Our Protestant brothers and sisters often wonder at the complexity of Catholic doctrine. In particular, they may find it difficult to reconcile what they view as the “simplicity” of Jesus’ teachings with those of the Church today.

These Christians recognize — and Catholics acknowledge — that not all the Church’s teachings are explicitly found in Scripture or the preaching of the early Fathers. Some doctrines were not stated fully and clearly until much later in the life of the Church. 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. Their growth in richness and complexity represents the change from an embryonic form into maturity. But how are we to demonstrate whether or not a particular doctrine (or body of doctrines) is a genuine development and not a corruption of the Christian faith?

One Catholic theologian who sought to provide an answer to this question was the eminent English convert Cardinal John Henry Newman (1801-1890). Newman identified seven “notes” or characteristics of authentic developments, as opposed to doctrinal corruptions, in his famous work “Essay on the Development of Christian Doctrine” (University of Notre Dame, 1989; page numbers below refer to citations from this edition). Let’s examine these characteristics one at a time.

Unity of Type

The first note of genuine development Newman calls unity of type. He considered this first criterion the most important of the seven.

What he means by type is the external expression of an idea. 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. 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. 171).

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. 176). 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.

He notes that some of the Jewish religious leaders of Jesus’ time illustrated this problem. Christ frequently condemned them for following the letter of the law, but not its spirit — that is, its development.

Continuity of Principles

The second note of genuine development is continuity of principles.

Newman insists that for a development to be faithful, it must preserve the principle with which it started. While doctrine may grow and develop, principles are permanent.

Newman identifies the Incarnation as the fundamental truth of the Gospel. Then he goes on to identify nine principles of the Christian religion: dogma, faith, theology, sacraments, Scripture and its mystical interpretation, grace, asceticism, the harm of sin, and the potential of matter to be sanctified.

In reference to these principles, Newman says:

“While the development of doctrine in the Church has been in accordance with, or in consequence of, these immemorial principles, the various heresies, which have from time to time arisen, have in one respect or other, as might be expected, violated those principles with which she rose into existence, and which she still retains” (p. 354).

The fifth-century theological movement known as Pelagianism provides an example of teaching that contradicted one of these principles. Pelagians denied the reality of original sin and, as a consequence, denied that our salvation required any grace beyond what is already given us in human nature.

As a result, the Church recognized the movement as a heretical corruption rather than a development of the Christian faith, and so condemned its teachings.

Power of Assimilation

The third note of genuine development is power of assimilation.

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.

In Newman’s terminology, then, when we make use of these re-sources we are assimilating them. The food, water and air we consume don’t change who or what we are in any meaningful way. Rather, they serve a valuable function in that they ensure our continued growth and vitality.

For Newman, a true doctrinal development is capable of assimilating external realities (such as non-Christian philosophical concepts, customs or rites) without in any way violating its principles. In fact, in the process of assimilation it’s the external realities themselves that are transformed (once they are assimilated), not the doctrine.

In Newman’s view, the more powerful, independent and vigorous the idea, the greater its power to assimilate external ideas and concepts without losing its identity.

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.

Logical Sequence

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.

Newman compares this process to the growth of a tree. Someone looking at an oak tree could very easily draw the conclusion that it has nothing at all in common with an acorn. Yet the mature oak tree is the logical development of the acorn.

Over time an acorn grows roots, bursts forth from the soil, begins to soar toward the sun, develops branches and grows leaves. Each step along the way is the logical development of the previous step. Thus it is with the authentic development of doctrines as well.

One example Newman gives of a development through logical sequence is the dogma of purgatory. The original teaching of Christ and the apostles included the insistence that perfection is necessary to enter heaven and enjoy God’s immediate presence. Yet the reality is that many who die in friendship with God, though ultimately destined for heaven, are far from perfect at that point. So the need for a purging process after death, before entrance into heaven, is logically implied.

Anticipation of Its Future

The fifth note of genuine development, which could be seen as a corollary of the previous one, is anticipation of its future.

Doctrines in some way imply or allude to their later development. So authentic developments will have some logical connection to the original deposit of faith, however vague the “embryonic” form might have been in the earliest days of the Church.

For example, the Church solemnly declared at the fourth-century Council of Nicaea that Jesus Christ, the Son of God, was himself truly and fully God, one in substance (or being) with the Father. Such a declaration is nowhere found explicitly in Scripture. Yet it expounded a point of doctrine that was implied by Scripture and the ancient baptismal formula of the Church.

Conservative Action

The sixth note of genuine development is conservative action upon its past.

In other words, a development is not a corruption if the doctrine proposed builds upon the doctrinal developments that precede it, often clarifying and strengthening them. A corrupt doctrine, on the other hand, is one that contradicts or reverses a preceding doctrinal development.

The differences between the Apostles’ Creed and the Nicene Creed are a perfect illustration of this criterion. When we compare the two creeds we realize that, while the Nicene Creed is significantly longer, it in no way reverses the tenets of the Apostles’ Creed. In fact, the former strengthens and expounds upon the points of the latter.

Chronic Vigor

The seventh note of genuine development is chronic — that is, abiding — vigor.

As long as a doctrine maintains its life and vigor, its ongoing development is assured. However, once a corruption enters into the process, it leads, by its nature, to death and decay.

Corrupted doctrines fail to display much historical longevity and ultimately die off. As Newman says, “The course of heresies is always short; it is an intermediate state between life and death, or what is like death; or, if it does not result in death, it is resolved into some new, perhaps opposite, course of error, which lays no claim to be connected with it” (p. 204).

In other words, once the original burst of apparent vitality wears itself out, many times the only thing left of a heresy is its external form. This form, however, is more like a corpse than a living thing. To take Pelagianism once more as an example, this heresy thrived only briefly, quickly dying off within 150 years.

A final observation: In general, the seven notes are best applied to the entire process of doctrinal growth in the Church, though it’s certainly possible to apply some of the criteria to individual doctrines.

Necessary Change

When we talk with our Protestant friends about the development of doctrine, we should point out that nearly every Christian tradition accepts this reality in some form or another. For example, the Nicene Creed’s profession of the Blessed Trinity doesn’t appear explicitly in Scripture; instead, it’s a development of truths found in Scripture. Yet most Protestant denominations affirm this doctrine.

Newman’s seven criteria help us see that some kinds of doctrinal change, resulting in greater complexity, are not only legitimate but also necessary. To borrow Newman’s analogy: An acorn that somehow changed into a walnut would be a mutation. But an acorn that never developed into an oak would be lifeless.

So it is with the “acorn” of the Gospel.