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<?xml version="1.0" standalone="yes"?> <Paper uid="W98-0316"> <Title>Discourse Markers in Spontaneous Dialogue: A Corpus based study of Japanese and English Masahito KAWAMORU Takeshi KAWABATA t Nippon Telegraph and Telephone, NTT Basic Research Laboratories t kawamori~atom.brl.ntt.co.jp kaw~idea.brl.ntt.co.j p</Title> <Section position="2" start_page="0" end_page="98" type="abstr"> <SectionTitle> Abstract </SectionTitle> <Paragraph position="0"> A spontaneously spoken, natural Japanese discourse contains many instances of the so-called redundant interjections and of back-channel utterances. These expressions have not hitherto received much attention and few systematic analyses have been made, since they were regarded as useless, spurious expressions.</Paragraph> <Paragraph position="1"> On the basis of the analysis of spoken dialogue corpus, we claim that these utterances have the characteristics of discourse markers, which delimit and define units of discourse. Our corpus consists of task-oriented dialogues conducted both in Jacanese and in English.</Paragraph> <Paragraph position="2"> The analysis of the Japanese c,:rpus shows that about half of the turns are started with these so-called redundant utterances, while the English corpus shows that about 25 % of the turns start with corresponding English expressions. This suggests that at least in the case oi&quot; Japanese, these so-called redundant utterances have much to do with units of discourse, the building blocks of discourse relations, and that they do indeed function as discourse markers.</Paragraph> <Paragraph position="3"> We show that these utterances comprise a well-defined category, characterizable in a regular manner by their prosodic properties. Prosodic patterns of discourse markers occurring in the recorded corpus have been analyzed. Several pitch patterns have been found that characterize the most frequently used Japanese discourse markers. Based on these characteristic pitch patterns, a system of discourse markers can be designed so that a relatively small number of basic forms are shown to give rise to most of the discourse markers, with intonation patterns corresponding to the functions of discourse markers.</Paragraph> <Paragraph position="4"> Introduction Japanese is an agglutinative language with predominantly verb final sentence patterns. It is to be expected, therefore, that Japanese sentence units are rather easy to recognize, and textbooks and written forms of Japanese indeed vindicate such an expectation. null A spontaneously spoken Japanese discourse, however, is full of features which are not part of its written counterpart: phrases ending with conjunctions, interjections with verbs attached, unfinished utterances and other disfluencies.</Paragraph> <Paragraph position="5"> Aizuchi, or back-channel utterances, and other so-called redundant utterances, such as hai, un, anoo and ee, are especially abundant in Japanese discourse.</Paragraph> <Paragraph position="6"> These are often taken as the manifestation of the irregularity and non-systematic nature of spoken language. Especially when one wants to recognize 'sentences' in discourse, these utterances inevitably stand in one's way, destroying the sentential structures expected by grammar. Because of these utterances, from the stand point of the conventional grammar, clarifying such matters as which utterances constitute one sentence and which utterances belong to two different sentence units becomes extremely difficult. If the task of discerning sentence units~ the building blocks of discourse, is difficult, the difficulty of discerning discourse structure is enormous.</Paragraph> <Paragraph position="7"> If these utterances are really just noise, then they are hindrance to the understanding of discourse, and spoken discourse would be far more difficult for people to understand than written texts. But this flies in the face of the fact that people do communicate and understand each other in spoken language, and quite easily for that. Given that spoken language is full of such so-called redundant utterances and that people can nevertheless communicate rather easily, we have to conclude that these utterances are not just noise after all; their function in discourse is effective, and they contribute somewhat to the understanding of spoken discourse. We believe that these utterances have important functions in discourse, as what is called discourse markers.</Paragraph> <Paragraph position="8"> As was reported in \[Kawamori et al., 1994\], there are fair indications that these expressions play crucial roles in determining discourse structures, especially with respect to units of surface discourse as well as of speech acts and planning. Elucidating such roles can not only clarify syntactically relevant features of discourse but may shed light on intended meaning and other issues concerning pragmatics \[Takubo, 1994\]. Aside from the fact that since spoken discourse is full of these expressions, one cannot avoid treating these phenomena in order to understand and explain the language in actual use, we are interested in these utterances because they have particular functions, not required in written language but specifically called for in its spoken counterpart. null In addition to these theoretical interests, clarifying these phenomena serves more practical purposes also. For example, constructing a truly friendly human-machine interface would require a systematic knowledge of these features. Moreover, since written language generally lacks many discourse markers abundant in its spoken counterpart, interfaces between these two media would invariably have to be able to handle discourse markers. For example, a machine designed to take the dictation of its human interlocutor could not do without the ability to discern these discourse markers, unless correct dictation means interspersing every phrase with ah's and uh's. The inability to handle these features would limit the capacity of an expert system \[Pollack et al., 1982\], \[Whittaker and Stenton, 1988\].</Paragraph> <Paragraph position="9"> Corpus In order to analyze spontaneously spoken discourse, we have been collecting task-oriented dialogues. Although we are mainly concerned with spoken Japanese, we are also collecting English dialogues for comparison. The corpus is still growing.</Paragraph> <Paragraph position="10"> The Japanese corpus comprises 312 dialogues, whose total recording time is about 18 hours (1081 minutes).</Paragraph> <Paragraph position="11"> The recorded conversations are transcribed and the size of the resulting text is about 1 megabyte, which roughly corresponds to 500,000 characters in Japanese orthography and contains approximately 29,000 turns. The transcription is made using a tool that automatically segments speech data into units separated by pauses.</Paragraph> <Paragraph position="12"> Hence a turn is defined prosodically rather than syntactically or semantically.</Paragraph> <Paragraph position="13"> The English corpus comprises 77 dialogues. The recording time is about 4 hours, and the text size is about 400 kilobytes with approximately 5000 turns.</Paragraph> <Paragraph position="14"> The same tool is used for transcription. The tasks of the English dialogues are the same as those of aapanese.</Paragraph> <Paragraph position="15"> The subjects are all native speakers of the North American variety of English, with varying degrees of exposure to Japanese culture and language.</Paragraph> <Paragraph position="16"> Japanese Discourse Markers Schiffrin \[Schiffrin, 1987\] gives the operational definition of discourse markers as &quot;sequentially dependent elements which bracket units of talk&quot;, units that include such entities as sentences, propositions, speech acts, and tone units, the exact nature of which she deliberately leaves vague. She also suggests that, conversely, discourse markers themselves may define &quot;some yet undiscovered units of talk&quot;. \[Hirschberg and Litman, 1987\] state that they &quot;may, instead of making a 'semantic' contribution to art utterance (i.e., affecting its truth conditions), be used to convey explicit information about the structure of a discourse.&quot; Other terms used to designate discourse markers are 'cue phrase', 'clue word', and 'discourse particles'. Examples of English discourse markers are: okay, but, now, anyway, by the way, in any case, that reminds me.</Paragraph> <Paragraph position="17"> Unlike their English counterparts, many Japanese discourse markers are not lexical; they are not generally regarded as comprising a well-defined category. For example, in English, such words as &quot;well&quot; and &quot;now&quot; not only function as discourse markers, but also have their inherent senses like &quot;in a good manner&quot; and &quot;the present time&quot;. Their status as 'words' are unquestionable. Their Japanese counterparts, eeto and hal, on the other hand, have no other functions than as discourse markers. They have no 'meaning' by themselves, and they are never used in written language.</Paragraph> <Paragraph position="18"> This fact explains why little consensus exists among researchers as to which 'words' constitute Japanese discourse markers and why these utterances have conventionally been bundled into interjections, given up as standing &quot;outside the domain of the well-formed sentence itself,&quot; \[Martin, 1975\].</Paragraph> <Paragraph position="19"> Another consequence of this fact is that the disambiguation between lexical and non-lexical uses. or that between non-cue and cue usages, of words used as discourse markers does not constitute a particularly urgent problem in Japanese, because most of the time there is nothing to be disambiguated. On the other hand, the question of distinguishing among the different functions born by discourse markers becomes important, since one discourse marker can have different functions depending on the context or its prosodic features.</Paragraph> <Paragraph position="20"> Although there is no received categorization, Japanese discourse markers can naturally be divided into two main groups: phrasal and non-phrasal markers. null Phrasal markers are those phrases that are routinely used for conveying information about the structure of discourse. They are lexical phrases, like sore-kara-desune 'and then' and sou.shimasu-to 'the case being so', or words, like toiuka 'rather' and yappari 'as expected', usually complex in form, with inherent meaning directly related to the discourse.</Paragraph> <Paragraph position="21"> Non-phrasal (particle) discourse markers can be further grouped into four categories: fillers, responsives, (sentence) final particles, and conjunctives and other adverbial expressions. The so-called redundant expressions and interjections belong to the first two categories. As was noted above, the expressions belonging to these categories are usually not recognized as part of the language proper, and therefore not given the status of morpheme. null Sentence final particles are morphemes like -yo and ne that are attached to the end of a sentence or a phrase to express speaker's attitudes \[Kawamori, 1991\]. Their role in conversation is somewhat similar to that played by French quoi and German doch and jo.</Paragraph> <Paragraph position="22"> Other particles, mostly conjunctive in nature and expressing various discourse relations, like -node 'because', -kedorno 'though', -to 'then', -ga 'but', also function as discourse markers. Their functions are similar to those of ordinary conjunctives, but particles are more common in spoken language. They are not only used to connect sentences but also to end sentences with, indicating that in conversation they are more like sentence final particles than pure conjunctives.</Paragraph> <Paragraph position="23"> Conjunctive adverbials are expressions like ja (then), de 'then', ato 'in addition' - many of which are derived from conjunctions and conjunctive particles - that are used to express various relations between sentences.</Paragraph> <Paragraph position="24"> Discourse Markers and Units of Discourse That these non-phrasal markers are indeed discourse markers as defined by Schiffrin can be shown by the analysis of our corpus. We selected 59 dialogues from our Japanese corpus, and found out that 3,210, or 49.3%, of the total turn of 6,507 start with either a filler or a responsive. On the other hand, 4,308, or 66.2%, of the turns end with a particle, filler, or responsive. This seems to suggest that these expressions are indeed used to &quot;bracket units of talk&quot;.</Paragraph> <Paragraph position="25"> These units are not necessarily sentences in the conventional grammatical sense, but are closer to what the traditional Japanese linguistics call bunse~su, or sentential clause, though strictly speaking, they are not what are usually regarded as well-formed bunsetsu.</Paragraph> <Paragraph position="26"> This also shows how precarious the status of sentence is in spoken Japanese discourse, as mentioned at the outset, since it is possible that in at least half of the time, a turn does not consist of a sentence. This suggests that the discourse structure of dialogue cannot be understood in terms of the traditional grammar based on sentence, or well-formed bunsetsu, \[Dohsaka and Shimazu, 1996\].</Paragraph> <Paragraph position="27"> For comparison, we looked at 13 of the English dialogues on a similar task, and found that 930, or 25.9 %, of the 3,584 turns start with uh, ah, OK, urn, or right.</Paragraph> <Paragraph position="28"> We did not specifically look at what comes at the end of each turn, but it appears that an English dialogue tends to have a longer turn with a finished sentence.</Paragraph> <Section position="1" start_page="94" end_page="98" type="sub_section"> <SectionTitle> Responsives and Fillers </SectionTitle> <Paragraph position="0"> Since responsives and fillers are those expressions that have hitherto been categorized as jouchou-go (redundant words) or fuyou-go (unnecessary words) and hence regarded as redundant or needless \[Takagi et al., 1993\],\[Kobayashi et al., 1993\], little attention has been paid to give a systematic account of their forms, much less their functions. But, as we said in the introduction, the elucidation of their exact status is more urgent, in that they occur so frequently in spoken language. In the following we look more closely at responsives and fillers and try to characterize their nature.</Paragraph> <Paragraph position="1"> Responsives are what \[Kawamori et al., 1994\] call interjectory responses and roughly correspond to what in Japanese are traditionally referred to as aizuchi, or back-channel utterances in English. These expressions are rather limited in their realization: there are only a few expressions belonging to this class in the Standard Japanese. Their forms seem to be restricted to expressions with two morae.</Paragraph> <Paragraph position="2"> An example of a responsive discourse marker is hal, one of the most frequently used words in spoken Japanese as well as one of the most complex and difficult to analyze. If used in response to a question, hai means a simple &quot;yes&quot;, while if it is in reply to a request, it means an accepting &quot;OK&quot;. When used by itself, at the beginning of a sentence, it usually means, &quot;now&quot; or &quot;well&quot;. In addition to all these functions, it also has its most common use as an expression of acknowledgment, as does &quot;uh-huh&quot; in English. Of the responsives, hal is by far the most commonly used, and most neutral in style.</Paragraph> <Paragraph position="3"> Fillers are those expressions which have ordinarily been taken as rather 'meaningless' or 'unimportant'.</Paragraph> <Paragraph position="4"> They are usually characterizable as consisting of one or two vowels, with or without consonants. Their syllable compositions are generally very simple. The expressions of this class have functions, and forms, rather similar to the fillers in English, like mm and ah. Typical examples of fillers are anoo and eeto.</Paragraph> <Paragraph position="5"> Another type of fillers are shorter than the fillers discussed above, and often amount to no more than a catch of voice. Examples are a and e. The phonological characteristics of this type of fillers seem to be somewhat similar to those of responsives, but the exact clarification is rather difficult because these expressions are uttered in extremely short duration, usually less than 100 milliseconds, making it almost impossible to detect then as voiced sounds.</Paragraph> <Paragraph position="6"> Taxonomy of Responsives and Fillers The inventories of these discourse markers in literature, such as listed by \[Takubo, 1994\], \[Kobayashi et al., 1993\], and \[Takagi e~ al., 1993\], together with the characterizing features discussed above, seem to suggest that these discourse markers can be classified in a simple way in terms of the three dimensions: the phonetic form of the marker, the tone of a vowel, and the length of a vowel. More concretely, the following three can be offered as important aspects in classifying filler and responsive discourse markers: Sound forms These are the basic phonetic forms that constitute the realizations of discourse markers. These forms can be further divided into two groups in the following way: Regular Type: (Type R) This group is composed of those markers that are regularly constructed from two elements: the initial sound plus the main vowel.</Paragraph> <Paragraph position="7"> These discourse markers can be summarized in the following table.</Paragraph> <Paragraph position="8"> i \[ vowels !,,initial sound a e ua o I'1 a &quot; e un o /h/ ha he hun ho /m/ ma - mo In the table, the mark ' stands for a glottal stop; in practice it shows that there is no noticeable consonant, The 'vowel' un is so-called because it is not /u/ plus /n/, but rather a nasalised u. Note that the basic phonetic forms of both fillers and responsives are included in this group. The table indicates that there are 10 basic phonetic forms of discourse markers, including o, ho, and mo. Those forms in the o column may not actually be fillers but simple interjections, for the usages of their actual instances seem to differ from those of the fillers. We include them in the table for the sake of completeness.</Paragraph> <Paragraph position="9"> Independent Type: (Type I) The other group of sound forms is made up of those fillers/responsives with more than one morn that do not belong to the above regular type. These are small in number, and can be summarized as follows: hal, ano, kono, sono, eeto Note that to in eeto may be regarded as a separate particle, for unto and or-to are also possible. In fact, in familiar occasions, people often use such expressions as hal-fro and a-fro. If this is true then eeto should be regarded as ee plus to, and not as a single form.</Paragraph> <Paragraph position="10"> It is further to be noted that, again, responsives and fillers share a type. Consideration of the sound forms, therefore, leads us to believe that fillers and responsives somehow constitute a larger, more general category which comprises phonetically related, but prosodically and functionally distinct, elements.</Paragraph> <Paragraph position="11"> Length In addition, the length of a vowel is also to be considered. In Japanese, the long vowel and its short counterpart are phonemically distinct so that a word with a short vowel is distinguished lexically from a corresponding word with a long vowel, as can be seen from obasan (aunt) and obaasan (grand mother). Similarly, a discourse marker with a short vowel often has different functional/semantical features than does its long vowel counterpart. The filler anoo with the long vowel oo is usually thought to be different, lexically and functionally, from ano with the short o.</Paragraph> <Paragraph position="12"> Hence we add the following four features concerning the lengths of vowels in our inventory: * H+H (for a lengthened vowel at higher pitch), * L+L (for a lengthened vowel at lower pitch), * H- (for a short vowel with an abrupt stop at higher pitch), * L- (for a short vowel with an abrupt stop at lower pitch).</Paragraph> <Paragraph position="13"> Notice that + and - are used in a different manner from the way they are meant in \[Pierrehumbert and Hirschberg, 1990\]. With such an inventory of symbols for representation, we can describe the prosodic characteristics of Japanese discourse markers\[Kawamori et al., 1996\].</Paragraph> <Paragraph position="15"> Any of the sound forms can take on one of these lengths, although some of them may not actually be used in discourse. For example, the sound form a often takes L-; this usually shows awareness or acknowledgment. It is often found in an utterance like the following: null</Paragraph> <Paragraph position="17"> a with the higher H-would usually imply some element of surprise.</Paragraph> <Paragraph position="18"> The long H+H accompanying a, often written as an, signals some kind of hesitation, as in: (2) aa, hai</Paragraph> <Paragraph position="20"> Similarly, the other markers in Type R above may have either of the long or short tones.</Paragraph> <Paragraph position="21"> Those of Type I also can be realized with either a long vowel or a short one. ano as a filler is usually uttered with H+H, but it may also have L-. Although hai is usually short HL%, in a situation where one calls out to reply, H+H plus LX may be used. Table 1 summarizes these points succinctly.</Paragraph> <Paragraph position="22"> Pitch The two pitches, H and L, can be used to characterize different markers. As noted above, a with H+H can signal hesitation, but the same a with HL%, also written aa, is usually taken as a responsive, albeit an impolite, or arrogant, kind. The sound form e with L-is usually interpreted in a similar way to what a with L-is interpreted. But e with H-% is usually used to express a question, rather like English Pardon? or huh?.</Paragraph> <Paragraph position="23"> We analyzed another set of recorded dialogues and observed the pitch pattern of the token utterance of a responsive discourse marker. There were 308 token utterances of the form has. Of these 292 had the form HL%, as predicted. This is approximately 95 percent of the cases. There are 16 instances in which hai did not have HL% pattern. Of these, 8 were either immediately following or immediately followed by some other utterances, including two instances of hal hal.</Paragraph> <Paragraph position="24"> Single utterances of hal that do not have HL% pattern comprise fewer than 3 percent. These had the pattern HL+LS: or HL+L with the lengthening of the last vowel. There were 60 token utterances of un, which may be considered an informal counterpart of hal. Of these, 49, or approximately 82 percent, were of the pitch pattern HAY,.</Paragraph> <Paragraph position="25"> A possibly more interesting, and perhaps more challenging, case is that of ee, for ee is both a filler and a responsive. Our result shows that there were 96 occurences of the token form ee, of which 76, or about 80 percent, were of (L)H+H pattern. The HL% pattern comprised fewer than 10 percent of the total 96, while other patterns counted 11, or slightly more than 10 percent. As it stands, this result does not refute our characterization, but it only shows that ee may be used more often as a filler than a~ a responsive. The results are succinctly summarized in Table 2.</Paragraph> <Paragraph position="26"> This way of characterizing discourse markers, more precisely fillers and responsives, is interesting because it gives a good idea of the domain of discourse markers by systematically offering us a large sample of these expressions.</Paragraph> <Paragraph position="27"> As was noticed earlier in this paper, \[Takubo, 1994\] gives a rather comprehensive, though not exhaustive, list of discourse markers, a list that arranges discourse markers into groups defined in terms of operational, or performative, concepts. \[Takagi et al., 1993\] and \[Kobayashi et al., 1993\] also give similar lists. It is worth noticing that all the discourse markers listed in these are accounted for in the categorization in this section. null Phoricity Our taxonomy of discourse markers shows that there is a dividing line between two types of fillers. One of them is the type that is composed of such fillers as aL_,eL_, and ell_ ; the other is the long type, which includes eetoH+ H and anooLH+H. The former may be called anaphoric because a member of this class is generally uttered when there is an antecedent situation, either linguistic or otherwise, that triggers its utterance: a situation that is surprising, outstanding, or simply salient for some reason. The latter class, on the other hand, may be called cataphoric, for its member is usually used to prepare the listener, and possibly the speaker also, for imminent continuance of speech by signaling, for example, hesitation. Responsives are by definition anaphoric, because they always presuppose something to which they are used to reply. We call the property of being anaphoric or cataphoric phoricit~ of that expression.</Paragraph> <Paragraph position="28"> This demarcation in fillers, along with the remark above about the more general, comprehensive category comprising both fillers and responsives, shows that there are in fact three distinctive categories among fillers and responsives: anaphoric fillers, cataphoric fillers, and responsives. Moreover there are three prosodic characteristics that correspond to these three categories: the typical prosody of an anaphoric filler is either L-or It-; that of a cataphoric filler is (L)H+H; and * that of a responsive is HLY,. This situation is summarized in Table 3.</Paragraph> <Paragraph position="29"> Whether the correspondence between the phoricity of an expression and its prosodic pattern is universal or not remains to be seen. It would be interesting to pursue this in comparison with other languages other than English and Japanese.</Paragraph> <Paragraph position="30"> The correlation between the typical prosodic characteristics of fillers and responsives and the three categories discerned among them also defines the possibility of linear precedence relation among these discourse markers and discourse units.</Paragraph> <Paragraph position="31"> As noted above there are cases in which the speaker refers back to his own utterance with a hal. There are many examples of a with L-preceding hal. But it is rare to find ee with the H+It prosody followed by hai. The following are frequently observed sequences of discourse markers: in, hai),<a, a,,oo), <soudesu, ha/); while these are rarely observed: (hai, a), (eeto, e>, (soudesu, a).</Paragraph> <Paragraph position="32"> Summarizing, we get the following rough generalization: null * Fillers with L-or It-, the anaphoric fillers, such as a L-,e L-, and e It-, come at the beginning of a 'unit'; * hal and other responsives with tIL% come at the end of a 'unit'. (Sometimes it may be the only unit.) * The cataphoric fillers, such as ano It + H,eH + ti, and eL + L, come in between some 'units'.</Paragraph> <Paragraph position="33"> Such generalization helps us to formulate a rule that possibly characterizes the way discourse markers occur in daily discourses. One possible way of doing so would be to posit a rule like the following: (r-)(({L)r q- r)', UNIT)+(HLY,), where UNIT is some antecedently defined unit of discourse, possibly bunsetsu, r is either H or L, the raised + indicates the possibility of iterating the same element once or more times, and the raised * indicates the possibility of iterating the same element zero or more times.</Paragraph> <Paragraph position="34"> While imperfect as it stands, this rule 'defines' many surface strings as well-formed discourses. For example, the following is well-formed according to this rule: (3) a anoo tokyoo-ni eeto detaindesuyo hal L- LH+H LH+H HL% Tokyo-TOWARD want-to-go-out 'I want to go to Tokyo.' This characterization itself is rather too simple, and more work has to be done to improve upon it, a task which is beyond the scope of this paper and is to be taken up in a later work. But such a rule will be useful in devising a 'grammar' of the spontaneously spoken language taken in its totality, an attempt made by, for example, \[Nakano et al., 1994\]. Indeed, once a truly natural discourse is taken seriously, an attempt at such a grammar, and a formulation such as in this section, seems not only indispensable but also inevitable.</Paragraph> <Paragraph position="35"> Another thing to be noted is that such a rule underscores the fact that these expressions are not to be regarded as redundancies, but rather as legitimate discourse markers, as has been claimed at the outset. Concluding Remarks We looked at Japanese discourse markers, comparing them with their English counterparts. Although many English discourse markers are phrasal or lexical, with independent status as words, many Japanese discourse markers are non-phrasal and some of them have been denied the status of being discourse markers, dismissed as redundant or spurious.</Paragraph> <Paragraph position="36"> We claimed, on the basis of the analysis of spoken dialogue corpus, that these utterances have the characteristics of discourse markers, which delimit and define units of discourse. Our corpus consists of task-oriented dialogues conducted both in Japanese and in English.</Paragraph> <Paragraph position="37"> The analysis of the Japanese corpus shows that about half of the turns are started with these so-called redundant utterances, while the English corpus shows that about 25 % of the turns start with corresponding English expressions. This suggests that at least in the case of Japanese, these so-called redundant utterances have much to do with units of discourse, the building blocks of discourse relations, and that they do indeed function as discourse markers.</Paragraph> <Paragraph position="38"> We also examined the formal properties of these non-phrasal discourse markers, fillers and responsives, specifically looking at their prosodic features. Our analysis suggested that the intonational characteristics of these markers are category-dependent, in that markers of a category share similar intonational patterns. The existence of natural phonological demarcations among the discourse markers suggests a systematic categorization of these expressions, a taxonomy of discourse markers that may enable us to systematize the seemingly chaotic, ad-hoc way these expressions are currently treated. We noted that the phoricity of a discourse marker corresponds to a certain prosodic pattern. Although whether such a correspondence is universal or not remains to be seen, it would be interesting to pursue this in comparison with other languages other than English and Japanese.</Paragraph> <Paragraph position="39"> Our taxonomy would in turn suggest the possibility of developing a system of linear precedence relations among discourse markers and discourse units, with rules governing when and where a discourse marker may occur in an utterance. Such a 'syntax' of discourse markers naturally has an important bearing on constructing a grammar of natural, spoken discourse \[Nakano et al., 1994\].</Paragraph> <Paragraph position="40"> On the other hand, the presumed categoricity does not seem to be so fine-grained as to provide clear-cut phonological telltales distinguishing among the &quot;functional meanings&quot; of a member of one category: the different functional meanings of hat, for example, does not seem to be disambiguated solely by the differences in pitch patterns. Such finer-grained distinctions could only be made with a help of context; one has to take into account what type of expression or speech act precedes the discourse marker, and in what position of a phrase the marker occurs \[Walker and Whittaker, 1990\].</Paragraph> </Section> </Section> class="xml-element"></Paper>