Zen tells its own beginning as a scene: the Buddha holds up a flower before an assembly, only his disciple Mahākāśyapa smiles, and the Buddha declares a transmission of the teaching outside the scriptures. The scripture usually cited for the scene is the Dafantian wang wenfo jueyi jing, the sūtra of the Great Brahmā King's questions to the Buddha. In 1905 Kaiten Nukariya, a Sōtō Zen priest and since 1901 the principal of one of his school's colleges, published a study arguing that this sūtra was apocryphal. The argument took away the scriptural support for the doctrine on which Zen rests its claim to authority: a special transmission outside the scriptures.
He came to that work from a modern training. Born in 1867, the year before the Meiji Restoration, he was ordained at ten in a Sōtō temple and took the name Kaiten. The new government separated Shinto from Buddhism, and many temples were destroyed in the years after 1868. From the Sōtō academy he went on in 1891, at twenty-four, to Keiō, the private school in Tokyo that taught Western learning, where he studied Buddhism with the methods of positivist scholarship. Nukariya translated Buddhism and Its Christian Critics by Paul Carus, a German-American writer on religion, and brought out an edition of Shutsujō kōgo, in which the eighteenth-century Osaka scholar Tominaga Nakamoto had argued that the Mahāyāna sūtras were not the Buddha's words. Many Buddhist scholars feared that a school resting on those sūtras would collapse if this were granted; Nukariya held that critical history could modernise Buddhism and leave the Mahāyāna its value.
In 1911 the Sōtō school sent him abroad for three years to study religion in America and Europe, and there he wrote The Religion of the Samurai in English, mostly from memory, its preface says, finishing it at Harvard Square in April 1913. Its central claim fits his scholarship. Zen, he argued, takes its authority from no scripture: the universe itself is its scripture, and the Buddha is a predecessor whose insight each practitioner sets out to equal, not a superhuman founder whose words must be obeyed. A Zen grounded in that way could lose a proof-text without losing anything it rested on. He wrote for Western readers who knew Buddhism through the older Pāli texts and called it pessimistic, and he argued in their terms, setting Zen beside the theory of evolution and disputing the Harvard psychologist Hugo Münsterberg on what gives a life value. The title carried a second argument as well: that Zen had come to Japan as the faith of the warrior class and had revived since the Russo-Japanese War as an ideal for the rising generation.
Back in Japan in 1914, Nukariya received a doctorate in 1915 and became head of the Sōtō school's university in 1921. When it became Komazawa University in 1925 he was its first president, and he gave it the principle gyōgaku ichinyo, practice and learning as one. He also completed a two-volume history of Zen thought in Japanese. In July 1934 he collapsed with a stroke while lecturing in Tokyo and died.