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Thinkers

Yi I

Confucian · East Asia · 1536 to 1584

Korean scholar who held that principle and energy are bound together, and who urged practical reform of government.

What it is

Yi I (1536 to 1584), better known by his pen name Yulgok, was a Korean scholar of the Joseon period and one of the leading Neo-Confucian thinkers of his country. Neo-Confucianism was the body of thought, grown out of the teaching of Confucius, that Korean scholars of the Joseon period studied and debated.

He is usually named beside Yi Hwang, known as T'oegye. The two men developed different pictures of how the world is put together, and each is linked with a school of followers. Yulgok is the one who pressed back against T'oegye's way of reading the tradition, while still working within it.

The main ideas

  • A challenge from inside. Yulgok did not leave Neo-Confucianism. He argued with T'oegye about how it should be understood,. He challenged it from within, on the ground of Zhu Xi's own thought.
  • Principle and vital force. Neo-Confucian thinkers describe the world through two partners, principle, the order or pattern in things, and vital force, the energy that moves them. How the two relate, in the world and in human feeling, is the matter on which Yulgok and T'oegye are set side by side.
  • Self-cultivation. He held that a person must work on the heart and mind, with the aim of becoming a sage, and that integrity is the base of that work.

What it looks like in practice

Picture someone who wants to become a better person and asks where to begin, and who is told that a question can be argued from inside a tradition without leaving it. That is the kind of stance Yulgok took toward T'oegye. This is an illustration, not a passage from his writing.

People and texts

  • Yi Hwang (T'oegye) is the thinker with whom Yulgok is paired. Their theories of the universe are said to have led to rival schools of thought within Neo-Confucianism.
  • Zhu Xi is the Chinese thinker whose version of Confucian teaching both men were working with.

Questions and criticism

  • One thing or two? Are principle and vital force two separate things, one thing, or neither? It is fair to ask whether any answer to that is a real answer or a way of keeping both sides.
  • Philosophy and government. Did his ideas about the world shape what he thought a state should do? This page does not settle that question.
  • One school or two. Because later followers split into rival schools, it is fair to ask how far the two men really differed, and how far the schools exaggerated it.

Close neighbours

The pages on Zhu Xi, Yi Hwang and Confucius sit closest to Yulgok. The first two show the tradition he was arguing inside, and the third its root.

Written by epchē in our own words, and checked against independent sources on 29 October 2026. The sources are listed below.

Who they connect to

Influenced by

  • Zhu Xi · He built on the teaching of Zhu Xi while reading it his own way.

Reacted against

  • Yi Hwang · He argued with the older scholar and denied that principle and feeling can move apart.

Other Confucian thinkers

Sources we used

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