The explicit formulation of an aesthetics in the Western sense only started in Japan a little over two hundred years ago. But, by the Japanese aesthetic we tend to mean, not this modern study, but a set of ancient ideals that include wabi (transient and stark beauty), sabi (the beauty of natural patina and aging), and yûgen (profound grace and subtlety). These ideals, and others, underpin much of Japanese cultural and aesthetic norms on what is considered tasteful or beautiful. Thus, while seen as a philosophy in Western societies, the concept of aesthetics in Japan is seen as an integral part of daily life.
The Japanese aesthetic ideals are most heavily influenced by Buddhism. In the Buddhist tradition, all things are considered as either evolving from or dissolving into nothingness. Koren says that this 'nothingness' is not empty space. It is, rather, a space of potentiality. Let me use an analogy, if we take the seas as representing 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.
Wabi-sabi is the aesthetic defined as the beauty of things "imperfect, impermanent, and incomplete" (Koren, below). Things in bud, or things in decay, as it were, are more evocative of wabi-sabi than things in full bloom because, like the falling cherry blossom, 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. 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: asymmetry, irregularity;
Koko: basic, weathered;
Shizen: without pretense, natural;
Yugen: subtly profound grace, not obvious;
Datsuzoku: unbounded by convention, free;
Each of these things are found in nature but can suggest virtues of human character and appropriateness of behaviour. This, in turn suggests that virtue and civility can be instilled through an appreciation of, and practice in, the arts. Hence, aesthetic ideals have an ethical connotation and pervades much of the Japanese culture.
As can be seen from the above list, in the Zen tradition Yūgen is just one of the components of Wabi Sabi. Nevertheless, it is an important separate concept in traditional Japanese aesthetics and strongly informs the notion of Wabi Sabi.
The exact translation of the word depends on the context. In the Chinese philosophical texts the term was taken from, yūgen meant "dim", "deep" or "mysterious". Yugen suggests that beyond what can be said but it is not an allusion to another world. It is about this world, this experience. All of these are portals to yugen:
" 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.
And, subtle shadows of bamboo on bamboo."
Zeami was the originator of the dramatic art form, Noh theatre, and wrote the classic book on dramatic theory (Kadensho). He uses images of nature as a constant metaphor. For example, "snow in a silver bowl" represents "the Flower of Tranquility". Yugen is said to mean “a profound, mysterious sense of the beauty of the universe… and the sad beauty of human suffering”.
Wabi, sabi, and yugen refers to a mindful approach to everyday life reminiscent of the mindfulness in the arts.
Geidō refers to the way of the traditional Japanese arts: Noh (theater), kadō (Japanese flower arrangement), shodō (Japanese calligraphy), Sadō (Japanese tea ceremony), and yakimono (Japanese pottery). All of these ways carry an ethical and aesthetic connotation and appreciate the process of creation. To introduce discipline into their training, Japanese warriors followed the example of the arts that systematized practice through prescribed forms called kata - think of the tea ceremony. Training in combat techniques incorporated the way of the arts (Geidō), practice in the arts themselves, and instilling aesthetic concepts (for example, yugen) and the philosophy of arts (geido ron). This led to combat techniques becoming known as the martial arts (even today, David Lowry shows, in the 'Sword and Brush: the spirit of the martial arts', the affinity of the martial arts with the other arts). All of these arts are a form of tacit communication and we can, and do, respond to them by appreciation of this tacit dimension.
After the introduction of Western notions in Japan, Wabi Sabi aesthetics ideals have been re-examined with Western values, by both Japanese and non-Japanese. Therefore, recent interpretations of the aesthetics ideals inevitably reflect Judeo-Christian perspectives and Western philosophy.
Koren (below) says that “The immediate catalyst for [his] book was a widely publicized tea event in Japan. ... It suddenly dawned on me that wabi-sabi, once the preeminent high-culture Japanese aesthetic and the acknowledged centerpiece of tea, was becoming—had become?—an endangered species …”
I agree with Koren wholeheartedly and his book is an important contribution to the literature.
Wabi-Sabi: for Artists, Designers, Poets & Philosopher by Leonard Koren
Wabi Sabi is best thought of as looking upon nature in itself as a spiritual exercise. The photographs throughout the book are a clue as to where to look but they are not the thing itself: put the book down and go out and look.
Much of this review is taken from my contribution to Wikipedia.