This research explores Japanese EFL learners’ repeated pragmalinguistic errors in using modal verbs for social functions. They may lead to stabilization (a temporal stop of learners’ development) and fossilization (a permanent loss of learners’ progress). Data from online forum discussions show that participants utilized limited English modal functions, while some seemed to have acquired certain pragmalinguistic norms adequately without continuous intervention. Findings are discussed based on Han’s (2009, 2013) selective fossilization hypothesis.