Your motive for doing something is your reason for doing it.
近义词reason , grounds , motivation
双语例句例： Police have ruled out robbery as a motive for the killing.
警方已排除了出于抢劫的动机而杀人的可能。
例： the motives and objectives of British foreign policy.
英国对外政策的动机和目标。
例： The doctor's motive was to bring an end to his patient's suffering.
这位医生的初衷是不再让他的病人承受痛苦。