Japanese/Korean Linguistics

This study examines the acquisition order of Korean verb conjugational morphemes in first language (L1) development using Mean Length of Utterance (MLU) as a key indicator. Based on longitudinal spontaneous speech data from the Ryu Corpus (CHILDES), the study analyzes the emergence of grammatical forms such as tense, aspect, negation, and politeness. Results show that verb conjugational morphemes begin to appear at MLU 2.4–2.6, with significant grammatical expansion occurring at MLU 2.9–3.2. The acquisition follows a general sequence: present → past → imperfective → future. Negative forms, especially the pre-verbal an, are acquired early, while polite forms emerge later. The findings suggest that MLU is a more reliable measure of grammatical development than age, offering a more consistent framework for understanding Korean L1 acquisition.