义务缺口：大语言模型与义务的模态语言
The Deontic Gap: Large Language Models and the Modal Language of Obligation
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中文总结 AI 辅助
本研究发现大语言模型的义务情态使用模式与当代人类存在缺口，其情态使用反映训练的正式书面资源，少用标记即时人际义务的情态结构。
中文摘要 AI 辅助
诸如 must、should、have to 等情态助动词，在说话者权威和人际立场语境中标记必要性与义务。本研究考察大语言模型（LLMs）是否再现当代人类的义务情态使用模式。在三个主要语料库、一个外部基准、两项控制复现实验以及自然主义的11个模型复现实验中，AI生成文本始终比当代人类更少使用肯定义务情态词（must、should、have to、had to）。以谷歌图书Ngram语料库（1920-2022）作为已出版散文记录的启发式校准，历史对比显示AI的情态频率处于正式出版英语的范围内，而非正式数字语境中当代人类的情态使用率常超过20世纪书籍基准。短语层面分解表明，AI-人类的情态缺口集中于人际立场核心结构（should、have to、had to），而AI在教学和问答语境中对 need to 的使用与人类相当或超出，但在说服性学生写作中并非如此，说明情态特征具有体裁条件性。研究发现表明，LLM的情态使用反映了其训练所用的正式书面资源，同时少用当代人类作家用以标记即时人际义务的情态结构。
英文摘要
Modal auxiliaries such as must, should, and have to mark necessity and obligation within the contexts of speaker authority and interpersonal stance. We examine whether large language models (LLMs) reproduce contemporary human patterns of deontic modal usage. Across three primary corpora, an external benchmark, two controlled replications, and a naturalistic eleven-model replication, AI-generated text consistently underuses positive deontic modals (must, should, have to, had to) relative to contemporary humans. Historical comparison with the Google Books Ngram corpus (1920-2022), used as a heuristic calibration against the published-prose record, shows that AI modal frequencies fall within the range of formal published English, whereas contemporary human modal rates in informal digital contexts often exceed twentieth-century book baselines. Phrase-level decomposition shows that the AI-human modal gap is concentrated in constructions central to interpersonal stance (should, have to, had to), while AI matches or exceeds humans on need to in instructional and question-answering contexts but not in persuasive student writing, indicating that the modal profile is genre-conditional. The findings suggest that LLM modal usage reflects the formal written resources on which these models were trained, while underusing the modal constructions through which contemporary human writers mark immediate, interpersonal obligation.
