Preface. 'My dear friend, this is the fourth book "on the exposure and refutation of false science." In it, as promised, I shall support my previous arguments with our Lord's own words, so that you may be supplied with all sorts of reasons in your controversy with all the heretics. And when you have beaten them back at every point, you will, I trust, prevent them from advancing further into the depth of error and drowning in the sea of ignorance; but, turning their course into the port of truth, will enable them to receive salvation. But in order to convert them one must have a sound knowledge of their tenets and arguments. For it is impossible to cure the sick if one is not acquainted with their form of malady.