Which C.S. Lewis book develops the idea of the “Tao” as a shared moral law?

The C.S. Lewis book that develops the idea of the Tao as a shared moral law is The Abolition of Man.

The book grew out of three lectures Lewis delivered at the University of Durham in 1943. In the lectures, he criticized an approach to education that he believed separated facts from value judgments and treated moral responses as merely subjective feelings.

Lewis used “the Tao” as a broad term for the traditional moral principles found across cultures and religions. His examples draw on sources including Chinese thought, classical philosophy, Judaism, Christianity, and other traditions. He argued that rejecting objective value would weaken the moral framework needed for human action.

The title refers to Lewis’s warning that technological power without moral limits could reduce humanity’s ability to govern itself. The work is philosophical rather than fictional and is distinct from Mere Christianity, which presents a more accessible case for Christian belief.