Yugen is one of the basic ideas of Japanese culture in the area of various arts such as literature, paintings, performing arts and architecture.
Originally it was a word of Chinese origin used in Chinese thought like Buddhism and the thought of Laozi and Zhuangzi, but since FUJIWARA no Toshinari, a famous poet from the late Heian period to the early Kamakura period, who selected poems of Senzai Wakashu, often used the word to criticize waka poems, it became a major word in treatises on waka poetry. It is often used together with Ushin that is also an idea of the art of waka poetry but they have originally different meanings.
After that it continued to affect Japanese artistic culture like Noh, Zen, Renga (linked verse), Sado (tea ceremony), Haikai (amusing and playful waka) in the medieval period and later and it is also used as a general word today.
Yugen in waka
It is written "meanings go to Yugen" in Manajo of "Kokin wakashu" in ancient time.
MIBU no Tadamine, one of the compilers of "Kokin wakashu", expressed it as follows: "Words are flowing, but meanings are entering Yugen. It is the highest rank of any waka." to explain the Kojo style of a treatise on waka poetry "Wakatai Jissyu (the Ten Styles of Waka)", and considered the Kojo style as the highest rank of Jissyu.
FUJIWARA no Mototoshi, a poet in the late Heian period, left judgment words for an Utaawase (poetry competition) as follows:
"The words flowed and then entered Yugen. It is really high level." "The words are similar to those of an old style, but the meanings seem to reach Yugen." "The words are similar to those of an old style, but the meanings seem to reach Yugen."
FUJIWARA no Toshinari who studied under Mototoshi often used Yugen as a criticism word like "It reached Yugen already." "It sounds just like Yugen." "It is the Yugen style." "A Yugen mind." "It looks like Yugen." in his judgment words of Utaawase.
Also FUJIWARA no Sadaie, a sun of FUJIWARA no Toshinari and a compiler of "Shin (new) Kokin wakashu" and "Hyakunin Issyu" (one hundred waka poems), mentioned Yugen style as one of the ten styles of waka in a treatise on waka poetry "Maigetusho" (monthly comment).
Chomei KAMONO defined Yugen as "suggested feelings that do not appear on words and invisible atmosphere" "inherent virtue of meanings deeply felt in mind and very attractive words" in Q&A of his book "Mumyosho" (an essay on tanka poetry).
In a treatise on waka poetry "Shotetsu Monogatari" (Tale of Shotetsu), Shotetsu, a poet in the Muromachi period, wrote as follows:
"Most people consider Yugen as suggested feelings and do not expect more in Yugen. "
"Or they consider Yugen as a vague feeling of sadness." "But suggested feelings and Yugen are completely different." "While everyone considers them in the same meaning."
Yugen in Renga
In his book "Kyushu Mondo" Yoshimoto NIJO, a successful Renga poet in the period of the Northern and Southern Courts, wrote "Renga is working only when reaching Yugen." And in an explanation of "Iji (willpower)" as an attitude in "Jumonsaihisyo", he explained about the universal need of "being in the right, not distorted and being Yugen."
Shinkei, a monk of the Tendai sect in mid-Muromachi period and a famous Renga poet wrote "Yugen is something what is in people's minds and unable to be expressed in words" in his book "Shinkei sozu teikin". Also in his poetry criticism "Sasamegoto" (Murmurings) he wrote "for ancient people the most important thing in Yugen was heart" and having aesthetic appreciation while ordinary people consider Yugen only as "something that has deep flavor." Also he wrote about emotions, images left in people's minds and suggested feelings in Renga that Yugen and Aware (a vague feeling of sadness) should be where words are likely to have no reasons to be left.
Sogi, a Renga poet in late Muromachi period used expressions of "appearance that is magnificent, Yugen and Ushin" in his book "Azuma Mondo"(East Country Dialogues) and "Yugen and magnificent" in "Chorokumon", which is considered as his ideal in Renga.