Now it was not the Manicheans or Donatists who were the most dangerous people in the time of Augustine,--nor were their doctrines likely to be embraced by the Christian schools, especially in the West; but it was the Pelagians who in high places were assailing the Pauline theology. And they advocated principles which lay at the root of most of the subsequent controversies of the Church. They were intellectual men, generally good men, who could not be put down, and who would thrive under any opposition. Augustine did not attack the character of these men, but rendered a great service to the Church by pointing out, clearly and luminously, the antichristian character of their theories, when rigorously pushed out, by a remorseless logic, to their necessary sequence. Whatever value may be attached to that science which is based on deductions drawn from the truths of revelation, certain it is that it was theology which most interested Christians in the time of Augustine, as in the time of Athanasius; and his controversy with the Pelagians made then a mighty stir, and is at the root of half the theological discussions from that age to ours. If we would understand the changes of human thought in the Middle Ages, if we would seek to know what is most vital in Church history, that celebrated Pelagian controversy claims our special attention. It was at a great crisis in the Church when a British monk of extraordinary talents, persuasive eloquence, and great attainments,--a man accustomed to the use of dialectical weapons and experienced by extensive travels, ambitious, ardent, plausible, adroit,--appeared among the churches and advanced a new philosophy. His name was Pelagius; and he was accompanied by a man of still greater logical power than he himself possessed, though not so eloquent or accomplished or pleasing in manner, who was called Celestius,--two doctors of whom the schools were justly proud, and who were admired and honored by enthusiastic young men, as Abélard was in after-times.