This paper presents aspects of eight advanced Korean EFL speakers' acquisition of English unaccusative verbs over a period of five years. It examines how three factors−L1 morphology, pragmatic causation, and animacy−have affected their English unaccusative verb grammar during that time. A forced-elicitation grammaticality judgment task was performed three times over this period. It showed that L1 morphology was the most persistent among these factors. The results are compared with Chung (2014), a cross-sectional study, where the same method was used. The findings reveal that the Korean EFL subjects' overpassivization of English unaccusatives is not fossilized, which differs from the findings of Han (2006), who examined two Chinese native learners of English. It also indicates that instruction can play an important role in long-term L2 learning.

There are two types of unaccusative verbs in English: change-type verbs and happen-type verbs. Korean learners of English seem to have serious acquisition problems of these verbs. The purpose of this study is to find the way to increase the acquisition rate of these verbs depending on two kinds of teaching methods: explicit focus-on-form instruction and implicit focus-on-form instruction and to observe which instructional technique is more effective in the Korean EFL learners' acquisition of these verbs. Through 10 weeks of instruction, this study showed that the learners who received the explicit focus-on-form instruction performed better than those who received the implicit instruction regarding the learning of English unaccusative verbs. Therefore, these results can be interpreted as providing evidence for facilitating the effectiveness of input enhancement for the L2 learning of English unaccusative verbs.

This paper examines Korean learners’ difficulties with English unaccusative verb acquisition. 41 high school students, comprising the low proficiency group and 50 university students, constituting the high proficiency group, participated in judging two kinds of grammaticality tests (context-given and context-free). The first results revealed that at their English proficiency levels, context did not make any difference in judging the grammaticality of unaccusative verb. The second results showed that both groups of learners had more difficulty in acquiring melt-type (unaccusative verbs with transitive counterparts) than die-type (unaccusative verbs without transitive counterparts), and had the most difficulty unlearning NP-be+Ven structure of melt-type, followed by NP-V-NP structure of die-type and NP-be+Ven structure of die-type. It is suggested that the results of this study can be applied to learning and teaching unaccusative verbs in English classrooms and that future research focus on the possibility of advanced learners’ accepting nativelike NP-V order of unaccusative verbs.