The word 理由 is formed by combining two conceptual characters: 理, which represents "principle" or "inherent logic", and 由, which means "source", "cause", or "origin". Together, they conceptually fuse to create the meaning of "reason" or "justification", where 由 provides the foundational cause or starting point, and 理 provides the coherent principle or explanation that makes it valid. It is the logical source or the principled cause for something.