The capital of Kyoto in the Heian period. When someone in an aristocratic household fell to an illness no one could explain, the figure summoned alongside the physician was a monk known as a genza (efficacy-worker). Healing sickness and subduing possessing spirits through kaji prayer rites. The Pillow Book and the Konjaku monogatari portray these genza again and again, praying until the sweat ran. Sei Shōnagon, in her passage on "dispiriting things," even pokes fun at a genza who prays and prays, the spirit refuses to budge, and his chanting trails off into yawns. The people of that age, in other words, watched a monk's prayer with searingly practical eyes: does it work, or does it not?

Gen is exactly that: efficacy. Prayer and practice answering surely, appearing as a visible sign. The meaning survives today in words like reigen aratakana (of manifest miraculous efficacy) and kōken (proven efficacy). One who has obtained gen is a genza; and the path of "cultivating" gen, acquiring it through practice, is Shugendō. Dictionaries often explain the name as short for shugyō tokugen (practicing and obtaining gen) or "real practice, real verification."

And here a question rises. A visible efficacy, acquired through practice. Is such a thing truly taught as Buddhist doctrine? Or is it a peculiar belief confined to Shugendō? To state the conclusion first: the doctrinal substance of gen is what esoteric Buddhism calls shitsuji, the Sanskrit siddhi (accomplishment). And its roots reach down into the oldest stratum of Buddhism. Let us verify it, starting from the deepest level and working our way up.

The expression "to cultivate gen" is not a Japanese invention. The languages that carried Buddhism share words of the very same structure.

In Sanskrit, practice is sādhana, and the accomplishment that practice bears is siddhi. These two words form a pair born of the same verbal root: "to bring to accomplishment" (√sādh) and "to be accomplished" (√sidh). The practitioner (sādhaka) cultivates the practice (sādhana) and obtains the accomplishment (siddhi). This chain of vocabulary has the same shape as the structure of shugen: cultivating gen to obtain gen.

Tibetan is clearer still: from sgrub (to cultivate, to accomplish) the words run to dngos grub (accomplishment) and then to grub thob (one who has obtained accomplishment). The chain matches the Japanese "cultivate → gen → genza" right down to how the words are built. What is more, the Tibetan rendering dngos grub is an interpretive translation, "dngos (actual, real) + grub (accomplishment)," that is, "real accomplishment." The very form of the translated word shows that gen is not an abstraction but an effect verified in actuality.

This siddhi the Chinese translations of the scriptures transcribed as 悉地 (shitsuji). The true identity of the gen in shugen is none other than this siddhi.

From its oldest layer, Buddhism has confronted head-on the question of whether practice yields a verifiable fruit. In the Pāli Sāmaññaphala Sutta (the Fruits of the Ascetic Life, Dīgha Nikāya 2), King Ajātaśatru of Magadha asks the Buddha: the elephant trainer, the cook, the weaver, each earns visible fruit in this world by his craft. Does the practice of a renunciant, then, likewise bear a fruit verifiable here and now? No question put to the world of faith could be more candid.

What matters is that while the supernormal powers are counted among these "visible fruits of the ascetic life," the highest fruit remains liberation. From its starting point, the tradition of gen already carried this orientation: the powers are real, but they are not the summit.

Visible efficacy, supernormal power. Where does it arise from? Is it an inborn psychic gift, or something obtained through cultivation? To this question the thinkers of India answered with astonishing diligence, by classification. And inside and outside Buddhism alike, almost the same classification took shape.

The root text of the Yoga school, the Yoga Sūtras, lists five causes from which siddhi arises: birth, herbs, mantra, austerity, and samādhi (deep meditative absorption). On the Buddhist side, Vasubandhu's Abhidharmakośa, the great systematization of Buddhist doctrine, likewise classifies the bases of supernormal power into five kinds: cultivation (meditation), birth, mantra, medicine, and karma. Across the schools, nearly the same items line up.

The premise of Shugendō, that gen is not an inborn psychic gift but something cultivated and brought forth through practice, is fully backed by the Indian primary sources. Entering the mountains, standing under waterfalls, reciting mantras: the severe shape of that practice turns out to be a way of cultivating, all at once, three of the five causes of power, austerity, mantra, and samādhi.

It was esoteric Buddhism that systematized this "verifiable fruit" with precision, as a body of practice. The key word is siddhi. The fundamental scripture of Shingon Buddhism, the Mahāvairocana Sutra, bears the full title Sutra of the Wondrous Working and Kaji of Mahāvairocana's Attainment of Buddhahood (Dai-birushana jōbutsu jinpen kajikyō). The wondrous working of the Buddha, and the mutual resonance (kaji) of Buddha and practitioner: the very title of the sutra announces the theme of gen. In its opening chapter, the sutra teaches as follows.

As the Mahāvairocana Sutra teaches, "if one seeks and desires the higher, middling, or lower siddhi in this present life" (T18p0052a19), siddhi is divided into three grades, higher, middling, and lower, and is held to be obtainable in this very life. In Japan, too, the Heian scholar-monk Saisen wrote in his commentary on the "Stages of Mind" chapter that "by the august power of gen of the practice of the Three Mysteries, one is able to obtain accomplishment," stating plainly the understanding that the power of gen in the practice of the Three Mysteries brings forth siddhi (Taishō No. 2215).

In The Meaning of Attaining Buddhahood in This Very Body, Kōbō Daishi Kūkai set out the whole picture of siddhi (gen) with concise clarity.

The swiftness with which gen appears is also central to Kūkai's vision. The exoteric teachings place buddhahood in the distant future of three incalculable eons, but esoteric Buddhism teaches realization in this very body, without passing through the three eons (Treatise on the Differences Between the Exoteric and Esoteric Teachings, Taishō No. 2427). Further, his introduction to the Mahāvairocana Sutra contains the line, "the boundless powers of penetration are possessed from the origin, without contriving" — gen is not added on from outside but inherently present (Taishō No. 2211). Shugendō, which values the immediate manifestation of gen in this present world, stands on this esoteric position of "swiftness."

Strong restraints have been built into the tradition of gen from the very beginning. We begin with the Buddha's own words.

The tradition of gen, then, has acknowledged the reality of the powers while consistently rejecting their display and their elevation into an end. The power of gen is something that appears of itself in accord with awakening, and is to be offered to the work of saving beings. This is the ethics of gen that the primary sources set forth.

This teaching of siddhi and efficacy unfolded in Japan in its own distinctive way. We trace its path of 1,200 years.

In the Heian period, esoteric monks who manifested outstanding efficacy through kaji prayer rites were called genza, and at the court and among the aristocracy they undertook the healing of illness and the subduing of possessing spirits. Upon this lineage of the genza there appeared people who tempered the power of gen through practice in the mountains, and through the medieval period a distinct path took shape: Shugendō.

Shugendō looks up to En no Gyōja (En no Ozunu) as its founder. The historical En no Ozunu appears in the official history Shoku Nihongi, in the entry for the year 699, as a figure who lived on Mount Katsuragi and was famed for his thaumaturgy. The traditions that he commanded demon-spirits derive from later tales, and the very designation "founder of Shugendō" was itself shaped in later ages; yet the name of En no Gyōja preserves an ancient memory of mountain ascetics answering the people with gen.

From the medieval period onward, Shugendō divided into two main streams. The Tōzan-ha, grounded in Shingon esotericism (Tōmitsu) and based at Sanbōin of Daigoji; and the Honzan-ha, of the Tendai line, based at Shōgoin. The Tōzan-ha looks up as its ancestor to the Shingon monk Shōbō (Rigen Daishi, 832–909), founder of Daigoji (its establishment as an organized order came in the Muromachi period, and Shōbō was retrospectively made the founding patriarch). Though their lineages of teaching diverge, they share one thing: both place the core of gen in the siddhi and kaji of esoteric Buddhism.

In 1872, by decree of the Grand Council of State, the Shugen school was abolished, and its practitioners were ordered to enter the parent Tendai and Shingon schools. The Tōzan-ha line entered the Shingon school, and its lineage is carried on today by the Daigo branch of Shingon Buddhism and others. The Honzan-ha line was revived after the war as the Honzan Shugen school. Across more than a thousand years, the path of gen continues, changing the form of its lineage as it goes.

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Let us return, once more, to the first question. What is the gen of shugen? It is accomplishment verified in actuality through practice, that is, siddhi. Beginning with the sandiṭṭhika of the Pāli canon (the fruit verifiable here and now), from Sanskrit sādhana to siddhi, from Tibetan sgrub to dngos grub, and from the Japanese shu (to cultivate) to gen. Though the languages and the lands changed, a single conviction, that practice bears a sure fruit, has been handed down unbroken for 2,500 years.

Byōdōji is a temple of the Kōyasan Shingon school. The Tōmitsu on which Tōzan-ha Shugendō relied, the Mahāvairocana Sutra, the Susiddhikara Sutra, and the teaching of Kūkai, is the very teaching on which we ourselves rely in our daily homa and kaji prayer rites. When the homa fire rises in the main hall, what is being cultivated there is none other than the teaching of siddhi and kaji that this article has traced. To understand the gen of Shugendō is to understand the doctrinal core of why the prayer of esoteric Buddhism has been taught to "work."