Measure words are measurably different from sortal classifiers (2023)

Abstract: Nominal classifiers categorize nouns based on salient semantic properties. Past studies have long debated whether sortal classifiers (related to intrinsic semantic noun features) and mensural classifiers (related to quantity) should be considered as the same grammatical category. Suggested diagnostic tests rely on functional and distributional criteria, typically evaluated in terms of isolated example sentences obtained through elicitation. This paper offers a systematic re-evaluation of this long-standing question: using 981,076 nominal phrases from a 489 MB dependency-parsed word corpus, corresponding extracted contextual word embeddings from a Chinese BERT model, and information-theoretic measures of mutual information, we show that mensural classifiers can be distributionally and functionally distinguished from sortal classifiers justifying the existence of distinct syntactic categories for mensural and sortal classifiers. Our study also entails broader implications for the typological study of classifier systems.

## introduction classifier systems constitute a major feature of east and south-east asian languages (li, 2013). classifiers categorize referent nouns based on salient semantic features such as humanness, animacy, shape, or others (aikhenvald and mihas, 2019). in mandarin, classifiers are obligatory when a noun is preceded by a number, a demonstrative, or a quantifier (li and thompson, 1989). for example, the classifier (in bold font) cannot be omitted in the following examples from li (2013): 两 liǎng *(个 gè) 学生 xuéshēng 'two students', 这 zhè *(种 zhǒng) 动 物 dòngwù 'this kind of animal', 每 měi *(本 běn) 书 shū 'every book'. in other contexts, however, classifiers can be optional. in addition to sortal classifiers, which categorize nouns in terms of intrinsic semantic features, classifier systems also include mensural classifiers (or measure words), that are related to noun quantity. while sortal classifiers, like 张 zhāng, are typically associated with nouns displaying specific intrinsic semantic features, e.g., flat properties such as for the noun 地图 dìtú 'map', mensural classifiers like 组 zǔ 'group', 斤 jīn 'half kilogram', or 美元 měiyuán 'us dollar' are usually characterized as being less restricted by the semantics of the nouns they combine with. in this paper, mensural classifiers like 组 zǔ 'group' will be referred as quantity, those like 斤 jīn 'half kilogram' and 美元 měiyuán 'us dollar' will be referred as measurement and currency units respectively. in addition, dryer et al. (2005) and li (2013) indicate that sortal classifiers tend to be combined with countable nouns (e.g., 三 sān 本 běn 书 shū 'three books', 三 sān 只 zhī 碗 wǎn 'three bowls') while mensural classifiers refer to quantities of mass nouns (or "nouns with low countability") such as 三 sān 箱 xiāng 水 shuǐ 'three boxes of water' and 三 sān 斤 jīn 米 mǐ 'three half-kilograms of rice'. however those distinctions are not systematic: countable nouns can also be modified by mensural classifiers and mass nouns by sortal classifiers. for instance, the countable noun, 书 shū 'book' can be found in a nominal phrase such as 三 sān 箱 xiāng 书 shū 'three boxes of books', and the mass noun, 米 mǐ 'rice' can be modified by a sortal classifier in 三 sān 粒 lì 米 mǐ 'three grains of rice'. given their apparent similarities and differences, typological and general linguistic studies have long debated whether sortal and mensural classifiers should be considered as the same syntactic category (e.g., lyons, 1977; li and thompson, 1989) or two different categories (e.g., nguyen, 2004; singhapreecha, 2001; her and hsieh, 2010). in these studies, suggested diagnostic tests rely on functional and distributional criteria, typically evaluated in terms of isolated example sentences (goldhahn et al., 2012) using the corenlp parser (chen and manning, 2014). the examples show noun phrases including the sortal classifier 张 zhāng and three measure words for quantities 组 zǔ 'group', measurements 斤 jīn 'half kilogram', and currencies měiyuán 'us dollar'. our study is based on 981,076 manually validated noun phrases extracted from a 489mb corpus of mandarin chinese that is part of the leipzig corpora collection (goldhahn et al., 2012), an open access collection of pre-cleaned data. we preparsed the data using the corenlp chinese dependency parser (chen and manning, 2014). our results show that mensural classifiers can be distributionally and functionally distinguished from sortal classifiers. additionally two traditional subtypes of mensural classifiers (i.e., measurement and currency units) emerge as distinct from the other men-sural classifier subtype (which we will refer to as quantity). ## measuring categorial differences the goal of our study is to quantitatively evaluate whether distributional and functional properties of words traditionally labeled sortal vs. mensural classifiers suggest that they constitute a single or two separate syntactic categories in mandarin chinese. based on 981,076 manually validated noun phrases extracted from a 489mb corpus, we analyze the syntactic distributions of sortal and mensural classifiers, as well as the differences in their communicative function for natural language use. we used contextual word embeddings as a measure of classifier distributions and mutual information (mi) (cover and thomas, 2012) as a measure of their contribution to facilitating noun predictability. ## discussion and relation to previous work there is a longstanding debate as to whether mensural and sortal classifiers should be considered as the same grammatical category in mandarin chinese (or in classifier languages in general). despite a general consensus that categorization should be performed on the basis of observable distributions and functions, researchers' conclusions diverge. for some, sortal and mensural classifiers should be considered as one category since they can occur in similar contexts (e.g., lyons, 1977; cheng and sybesma, 1999; paik and bond, 2002; bender and siegel, 2004; gebhardt, 2011). @xcite others argue that sortal and mensural classifiers should be considered as distinct since they cannot be modified in the same way (her and hsieh, 2010; singhapreecha, 2001; nguyen, 2004). her and hsieh (2010) specifically argue that the difference between sortal and mensural classifiers is mainly semantic but has consequences on distributional properties: mensural classifiers are semantically substantive and block numeral quantification and adjective modification of the noun, whereas sortal classifiers are semantically null and not as restrictive. @xcite similar differences are also claimed to exist in other classifier languages, such as thai (singhapreecha, 2001) or vietnamese (nguyen, 2004). in vietnamese, for instance, mensural classifiers are described as sometimes occurring with modifiers inserted between the classifier and the head noun, whereas nothing can be inserted between a sortal classifier and its head noun. in general, previous literature arguing for separate categories for sortal and mensural classifiers tends to highlight that mensural classifiers can occur with more modifiers than their sortal counterparts. this is another way of saying that mensural classifiers are considered to allow a wider range of distributions than sortal classifiers. our results appear to corroborate that claim. overall, in our results sortal and mensural classifiers do not appear to significantly overlap in their distributions, suggesting the existence of two distinct categories from a distributional perspective. but the umap plot in figure 1 also shows more different distributions for mensural classifiers than for sortals, especially if generic quantities, currencies, and units of measure are analyzed as one group. as an overarching category, mensural classifiers -including quantities, units of measurements, and currencies -appear to have a very diverse range of distributions. given the very specific distributions for currencies and measurements, our data and the results of our analysis of classifier distributions appears to suggest that those might be better distributionally analyzed as three separate categories. even if we only compare generic quantities to sortal classifiers, the range of projections associated with the mensural classifiers clearly exceeds that of the sortals, in line with conclusions drawn by proponents of separate syntactic categories. from a functional perspective, some researchers have attempted to argue that mensural classifiers should be considered as belonging to the same syntactic category as their sortal counterparts because of the parallel roles they play within noun phrases (see lyons, 1977; cheng and sybesma, 1999; paik and bond, 2002; bender and siegel, 2004; gebhardt, 2011, among others). @xcite the results of our tests to differentiate sortal and mensural classifiers: numeral/adjectival stacking modification, de-insertion, and gesubstitution. our study focuses on differences in the communicative function across classifier types. while we assume, based on evidence found for german gendered articles (dye et al., 2017, 2018), that all classifiers will to some degree help anticipate the upcoming noun in the noun phrase they occur in, we wanted to test whether there would be a significant difference in the amount of mi effectively shared between the classifiers and their head noun. such a significant difference would then suggest the existence of multiple syntactic categories associated with classifiers. related work by liu et al. (2019) used mi to investigate how systematically classifiers can be predicted from the semantics of a given noun. the answer to that question would be relevant to questions related to classifier learning, but is distinct from our study. by focusing on the relation between noun entropy and its reduction in the presence of a classifier, we are specifically targeting the predictive value of classifiers in noun phrase processing. @xcite our results show that there are significant differences in how much different types of classifiers help predict upcoming head nouns, with currency and measure units being the most predictive, classifiers denoting generic quantities ranking second, and sortal classifiers being the least helpful. interestingly, while our results do suggest the existence of three different classifier categories from a functional perspective, the observed functional contributions are the opposite of what previous literature would have suggested. proponents of distinct classifier categories typically argue that while sortal classifiers are associated with nouns based on their referents' inherent properties (such as shape, humanness, animacy, etc.), mensural classifiers denote quantities not directly related to the nouns' meanings (see for example jarkey and komatsu, 2019; unterbeck, 1994), suggesting that sortal classifiers would be more specifically linked to the nouns they combine with. @xcite what we see in the results of our mi calbe used to quantify nouns. @xcite lau and grüter (2015) also investigate classifiers from a processing perspective, but using an experimental approached based on eye-tracking experiments involving l2 speakers of mandarin. ## conclusion the distinction between sortal and mensural classifiers has been a long-standing debate in the fields of chinese, (south-)east asian linguistics, general linguistics and linguistic typology. previous literature attempted to solve this problem using isolated example sentences and categorical grammaticality judgements. in this paper, we instead systematically re-evaluate the distributional and functional properties of classifiers using quantitative methodologies. using 981,076 noun phrases from a 489mb dependency-parsed corpus of mandarin chinese, we show that mensural and sortal classifiers are indeed measurably different both in their distributions and their functional contribution to noun phrase processing. we further find that mensural classifiers do not constitute a homogeneous class. based on both their very specific distributions and they very significantly different functional contributions, units of measurement and currency can be classified as one if not two classes that are distinct from both sortal classifiers and generic measure words. our results also include two broader typological implications: since (i) sortal and mensural classifiers can be reliably identified as distinct categories in at least one language, (ii) the most promising line of analysis for further typological investigations into classifier systems will investigate whether languages with classifier systems cluster into two discrete types: those with separate categories for sortal and mensural classifiers, and those without a clear sortal/mensural split.