Unsupervised Adverbial Identification in M odern C hinese Literature (2021)

Abstract: In many languages, adverbials can be derived from words of various parts-of-speech. In Chinese, the derivation may be marked either with the standard adverbial marker DI, or the non-standard marker DE. Since DE also serves double duty as the attributive marker, accurate identification of adverbials requires disambiguation of its syntactic role. As parsers are trained predominantly on texts using the standard adverbial marker DI, they often fail to recognize adverbials suffixed with the non-standard DE. This paper addresses this problem with an unsupervised, rule-based approach for adverbial identification that utilizes dependency tree patterns. Experiment results show that this approach outperforms a masked language model baseline. We apply this approach to analyze standard and non-standard adverbial marker usage in modern Chinese literature.

## introduction in many languages, adverbials can be derived from words of other parts-of-speech (pos). the adverbials are often morphologically marked in the derivation process. in english, the most common marker is the suffix "-ly", for example in the derivation of "happily" from the adjective "happy". in chinese, the focus of our study, the standard adverbial marker is di (地) foot_0 , which can be suffixed to a wide variety of adverbs, adjectives and verbs to form adverbials. however, a non-standard adverbial marker, the suffix de (的), is also used frequently, in some contexts on par with the standard marker @xcite . chinese parsers tend to be trained on standard texts that mostly employ the standard adverbial marker. indeed, many chinese treebank guidelines @xcite mention only di as the adverbial marker. as a result, even stateof-the-art parsers might not accurately detect adverbials formed with the non-standard marker. this affects not only parser accuracy but also downstream nlp tasks, as well as linguistic research on the de vs. di choice. this paper investigates the task of adverbial identification, including adverbials marked both in the standard and non-standard manner. due to the lack of annotated data for non-standard adverbials, our research focus is on unsupervised methods. we propose a simple yet effective approach for adverbial identification based on pos tag and dependency tree patterns. in an evaluation on texts drawn from modern chinese literature, our approach achieved over 87% accuracy, outperforming a state-of-theart masked language model. 2 to our knowledge, this is the first reported study on identifying deand di-adverbials in chinese text. the rest of the paper is organized as follows. the next section provides the necessary linguistic background for adverbials in chinese. section 3 summarizes previous work. section 4 describes our approach and the baselines. section 5 presents our evaluation dataset. section 6 discusses experimental results. section 7 applies our research to the analysis of adverbial marker choice of a prominent chinese author. finally, section 8 concludes. ## adverbials in chinese every suffixed adverbial in chinese can be rendered in one of two forms. the adjective gaoxing 高兴 'happy', for example, can be transformed into an adverbial either with the standard di suffix (gaoxing-di 高兴地 'happily') or the non-standard de suffix (gaoxing-de 高兴的 'happily'). we will henceforth refer to the former as "di-adverbials" and the latter as "de-adverbials". detecting the de-adverbials can be challenging because of the dual role of the de suffix: it serves both as the non-standard adverbial marker and as the (standard) attributive marker. a de-suffixed word can therefore potentially be either an adverbial or an adjectival phrase. for example, gaoxing-de is an adverbial in the expression gaoxing-de chang zhe ge 'happily sing a song', but it is an adjectival phrase in the expression gaoxing-de rizi 'happy day' ( in the rest of this paper, we will use the term base word to refer to the word from which the adverbial is derived, and head word to refer to the word modified by the adverbial. in figure 1a , the adverbial gaoxing-de 'happily' has gaoxing 'happy' as its base word and chang 'sing' as its head word. ## background during the vernacular language movement @xcite , chinese intellectuals proposed to use de as the standard attributive marker and di as the standard adverbial marker ( neglection of the de-adverbials hampers both parsing accuracy and linguistics research. when parsers fail to recognize de-adverbials and other adverbials that modify adjectives, adverbs or a sentence @xcite , accuracy in adverbial identification would be affected @xcite . research on linguistic variation in chinese often addressed de as possessive and attributive marker, but not as adverbial marker @xcite . because of the ambiguity with the de suffix, most quantitative analyses on di-vs. de-adverbial usage required manual annotation or was restricted to relatively small sample sizes @xcite @xcite . previous research has utilized both rule-based and machine learning approaches to study chinese numeral classifiers that form quantity noun phrases @xcite . similar to our study, it was found effective to leverage syntactic criteria and linguistic rules to analyze relations between numeral classifiers, nominal head words and nouns. ## approach while the di suffix is a reliable identifier for diadverbials, a naive search for the de suffix would yield low precision in retrieving de-adverbials since de may also mark attributives. it is essential to determine the pos of the head word: de marks an adverbial if the head word is an adjective or verb, but it marks an attributive if the head word is a noun. ## data there is no publicly available, large-scale corpus of chinese text with annotations on adverbial markers. we focused on modern chinese literary works written during and after the vernacular language movement, when the division of labor between de and di was formalized. we created a corpus by extracting all works by four prominent chinese authors (guo moruo, lao she, lu xun, and mao duo) posted on the baiwan shuku website. 6 there are a total of 911 works containing over 6 million characters. a native speaker of chinese with formal training in linguistics examined three words in this corpus: manman 慢慢 'slow', keqi 客气 'courteous', and gaoxing 高兴 'happy'. each of the 1,057 occurrences was labelled as a base word in a de-adverbial (447 instances); a base word in a di-adverbial (465 instances); or neither (145 instances). ## experimental results pos+base+head. as shown in pos only. the adverbials extracted by this approach were almost always true positives, with high precision for both de-and di-adverbials. the recall, however, was affected by noise in pos tagging, especially for de-adverbials that do not modify verbs. pos+base. this method outperformed the proposed approach in recall both for di-adverbials (94.62%) and de-adverbials (97.32%). however, it suffered from low precision (76.66% for diadverbials and 76.45% for de-adverbials), partly due to false positives with incompatible head word pos. masked language model (mlm). this model achieved 100% precision but at the expense of low recall, especially for de-adverbials (66.00%). it had difficulty recognizing a de-adverbial especially when the verb is located at a long distance, in which case it tends to rank de higher than di. ## application as an application of this research, we present a case study on the de-vs. di-adverbial usage of lu xun, arguably the most influential writer in modern chinese literature. literary works are ideal for studying adverbial markers since marker choices are more likely to be consciously rather than randomly made. we used the pos+base+head method (section 4.1) to automatically label all suffixed adverbials in his writings in our corpus. over his career lu xun chose the de suffix 56.9% of the time and the di suffix in the rest. this overall figure, however, masks three distinct periods in which his marker usage varied. figure 2 shows a diachronic analysis, where each data point represents the average percentage of deadverbials and di-adverbials within the 5-year window centered on the year on the horizontal axis. the initial period, from 1917 to 1924, was dominated by the non-standard marker de. as he came under the influence of the vernacular movement, lu xun entered a second period around 1925. the de percentage dropped dramatically from 65.7% in 1924 to 44.7% in 1925, reflecting his "innovative work in style" in several significant publications in 1925 @xcite . in the 1930s, the call for a "mass language" gathered steam towards the end of the vernacular movement, with the goals of eradicating illiteracy and giving ordinary people access to writing. subsequently the latinized new writing movement blurred the distinction between the two markers, leading to the re-emergence of the unified use of de. an advocate of latinization, lu xun reverted to non-standard markers, with the de percentage approaching a similar level as the initial period. ## conclusions this paper has presented the first study on identifying both standard and non-standard adverbial markers. we have proposed an unsupervised, rulebased algorithm based on dependency tree patterns. in an evaluation on modern chinese literary text, our proposed method achieved an accuracy of over 87%, outperforming a state-of-the-art masked language model. finally, we applied it on a diachronic analysis of adverbial marker choice in the works of a prominent author. in future work, we aim to further improve performance in adverbial identification by incorporating supervised methods. as the de vs. di choice continues to evolve, it would also be interesting to examine contemporary authors and analyze their adverbial marker usage in comparison to those in the last century.