To his most beloved lord William, by the grace of God prince of Montpellier, whom not only the title of a noble race marks out, but whom also the nobility of a noble mind marks out beforehand, Master Alanus, his in all things and through all things, dedicates his work.
Since among all the princes of this world I see you specially clothed in the arms of the Christian faith, and not abandoning the little boat of Peter amid so many raging storms of this age's tempests, this work, On the Catholic Faith, I devote, completed, to your discretion.
Although the catholic faith rests resplendent not only on the foundations of divine reasonings, but also of human ones, and stands upon theological authorities as upon the greatest unbreakable supports, nevertheless, on account of new heretics, nay, raging in the oldest and the very newest heresies, given over to philosophical speculations, yet bound to the mirrors of the senses, I am compelled to render, through eloquent reasonings, an account of the reasonable faith. These differ in this from the ancient heretics: that those men strove to storm our faith with human reasonings; these men, however, relying on no reasoning human or divine, according to their own will and pleasure, fashion monstrous things. In former times, indeed, different heretics at different times are read to have dreamed different doctrines, at variance with one another, which are known to have been condemned by the public edicts of the universal Church. But in our own times, new heretics, nay, old ones and inveterate, rehashing worn doctrines, out of diverse heresies compound one general heresy, and, as it were, out of diverse idols one idol, out of diverse monsters one monster, and as it were out of diverse poisonous herbs they compound one common poison.
But because the doctrines are ancient, one must not labor at new inventions, but must be met with authentic reasonings, by which impious doctrines are handed down to have been destroyed by men of illustrious genius, and exercised in every discipline, as by Augustine, Hilary, Jerome, and the other orthodox Fathers. But because the same seeds of heresies sprout up revived, the same defenses of the ancient Fathers must be opposed to them, and if some new heresy should emerge, it must be weakened by firm arguments. And because I behold in you, most strenuous prince, a special son of the faith and its defender, to you I devote this work, and from you I await the examination of this work. This work, moreover, is separated into the distinctions of four volumes: the first of which is known to be published against heretics1; the second, against the Waldensians; the third, against the Jews; the fourth, against the pagans2.