BY transmitting to thee, my very dear friend, this fourth book of the work which is [entitled] The Detection and Refutation of False Knowledge, I shall, as I have promised, add weight, by means of the words of the Lord, to what I have already advanced; so that thou also, as thou hast requested, mayest obtain from me the means of confuting all the heretics everywhere, and not permit them, beaten back at all points, to launch out further into the deep of error, nor to be drowned in the sea of ignorance; but that thou, turning them into the haven of the truth, mayest cause them to attain their salvation.