質問: My current understanding is that 下りる means to go down, for example, 階段を下りる (Go down the stairs); while 降りる means to get off some form of transport, for example, 飛行機から降りる (Get off from the aeroplane). Is this understanding correct so far? However, which one is used to "go down a mountain", and possibly other uses for going down?
回答: If I had to try to generalize, I'd say: * 下りる is used for *moving downward*, including a number of metaphorical or idiomatic uses * 降りる is used mainly for *falling back* or *getting out of a vehicle* But I think it helps to be more specific, so I've put together a little outline with some examples: 下りる === * **Move downward** [descend, climb down, fall, fly down, land] + 山を下りる + はしごを下りる + 階段を下りる + 幕が下りる + 飛行機が下りる + 宇宙船が下りる * **Grant or issue** [permission, a license, payment, pension] + 許可が下りる + ビザが下りる + 金が下りる * **Feel relieved** [like a weight has been lifted off your shoulders] + 肩の荷が下りる * **Lock** + 錠が下りる * **Discharge from the body** + 血が下りる 降りる === * **Getting off/out of things**, particularly modes of transportation [train, boat, bus, car, taxi, plane, horse, elevator] + タクシーから降りる + 電車から降りる + 馬から降りる + 飛行機から降りる + 屋根から降りる + 椅子から降りる (these examples work with を as well) * **Quitting, withdrawing, pulling back** [from a job, a game, a position] + 仕事を降りる + 役職を降りる + 勝負を降りる + マウンドを降りる * **When something descends upon the landscape** [shadow falls, dew or frost form] + 霜が降りる + 露が降りる + 闇が降りる