Hara Tanzan (原坦山) (December 5, 1819 – July 27, 1892) was a Soto Buddhist monk, head monk at the Saijoji temple in Odawara and a professor of Philosophy at the University of Tokyo during the Bakumatsu and Meiji periods. He was a forerunner of the modernization of Japanese Buddhism and the first (in Japan) to attempt to incorporate concepts from the natural sciences into Zen Buddhism.
Hara was born in Iwakitaira Domain. At the age of 15, Hara enrolled at the Shoheizaka Academy (昌平坂学問所) where he studied both Confucianism and medicine, the latter under Taki Genken. At the age of 20 or 26, he entered Buddhist priesthood, though he would go on to study Western medicine later in life.
Hara became the first lecturer at Tokyo University's Department of Indian Philosophy and Buddhist Studies in 1879. He was later also superintendent of the Soto-shu Daigaku-rin (currently Komazawa University).
Hara figures in several well-known koans. He was well known for his disregard of many of the precepts of everyday Buddhism, such as dietary laws.
This is one of the most famous stories of Tanzan.
In Tokyo in the Meiji era there lived two prominent teachers of opposite characteristics. One, Unsho, an instructor in Shingon, kept Buddha's precepts scrupulously. He never drank intoxicants, nor did he eat after eleven o'clock in the morning.
The other teacher, Tanzan, a professor of philosophy at the Imperial University, never observed the precepts. When he felt like eating he ate, and when he felt like sleeping in the daytime he slept.
One day Unsho visited Tanzan, who was drinking wine at the time, not even a drop of which is supposed to touch the tongue of a Buddhist.
'Hello, brother,' Tanzan greeted him. 'Won't you have a drink?'
'I never drink!' exclaimed Unsho solemnly.
'One who does not drink is not even human,’ said Tanzan.
'Do you mean to call me inhuman just because I do not indulge in intoxicating liquids!' exclaimed Unsho in anger. Then if I am not human, what am I?'
'A Buddha.' answered Tanzan.