Is J apanese CCGB ank empirically correct? A case study of passive and causative constructions (2023)

Abstract: The Japanese CCGBank serves as training and evaluation data for developing Japanese CCG parsers. However, since it is automatically generated from the Kyoto Corpus, a dependency treebank, its linguistic validity still needs to be sufficiently verified. In this paper, we focus on the analysis of passive/causative constructions in the Japanese CCGBank and show that, together with the compositional semantics of ccg2lambda, a semantic parsing system, it yields empirically wrong predictions for the nested construction of passives and causatives.

## introduction the process of generating wide-coverage syntactic parsers from treebanks was established in the era of probabilistic context-free grammar (cfg) parsers in the 1990s. however, it was believed at that time that such an approach did not apply to linguistically-oriented formal syntactic theories. the reason was that formal syntactic theories were believed to be too inflexible to exhaustively describe the structure of real texts. this misconception was dispelled by the theoretical development of formal grammars and the emergence of linguistically-oriented treebanks. 1 in particlar, combinatory categorial grammar (ccg) @xcite and ccgbank @xcite gave rise to the subsequent developments of ccg parsers such as c&c parser @xcite and easyccg parser @xcite , and proved that wide-coverage ccg parsers could be generated from treebanks in a similar process to probablistic cfg parsers. this trend has also impacted research on japanese syntax and parsers. @xcite revealed that ccg, as a syntactic theory, enables us to provide a wide-coverage syntactic description of the japanese language. it motivated the development of the japanese ccgbank @xcite , followed by japanese ccg parsers such as jigg @xcite and depccg @xcite . the difficulty in developing the japanese ccg-bank lay in the absence of cfg treebanks for the japanese language at that time. 2 while ccgbank was generated from the penn treebank, which is a cfg treebank, the only large-scale treebank available for japanese was the kyoto corpus 3 , which is a dependency tree corpus, from which @xcite attempted to construct a japanese ccgbank by automatic conversion. the syntactic structures of ccg have more elaborated information than those of cfg, such as argument structures and syntactic features. thus, it is inevitable that a dependency tree, which has even less information than that of cfg, must be supplemented with a great deal of linguistic information. @xcite had to guess them systematically, which is not an obvious process, and ad-hoc rules had to be stipulated in many places to accomplish it, including the "passive/causative suffixes as s\s analysis," which we will discuss in section 3. since ccgbank serves as both training and evaluation data for ccg parsers, syntactic descriptions 2 recently, a large-scale cfg treebank for the japanese language is available as a part of ninjal parsed corpus of modern japanese https://npcmj.ninjal.ac.jp/ , and there is also an attempt to generate a treebank of better quality by using it @xcite . however, the questions of what is empirically problematic about the japanese ccgbank and, more importantly, why it is, remain undiscussed. the importance of answering these questions as we do in this paper is increasing, given that attempts to generate a ccgbank from a dependency corpus such as universal dependency are still ongoing (cf. @xcite ). taro-ga taro-nom t /(t \n p ga ) jiro-ni jiro-dat t /(t \n p ni ) homera praise s\n p ga \n p o re passive s\n p ga \n p ni \(s\n p ga \n p ni|o ) s\n p ga \n p @xmath0, which inherit any empirical fallacies in ccgbank: thus the validity of the syntactic structures in ccgbank is important. however, little research from the perspective of formal syntax has been conducted regarding the adequacy of syntactic structures contained in treebanks. this paper aims to assess the syntactic structures exhibited by the japanese ccgbank from the viewpoint of theoretical linguistics. specifically, we focus on the syntax and semantics of case alternation in passive and causative constructions in japanese, a linguistic phenomenon analyzed differently in the standard japanese ccg and ccgbank, and show that the syntactic analysis of the japanese ccgbank contains empirical fallacies. ## passive and causative constructions in japanese we first present some empirical facts about japanese passives and causatives and how they are described in the standard japanese ccg @xcite . ga-marked noun phrases (henceforth n p ga ) in passive sentences correspond to nimarked noun phrases (henceforth n p ni ) or omarked noun phrases (henceforth n p o ) in the corresponding active sentences, which is expressed as (1) in the form of inferences. taro-nom jiro-ni jiro-dat homera-re-ta praise-passive-@xmath1.) 'taro is praised by jiro.' =⇒ 'jiro praised taro.' next, n p ni or n p o in causative sentences correspond to n p ga in the corresponding active sentences, which is also expressed in the form of inference as in (2). (2) taro-ga taro-nom jiro-{ni|o} jiro-{dat|acc} hasira-se-ta run-causative-@xmath2.) 'taro made jiro run.' =⇒ 'jiro run.' according to @xcite , the syntactic structure of the left-side sentences of (1) and ( 2 ) are as shown in figure 1 . for simplicity (omitting analysis of tense, etc.), let us assume that the semantic representations of taro-ga, jiro-{ni|o}, homera, hasira, and ta are respectively defined as λp.p (t),λp.p (j), λy.λx.λk. (e : ev) × praise(e, x, y) × ke, λx.λk. (e : ev) × run(e, x) × ke, id by using event semantics @xcite with continuations @xcite in terms of dts (dependent type semantics) @xcite , where id is the identity function and ev is the type for events. then the core of the analysis of case alternation is to define semantic representations of the passive suffix re and the causative suffix se, homomorphically to their syntactic categories, as 1 ) and (2) in ccgbank passive constructions, n p ga corresponds to the n p o or n p ni , and n p ni corresponds to n p ga , in their active counterparts. in causative constructions, n p ni|o corresponds to n p ga in their active counterparts. assuming the event continuation k is replaced by the term λe.⊤ at the end of the semantic composition (where ⊤ is an enumeration type with only one proof term and plays the role of "true"), the semantic composition ends up in the following representations for the left-side sentences of (1) and (2), respectively. the constituent hasira-sera-re is the passivization of hasira-sera, the matrix predicate of the left-side sentence of (2) that is equivalent to the right-side sentence of ( 9 ), and thus also entails the right-side sentence of (2). the semantic representation of hasira-sera-re is obtained by a functional application of (4) to the semantic representation of hasira, followed by a functional application of (3), as follows. ## ccg2lambda and the s\s analysis analysis using a compositional semantic system ccg2lambda @xcite relies on the syntactic structures output by the japanese ccg parsers jigg or depccg. as mentioned in section 1, the output of these ccg parsers depends on japanese ccgbank. in japanese ccgbank, the lexical assignments for the left-side sentences of (1) and ( 2 ) are as shown in figure 2 , in which both the passive suffix re and the causative suffix se have the syntactic category s\s. let us glance over how non-passive sentences in ccgbank are semantically analyzed. the semantic representation of the two-place predicate homera is given as follows (slightly simplified). this appears to be considerably more complex than that of homera in the previous section. this is because in ccg2lambda, the relations between ag (=agent) and x 1 , e and between th (=theme) and x 2 , e are relativized by the higher-order variables c 1 , c 2 . after taking an n p ni for q 2 and an n p ga for q 1 to become the constituent of syntactic category s, ccg2lambda applies to it the function λs.s(λxet.(t (e) = x), λxet.(t (e) = x), id). this causes λxet.(t (e) = x) to be assigned to c 1 and c 2 to specify ag(e) = x 1 and th(e) = x 2 , and id to be assigned to k. assuming λp.p (t) and λp.p (j) for the semantic representations of taro-ga and jiro-ni, the semantic representation of the right-side of (1) is obtained as (12), which is a standard neo-davidsonian semantic representation @xcite for jiro praised taro. by contrast, in ccg2lambda the semantic representation of re is overwritten by the semantic template as (13 v is instantiated by the semantic representation of the adjacent transitive verb (=homera in this case). the semantic representation of homera-re thus becomes (14 that is, the semantic roles received by c 1 , c 2 in (11) are discarded, and instead c 1 is given th and c 2 is given ag. by applying λp.p (t), λp.p (j), and λs.s(λxet.(t (e) = x), λxet.(t (e) = x), id) sequentially, the left-side of ( 1 because this is the same as (12), the inference (1) is correctly predicted. similarly, for causative suffixes, given a semantic template (16 thus, the left-side of the (2) will be ( 18 however, this analysis produces incorrect predictions for nesting: the semantic representation of hasira-sera-re is obtained by applying (13) to ( 17 ), which ends up in ( 19 ). notice that (19) is identical to the one obtained by applying passive suffix re directly to hasira (i.e., hasira-re). from here, neither the right-side of ( 9 ) = (2) nor the left-side of (2) is implied. this error occurs because the passive suffix globally assumes that the first argument is given th and the second argument is given ag. on the contrary, the nesting example shows that the passive suffix connects the first and the second arguments in matrix with the second and the first argument of the verb, respectively. capturing this behaviour of the passive suffix requires the verb's first and second arguments to be accessible from the syntax and the semantics of the passive suffix, which means the syntactic category of the passive suffix should be exactly s\n p ga \n p ni \(s\n p ga \n p ni|o ). ## conclusion in this paper, we showed that the syntactic analysis of japanese ccgbank together with the semantic analysis of ccg2lambda produces false predictions for passive and causative nesting, which means that the current syntactic analysis of passive/causative constructions in japanese ccgbank does not have a semantic support that correctly predicts the inferences such as (1), (2), and (9). in other words, the claim that re and se have the syntactic category s\s cannot be maintained. since the standard analysis described in section 2 correctly explains all of those inferences, the burden of proof is clearly on the ccgbank side. an important implication of this paper is that there is a need for outreach to the linguistic community, where not all linguists regard a treebank as an output of a linguistic analysis. we suggest that we should treat treebanks as outputs of some linguistic analyses and try to provide counterexamples in this way in order to keep treebanks and also the subsequent development of syntactic parsers sound from the linguistic perspective.