4.0. Introduction

This chapter examines the linguistic definition of the Chinese word and establishes its formal representation in CPSG95.  This lays a foundation for the treatment of Chinese morpho-syntactic interface problems in later chapters.

To address issues on interfacing morphology and syntax in Chinese NLP, the fundamental question is:  what is a Chinese word?  A proper answer to this question defines the boundaries between morphology, the study of how morphemes combine into words, and syntax, the study of how words combine into phrases.  However, there is no easy answer to this question.

In fact, how to define Chinese words has been a central topic among Chinese grammarians for decades (Hu and Wen 1954; L. Wang 1955;  Z. Lu 1957; Lin 1983; Lü 1989; Shi 1992; Dai 1993; Zhao and Zhang 1996).  In late 50's, there was a heated discussion on the definition of Chinese word in China.  This discussion was induced by the campaign for the Chinese writing system reform (wenzi gaige yundong).  At that time, the government policy was to ultimately replace the Chinese characters (hanzi) by a Romanized writing system.  The system of pinyin, based on the Latin alphabet, was designed to represent the pronunciation of the characters in the Contemporary Mandarin.  The simplest way is to use pinyin as a writing system and simply translate Chinese characters into syllables in pinyin.  But it was soon found impractical due to the many-to-one correspondence from hanzi to syllable.  Text in pinyin with no  explicit word boundary delimiters is hardly comprehensible.   Linguists agree that the key issue for the feasibility of a pinyin-based writing system is to establish a standard or definition for Chinese words (Z. Lu 1957).  Once words can be identified by a common standard, the pinyin system can in principle be adopted for recording the Chinese language by using space and punctuation marks to separate words.  This is because the number of homophones at the word level is dramatically reduced when compared with the number of homophones at the hanzi (morpheme or mono-syllabic) level.

But the definition of a Chinese word is a very complicated issue due to the existence of a considerable amount of borderline cases.  It has never been possible to reach a precise definition which can be applied to all circumstances and which can be accepted by linguists from different schools.

There have been many papers addressing the Chinese wordhood issue (e.g. Z. Lu 1957; Lin 1983; Lü 1989; Dai 1993).  Although there are still many problems in defining Chinese words for borderline cases and more debate will continue for many years to come, the understanding of Chinese wordhood has been deepened in the general acknowledgement of the following key aspects:  (i) the distinct status of Chinese morphology;  (ii) the distinction of different notions of word;  and (iii) the lack of absolute definition across systems or theories.

Almost all Chinese grammarians agree that unlike Classical Chinese, Contemporary Chinese is not based on single-morpheme words.   In other words, the word and the morpheme are no longer co-extensive in Contemporary Chinese.[1]  In fact, that is the reason why we need to define Chinese morphology.  If the word and the morpheme stand for the same linguistic object in a language, like Classical Chinese, the definition of  morpheme will entail the definition of word and there is no role of morphology.

As it stands, there is little debate on the definition of morpheme in Chinese.  It is generally acknowledged that each syllable (or its corresponding written form hanzi) corresponds to (at least) one morpheme.  In a characteristic ‘isolating language’ - Classical Chinese is close to this, there is no or very poor morphology.[2]  However, Contemporary Chinese contains a significant number of bound morphemes in word formation (Dai 1993).  In particular, it is observed that many affixes are highly productive (Lü et al 1980).

It is widely acknowledged that the grammar of Contemporary Chinese is not complete without the component of morphology (Z. Lu 1957; Chao 1968; Li and Thompson 1981; Dai 1993; etc.).   Based on this widely accepted assumption, one major task for this thesis is to argue for the proper place to cut the line between morphology and syntax, and to explore effective ways of interleaving the two for analysis.

A significant development concerning the Chinese wordhood study is the  distinction between two different notions of word:  grammar word versus vocabulary word.  It is now clear that in terms of grammar analysis, a vocabulary word is not an appropriate notion (Lü 1989; more discussion to come in 4.1).

Decades of debate and discussion on the definition of a Chinese word have also shown that an operational definition for a grammar word precise enough to apply to all cases can hardly be established across systems or theories.  But a computational grammar of Chinese cannot be developed without precise definitions.  This leads to an argument in favor of the system internal wordhood definition and interface coordination within a grammar.

The remaining sections of this chapter are organized like this.  Section 4.1 examines two notions of word.  Making sure that we use the right notion based on some appropriate guideline, some operational methods for judging a Chinese grammar word will be developed in 4.2.  Section 4.3 demonstrates the formal representation of a word in CPSG95.  This formalization is based on the design of expectation feature structures and the structural feature structure  presented in Chapter III.

4.1. Two Notions of Word

This section examines the two notions of word which have caused confusion.  The first notion, namely vocabulary word, is easy to define.  However, for the second notion, namely, grammar word, unfortunately,  no operational definition has been available.  It will be argued that a feasible alternative is to system internally define a grammar word and the labor division between Chinese morphology and syntax.

A grammar word stands for the grammatical unit which fits in the hierarchy of morpheme, word and phrase in linguistic analysis.  This gives the general concept of this notion but it is by no means an operational definition.  Vocabulary word, on the other hand, refers to the listed entry in the lexicon.  This definition is simple and unambiguous once a lexicon is given.  The lexical lookup will generate vocabulary words as potential building blocks for analysis.

On one hand, vocabulary words come from the lexicon;  they are basic building blocks for linguistic analysis.  On the other hand, as the ‘resulting’ unit for morphological analysis as well as the ‘starting’ or ‘atomic’ unit for syntactic analysis, the grammar word is the notion for linguistic generalization.  But it is observed that a vocabulary word is not necessarily a grammar word and vice versa.  It is this possible mismatch between vocabulary word and grammar word that has caused a problem in both Chinese grammar research and Chinese NLP system development.

Lü (1989) indicates that not making a distinction between these two notions of word has caused considerable confusion on the definition of Chinese word in the literature.  He further points out that only the former notion should be used in the grammar research.

Di Sciullo and Williams (1987) have similar ideas on these two notions of word.  They indicate that a sign listable in the lexicon corresponds to no certain grammatical unit.[3]   It can be a morpheme, a (grammar) word, or a phrase including sentence.  Some examples of different kinds of Chinese vocabulary words are given below to demonstrate this insight.

(4-1.) sample Chinese vocabulary words

(a) 性           bound morpheme, noun suffix, ‘-ness’
(b) 洗           free morpheme or word, V: ‘wash’
(c) 澡           word (only used in idioms), N: ‘bath’
(d) 澡盆        compound word, N: ‘bath-tub’
(e) 洗澡        idiom phrase, VP: ‘take a bath’
(f) 他们         pronoun as noun phrase, NP: ‘they’
(g) 城门失火，殃及池鱼
idiomatic sentence, S:
‘When the gate of a city is on fire, the fish in the
canal around the gate is also endangered.’

The above signs are all Chinese vocabulary words.  But grammatically, they do not necessarily function as a grammar word.  For example, (4-1a) functions as a suffix, smaller than a word.  (4-1e) behaves like a transitive VP (see 5.1 for more evidence), and (4-1g) acts as a sentence, both larger than a word.  The consequence of mixing up these different units in a grammar is the loss of power for a grammar to capture the linguistic generality for each level of grammatical unit.

The definition of grammar word has been a contentious issue in general linguistics (Di Sciullo and Williams 1987).  Its precise definition is particularly difficult in Chinese linguistics as there is a considerable amount of phenomena marginal between Chinese morphology and syntax (Zhu 1985; L. Li 1990; Sun and Huang 1996).  The morpheme-word-phrase transition is a continuous band in the linguistic reality.  Different grammars may well cut the division differently.  As long as there is no contradiction in coordinating these objects within the grammar, there does not seem to exist absolute judgment on which definition is right and which is wrong.

It is generally agreed that a grammar word is a smallest unit in syntax (Lü 1989), as also emphasized by Di Sciullo and Williams (1987) on the 'syntactic atomicity' of word.[4]  But this statement only serves as a guideline in theory, it is not an operational definition for the following reason.  It is logically circular to define word, smallest unit in syntax, and syntax, study of how words combine into phrases, one upon the other.

To avoid this 'circular definition' problem, a feasible alternative is to system internally define grammar word and the labor division between Chinese morphology and syntax, as in the case of CPSG95.  Of course, the system internal definition still needs to be justified based on the proposed morphological or syntactic analysis of borderline phenomena in terms of capturing the linguistic generality.  More specifically, three things need to be done:  (i) argue for the analysis case by case, e.g. why a certain construction should be treated as a morphological or syntactic phenomenon, what linguistic generality is captured by such a treatment, etc.;  (ii) establish some operational methods for wordhood judgment to cover similar cases;  (iii) use formalized data structures to represent the linguistic units after the wordhood judgment is made.  Section 4.2 will handle task (ii) and Section 4.3 is devoted to the formal definition of word required by task (iii).   The task in (i) will be pursued in the remaining chapters.

Another important notion related to grammar word is unlisted word.  Conceptually, an unlisted word is a novel construction formed via morphological rules, e.g. a derived word like ke-du-xing (-able-read-ness: readability), foolish-ness, a compound person name (given name + family name) such as John Smith, mao-ze-dong (Mao Zedong).  Unlisted words are often rule based.  This is where productive word formation sets in.

However, unlisted word is not a crystal clear notion, just like the underlying concept grammar word.  Many grammarians have observed that phrases and unlisted words in Chinese are formed under similar rules (e.g. Zhu 1985; J. Lu 1988).  As both syntactic constructions and unlisted words are rule based, it can be difficult to judge a significant amount of borderline constructions as morphological or syntactic.

There are fuzzy cases where a construction is regarded as a grammar word by one and judged as a syntactic construction by another.  For example, while san (three) ge (CLA) is regarded as a syntactic construction, namely numeral-classifier phrase, in many grammars including CPSG95, such constructions are treated as compound words by others (e.g. Chen and Liu 1992).  ‘Quasi-affixation’ presents another outstanding ‘gray area’ (see 6.2).

The difficulty in handling the borderline phenomena leads back to the argument that the labor division between Chinese morphology and syntax should be pursued system-internally and argued case by case in terms of capturing the linguistic generality.  To implement the required system internal definition, it is desirable to investigate practical wordhood judgment methods in addition to case-by-case arguments.  Some judgment methods will be developed in 4.2.  Case-by-case arguments and analysis for specific phenomena will be presented in later chapters.  After the wordhood judgment is made, there is a need for the formal representation.  Section 4.3 defines the formal representation of word with illustrations.

4.2. Judgment Methods

This section proposes some operational wordhood judgment methods based on the notion of ‘syntactic atomicity’ (Di Sciullo and Williams 1987).  These methods should be applied in combination with arguments of the associated grammatical analysis.  In fact, whether a sign is judged as a morpheme, a grammar word or a phrase ultimately depends on the related grammatical analysis.  However, the operationality of these methods will help facilitate the later analysis for some individual problems and avoid unnecessary repetition of similar arguments.

Most methods proposed for Chinese wordhood judgment in the literature are not fully operational.  For example, Chao (1968) agrees with Z. Lu (1957) that a word can fill the functional frame of a typical syntactic structure.  Dai (1993) points out that this method may effectively separate bound morphemes from free words, it cannot differentiate between words and phrases, as phrases may also be positioned in a syntactic frame.  In fact, whether this method can indeed separate bound morphemes from free words is still a problem.  This method cannot be made operational unless the definition of ‘frame of a typical syntactic structure’ is given.  The judgment methods proposed in this section try to avoid this ‘lack of operationality’ problem.

Dai (1993) made a serious effort in proposing a series of methods for cutting the line between morphemes and syntactic units in Chinese.  These methods have significantly advanced the study of this topic.  However, Dai admits that there is limitation associated with these proposals.  While each proposed method provides a sufficient (but not necessary) condition for judging whether a unit is a morpheme,  none of the methods can further determine whether this unit is a word or a phrase.  For example, the method of syntactic independence tests whether a unit in a question can be used as a short answer to the question.  If yes, the syntactic independence is confirmed and this unit is not a morpheme inside a word.  Obviously, such a method tells nothing about the syntactic rank of the tested unit because a word, a phrase or clause can all serve as an answer to a question.  In order to achieve that, other methods and/or analyses need to be brought in.

The first judgment method proposed below involves passivization and topicalization tests.  In essence, this is to see whether a string involves syntactic processes.  As an atomic unit, the internal structure of a word is transparent to syntax.  It follows that no syntactic processes are allowed to exert effects on the internal structure of a word.[5]  As  passivization and topicalization are generally acknowledged to be typical syntactic processes, if a potential combination A+B is subject to passivization B+bei+A and topicalization B+…+NP+A, it can be concluded that A+B is not a word:   the relation between A and B must be syntactic.

The second method is to define an unambiguous pattern for the wordhood judgment, namely, judgment patterns.  Judgment patterns are by no means a new concept.  In particular, keyword based judgment patterns have been frequently used in the literature of Chinese linguistics as a handy way for deterministic word category detection (e.g. L. Wang 1955;  Zhu 1985; Lü 1989).

The following keyword (i.e. aspect markers) based patterns are proposed for  judging a verb sign.

(4-2.)
(a) V(X)+着/过 à word(X)
(b) V(X)+着/过/了+NP à word(X)

The pattern (4-2a) states that if X is a sign of verb, no matter transitive or intransitive, appearing immediately before zhe/guo, then X is a word.  This proposal is backed by the following argument.  It is an important and widely acknowledged grammatical generalization in Chinese syntax that the aspect markers appear immediately after lexical verbs (Lü et al 1980).

Note that the aspect marker le (LE) is excluded from the pattern in (4‑2a) because the same key word le corresponds to two distinctive morphemes in Chinese:  the aspect le (LE) attaches to a lexical V while the sentence-final le (LEs) attaches to a VP (Lü et al 1980).  Therefore, judgment cannot be reliably made when a sentence ends in X+le, for example, when X is an intransitive verb or a transitive verb with the optional object omitted.  However, le in pattern (4-2b) has no problem since le is not in the ambiguous sentence final position.  This pattern says that if any of the three aspect markers appears between a sign X of verb and NP, X must be a word:  in fact, it is a lexical transitive verb.

There are two ways to use the judgment patterns.  If a sub-string of the input sentence matches a judgment pattern, one reaches the conclusion promptly.  If the input string does not match a pattern directly, one can still make indirect use of the patterns for judgment.  The idiomatic combination xi (wash) zao (bath) is a representative example.   Assume that the vocabulary word xi zao is a grammar word.  It follows that it should be able to fill in the lexical verb position in the judgment pattern (4-2a).  We then make a sentence which contains a sub-string matching the pattern to see whether it is grammatical.  The result is ungrammatical:  *ta (he) xi-zao (V) zhe (ZHE);  *ta (he) xi-zao (V) guo (GUO).  Therefore, our assumption must be wrong:  xi zao is not a grammar word.  We then change the assumption and try to insert aspect markers inside them (it is in fact an expansion test, to be discussed shortly).  The new assumption is that the verb xi alone is a grammar word.  What we get are perfectly grammatical sentences and they match the pattern (4-2b):  ta (he) xi (V) zhe (ZHE) zao (bath): ‘He is taking a bath’;  ta (he) xi (V) guo (GUO) zao (bath): ‘He has taken the bath’.  Therefore the assumption is proven to be correct.  This way, all V+X combinations can be judged based on the judgment patterns (4-2a) or (4-2b).

The third method proposed below involves a more general expansion test.  As an atomic unit in syntax, the internal parts of a word are in principle not separable.[6]  Lü (1989) emphasized inseparability as a criterion for judging grammar words.  But he did not give instructions how this criterion should be applied.  Nevertheless, many linguists (e.g. Bloomfield 1933; Z. Lu 1957;  Lyons 1968; Dai 1993) have discussed expansion tests one way or another in assisting the wordhood judgment.

The method of expansion to be presented below for wordhood judgment is called X-insertion.  X-insertion is based on Di Sciullo and Williams’ thesis of the syntactic atomicity of word.  The rationale is that the internal parts of a word cannot be separated by syntactic constituents.

As a method, how to perform X-insertion is defined as follows.   Suppose that one needs to judge whether the combination A+B is a word.   If a sign X can be found to satisfy the following condition, then A+B is not a word, but a syntactic combination:  (i) A+X+B is a grammatical string,  (ii) X is not a bound morpheme, and (iii) the sub-structure [A+X] is headed by A or the sub-string [X+B] is headed by B.

The first constraint is self-evident:  a syntactic combination is necessarily a grammatical string.  The second constraint aims at  eliminating the danger of wrongly applying an infix here.  In fact, if X is a morphological infix, the conclusion would be just opposite:  A+B is a word.  The last constraint states that X must be a dependant of the head A (or B).  Otherwise it results in a different structure.  There is no direct structural relation between A and B when A (or B) is a dependant of the head X in the structure.  Therefore, the question of whether A+B is a phrase or a word does not apply in the first place.

After the wordhood judgment is made on strings of signs based on the above judgment methods and/or the arguments for the analysis involved, the next step is to have them properly represented (coded) in the grammar formalism used.  This is the topic to be presented in 4.3 below.

4.3. Formal Representation of Word

The expectation feature structure and structural phrase structure in the mono-stratal design of CPSG95 presented in Chapter III provide means for the formal definition of the basic unit word in CPSG95.  Once the wordhood judgment for a unit is made based on arguments for a structural analysis and/or using the methods presented in Section 4.2., the formal representation is required for coding it in CPSG95.

This type of formalization is required to ensure its implementability in enforcing a required configurational constraint.  For example, the suffix -xing expects an adjective word to form an abstract noun, such constraints [CATEGORY a] and @word can be placed in the morphological expectation feature [SUFFIXING].  These constraints will permit, for example, the legitimate derived word [yan-su]-xing] (serious-ness), but will block the following combination *[[fei-chang yan-su]-xing] (very-serious-ness).  This is because [fei-chang yan-su] violates the formal constraint as given in the word definition:  it is not an atomic unit in syntax.

In CPSG95, word is defined as a syntactically atomic unit without obligatory morphological expectations, formally represented in the following macro.

word macro
a_sign
PREFIXING saturated | optional
SUFFIXING saturated | optional
STRUCT no_syn_dtr

Note that the above formal definition uses the sorted hierarchy [struct] for the structural feature structure and the sorted hierarchy [expected] for the expectation feature structure.  The definitions of these feature structures have been given in the preceding Chapter III.

Based on the sorted hierarchy struct: {syn_dtr, no_syn_dtr}, the constraint [no_syn_dtr] ensures that the word sign do not contain any syntactic daughter.[7]  This prevents syntactic constructions from being treated as words.  On the other hand, since [saturated], [obligatory] and [optional] are three subtypes of [expected], the constraint [saturated|optional] prevents a bound morpheme, say a prefix or suffix which has obligatory expectation in [PREFIXING] or [SUFFIXING], from being treated as a word.

This macro definition covers the representation of mono-morpheme words, e.g. e ‘goose’, du ‘read’, etc., or multi-morpheme words, e.g. xiao-kan ‘look down upon’, tian-e ‘swan’, etc., as well as unlisted words such as derived words whose internal morphological structures have already been formed.  Some typical examples of word are shown below.

For a derived word, note that the specification of [PREFIXING satisfied] and [STRUCT prefix], or [SUFFIXING satisfied] and [STRUCT suffix], assigned by the corresponding PS rule is compatible with the macro word definition.

The above word definition is an extension of the corresponding representation features from HPSG (Pollard and Sag 1987).  HPSG uses a binary structural feature [LEX] to distinguish lexical signs, [LEX +], and non-lexical signs, [LEX -].  In addition, [sign] is divided into [lexical_sign] and [phrasal_sign].[8]  Except for the one-to-one correspondence between [phrasal_sign] and [syn_dtr] in terms of rank (which stands for non-atomic syntactic constructs including phrases), neither of these HPSG binary divisions account for the distinction between a bound morpheme and a free morpheme.  Such a distinction is not necessary in HPSG because bound morphemes are assumed to be processed in the preprocessing stage (e.g. lexical rules for English inflection, Pollard and Sag 1987) and do not show themselves as independent input to the parser.  As CPSG95 involves both derivation morphology and syntax in an integrated general grammar, the HPSG binary divisions are no longer sufficient for formalizing the word definition.  ‘Word’ in CPSG95 needs to be distinguished with proper constraints from not only syntactic constructs, but also from affixes (bound morphemes).

In CPSG95, as productive derivation is designed to be an integrated component of the grammar, the word definition is both specified in the lexicon for some free morpheme words and assigned by the rules in morphological analysis.  This practice in essence follows one  suggestion in the original HPSG book:  "we might divide rules of grammar into two classes: rules of word formation, including compounding rules, which introduce the specification [LEX +] on the mother, and other rules, which introduce [LEX -] on the mother." (Pollard and Sag 1987:73).

It is worth noticing that words thus defined can fill either a morphological position or a syntactic position.  This reflects the interface nature of word:  word is an eligible unit in both morphology and syntax.  This is in contrast to bound morphemes which can only be internal parts of morphology.

In morphology, derivation combines a word and an affix into a derived word.  These derivatives are eligible to feed morphology again.   This is shown above by the examples in (4-5) and (4-6).  The adjective word ke‑du (read-able) is derived from the prefix morpheme ke- (-able) and the word du (read).  Like other adjective words, this derived word can further combine with the suffix –xing (-ness) in morphology.  It can also directly enter syntax, as all words do.

To syntax, all words are atomic units.  If a lexical position is specified, via the macro constraint @word in CPSG95, in a syntactic pattern, it makes no difference whether a filler of this position is a listed grammar word, or an unlisted word such as a derivative.  Such distinction is transparent to the syntactic structure.

4.4. Summary

Efforts have been made to reach a better understanding of Chinese wordhood in theory, methodology and formalization.  The main spirit of the HPSG theory and Di Sciullo and Williams' ‘syntactic atomicity’ theory has been applied to the study of Chinese wordhood and its formal representation.  Some effective wordhood judgment methods have also been proposed, based on theoretical guidelines.

The above work in the area of Chinese wordhood study provides a sound foundation for the analysis of the specific Chinese morpho-syntactic interface problems in Chapter V and Chapter VI.

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[1] For Classical Chinese, word, morpheme, syllable and hanzi are presumably all co-extensive.  This is the so-called Monosyllabic Myth of Chinese (DeFrancis 1984: ch.8).  The development of large numbers of homophones, mainly due to the loss of coda stops, has led to the development of large quantities of bi-syllabic and poly-syllabic word-like expressions (Chen and Wang 1975).

[2] Classical Chinese arguably allows for a certain degree of compounding.  In the linguistic literature, some linguists (e.g. Sapir 1921; Zhang 1957; Jensen 1990) did not strictly distinguish Contemporay/Modern Chinese from Classical Chinese and they held the general view that Chinese has little morphology except for limited compounding.  But this view of Contemporary Chinese has been criticized as misconception (Dai 1993) and is no longer accepted by the community of Chinese grammarians.

[3] Di Sciullo and Williams call a sign listable in the lexicon listeme, equivalent to the notion vocabulary word.

[4] In the literature, variations of  this view include the Lexicalist position (Chomsky 1970), the Lexical Integrity Hypothesis (Jackendoff 1972), the Principle of Morphology-Free Syntax (Zwicky 1987), etc.

[5] This type of ‘atomicity’ constraint (Di Sciullo and Williams 1987) is generally known as Lexical Integrity Hypothesis (LIH, Jackendoff 1972), which states that syntactic rules or operations cannot refer to part of a word.  A more elaborate version of LIH is proposed by Zwicky (1987) as a Principle of Morphology-Free Syntax.  This principle states that syntactic rules cannot make reference to the internal morphological composition of words.  The only lexical properties accessible to syntax, according to Zwicky, are syntactic category, subcategory, and features like gender, case, person, etc.

[6] Of course, in theory a word may be separated by morphological infix.  But except for the two modal signs de3 (can) and bu (cannot) (see Section 5.3 in Chapter V), there does not seem to exist infixation in Mandarin Chinese.

[7] In terms of rank, [no_syn_dtr] in CPSG95 corresponds to the type [lexical_sign] in HPSG (Pollard and Sag 1987).  A binary division between [lexical_sign] and [phrasal_sign] is enough in HPSG to distinguish the atomic unit word from syntactic construction.  But, as CPSG95 incorporates derivation in the general grammar, [no_syn_dtr] covers for both free morphemes and bound morphemes.  That is why the [no_syn_dtr] constraint on [STRUCT] alone cannot define word in CPSG95;  it needs to involve constraints on morphological expectation structures as well, as shown in the macro definition.

[8] Note that there are [LEX -] signs which are not of the type [phrasal_sign].

[Related]

PhD Thesis: Morpho-syntactic Interface in CPSG (cover page)

PhD Thesis: Chapter I Introduction

PhD Thesis: Chapter II Role of Grammar

PhD Thesis: Chapter III Design of CPSG95

Overview of Natural Language Processing

Dr. Wei Li’s English Blog on NLP