fl) to 
the expression %hika...nai" which consists of the modal 
particle "shika" and auxiliary verb "nai", we get the 
logical representation of the sentence Is10) by the 
procedure of ~,-calculus shown in Fig. I. 
(fl)"shika...nai'-- ~LP,kQkR(3x(P(x)ARQ(x)) 
AVx(-,P(x)~R--Q(x))). 
As can be seen from the example, the logical formula for 
the implicative meaning is very individual. This 
concludes that specification of it for each meaning is 
very complicated and hard, and a more effective method 
is therefore needed. 
5. Information and constraints on modality 
analysis 
(1) l,exicai meaning 
The lexical meaning assigned to each modality 
expression is the most fundamental information. So we 
need to specify and provide it. For example, the lexical 
meaning of the auxiliary verb "ta" is generally the 
"past" tense as in : 
(slS)Hiroko ga hashit ta. (Hiroko ran.) 
\[past\]Run(H.;roko). 
(2) Predicate features 
Predicate features are available for disambiguating 
the meaning of modality. 
Though the aspect auxiliary verb "teiru" is 
ambiguous in meaning, we can resolve it by using 
predicate features such as the "stative", "continuous" 
and "spontaneous", as in : 
30 
(sl6)Hiroko ga hashit teiru. (Hiroko is running.) 
\[durative\]Run(Hiroko), 
(sl7)Akaxi ga kie teiru. (The light is turned off.) 
\[terminative-state\]Turn-off(the-Light), 
where the verb mnashiru (run)" has the "continuous" 
feature while the verb "kieru (turn off)" has the 
"spontaneous" feature. The aspect expression "teiru" 
following a "continuous" verb usually means the 
"durative" aspect, and "teiru" following a 
"spontaneous" verb usually means the "terminative- 
state" aspect. 
The "spontaneity" meaning of "reru" or "rareru" is 
realized only when it follows the verbs having 
spontaneity feature such as "omoidasu (remember)" and 
"anjiru (care)". 
(3) Noun phrases and adverbs 
Some kinds of noun phrases, adverbs, and their 
semantic categories can be utilized to disambiguate the 
meaning of modality, when they occur simultaneously 
with it. 
(sl8)Hiroko ga yasai wo i.m.a tabe teiru, 
(Hiroko is eating vegetables now.) 
3x(Vegetable(x) 
A\[durative\]Eat"(Hiroko,x,now)). 
"Hiroko"-- ,\PP.\QQ( HirokoJ 
"yasai"-- .\PP.\xVegetable(x} 
"shika...n a\]"-- ,~.P,\Q,k R( qx( P( x )Zk RQ( x )I 
AVx~ ~PfxJDR~QIxJJ) 
"taberu"-- .~ySzEatfz,yJ 
"yasai shlka._ nai" 
-- ),PP.kx Vegetable( x hkR.\S~T( 3ul R(uJATS(uJ~ 
AVu( ~ R(ul DT ~ S(u))t 
-- SR.\SLT( -3u(R(uJATS( u))AVu( ", R{ u~ DT ~ S(u)~) 
.\ x Vegetable( x; 
-- .\ShT( B u(.kx Vegetable( x J( u J/x.TS(u)) 
AVu( ~ .\x Vegetable( x }( u~ ~T ~ S( u J)) 
--,\S~T("\]u(Vegetable(u~ATS(u) JAVut -~ Vegetable(u# DT ~ S( u~)~ 
"yasai shika tabe nai" 
-- S$},Tf 3u(Vegetabie(u)ATS(u)) 
AVu( "- Vegetable(u) DT " S( ul)lAyAzEat(z.yl 
--.~T( 3tu Vegetable( u)AT,\y,kzEat(z,yi( u D 
AVu( ~ Vegetable(u} DT -~ ~ykzEat(z,y fl u)}) 
--.kTf3u(Vegetable(u)AT .\zEat(z.u)l 
AVu( ~ Vegetable(u)DT ~ .kzEatiz. u:)) 
"Hiroko wa yasai shika tabe hal" 
--.\PP.~QQ(H iroke JAT( qu( Vegetable4 uJ/\T,kzEat(z.u J) 
,~,Vu, "- Vegetable( uJ DT ~ .kzEat(z.uJD 
--,kT( =l,J(Vegetable(u}/kTSzEat(z,uU 
AVu( -, Vegetable(ul S,T -, .\zEat( z,unJhPP(ilirokoj 
--( 3u( Vegetable( ul/, kPP(HirokoJkzEat(z.u)} 
/~Vu( ~ Vegetable(ul D.\PPf H irokoJ ~ ,t, zF, a'(z,ul)) 
--( 3u(Vegetabie(u~A ~.zEat(z.ui(Hiroko)) 
AVu( -- Vegetable( a J D " kzEat( z,u}( I I irokol)J 
~(~u(Vegetable(ut/k Eat( I l iroko,,,)J ' 
AVu( ~ Vegetable(u) D "~ Eat( Hiroko,ulD 
Fig. 1. Logical analysis of the setltence (sl0) 
(s19)Hiroko ga yasai wo sudeni tabe teiru. 
(Hiroko has already eaten vegetable.) 
3x(Vegetable(x)A\[terminative-state\] 
Eat'(Hiroko,x,already)). 
In the above examples, the adverb "ima (now)" is 
concerned with the "durative" aspect, while "sudeni 
(already)" is concerned with the "terminative-state" 
aspect. The argument z of the predicate Eat"'(x,y,z) 
represents time information. 
(4) Modal particles 
As discussed in Section 3 (sentences (s8) and (s9)), 
the modal particle "wa" occurring simultaneously with 
negation suggests partial negation. 
(5) Conjunctive relations 
Conjunctive relations are related to the scope of 
modality. If the subordinate clause has the following 
conjunctive relations represented by 
(a) the conjunctive particle "te", or 
(b) a relative noun such as "toki (trine)" or "mae 
(before)" modified by embedded sentences, 
the transfer of negation can be predicted as in sentence 
(s14). Otherwise, the transfer will never occurs as 
follows : 
(s20)Taro wa hige wo sot ta ga 
kaisha e ika nakat ta. 
(Though Taro shaved his beard, 
he did not go to the company.) 
\[past\]Shave(Taro,beard) 
A\[ past\] ~ Go(Taro,Company). 
(6) Semantic relations between the subordinate 
clause and the main clause 
This information is used to determine the scope of 
negation in the main clause. In the subordinate clause 
with the conjunctive particle "te", if the event expressed 
by it is subsidiary for the occurrence of the event in the 
main clause, the transfer of negation can occur. On the 
other hand, if the subordinate event is indispensable to 
the occurrence of the main event, the transfer never 
occurs. For example, in (s14), since the modifier event 
Shave(Taro,beard) is a subsidiary event for the 
occurrence of the main event Go(Taro,Company), the 
transfer of negation is possible. In the following 
sentence (s21), however, since the event Go(Taro, 
Washington) is an indispensable event for the 
occurrnece of the main event See(Taro,White-House), 
the transfer ts impossible : 
(s21)Taro wa Washington e it te 
White House wo mi nakat ta. 
(Taro did not see the White House 
when he went to Washington.) 
\[past\]Go(Taro,Washington) 
A\[past\] -, See(Taro,the-White-House). 
31 
6. Modality analysis 
6.1 Strategy of the modality analysis 
Considering the five modality functions defined in 
Section 3, it is apparent that the logical analysis 
method alone is not effective for modality analysis. 
There are three reasons for this : 
(1) Reference to other expressions is needed to 
resolve the ambiguity of the modality function, 
(2) Structural modification occurs when the scope 
of negation is transferred, 
(3) Analysis of the implicative meaning sometimes 
cause the change of logical expression. 
There remains, however, the problem of taking the 
individuality of each modality into account. For some 
kinds of modality, the result of the case analysis or the 
conjunctive analysis is used to analyze it. These 
represent the reasons why we propose an analysis 
method consisting of the following three modules 
combined with the case analysis and the conjunctive 
analysis : 
( 1)pre-case-analysis : 
activated before the case analysis, 
(2)post-case-analysis : 
activated after the case analysis, 
(3)post-conjunctive-analysis : 
activated after the conjunctive analysis. 
The relationship of these three modules to the case 
analysis and the conjunctive analysis is shown in Fig. 
2. 
ore-case.analysis : 
I surface and semantic modification of the case frame 
f \[ case analysis \] 
post-case-analysis : \[ 
(I} disambiguation of the modality function \[ E 
(2) determination of the scop~ of negation \[ 
(31 addition of the implicative meaning 
I c°njunctive analysis I 
post-conju nctive-an alysis : 
I determinatioa of the scope of the modality 
in the main clause 
Fig. 2. Framework of the m,dality analysis 
6.2 Algorithms of each sub-analysis 
(1) Pre-case-analysis 
The modality whose analysis requires only lexical 
meaning or which causes a change of the case structure 
is analysed at this stage. The case frame to be assigned 
to the predicate is mcdified by utilizing the result of 
this analysis before starting the case analysis. As for 
the semantically ambiguous auxiliary verb "reru" or 
"rareru", its role is only predicted at this stage, because 
it is also concerned with the modification of the case 
structure. After case analysis, the plausibility of the 
prediction is evaluated. The modification of the case 
frame is as follows : 
(a) For the "passive" meaning of "reru" or "raxeru" 
(which causes a surface change to the case 
structure as mentioned in Section 3.2), the 
object case of the original case frame is changed 
into the surface subjective case, and the modality 
category "passive" is assigned to the meaning 
structure. If two object cases exist, two possible 
modifications are performed. 
(b) With the modality causing a semantic change to 
the case structure (for the modality function 
stated in Section 3.3), a new case is added as 
follows: 
(bl)For the "causative", "affected-passive", 
"hope" or "request" meaning : A new agent (e.g. 
causative-agent / affected-agent) is added, and 
the case particle of the original subjective case is 
changed from "ga" to "hi", 
(b2)With the "benefit" meaning : A beneficiary 
case is added. The case particle in this case is 
"hi". 
Also the modality category corresponding to 
each meaning (e.g. "causative", "affected- 
passive") is assigned to the meaning structure. 
(2) Post-case-analysis 
The modality whose analysis requires case structure 
information is analyzed at this stage. This module 
determines the function of the modality as follows : 
(a) \[f the category of the modality expression is 
unique, this category is assigned to the meaning 
:;tructure. 
(b) if a daemon (a procedure to resolve ambiguities 
by using heuristics) is attached to the rnodality 
expression, it performs the three tasks : 
(bl) disambignating the function of the modality 
expression, 
(b2) detcrmining the scope, 
(b3) adding the implicative meaning. 
The daemon utilizes the information mentioned in (I) - 
(4) in Sect, ion 5. For example, a daemon attached to the 
aspect expression "teiru" works as shown in Fig. 3. 
(3) Post-conjunctive-analysis 
Following the conjunctive analysis between the 
subordinate clause and the main clause, this module is 
activated to determine whether the modality in the 
main clause also operates on the subordinate clause. 
This module utilizes heuristics consisted of all of the 
32 
Is there a case element (noun phrase or adverb) suggesting "terminative-state" or "durative" or "iterative" aspect? \[ 
no 
Does "teiru" follow 
"reru" or ~rarerxl'~. 
yes ~, 
I terminative- state aspect 
~ yes 
\[ terminative-state \[ \[ or durative 
~no \[ or iterative aspect 
I Is the feature of the predicate "spontaneous~ I 
no~ , ~y. 
I state I 
Fig. 3. Daemon which disambiguates the meaning of the aspect expression "teiru" 
information presented in Section 5. An example of 
heuristics which analyze the scope of the auxiliary verb 
"ta" is shown in Fig. 4. 
For negation in the main clause, the transfer of 
negation is considered. Whether or not the modifier 
event is subsidiary for the occurence of the main event 
is tested using the semantic relations assigned to the 
)redicate of the main clause. 
Is conj unction of the subordinate clause conjunctive particle "te" "to" "ba n or "renyou~chuushi"? 
and Does the subordinate clause have time information 
such as time cases? 
no Jr Jfyes 
operate time ir~'ormation in the main ~ I. no operation I clause over the subordinate clause 
Fig 4. Heuristics which analyse the scope 
of the auxiliary verb "ta" 
6.3 Application to Japanese analysis 
(I) Extended case analysis 
We have already proposed a method named 
extended case analysis for Japanese sentences. IvT Input 
to the extended case analysis is an ordered list of word 
frames produced by a morphological analysis. The 
analysis begins to predict a constituent construction of 
the sentence to be analyzed by utilizing syntactic 
structure patterns, and then enter into the detail 
analysis of semantic relations between pairs of the 
modifier and the modificant by utilizing semantic 
relation frames. There are four types of the semantic 
relations, namely, case relation, noun concept relation, 
embeding relation and conjunctive relation. All of 
these semantic relations are analyzed in a uniform 
framework. The both analyses go on iteratively and/or 
recursively from a small chunk of constituents to large 
one. Each iteration and recursion executes both the 
prediction of the syntactic structure and the analysis of 
semantic structure. The modality analysis is 
incorporated into those processes. 
Let us show the modaiity analysis process for the 
following example sentence : 
(s22)Niku wa nokot teite, 
yasai dake ga Kiroko ni tabe rare teita. 
Meat had remained, and 
only vegetables had been eaten by Hiroko. 
At first, it is analysed that this sentence is a complex 
sentence by utilizing syntactic structure patterns. 
After semantic structures of the modifier and the main 
clause are analysed, conjunctive relation between these 
clauses is analyzed. Now, we show analysis of the main 
sentence. 
The following case elements and a predicate are 
analysed by applying structure patterns before starting 
case analysis : 
case1 = "yasai", "ga", "dake", 
case2 = ~liroko", "ai", 
predicate = "taberu", "rareru", %eiru", %a', 
where "dake", "rarern', "teiru", and "ta" are modality 
exp~'essions. "Hiroko" and "yasai" have semantic 
categories, \[human\] and \[food\] respectively in each 
word frame. 
(2) Modification of case frame 
Case frame is prepared for each meaning of each 
predicate. An intrinsic case frame for the verb "taberu 
(eat)" is as follows (Optional cases such as time and 
place are omitted here) : 
\[the intrinsic case frame of the verb "taberu (eat)"\] : 
Agent -- \[human\], "ga", 
Object = \[food\], ~wo". 
Each case slot in the case frame is assigned semantic 
categories and case particles as constraints to be 
satisfied by the filler. 
The following alternative case frames produced by 
modifying the intrinsic frame are also prepared before 
starting case analysis because of the existence of the 
auxiliary verb ~rareru" : 
\["passive" modification of the case frame\] : 
Agent = \[human\], "hi", 
Object = \[food\], "ga", 
\["affected-passive" modification of the case frame\] : 
Affected-agent - \[human\], "ga", 
Agent = \[human\], "ni", 
Object - \[food\], "wo". 
These three case frames are examined whether each 
case element in the sentence satisfies constraints. As a 
result, in this case, "passive" modification case frame is 
selected as a best matching, and case role of each case 
element is determined as follows : 
casel= Object, case2 = Agent. 
This result is showing that the meaning of ~rareru" is 
"passive". 
(3) Determination of meaning of modality 
Modality by modal particles in case elements and 
attxiHary verbs are analyzed. Analysis of "teiru" is 
:33 
performed by the heuristics shown in Fig. 3, where the 
meaning is determined as "terminative-state" judging 
from the fact that "teiru" follows "raxeru". The 
meaning of the modal particle "dake" is multiple, that 
is, "limitation" and "degree". In this case, "limitation" 
is selected by heuristics. 
(4) Determination of scope of modality in the main 
clause 
After conjunctive analysis between the modifier and 
the main clause, scope of the auxiliary verb "ta" in the 
main clause is analyzed. Using heuristics shown in 
Fig. 4, it is analyzed that "ta" also operates on the 
subordinate clause. 
In a result, the meaning structure of (s22) is 
obtained as follows : 
3x((Meat(x)A\[past\]\[terminative-state \]Remain(x)) 
A3x((Vegetable(x) 
A\[past\]\[terminative-state\]Eat(Hiroko,x)) 
AVx(( -- Vegetable(x) 
~-, \[pastl\[terminative-state\]Eat(Hiroko,x)) 
A{Focus(x)}). 
An English sentence corresponding to this semantic 
structure is shown in (s22). 
6.4 Virture of modality analysis 
We show contributions of modality analysis to 
understanding and quality of translation for the 
following example sentences. 
(s23) Densha wa senro no ue shika hashiru 
kotogadeki na_Ai ga, watashi ga kinou 
eiga de mita densha wa sofa wo tobu 
kotomodeki ta. 
Though a train can run only on a railroad, the train \[ 
saw in a movie yesterday could also fly. 
(s24) Anata wa densha ga sora wo tobu 
kotogadekiru to omoi masu ka. 
Do you think that a train can fly? 
(1) \[speech act\] As shown in (s24), modality contains 
much information concerning speech act (question, 
command, guess, intention, etc.). In conversational 
systems such as qustion answering systems, these 
meaning can be used for selecting apropriate reactions. 
(2) \[type of object\] Analysis results of aspect or tense are 
used for determining the type of objects. 
The subordinate clause of (s23) describes a general 
character of'densha (trmn)", and the first occurrence of 
"densha" denotes a generic object. On the other hand, 
the second occurrence of "denaha" is modified by an 
embedded sentence, and "densha" denotes a specific 
object which "I saw in a movie yesterday". Like this, if 
the character of the event is analysed by the analysis of 
aspect or tense, the character of the objects can be 
specified. 
(3) \[translation\] As shown in the translated sentences 
in (s23) and (s24), results of the modality analysis are 
clearly realized in quality of translated sentences. In 
these sentences, modality such as "limitation", 
"negation", "ability", "past", "quetion" appears. 
7. Conclusion 
We proposed an analysis method for Japanese 
modality. In this purpose, we classified the meaning of 
modality into four categories, and then defined five 
modality functions which characterize the role of 
modality. By employing logical expressions to 
represent the meaning structure, we could effectively 
specify the modality function. Though logical 
expression has the same expressive power as frames or 
semantic networks, a more concise semantic 
representation can be realized by this method. 
Although we dealt with the modality analysis 
restricted within the scope of one sentence in this paper, 
we must investigate the effect of discourse information 
on the analysis of modality in the future. 
We have applied this modality analysis method to 
the Japanese sentence analysis in the Japanese- 
English experimental machine translation system, 
LUTE.IV! 
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\[3\]Karttunen, L. and S. Peters : Conventional 
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\[4\] Kubo, S. : A Study of Japanese Adverbial Particles 
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34 
