The unity or preservation of type refers to the continual presence of a main idea despite its changing external expression.
When we see change in the teaching on a subject, can we discern nevertheless that the main idea remains unchanged?
If so, we know that the change is a genuine development, not a corruption.
Newman warns that the presence of any alteration in the external expression of an idea shouldn’t lead us to conclude that it’s a corruption, instead of a development, of the essential idea.
While doctrine may grow and develop, principles are permanent.
Newman identifies the Incarnation as the fundamental truth of the Gospel.The third note of genuine development is In introducing this criterion, Newman notes that in the physical world living things are characterized by growth, not stagnancy, and that this growth comes about by making use of external things.For example, as human beings we grow by taking into our bodies external realities such as food, water and air.To illustrate this point, he uses the “analogy of physical growth, which is such that the parts and proportions of the developed form, however altered, correspond to those which belong to its rudiments” (p. In this sense, a full-grown bird is the development of an egg and not its corruption, even though they bear little physical resemblance to one another.Newman offers the further caveat that many times “real perversions and corruptions are often not so unlike externally to the doctrine from which they come, as are changes which are consistent with it and true developments” (p. In fact, according to Newman, a major source of religious corruption is clutching too tightly to doctrines at one stage of their development and refusing to allow their future growth.The fourth note of genuine development is logical sequence.By this Newman means that a doctrine that’s defined and professed by the Church at a point historically distant from its original founding can be considered a development, and not a corruption, if it can be shown to be the logical outcome of the original teaching.In the ancient Church, for example, Christian theology came to make use of philosophical terms and categories from contemporary Greek culture.These forms of thought were employed to refine the precision of doctrinal formulations, helping the Church to define more clearly what she believed.As a result, many Protestants conclude that Catholic teaching is a corruption of the original Gospel message.Catholics, on the other hand, see the doctrines of the Church as the necessary and logical development of the Gospel.