The preverbal adverbials hehu (何忽) and nahu (那忽) appeared in Middle Chinese, meaning to ask for reason, to interrogate, and to ask questions. Some previous studies viewed hehu and nahu as disyllabic words, which are simply equivalents to he (何) and na (那), meaning why and how. In spite of not explicitly stating hehu and nahu as words, some other studies considered hu (忽) as carrying no meaning and merely a particle to form a syllable. This paper finds that there are some differences between hehu and he, nahu and na through investigating corpus data from the same period, with a large number of examples in the Chinese Buddhist scriptures. Sentences with hehu and nahu as adverbials often express a sense of surprise and accusation caused by sudden occurrence or discovery of something. The expanded forms for hehu include ruhe hu (如何忽), yunhe hu (雲何忽), ruhe huran (如何忽然), yunhe huran (雲何忽然) and yunhe hu-er (雲何忽爾), while the expanded forms for nahu include naihe hu (奈何忽), naihe huran (奈何忽然), naihe hu-er (奈何忽爾) and naihe huyan (奈何忽焉). In the literature of past dynasties, the morpheme hu found in disyllabic words had a concrete meaning, and was not used as an auxiliary word to form a syllable. Therefore, it is proposed that the hu in hehu and nahu is not an auxiliary morpheme and it conveys a concrete meaning of sudden. Hehu and nahu are not disyllabic words, but solidified forms resulting from the combination of two monosyllabic words.
