The tradition of theological thought, from which I have given some prominent examples, contains a treasure trove of theories of doctrinal development that is for the most part ignored today. Yet, at a time when the Catholic doctrine of faith is under unprecedented pressure to change, this trove could provide a number of things, both ‘new’ and ‘old’ (Matthew 13:52): old, because if it loses living contact with its tradition, then the Church would no longer be the Church; and new, because the Church is not simply a club of traditional costumes that can afford to gather dust in a museum, but has a mission that it serves, along with its dogma. The fundamental question faced by theories of doctrinal development concerns the relationship that the old (without which the Church would no longer have roots) has with the new (without which the Church can have no future).