A few words on the 'Defensio Fidei Nicænæ' will be a fitting introduction to the account of the controversy which belongs properly to the eighteenth century. Bishop Bull's defence was written in Latin, and was therefore not intended for the unlearned. It was exclusively confined to this one question: What were the views of the ante-Nicene Fathers on the subject of the Trinity, and especially on the relation of the Second to the First Person? But though the work was addressed only to a very limited number of readers, and dealt only with one, and that a very limited, view of the question, the importance of thoroughly discussing this particular view can scarcely be exaggerated for the following reason. When, the attention of any one familiar with the precise definitions of the Catholic Church which were necessitated by the speculations of Arians and other heretics is called for the first time to the writings of the ante-Nicene Fathers, he may be staggered by the absence of equal definiteness and precision in them. Bishop Bull boldly met the difficulties which might thus occur. He minutely examined the various expressions which could be wrested into an anti-Trinitarian sense, showing how they were compatible with the Catholic Faith, and citing and dwelling upon other expressions which were totally incompatible with any other belief. He showed that the crucial test of orthodoxy, the one single term at which Arians and semi-Arians scrupled—that is, the Homoousion or Consubstantiality of the Son with the Father—was actually in use before the Nicene Council, and that it was thoroughly in accordance with the teaching of the ante-Nicene Fathers. This is proved, among other ways, by the constant use of a simile which illustrates, as happily as earthly things can illustrate heavenly, the true relation of the Son to the Father. Over and over again this is compared by the early fathers to the ray of light which proceeding from the sun is a part of it, and yet without any division or diminution from it, but actually consubstantial with it. He fully admits that the early fathers acknowledged a certain pre-eminence in the First Person, but only such a pre-eminence as the term Father suggests, a pre-eminence implying no inequality of nature, but simply a priority of order, inasmuch as the Father is, as it were, the fountain of the Deity, God in Himself,[431] while the Son is God of God, and, to recur to the old simile incorporated in the Nicene Creed, Light of Light.[432]

Bishop Bull's two subsequent works on the subject of the Trinity ('Judicium Ecclesiæ Catholicæ' and 'Primitiva et Apostolica Traditio') may be regarded as supplements to the 'Defence.' The object of the 'Judicium' was to show, in opposition to Episcopius, that the Nicene fathers held a belief of Our Lord's true and proper divinity to be an indispensable term of Catholic communion; his latest work was directed against the opinion of Zuicker that Christ's divinity, pre-existence, and incarnation were inventions of early heretics.[433]

It is somewhat remarkable that although in the interval which elapsed between the publication of these and of his first work the Trinitarian controversy in England had been assuming larger proportions and awakening a wider interest, Bull never entered into the arena with his countrymen. But the fact is, his point of view was different from theirs. He confined himself exclusively to the historical aspect of the question, while other defenders of the Trinity were 'induced to overstep the boundaries of Scripture proof and historical testimony, and push their inquiries into the dark recesses of metaphysical speculation.'[434] Chief among these was Dr. W. Sherlock, Dean of St. Paul's, who in 1690 published his 'Vindication of the Trinity,' which he describes as 'a new mode of explaining that great mystery by a hypothesis which gives an easy and intelligible notion of a Trinity in Unity, and removes the charge of contradiction.' In this work Sherlock hazarded assertions which were unquestionably 'new,' but not so unquestionably sound. He affirmed, among other things, that the Persons of the Godhead were distinct in the same way as the persons of Peter, James, and John, or any other men. Such assertions were not unnaturally suspected of verging perilously near upon Tritheism, and his book was publicly censured by the Convocation of the University of Oxford. On the other hand, Dr. Wallis, Professor of Geometry, and the famous Dr. South, published treatises against Dr. Sherlock, which, while avoiding the Scylla of Tritheism, ran dangerously near to the Charybdis of Sabellianism. Like all his writings, South's treatise was racy, but violently abusive, and such irritation and acrimony were engendered, that the Royal authority was at last exercised in restraining each party from introducing novel opinions, and requiring them to adhere to such explications only as had already received the sanction of the Church.

Chillingworth, in his Intellectual System, propounded a theory on the Trinity which savoured of Arianism; Burnet and Tillotson called down the fiercest invectives from that able controversialist Charles Leslie, for 'making the Three Persons of God only three manifestations, or the same Person of God considered under three different qualifications and respects as our Creator, Redeemer, and Sanctifier,' while Burnet argued that the inhabitation of God in Christ made Christ to be God.

Thus at the close of the seventeenth century the subject of the Trinity was agitating the minds of some of the chief divines of the age. It must be observed, however, that so far the controversy between theologians of the first rank had been conducted within the limits of the Catholic Faith. They disputed, not about the doctrine of the Trinity itself, but simply about the mode of explaining it.

Still these disputes between English Churchmen strengthened the hands of the anti-Trinitarians. These latter represented the orthodox as divided into Tritheists and Nominalists, and the press teemed with pamphlets setting forth with more or less ability the usual arguments against the Trinity. These were for the most part published anonymously; for their publication would have brought their writers within the range of the law, the Act of 1689 having expressly excluded those who were unsound on the subject of the Trinity from the tolerated sects. One of the most famous tracts, however, 'The Naked Gospel,' was discovered to have been written by Dr. Bury, Rector of Exeter College, Oxford, and was burnt by order of the Convocation of that University. 'A Historical Vindication of the Naked Gospel,' was also a work of considerable power, and was attributed to the famous Le Clerc. But with these exceptions, the anti-Trinitarians, though they were energetic and prolific in a certain kind of literature, had not yet produced any writer who had succeeded in making his mark permanently upon the age.

Thus the question stood at the commencement of the eighteenth century. In one sense the controversy was at its height; that is to say, some of the ablest writers in the Church had written or were writing upon the subject; but the real struggle between the Unitarians (so called) and the Trinitarians had hardly yet begun, for under the latter term almost all the disputants of high mark would fairly have come.

The new century found the pen of that doughty champion of the Faith, Charles Leslie, busy at work on the Socinian controversy. His letters on this subject had been begun some years before this date; but they were not finally completed until the eighteenth century was some years old. Leslie was ever ready to defend what he held to be the Christian faith against all attacks from whatever quarter they might come. Deists, Jews, Quakers, Romanists, Erastians, and Socinians, all fell under his lash; his treatise on the last of these, being the first in order of date, and by no means the last in order of merit among the eighteenth-century literature on the subject of the Trinity, now comes under our notice.

Although his dialogue is nominally directed only against the Socinians, it is full of valuable remarks on the anti-Trinitarians generally; and he brings out some points more clearly and forcibly than subsequent and more voluminous writers on the subject have done. For example, he meets the old objection that the doctrine of the Trinity is incredible as involving a contradiction, by pointing out that it rests upon the fallacy of arguing from a nature which we know to quite a different nature of which we know little or nothing.[435] The objection that the Christian Trinity was borrowed from the Platonists he turns against the objectors by asking, 'What is become of the master argument of the Socinians that the Trinity is contradictory to common sense and reason?—Yet now they would make it the invention of the principal and most celebrated philosophers, men of the most refined reason.'[436]

On the whole this is a very valuable contribution to the apologetic literature on the subject of the Trinity, for though Leslie, like his predecessors, sometimes has recourse to abstruse arguments to explain the 'modes' of the divine presence, yet he is far too acute a controversialist to lay himself open, as Sherlock and South had done, to imputations of heresy on any side; and his general method of treating the question is lucid enough, and full of just such arguments as would be most telling to men of common sense, for whom rather than for profound theologians the treatise was written.