internal cause; intrinsic motivation
Used in medical, psychological, or philosophical contexts to refer to a cause originating from within a system or person, as opposed to an external cause (外因).
It is important to distinguish between internal and external causes of illness.
The intrinsic motivation behind his actions is a strong curiosity.
endogenous; intrinsic
death from natural causes
Compound of 内 (internal) and 因 (cause). The exact historical derivation is uncertain, but the term is used in modern technical contexts.