structural:expansion
Religious polemics

In 1520 the reformer Martin Luther published three works in quick succession: An Appeal to the Christian Nobility of the German Nation (Aug.), Concerning the Babylonish Captivity of the Church (Oct.), and On the Liberty of a Christian Man (Nov.). In these books, Luther set out his doctrine of salvation through faith alone, rejected certain Catholic practices, and attacked abuses and excesses within the Catholic Church. In 1521, Henry VIII formally responded to Luther's criticisms with the Assertio, written with More's assistance. Pope Leo X rewarded the English king with the title " Fidei defensor" ("Defender of the Faith") for his work combating Luther's heresies.

Martin Luther then attacked Henry VIII in print, calling him a "pig, dolt, and liar". At the king's request, More composed a rebuttal: the Responsio ad Lutherum was published at the end of 1523. In the Responsio, More defended papal supremacy, the sacraments, and other Church traditions. More, though considered "a much steadier personality", described Luther as an "ape", a "drunkard", and a "lousy little friar" amongst other epithets. Writing under the pseudonym of Gulielmus Rosseus, More tells Luther that:

His saying is followed with a kind of apology to his readers, while Luther possibly never apologized for his sayings. Stephen Greenblatt argues, "More speaks for his ruler and in his opponent's idiom; Luther speaks for himself, and his scatological imagery far exceeds in quantity, intensity, and inventiveness anything that More could muster. If for More scatology normally expresses a communal disapproval, for Luther, it expresses a deep personal rage."

Confronting Luther confirmed More's theological conservatism. He thereafter avoided any hint of criticism of Church authority. In 1528, More published another religious polemic, A Dialogue Concerning Heresies, that asserted the Catholic Church was the one true church, established by Christ and the Apostles, and affirmed the validity of its authority, traditions and practices. In 1529, the circulation of Simon Fish 's Supplication for the Beggars prompted More to respond with the Supplycatyon of Soulys.

In 1531, a year after More's father died, William Tyndale published An Answer unto Sir Thomas More's Dialogue in response to More's Dialogue Concerning Heresies. More responded with a half million words: the Confutation of Tyndale's Answer. The Confutation is an imaginary dialogue between More and Tyndale, with More addressing each of Tyndale's criticisms of Catholic rites and doctrines. More, who valued structure, tradition and order in society as safeguards against tyranny and error, vehemently believed that Lutheranism and the Protestant Reformation in general were dangerous, not only to the Catholic faith but to the stability of society as a whole.