The Abolition of Man is a 1943 book by C. S. Lewis. Subtitled "Reflections on education with special reference to the teaching of English in the upper forms of schools", it uses a contemporary text about poetry as a starting point for a defense of objective value and natural law. Lewis goes on to warn readers about the consequences of doing away with ideas of objective value. It defends "man's power over nature" as something worth pursuing but criticizes the use of it to debunk values, the value of science itself being among them. The title of the book then, is taken to mean that moral relativism threatens the idea of humanity itself. The book was first delivered as a series of three evening lectures at King's College, Newcastle, part of the University of Durham, as the Riddell Memorial Lectures on 24–26 February 1943.

Lewis begins with a critical response to "The Green Book" by "Gaius and Titius": The Control of Language: A Critical Approach to Reading and Writing, published in 1939 by Alexander ("Alec") King and Martin Ketley. The Green Book was used as a text for upper form students in British schools.

Lewis criticises the authors for subverting student values and claims that they teach that all statements of value (such as "this waterfall is sublime") are merely statements about the speaker's feelings and say nothing about the object. Such a view, Lewis argues, makes nonsense of value talk. It implies, for example, that a speaker who condemns some act as contemptible is really only saying, "I have contemptible feelings."

By denying that values are real or that sentiments can be reasonable, subjectivism saps moral motivation and robs people of the ability to respond emotionally to experiences of real goodness and real beauty in literature and in the world. Moreover, Lewis claims that it is impossible to be a consistent moral subjectivist. Even the authors of The Green Book clearly believe that some things, such as improved student learning, are truly good and desirable.

Lewis cites ancient thinkers such as Plato, Aristotle and St. Augustine, who believed that the purpose of education was to train children in "ordinate affections", to train them to like and dislike what they ought and to love the good and hate the bad. Lewis claims that although such values are universal, they do not develop automatically or inevitably in children. Thus, they are not "natural" in that sense of the word, but they must be taught through education. Those who lack them lack the specifically human element, the trunk that unites intellectual man with visceral (animal) man, and they may be called "men without chests".

Lewis criticizes modern attempts to debunk natural values, such as those that would deny objective value to the waterfall, on rational grounds. He says that there is a set of objective values that have been shared, with minor differences, by every culture, which he refers to as "the traditional moralities of East and West, the Christian, the Pagan, and the Jew...". Lewis calls that the Tao, from the Taoist word for the ultimate "way" or "path" of reality and human conduct. (Although Lewis saw natural law as supernatural in origin, as evidenced by his use of it as a proof of theism in Mere Christianity, his argument in the book does not rest on theism.)

Lewis argued that the "chest," which he viewed as the seat of emotions and moral instincts, is essential for connecting reason (the head) with appetites (the belly). Without this connection, individuals become detached from their emotions and moral compass, leading to a lack of virtue and enterprise.

Without the Tao, no value judgments can be made at all, and modern attempts to do away with some parts of traditional morality for some "rational" reason always proceed by arbitrarily selecting one part of the Tao and using it as grounds to debunk the others.