And if the believing scientist does take his faith for a guide in some matters, when in all his researches in the history of the Christian religion and the Church he presupposes that God’s miraculous interference is not impossible, because the contrary would offend not only against his faith, but also against his common sense; when in pondering the ultimate reasons of all things he allows himself to be influenced by the idea that atheism is false, or at least not proved—for that there is a God both his faith and his reason tell him—then these presumptions are by no means inadmissible. The naturalist, too, presupposing certain results of science to be true, takes care not to get into conflict with them, and he will soon correct himself should he arrive at different results. If a mathematician should arrive at results conflicting with other proved results, he would infer therefrom that his calculation was faulty; why, then, cannot the Christian now and then be led by the truths of his faith, of which he is certain, without by doing so offending against the spirit of scientific truthfulness? Or may he not do so just because they are _religious_ truths, vouched for by a supernatural authority? As a fact many of them are established also by the testimony of reason. This is shown by the examples just mentioned. However, the question is not how a truth is vouched for, but whether it be a truth or not. If the scientist is assured that something is unquestionably true, then he owes it to the spirit of truthfulness to accept it. In doing so he will in no way be unfaithful to his scientific method; the truths of faith are to him not a source of proofs for the results of his profane science, but only hints, calling his attention to the fact that certain propositions are not proved, that they are even false. Much less is in historical questions the Catholic obliged to defend or praise everything of advantage to his Church, whether true or not. Hence _Mommsen_ is grossly mistaken when he states in his letter of protest mentioned above: “The appointment of a historian or philosopher, who must be a Catholic or a Protestant and who must serve his confession, evidently means nothing else but to prohibit the Protestant historian from presenting the powerful mental structure of the papacy in its full light, and the Catholic historian from appreciating the profound thought and the tremendous importance of heresy and Protestantism.” The Catholic is only bound to the truth. Or are the Christian truths of faith perhaps regrettable errors, hence presumptions that should not be made? If so, demonstrate it. Hitherto such demonstration has not succeeded. So long as the creed of the believing Christian cannot be refuted convincingly, he has the right to cling to it in the name of truth.