抄録
The purpose of this study is to investigate the effectiveness of explicit grammar instruction regarding the subordinate conjunctions if and when for Japanese learners of English (JLEs). In particular, this study focuses on their semantic differences that seem to be confusing to JLEs. Since if and when seem to satisfy all the conditions Shirahata (2015) proposed for the effectiveness of explicit grammar instruction, it can be assumed that explicit instruction promotes the acquisition of the semantic differences between the two conjunctions. For data collection, out of the 102 university JLE participants, 58 received three explicit instruction sessions, each of which was held once a week for three consecutive weeks. JLEs’ comprehension was examined through grammatical judgement tests administered before, a week after, and 11 weeks after the instruction session. The results show that the explicit instruction was effective, and the aftereffect was maintained at least for 11 weeks after the last instruction session. Accordingly, the results indicate that the assumptions proposed by Shirahata (2015) are valid in case of the conjunction acquisition whose meanings can be indistinguishable.
https://ror.org/04hx9jj82 
