Shomyo refers to the calling of God's name by the Brahman monks of India, the expression of prayer to God, and the versification and voicing of God's teachings (sutra); in other words, the act of chanting. From India, shomyo was transmitted to China, and along with Buddhism, from China to Japan, where it was adopted as part of esoteric Buddhism. The act of chanting shomyo was introduced as a method of salvation, an ascetic practice to be performed by believers themselves.
In the Tendai sect of Buddhism, during the late Heian Period, Ryonin (1072-1132) standardized and compiled the shomyo texts that had been introduced from China sometime in the middle of the 9th century, and built the original shomyo seminary at Raigoin, a temple in the Ohara region of Kyoto. From this time on, Tendai shomyo was called, Tendai Ohara Shomyo. To the south of Sanzenin, a temple in the heart of Ohara, runs the Ryo River, and to the north of it runs the Ritsu River. The Ryo flows wide in a gentle, curving motion, while the Ritsu's current is made up of a group of bouncing billows. By using these characteristics as a metaphor, shomyo was broken down into two styles: ryokyoku and rikkyoku. Simply put, ryokyoku shomyo might be described as foreboding and difficult to understand, as compared to rikkyoku shomyo, which is relatively easy-to-understand and easy-to-remember. Many of the ryokyoku texts are written in Bongo (Sanskrit transliterated into Japanese), and of those that are written in Kango (Chinese characters), most contain only one short extract from the original sutra. Rikkyoku, on the other hand, is made up of a collection of Kango verses. By repeating these phrases and adding a melody, the sutra began to sound like coherent musical compositions. This coherence gave rise to a form, and the flow of the melody created a tempo. The rikkyoku style is believed to have been the basis for many of the distinguishing features of Japanese music, and was later connected to the creation of Japanese traditional music. Which is to say, rikkyoku is musical and songlike whereas, in ryokyoku, chanting strikes the listener as being a stronger element. When structured, as in rikkyoku or music in general, singing becomes a method of communication between human beings. It is a method similar to speaking, which is structured by grammar. However, chanting is the act of linking oneself, as a human being, to God using the spiritual power of the voice. This is, at least, the ideal on which shomyo as it is found in esoteric Buddhism is based.