Rethinking the Relationship between the Power Law and Hierarchical Structures

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Hauptverfasser: Nakaishi, Kai, Yoshida, Ryo, Kajikawa, Kohei, Hukushima, Koji, Oseki, Yohei
Format: Preprint
Veröffentlicht: 2025
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author Nakaishi, Kai
Yoshida, Ryo
Kajikawa, Kohei
Hukushima, Koji
Oseki, Yohei
author_facet Nakaishi, Kai
Yoshida, Ryo
Kajikawa, Kohei
Hukushima, Koji
Oseki, Yohei
contents Statistical analysis of corpora provides an approach to quantitatively investigate natural languages. This approach has revealed that several power laws consistently emerge across different corpora and languages, suggesting universal mechanisms underlying languages. In particular, the power-law decay of correlations has been interpreted as evidence of underlying hierarchical structures in syntax, semantics, and discourse. This perspective has also been extended beyond corpora produced by human adults, including child speech, birdsong, and chimpanzee action sequences. However, the argument supporting this interpretation has not been empirically tested in natural languages. To address this gap, the present study examines the validity of the argument for syntactic structures. Specifically, we test whether the statistical properties of parse trees align with the assumptions in the argument. Using English and Japanese corpora, we analyze the mutual information, deviations from probabilistic context-free grammars (PCFGs), and other properties in natural language parse trees, as well as in the PCFG that approximates these parse trees. Our results indicate that the assumptions do not hold for syntactic structures and that it is difficult to apply the proposed argument not only to sentences by human adults but also to other domains, highlighting the need to reconsider the relationship between the power law and hierarchical structures.
format Preprint
id arxiv_https___arxiv_org_abs_2505_04984
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Rethinking the Relationship between the Power Law and Hierarchical Structures
Nakaishi, Kai
Yoshida, Ryo
Kajikawa, Kohei
Hukushima, Koji
Oseki, Yohei
Computation and Language
Statistical analysis of corpora provides an approach to quantitatively investigate natural languages. This approach has revealed that several power laws consistently emerge across different corpora and languages, suggesting universal mechanisms underlying languages. In particular, the power-law decay of correlations has been interpreted as evidence of underlying hierarchical structures in syntax, semantics, and discourse. This perspective has also been extended beyond corpora produced by human adults, including child speech, birdsong, and chimpanzee action sequences. However, the argument supporting this interpretation has not been empirically tested in natural languages. To address this gap, the present study examines the validity of the argument for syntactic structures. Specifically, we test whether the statistical properties of parse trees align with the assumptions in the argument. Using English and Japanese corpora, we analyze the mutual information, deviations from probabilistic context-free grammars (PCFGs), and other properties in natural language parse trees, as well as in the PCFG that approximates these parse trees. Our results indicate that the assumptions do not hold for syntactic structures and that it is difficult to apply the proposed argument not only to sentences by human adults but also to other domains, highlighting the need to reconsider the relationship between the power law and hierarchical structures.
title Rethinking the Relationship between the Power Law and Hierarchical Structures
topic Computation and Language
url https://arxiv.org/abs/2505.04984