John Henry Newman begins the introduction to his book An Essay on the Development of Christian Doctrine:

CHRISTIANITY has been long enough in the world to justify us in dealing with it as a fact in the world’s history. Its genius and character, its doctrines, precepts, and objects cannot be treated as matters of private opinion or deduction, unless we may reasonably so regard the Spartan institutions or the religion of Mahomet. It may indeed legitimately be made the subject-matter of theories; what is its moral and political excellence, what its due location in the range of ideas or of facts which we possess, whether it be divine or human, whether original or eclectic, or both at once, how far favourable to civilization or to literature, whether a religion for all ages or for a particular state of society, these are questions upon the fact, or professed solutions of the fact, and belong to the province of opinion; but to a fact do they relate, on an admitted fact do they turn, which must be ascertained as other facts, and surely has on the whole been so ascertained, unless the testimony of so many centuries is to go for nothing. Christianity is no theory of the study or the cloister. It has long since passed beyond the letter of documents and the reasonings of individual minds, and has become public property. Its “sound has gone out into all lands,” and its “words unto the ends of the world.” It has from the first had an objective existence, and has thrown itself upon the great concourse of men. Its home is in the world; and to know what it is, we must seek it in the world, and hear the world’s witness of it.

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The hypothesis, indeed, has met with wide reception in these latter times, that Christianity does not fall within the province of history,—that it is to each man what each man thinks it to be, and nothing else; and thus in fact is a mere name for a cluster or family of rival religions all together, religions at variance one with another, and claiming the same appellation, not because there can be assigned any one and the same doctrine as the common foundation of all, but because certain points of agreement may be found here and there of some sort or other, by which each in its turn is connected with one or other of the rest. Or again, it has been maintained, or implied, that all existing denominations of Christianity are wrong, none representing it as taught by Christ and His Apostles; that the original religion has gradually decayed or become hopelessly corrupt; nay that it died out of the world at its birth, and was forthwith succeeded by a counterfeit or counterfeits which assumed its name, though they inherited at best but some fragments of its teaching; or rather that it cannot even be said either to have decayed or to have died, because historically it has no substance of its own, but from the first and onwards it has, on the stage of the world, been nothing more than a mere assemblage of doctrines and practices derived from without, from Oriental, Platonic, Polytheistic sources, from Buddhism, Essenism, Manicheeism; or that, allowing true Christianity still to exist, it has but a hidden and isolated life, in the hearts of the elect, or again as a literature or philosophy, not certified in any way, much less guaranteed, to come from above, but one out of the various separate informations about the Supreme Being and human duty, with which an unknown Providence has furnished us, whether in nature or in the world.

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All such views of Christianity imply that there is no sufficient body of historical proof to interfere with, or at least to prevail against, any number whatever of free and independent hypotheses concerning it. But this, surely, is not self-evident, and has itself to be proved. Till positive reasons grounded on facts are adduced to the contrary, the most natural hypotheses, the most agreeable to our mode of proceeding in parallel cases, and that which takes precedence of all others, is to consider that the society of Christians, which the Apostles left on earth, were of that religion to which the Apostles had converted them; that the external continuity of name, profession, and communion, argues a real continuity of doctrine; that, as Christianity began by manifesting itself as of a certain shape and bearing to all mankind, therefore it went on so to manifest itself; and that the more, considering that prophecy had already determined that it was to be a power visible in the world and sovereign over it, characters which are accurately fulfilled in that historical Christianity to which we commonly give the name. It is not a violent assumption, then, but rather mere abstinence from the wanton admission of a principle which would necessarily lead to the most vexatious and preposterous scepticism, to take it for granted, before proof to the contrary, that the Christianity of the second, fourth, seventh, twelfth, sixteenth, and intermediate centuries is in its substance the very religion which Christ and His Apostles taught in the first, whatever may be the modifications for good or for evil which lapse of years, or the vicissitudes of human affairs, have impressed upon it.

Of course I do not deny the abstract possibility of extreme changes. The substitution is certainly, in idea, supposable of a counterfeit Christianity,—superseding the original, by means of the adroit innovations of seasons, places, and persons, till, according to the familiar illustration, the “blade” and the “handle” are alternately renewed, and identity is lost without the loss of continuity. It is possible; but it must not be assumed. The onus probandi is with those who assert what it is unnatural to expect; to be just able to doubt is no warrant for disbelieving.

His basic claim in these paragraphs is that we should assume that Christianity has remained substantially unchanged over time, and that the changes that have taken place are relatively minor ones, unless it is first proven otherwise.

Next, he contrasts this idea with Protestant forms of Christianity:

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Accordingly, some writers have gone on to give reasons from history for their refusing to appeal to history. They aver that, when they come to look into the documents and literature of Christianity in times past, they find its doctrines so variously represented, and so inconsistently maintained by its professors, that, however natural it be à priori, it is useless, in fact, to seek in history the matter of that Revelation which has been vouchsafed to mankind; that they cannot be historical Christians if they would. They say, in the words of Chillingworth, “There are popes against popes, councils against councils, some fathers against others, the same fathers against themselves, a consent of fathers of one age against a consent of fathers of another age, the Church of one age against the Church of another age:”—Hence they are forced, whether they will or not, to fall back upon the Bible as the sole source of Revelation, and upon their own personal private judgment as the sole expounder of its doctrine. This is a fair argument, if it can be maintained, and it brings me at once to the subject of this Essay. Not that it enters into my purpose to convict of misstatement, as might be done, each separate clause of this sweeping accusation of a smart but superficial writer; but neither on the other hand do I mean to deny everything that he says to the disadvantage of historical Christianity. On the contrary, I shall admit that there are in fact certain apparent variations in its teaching, which have to be explained; thus I shall begin, but then I shall attempt to explain them to the exculpation of that teaching in point of unity, directness, and consistency.

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Meanwhile, before setting about this work, I will address one remark to Chillingworth and his friends:—Let them consider, that if they can criticize history, the facts of history certainly can retort upon them. It might, I grant, be clearer on this great subject than it is. This is no great concession. History is not a creed or a catechism, it gives lessons rather than rules; still no one can mistake its general teaching in this matter, whether he accept it or stumble at it. Bold outlines and broad masses of colour rise out of the records of the past. They may be dim, they may be incomplete; but they are definite. And this one thing at least is certain; whatever history teaches, whatever it omits, whatever it exaggerates or extenuates, whatever it says and unsays, at least the Christianity of history is not Protestantism. If ever there were a safe truth, it is this.

And Protestantism has ever felt it so. I do not mean that every writer on the Protestant side has felt it; for it was the fashion at first, at least as a rhetorical argument against Rome, to appeal to past ages, or to some of them; but Protestantism, as a whole, feels it, and has felt it. This is shown in the determination already referred to of dispensing with historical Christianity altogether, and of forming a Christianity from the Bible alone: men never would have put it aside, unless they had despaired of it. It is shown by the long neglect of ecclesiastical history in England, which prevails even in the English Church. Our popular religion scarcely recognizes the fact of the twelve long ages which lie between the Councils of Nicæa and Trent, except as affording one or two passages to illustrate its wild interpretations of certain prophesies of St. Paul and St. John. It is melancholy to say it, but the chief, perhaps the only English writer who has any claim to be considered an ecclesiastical historian, is the unbeliever Gibbon. To be deep in history is to cease to be a Protestant.

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And this utter incongruity between Protestantism and historical Christianity is a plain fact, whether the latter be regarded in its earlier or in its later centuries. Protestants can as little bear its Ante-nicene as its Post-tridentine period. I have elsewhere observed on this circumstance: “So much must the Protestant grant that, if such a system of doctrine as he would now introduce ever existed in early times, it has been clean swept away as if by a deluge, suddenly, silently, and without memorial; by a deluge coming in a night, and utterly soaking, rotting, heaving up, and hurrying off every vestige of what it found in the Church, before cock-crowing: so that ‘when they rose in the morning’ her true seed ‘were all dead corpses’—Nay dead and buried—and without grave-stone. ‘The waters went over them; there was not one of them left; they sunk like lead in the mighty waters.’ Strange antitype, indeed, to the early fortunes of Israel!—then the enemy was drowned, and ‘Israel saw them dead upon the sea-shore.’ But now, it would seem, water proceeded as a flood ‘out of the serpent’s mouth, and covered all the witnesses, so that not even their dead bodies lay in the streets of the great city.’ Let him take which of his doctrines he will, his peculiar view of self-righteousness, of formality, of superstition; his notion of faith, or of spirituality in religious worship; his denial of the virtue of the sacraments, or of the ministerial commission, or of the visible Church; or his doctrine of the divine efficacy of the Scriptures as the one appointed instrument of religious teaching; and let him consider how far Antiquity, as it has come down to us, will countenance him in it. No; he must allow that the alleged deluge has done its work; yes, and has in turn disappeared itself; it has been swallowed up by the earth, mercilessly as itself was merciless.”

That Protestantism, then, is not the Christianity of history, it is easy to determine, but to retort is a poor reply in controversy to a question of fact, and whatever be the violence or the exaggeration of writers like Chillingworth, if they have raised a real difficulty, it may claim a real answer, and we must determine whether on the one hand Christianity is still to represent to us a definite teaching from above, or whether on the other its utterances have been from time to time so strangely at variance, that we are necessarily thrown back on our own judgment individually to determine, what the revelation of God is, or rather if in fact there is, or has been, any revelation at all.

Newman uses Chillingworth as an example of someone who disagrees with that Christianity has actually possessed historical continuity. There is no real continuity, says Chillingworth, because Christians throughout history have contradicted each other in every possible way. So we are left to our own devices, and to the Bible, if we want to know the teaching of Christ.

Newman responds that Protestantism is also not the “Christianity of history.” It is likely enough that Chillingworth would not find this a meaningful objection, since his whole point would be that history does not matter. However, Newman points out that such a situation would suggest that Christianity is not a revelation of God at all, but a matter of human opinion.

He goes on to acknowledge that Chillingworth has a certain point about the history of Christianity, and begins to discuss the explanation for this point offered by Anglicanism, which he considers as though a kind of mean between Catholicism and Protestantism.

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Here then I concede to the opponents of historical Christianity, that there are to be found, during the 1800 years through which it has lasted, certain apparent inconsistencies and alterations in its doctrine and its worship, such as irresistibly attract the attention of all who inquire into it. They are not sufficient to interfere with the general character and course of the religion, but they raise the question how they came about, and what they mean, and have in consequence supplied matter for several hypotheses.

Of these one is to the effect that Christianity has even changed from the first and ever accommodates itself to the circumstances of times and seasons; but it is difficult to understand how such a view is compatible with the special idea of revealed truth, and in fact its advocates more or less abandon, or tend to abandon the supernatural claims of Christianity; so it need not detain us here.

A second and more plausible hypothesis is that of the Anglican divines, who reconcile and bring into shape the exuberant phenomena under consideration, by cutting and casting away as corruptions all usages, ways, opinions, and tenets, which have not the sanction of primitive times. They maintain that history first presents to us a pure Christianity in East and West, and then a corrupt; and then of course their duty is to draw the line between what is corrupt and what is pure, and to determine the dates at which the various changes from good to bad were introduced. Such a principle of demarcation, available for the purpose, they consider they have found in the dictum of Vincent of Lerins, that revealed and Apostolic doctrine is “quod semper, quod ubique, quod ab omnibus,” a principle infallibly separating, on the whole field of history, authoritative doctrine from opinion, rejecting what is faulty, and combining and forming a theology. That “Christianity is what has been held always, everywhere, and by all,” certainly promises a solution of the perplexities, an interpretation of the meaning, of history. What can be more natural than that divines and bodies of men should speak, sometimes from themselves, sometimes from tradition? what more natural than that individually they should say many things on impulse, or under excitement, or as conjectures, or in ignorance? what more certain than that they must all have been instructed and catechized in the Creed of the Apostles? what more evident than that what was their own would in its degree be peculiar, and {11} differ from what was similarly private and personal in their brethren? what more conclusive than that the doctrine that was common to all at once was not really their own, but public property in which they had a joint interest, and was proved by the concurrence of so many witnesses to have come from an Apostolical source? Here, then, we have a short and easy method for bringing the various informations of ecclesiastical history under that antecedent probability in its favour, which nothing but its actual variations would lead us to neglect. Here we have a precise and satisfactory reason why we should make much of the earlier centuries, yet pay no regard to the later, why we should admit some doctrines and not others, why we refuse the Creed of Pius IV. and accept the Thirty-nine Articles.

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Such is the rule of historical interpretation which has been professed in the English school of divines; and it contains a majestic truth, and offers an intelligible principle, and wears a reasonable air. It is congenial, or, as it may be said, native to the Anglican mind, which takes up a middle position, neither discarding the Fathers nor acknowledging the Pope. It lays down a simple rule by which to measure the value of every historical fact, as it comes, and thereby it provides a bulwark against Rome, while it opens an assault upon Protestantism. Such is its promise; but its difficulty lies in applying it in particular cases. The rule is more serviceable in determining what is not, than what is Christianity; it is irresistible against Protestantism, and in one sense indeed it is irresistible against Rome also, but in the same sense it is irresistible against England. It strikes at Rome through England. It admits of being interpreted in one of two ways: if it be narrowed for the purpose of disproving the catholicity of the Creed of Pope Pius, it becomes also an objection to the Athanasian; and if it be relaxed to admit the doctrines retained by the English Church, it no longer excludes certain doctrines of Rome which that Church denies. It cannot at once condemn St. Thomas and St. Bernard, and defend St. Athanasius and St. Gregory Nazianzen.

This general defect in its serviceableness has been heretofore felt by those who appealed to it. It was said by one writer; “The Rule of Vincent is not of a mathematical or demonstrative character, but moral, and requires practical judgment and good sense to apply it. For instance, what is meant by being ‘taught always‘? does it mean in every century, or every year, or every month? Does ‘everywhere’ mean in every country, or in every diocese? and does ‘the Consent of Fathers‘ require us to produce the direct testimony of every one of them? How many Fathers, how many places, how many instances, constitute a fulfilment of the test proposed? It is, then, from the nature of the case, a condition which never can be satisfied as fully as it might have been. It admits of various and unequal application in various instances; and what degree of application is enough, must be decided by the same principles which guide us in the conduct of life, which determine us in politics, or trade, or war, which lead us to accept Revelation at all, (for which we have but probability to show at most,) nay, to believe in the existence of an intelligent Creator.”

Once you realize that Christianity has in fact changed throughout history, he says, you need to explain that fact. He dismisses the explanation that Christianity is simply a changeable thing, since he says that the adherents of this view either abandon the idea of divine revelation, or at least have a tendency to abandon it.

The Anglican view, he says, is that there is a common body of more or less unchanging doctrine which is the true revelation of Christ, and we should accept this common body of doctrine while rejecting whatever is added to it. He points out that there is a problem with this explanation: the body of doctrine accepted by Anglicans is not in fact historically more common than doctrines which imply the truth of Catholicism. He cites various examples such as the following:

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One additional specimen shall be given as a sample of many others:—I betake myself to one of our altars to receive the Blessed Eucharist; I have no doubt whatever on my mind about the Gift which that Sacrament contains; I confess to myself my belief, and I go through the steps on which it is assured to me. “The Presence of Christ is here, for It follows upon Consecration; and Consecration is the prerogative of Priests; and Priests are made by Ordination; and Ordination comes in direct line from the Apostles. Whatever be our other misfortunes, every link in our chain is safe; we have the Apostolic Succession, we have a right form of consecration: therefore we are blessed with the great Gift.” Here the question rises in me, “Who told you about that Gift?” I answer, “I have learned it from the Fathers: I believe the Real Presence because they bear witness to it. St. Ignatius calls it ‘the medicine of immortality:’ St. Irenæus says that ‘our flesh becomes incorrupt, and partakes of life, and has the hope of the resurrection,’ as ‘being nourished from the Lord’s Body and Blood;’ that the Eucharist ‘is made up of two things, an earthly and an heavenly:’ perhaps Origen, and perhaps Magnes, after him, say that It is not a type of our Lord’s Body, but His Body: and St. Cyprian uses language as fearful as can be spoken, of those who profane it. I cast my lot with them, I believe as they.” Thus I reply, and then the thought comes upon me a second time, “And do not the same ancient Fathers bear witness to another doctrine, which you disown? Are you not as a hypocrite, listening to them when you will, and deaf when you will not? How are you casting your lot with the Saints, when you go but half-way with them? For of whether of the two do they speak the more frequently, of the Real Presence in the Eucharist, or of the Pope’s supremacy? You accept the lesser evidence, you reject the greater.”

The Anglicans, or at least those with whom Newman once agreed, accepted the doctrine of the Real Presence, but of course rejected the idea of the authority of the Pope. This is not consistent, he says, because the Fathers who testify to the Real Presence also testify to the Pope’s authority, perhaps even more clearly.

After discussing briefly one other hypothesis which he dismisses as insufficient, he proposes his own:

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The following Essay is directed towards a solution of the difficulty which has been stated,—the difficulty, as far as it exists, which lies in the way of our using in controversy the testimony of our most natural informant concerning the doctrine and worship of Christianity, viz. the history of eighteen hundred years. The view on which it is written has at all times, perhaps, been implicitly adopted by theologians, and, I believe, has recently been illustrated by several distinguished writers of the continent, such as De Maistre and Möhler: viz. that the increase and expansion of the Christian Creed and Ritual, and the variations which have attended the process in the case of individual writers and Churches, are the necessary attendants on any philosophy or polity which takes possession of the intellect and heart, and has had any wide or extended dominion; that, from the nature of the human mind, time is necessary for the full comprehension and perfection of great ideas; and that the highest and most wonderful truths, though communicated to the world once for all by inspired teachers, could not be comprehended all at once by the recipients, but, as being received and transmitted by minds not inspired and through media which were human, have required only the longer time and deeper thought for their full elucidation. This may be called the Theory of Development of Doctrine; and, before proceeding to treat of it, one remark may be in place.

It is undoubtedly an hypothesis to account for a difficulty; but such too are the various explanations given by astronomers from Ptolemy to Newton of the apparent motions of the heavenly bodies, and it is as unphilosophical on that account to object to the one as to object to the other. Nor is it more reasonable to express surprise, that at this time of day a theory is necessary, granting for argument’s sake that the theory is novel, than to have directed a similar wonder in disparagement of the theory of gravitation, or the Plutonian theory in geology. Doubtless, the theory of the Secret and the theory of doctrinal Developments are expedients, and so is the dictum of Vincentius; so is the art of grammar or the use of the quadrant; it is an expedient to enable us to solve what has now become a necessary and an anxious problem. For three hundred years the documents and the facts of Christianity have been exposed to a jealous scrutiny; works have been judged spurious which once were received without a question; facts have been discarded or modified which were once first principles in argument; new facts and new principles have been brought to light; philosophical views and polemical discussions of various tendencies have been maintained with more or less success. Not only has the relative situation of controversies and theologies altered, but infidelity itself is in a different,—I am obliged to say in a more hopeful position,—as regards Christianity. The facts of Revealed Religion, though in their substance unaltered, present a less compact and orderly front to the attacks of its enemies now than formerly, and allow of the introduction of new inquiries and theories concerning its sources and its rise. The state of things is not as it was, when an appeal lay to the supposed works of the Areopagite, or to the primitive Decretals, or to St. Dionysius’s answers to Paul, or to the Cœna Domini of St. Cyprian. The assailants of dogmatic truth have got the start of its adherents of whatever Creed; philosophy is completing what criticism has begun; and apprehensions are not unreasonably excited lest we should have a new world to conquer before we have weapons for the warfare. Already infidelity has its views and conjectures, on which it arranges the facts of ecclesiastical history; and it is sure to consider the absence of any antagonist theory as an evidence of the reality of its own. That the hypothesis, here to be adopted, accounts not only for the Athanasian Creed, but for the Creed of Pope Pius, is no fault of those who adopt it. No one has power over the issues of his principles; we cannot manage our argument, and have as much of it as we please and no more. An argument is needed, unless Christianity is to abandon the province of argument; and those who find fault with the explanation here offered of its historical phenomena will find it their duty to provide one for themselves.

And as no special aim at Roman Catholic doctrine need be supposed to have given a direction to the inquiry, so neither can a reception of that doctrine be immediately based on its results. It would be the work of a life to apply the Theory of Developments so carefully to the writings of the Fathers, and to the history of controversies and councils, as thereby to vindicate the reasonableness of every decision of Rome; much less can such an undertaking be imagined by one who, in the middle of his days, is beginning life again. Thus much, however, might be gained even from an Essay like the present, an explanation of so many of the reputed corruptions, doctrinal and practical, of Rome, as might serve as a fair ground for trusting her in parallel cases where the investigation had not been pursued.

If you simply consider the abstract idea of “truth revealed by God,” Newman is saying, you would not necessarily expect that to change over time. Since Christianity does change over time, you need to explain that fact, and especially if you wish to believe that Christianity is composed of truths revealed by God. This has led to a situation where “infidelity itself is in a different,—I am obliged to say in a more hopeful position,—as regards Christianity,” and where “infidelity has its views and conjectures, on which it arranges the facts of ecclesiastical history; and it is sure to consider the absence of any antagonist theory as an evidence of the reality of its own.” In response, Newman has formulated his own theory, which he calls the “theory of the development of doctrine,” since he sees the other theories as inadequate. His theory ultimately implies that Catholic Christianity is the correct development of the Christianity handed down by the Apostles. In the above quotation Newman excuses himself for this, when he says,

That the hypothesis, here to be adopted, accounts not only for the Athanasian Creed, but for the Creed of Pope Pius, is no fault of those who adopt it. No one has power over the issues of his principles; we cannot manage our argument, and have as much of it as we please and no more. An argument is needed, unless Christianity is to abandon the province of argument; and those who find fault with the explanation here offered of its historical phenomena will find it their duty to provide one for themselves.

Above, Newman compared this discussion with development in other sciences such as the development of geology. This is probably a justified comparison. Just as Philip Gosse pointed out that Christian geologists wished to avoid the conclusion that the earth was ancient, but were forced by the facts to accept this, so Newman himself wished to explain the facts of Christian history in a form which would make Anglicanism acceptable, but ultimately he found this impossible.