Yūgen may be, among generally recondite Japanese aesthetic ideas, the most ineffable. The term is first found in Chinese philosophical texts, where it has the meaning of “dark,” or “mysterious.” Kamo no Chōmei, the author of the well-known Hōjōki (An Account of my Hut, 1212), also wrote about poetry and considered yūgen to be a primary concern of the poetry of his time. He offers the following as a characerization of yūgen: “It is like an autumn evening under a colorless expanse of silent sky. Somehow, as if for some reason that we should be able to recall, tears well uncontrollably.” Another characterization helpfully mentions the importance of the imagination: “When looking at autumn mountains through mist, the view may be indistinct yet have great depth. Although few autumn leaves may be visible through the mist, the view is alluring. The limitless vista created in imagination far surpasses anything one can see more clearly”. Mono no aware: the Pathos of Things. The meaning of the phrase mono no aware is complex and has changed over time, but it basically refers to a “pathos” (aware) of “things” (mono), deriving from their transience. In the classic anthology of Japanese poetry from the eighth century, the Manyōshū, the feeling of aware is typically triggered by the plaintive calls of birds or other animals. It also plays a major role in the world’s first novel, Murasaki Shikibu’s Genji monogatari (The Tale of Genji), from the early eleventh century. The somewhat later Heike monogatari (The Tale of the Heike Clan) begins with these famous lines, which clearly show impermanence as the basis for the feeling of mono no aware.
Stanford Encyclopaedia of Philosophy –