As an historian, Döllinger regarded Christianity as a force more than as a doctrine, and displayed it as it expanded and became the soul of later history. It was the mission and occupation of his life to discover and to disclose how this was accomplished, and to understand the history of civilised Europe, religious and profane, mental and political, by the aid of sources which, being original and authentic, yielded certainty. In his vigorous prime, he thought that it would be within his powers to complete the narrative of the conquest of the world by Christ in a single massive work. The separated churches, the centrifugal forces, were to have been treated apart, until he adopted the ampler title of a history of Christianity. We who look back upon all that the combined and divided labour of a thousand earnest, gifted, and often instructed men has done and left undone in sixty years, can estimate the scientific level of an age where such a dream could be dreamed by such a man, misled neither by imagination nor ambition, but knowing his own limitations and the immeasurable world of books. Experience slowly taught him that he who takes all history for his province is not the man to write a compendium.
The four volumes of Church History which gave him a name in literature appeared between 1833 and 1838, and stopped short of the Reformation. In writing mainly for the horizon of seminaries, it was desirable to eschew voyages of discovery and the pathless border-land. The materials were all in print, and were the daily bread of scholars. A celebrated Anglican described Döllinger at that time as more intentional than Fleury; while Catholics objected that he was a candid friend; and Lutherans, probing deeper, observed that he resolutely held his ground wherever he could, and as resolutely abandoned every position that he found untenable. He has since said of himself that he always spoke sincerely, but that he spoke as an advocate—a sincere advocate who pleaded only for a cause which he had convinced himself was just. The cause he pleaded was the divine government of the Church, the fulfilment of the promise that it would be preserved from error, though not from sin, the uninterrupted employment of the powers committed by Christ for the salvation of man. By the absence of false arts he acquired that repute for superior integrity which caused a Tyrolese divine to speak of him as the most chivalrous of the Catholic celebrities; and the nuncio who was at Munich during the first ten years called him the "professeur le plus éclaire, le plus religieux, en un mot le plus distingué de l'université."
Taking his survey from the elevation of general history, he gives less space to all the early heresies together than to the rise of Mohammedanism. His way lies between Neander, who cares for no institutions, and Baur, who cares for no individuals. He was entirely exempt from that impersonal idealism which Sybel laid down at the foundation of his review, which causes Delbrück to complain that Macaulay, who could see facts so well, could not see that they are revelations, which Baur defines without disguise in his Dreieinigkeitslehre: "Alle geschichtlichen Personen sind für uns blosse Namen." The two posthumous works of Hegel which turned events into theories had not then appeared. Döllinger, setting life and action above theory, omitted the progress of doctrine. He proposed that Möhler should take that share of their common topic, and the plan, entertained at first, was interrupted, with much besides, by death. He felt too deeply the overwhelming unity of force to yield to that atomic theory which was provoked by the Hegelian excess: "L'histoire n'est pas un simple jeu d'abstractions, et les hommes y sont plus que les doctrines. Ce n'est pas une certaine théorie sur la justification et la rédemption qui a fait la Réforme: c'est Luther, c'est Calvin." But he allows a vast scope to the variable will and character of man. The object of religion upon earth is saintliness, and its success is shown in holy individuals. He leaves law and doctrine, moving in their appointed orbits, to hold up great men and examples of Christian virtue.
Döllinger, who had in youth acted as secretary to Hohenlohe, was always reserved in his use of the supernatural. In the vision of Constantine and the rebuilding of the temple, he gives his reader both the natural explanation and the miraculous. He thought that the witness of the fathers to the continuance of miraculous powers could not be resisted without making history a priori, but later on, the more he sifted and compared authorities, the more severe he became. He deplored the uncritical credulity of the author of the Monks of the West; and, in examining the Stigmata, he cited the experience of a Spanish convent where they were so common that it became a sign of reprobation to be without them. Historians, he said, have to look for natural causes: enough will remain for the action of Providence, where we cannot penetrate. In his unfinished book on Ecclesiastical Prophecy he enumerates the illusions of mediæval saints when they spoke of the future, and describes them, as he once described Carlyle and Ruskin, as prophets having nothing to foretell. At Frankfort, where he spoilt his watch by depositing it in unexpected holy water, and it was whispered that he had put it there to mend it, everybody knew that there was hardly a Catholic in the Parliament of whom such a fable could be told with more felicitous unfitness.
For twenty years of his life at Munich, Görres was the impressive central figure of a group reputed far and wide, the most intellectual force in the Catholic world. Seeing things by the light of other days, Nippold and Maurenbrecher describe Döllinger himself as its most eminent member. There was present gain and future peril in living amongst a clever but restricted set, sheltered, supported, and restrained by friends who were united in aims and studies, who cherished their sympathies and their enmities in common, and who therefore believed that they were divided by no deep cleft or ultimate principle. Döllinger never outlived the glamour of the eloquence and ascendancy of Görres, and spoke of him long after his death as a man of real knowledge, and of greater religious than political insight Between the imaginative rhetorician and the measured, scrutinising scholar, the contrast was wide. One of the many pupils and rare disciples of the former complained that his friend supplied interminable matter for the sterile and unavailing Mystik, in order to amuse him with ropes of sand: and the severest censure of Döllinger's art as an historian was pronounced by Görres when he said, "I always see analogies, and you always see differences."
At all times, but in his early studies especially, he owed much to the Italians, whose ecclesiastical literature was the first that he mastered, and predominates in his Church history. Several of his countrymen, such as Savigny and Raumer, had composed history on the shoulders of Bolognese and Lombard scholars, and some of their most conspicuous successors to the present day have lived under heavy obligations to Modena and San Marino. During the tranquil century before the Revolution, Italians studied the history of their country with diligence and success. Even such places as Parma, Verona, Brescia, became centres of obscure but faithful work. Osimo possessed annals as bulky as Rome. The story of the province of Treviso was told in twenty volumes. The antiquities of Picenum filled thirty-two folios. The best of all this national and municipal patriotism was given to the service of religion. Popes and cardinals, dioceses and parish churches became the theme of untiring enthusiasts. There too were the stupendous records of the religious orders, their bulls and charters, their biography and their bibliography. In this immense world of patient, accurate, devoted research, Döllinger laid the deep foundations of his historical knowledge. Beginning like everybody with Baronius and Muratori, he gave a large portion of his life to Noris, and to the solid and enlightened scholarship that surrounded Benedict XIV., down to the compilers, Borgia, Fantuzzi, Marini, with whom, in the evil days of regeneration by the French, the grand tradition died away. He has put on record his judgment that Orsi and Saccarelli were the best writers on the general history of the Church. Afterwards, when other layers had been superposed, and the course he took was his own, he relied much on the canonists, Ballerini and Berardi; and he commended Bianchi, De Bennettis, and the author of the anonymous Confutazione, as the strongest Roman antidote to Blondel, Buckeridge, and Barrow. Italy possessed the largest extant body of Catholic learning; the whole sphere of Church government was within its range, and it enjoyed something of the official prerogative.
Next to the Italians he gave systematic attention to the French. The conspicuous Gallicans, the Jansenists, from whom at last he derived much support, Richer, Van Espen, Launoy, whom he regarded as the original of Bossuet, Arnauld, whom he thought his superior, are absent from his pages. He never overcame his distrust of Pascal, for his methodical scepticism and his endeavour to dissociate religion from learning; and he rated high Daniel's reply to the Provinciales. He esteemed still more the French Protestants of the seventeenth century, who transformed the system of Geneva and Dort. English theology did not come much in his way until he had made himself at home with the Italians and the primary French. Then it abounded. He gathered it in quantities on two journeys in 1851 and 1858, and he possessed the English divines in perfection, at least down to Whitby, and the nonjurors. Early acquaintance with Sir Edward Vavasour and Lord Clifford had planted a lasting prejudice in favour of the English Catholic families, which sometimes tinged his judgments. The neglected literature of the Catholics in England held a place in his scheme of thought, which it never obtained in the eyes of any other scholar, native or foreign. This was the only considerable school of divines who wrote under persecution, and were reduced to an attitude of defence. In conflict with the most learned, intelligent, and conciliatory of controversialists, they developed a remarkable spirit of moderation, discriminating inferior elements from the original and genuine growth of Catholic roots; and their several declarations and manifestoes, from the Restoration onwards, were an inexhaustible supply for irenics. Therefore they powerfully attracted one who took the words of St Vincent of Lérins not merely for a flash of illumination, but for a scientific formula and guiding principle. Few writers interested him more deeply than Stapleton, Davenport, who anticipated Number XC., Irishmen, such as Caron and Walshe, and the Scots, Barclay, the adversary and friend of Bellarmine, Ramsay, the convert and recorder of Fénelon. It may be that, to an intellect trained in the historic process, stability, continuity, and growth were terms of more vivid and exact significance than to the doctors of Pont-à-Mousson and Lambspring. But when he came forward arrayed in the spoils of Italian libraries and German universities, with the erudition of centuries and the criticism of to-day, he sometimes was content to follow where forgotten Benedictines or Franciscans had preceded, under the later Stuarts.
He seldom quotes contemporary Germans, unless to dispute with them, prefers old books to new, and speaks of the necessary revision and renovation of history. He suspected imported views and foregone conclusions even in Neander; and although he could not say, with Macaulay, that Gieseler was a rascal, of whom he had never heard, he missed no opportunity of showing his dislike for that accomplished artificer in mosaic. Looking at the literature before him, at England, with Gibbon for its one ecclesiastical historian; at Germany, with the most profound of its divines expecting the Church to merge in the State, he inferred that its historic and organic unity would only be recognised by Catholic science, while the soundest Protestant would understand it least. In later years, Kliefoth, Ritschl, Gass, perhaps also Dorner and Uhlhorn, obliged him to modify an opinion which the entire school of Schleiermacher, including the illustrious Rothe, served only to confirm. Germany, as he found it when he began to see the world, little resembled that of his old age, when the work he had pursued for seventy years was carried forward, with knowledge and power like his own, by the best of his countrymen. The proportion of things was changed. There was a religious literature to be proud of, to rely on: other nations, other epochs, had lost their superiority. As his own people advanced, and dominated in the branches of learning to which his life was given, in everything except literary history and epigraphies, and there was no more need to look abroad, Döllinger's cosmopolitan characteristic diminished, he was more absorbed in the national thought and work, and did not object to be called the most German of the Germans.
The idea that religious science is not so much science as religion, that it should be treated differently from other matters, so that he who treats it may rightly display his soul, flourished in his vicinity, inspiring the lives of Saint Elizabeth and Joan of Arc, Möhler's fine lectures on the early fathers, and the book which Gratry chose to entitle a Commentary on St. Matthew. Döllinger came early to the belief that history ought to be impersonal, that the historian does well to keep out of the way, to be humble and self-denying, making it a religious duty to prevent the intrusion of all that betrays his own position and quality, his hopes and wishes. Without aspiring to the calm indifference of Ranke, he was conscious that, in early life, he had been too positive, and too eager to persuade. The Belgian scholar who, conversing with him in 1842, was reminded of Fénelon, missed the acuter angles of his character. He, who in private intercourse sometimes allowed himself to persist, to contradict, and even to baffle a bore by frankly falling asleep, would have declined the evocation of Versailles. But in reasonableness, moderation, and charity, in general culture of mind and the sense of the demands of the progress of civilisation, in the ideal church for which he lived, he was more in harmony with Fénelon than with many others who resembled him in the character of their work.
He deemed it catholic to take ideas from history, and heresy to take them into it. When men gave evidence for the opposite party, and against their own, he willingly took for impartiality what he could not always distinguish from indifference or subdivision. He felt that sincere history was the royal road to religious union, and he specially cultivated those who saw both sides. He would cite with complacency what clever Jesuits, Raynaud and Faure, said for the Reformation, Mariana and Cordara against their society. When a Rhenish Catholic and a Genevese Calvinist drew two portraits of Calvin which were virtually the same, or when, in Ficker's revision of Böhmer, the Catholic defended the Emperor Frederic II. against the Protestant, he rejoiced as over a sign of the advent of science. As the Middle Ages, rescued from polemics by the genial and uncritical sympathy of Müller, became an object of popular study, and Royer Collard said of Villemain, Il a fait, il fait, et il fera toujours son Grégoire VII., there were Catholics who desired, by a prolonged sorites, to derive advantage from the new spirit. Wiseman consulted Döllinger for the purpose. "Will you be kind enough to write me a list of what you consider the best books for the history of the Reformation; Menzel and Buchholz I know; especially any exposing the characters of the leading reformers?" In the same frame of mind he asked him what pope there was whose good name had not been vindicated; and Döllinger's reply, that Boniface VIII. wanted a friend, prompted both Wiseman's article and Tosti's book.