Newman's famous 'Essay on the Development of Christian Doctrine' contains several markers for distinguishing authentic development from corruption. Although apparently clear, there are difficulties both in theory and in practice. To Newman, the question of development is one of ecclesiology, and is considered retrospectively: is the church that professes this 'developed' idea still the same, and can we understand what happened before in that light? Development is then something that happens to the church, rather than something that is done by theology. In my paper, I argue that theology in the catholic tradition has both a conservative and constructive task, and that the magisterium goes back and forth between stressing either one. The conservative task means it preserves what is good, also in what is apparently new. Pope Francis emphasizes the constructive task of theology: on a pastoral level, in forming consciences, but also in a systematic fashion, to respond to the challenges of this time. Fiducia Supplicans puts the coordination of these tasks to the test. Is it possible to offer a constructive evaluation of homosexual relationships while conserving traditional teaching on marriage? The instruction seems to assume it, but there are many blanks still left to fill in for theology. In this paper, I also give some first indications of what that might look like.