In an age which above all things prided itself upon its reasonableness, it would have been strange indeed if that doctrine of Christianity which is objected to by unbelievers as most repugnant to reason, had not taken a prominent place among the controversies which then abounded in every sphere of theological thought. To the thoughtful Christian, the question of questions must ever be that which forms the subject of this chapter. It is, if possible, even a more vital question than that which was involved in the Deistical controversy. The very name 'Christian' implies as much. A Christian is a follower of Christ. Who, then, is this Christ? What relation does He bear to the Great Being whom Christians, Jews, Turks, Infidels, and Heretics alike adore? What do we mean when we say that He is the Son of God Incarnate? That He is still present with his Church through his Holy Spirit? These are only other forms of putting the question, What is the Trinity? The various answers given to this question in the eighteenth century form an important part of the ecclesiastical history of the period. The subject carries us back in thought to the earliest days of Christianity. During the first four centuries, the nature of the Godhead, and the relation of the Three Persons of the Trinity to each other, were directly or indirectly the causes of almost all the divisions which rent the Church. They had been matters of discussion before the death of the last surviving Apostle, and the three centuries which followed his decease were fruitful in theories upon the subject. These theories reappear with but little alteration in the period which comes more immediately under our present consideration. If history ever repeats itself, it might be expected to do so on the revival of this discussion after an abeyance of many centuries. For it is one of those questions on which modern research can throw but little light. The same materials which enabled the inquirer of the eighteenth century to form his conclusion, existed in the fourth century. Moreover, there was a tendency in the discussions of the later period to run in an historical direction; in treating of them, therefore, our attention will constantly be drawn to the views of the earlier thinkers. With regard to these, it will be sufficient to say that their speculations on the mysterious subject of the Trinity group themselves under one or other of these four heads. 1. The view of those who contend for the mere humanity of Christ--a view which, as will be seen presently, is often claimed by Unitarians as the earliest belief of Christendom. 2. The view of those who deny the distinct personality of the Second and Third Persons of the Blessed Trinity. This was held with various modifications by a great variety of thinkers, but it passes under the general name of _Sabellianism_.