Yūgen is an important concept in traditional Japanese aesthetics. The exact translation of the word depends on the context.
To watch the sun sink behind a flower clad hill. To wander on in a huge forest without thought of return. To stand upon the shore and gaze after a boat that disappears behind distant islands. To contemplate the flight of wild geese seen and lost among the clouds… – Zeami Motokiyo
Japanese aesthetic ideals are most heavily influenced by Japanese Buddhism. In the Buddhist tradition, all things are considered as either evolving from or dissolving into nothingness. This ‘nothingness’ is not empty space. It is rather a space of potentiality.
An awareness of the Universe that triggers emotional responses too deep and powerful for words.
If the seas represent potential then each thing is like a wave arising from it and returning to it. There are no permanent waves. There are no perfect waves. At no point is a wave complete, even at its peak. Nature is seen as a dynamic whole that is to be admired and appreciated. This appreciation of nature has been fundamental to many Japanese aesthetic ideals, ‘arts,’ and other cultural elements. In this respect, the notion of ‘art’ (or its conceptual equivalent) is also quite different from Western traditions…
To contemplate the flight of wild geese seen and lost among the clouds…
Japanese aesthetics is a set of ancient ideals that include ‘wabi’ (transient and stark beauty), ‘sabi’ (the beauty of natural aging), and ‘yūgen.’ These ideals, as well as others, underpin much of Japanese cultural and aesthetic norms. Thus, while seen as a philosophy in Western societies, the concept of aesthetics in Japan is seen as an integral part of daily life. Wabi and sabi refers to a mindful approach to everyday life. Over time their meanings overlapped and converged until they are unified into wabi-sabi (侘寂), the aesthetic defined as the beauty of things “imperfect, impermanent, and incomplete.”
Things in bud or things in decay, as it were, are more evocative of wabi-sabi than things in full bloom because they suggest the transience of things. As things come and go, they show signs of their coming or going and these signs are considered to be beautiful.
To stand upon the shore and gaze after a boat that disappears behind distant islands.
In this, beauty is an altered state of consciousness and can be seen in the mundane and simple. The signatures of nature can be so subtle that it takes a quiet mind and a cultivated eye to discern them. In Zen philosophy, there are seven aesthetic principles for achieving wabi-sabi.
Fukinsei (不均整): asymmetry, irregularity; Kanso (簡素): simplicity; Koko: basic, weathered; Shizen (自然): without pretense, natural; Yugen (幽玄): subtly profound grace, not obvious; Datsuzoku (脱俗): unbounded by convention, free; Seijaku (静寂): tranquility, stillness.
Each of these things are found in nature but can also suggest virtues of human character and appropriateness of behaviour. This, in turn, suggests that virtue can be instilled through an appreciation of, and practice in, the arts. Hence, aesthetic ideals have an ethical connotation and pervade much of the Japanese culture.
Principle text source: Wikipedia – Japanese Aesthetics