|Kanji in this term|
/omo2pu/ → /omwopoju/ → /omwoɸoju/ → /omoɸoju/ → /oboɸoju/ → /oboju/ → /obojuru/ → /obojeru/ → /oboeru/
- the 未然形 (mizenkei, “irrealis form”) omopa of Old Japanese verb 思ふ (omopu, “think”, modern 思う omou) + ゆ (yu, Old Japanese verb suffix denoting intransitive or passive action):
- contraction and regular sound changes:
- omopoyu → omofoyu → obowoyu → oboyu
- This change is already evident by the early Heian period.
- regular historical grammatical shifts occurring for classical 下二段活用 (shimo nidan katsuyō, “lower bigrade conjugation”) verbs:
- oboyu → oboyuru → oboyeru → oboeru
- This set of shifts occurred during the Kamakura and Muromachi periods.
The verb was originally used in intransitive and passive contexts, in accordance with its derivation. It began to be used in more active and transitive contexts starting from roughly the mid-Heian period, with the learn and memorize senses appearing in the Kamakura period.
- (recall, remember): 思い出す (omoidasu)