Development of doctrine is a term used by John Henry Newman and other theologians influenced by him to describe the way Catholic teaching has become more detailed and explicit over the centuries, while later statements of doctrine remain consistent with earlier statements.
The term was introduced in Newman's 1845 book An Essay on the Development of Christian Doctrine. Newman used the idea of development of doctrine to defend Catholic teaching from attacks by some Anglicans and other Protestants, who saw certain elements in Catholic teaching as corruptions or innovations. He relied on an extensive study of early Church Fathers in tracing the elaboration or development of doctrine which he argued was in some way implicitly present in the Divine Revelation in Sacred Scripture and Tradition which was present from the beginnings of the Church.
He argued that various Catholic doctrines not accepted by Protestants (such as devotion to the Blessed Virgin Mary, or Purgatory) had a developmental history analogous to doctrines that were accepted by Protestants (such as the Trinity or the divinity and humanity of Christ). Such developments were, in his view, the natural and beneficial consequences of reason working on the original revealed truth to draw out consequences that were not obvious at first.
There is a more radical understanding of development of doctrine that is known as evolution of dogmas. This view, mixed in with philosophical currents such as vitalism, immanentism and historicism, was at the heart of the modernist controversy during the papacy of Pius X, and was condemned in the encyclical Pascendi. Although modernist intellectuals such as George Tyrrell and Alfred Loisy did at times cite the influence of Newman's ideas on their thinking, their goal was not so much to understand the ancient roots of Church doctrine but to make it evolve according to their own ideas in the liberal spirit of the times.