Studies of grammaticalization have paid special attention to semantic change mechanisms. This paper looks into eighteen mechanisms of semantic change that have been proposed in the study of grammaticalization and attempts to reclassify them according to their hierarchical status. Further, in order to establish true semantic- change mechanisms three criteria are proposed:rei) it should refer to semantic change;reii) it should refer to what language users do; and eiii) it should refer to a process that can be reasonably generalized. When these criteria were applied to the eighteen mechanisms, a total of ten mechanisms turned out to meet the requirements. These mechanisms are pragmatic inference, metaphor and metonymy, schematicization, reinterpretation, prototype extension, perspectivization, frame-of-focus variation, subjectification, and intersubjectification. What is notable in this hierarchical structure is that only schematicization belongs to metaphor and metonymy. From this exploration of mechanisms, what surfaces as notable is that metonymy is an important mechanism that has numerous different subtypes with unique characteristics.