“(Signed), “ALOIS. CARD. MACCHI. “ROME, Sept. 17, 1900.” “PREFACE “Behold, worthy reader, a new Index of the prohibited books, revised and published with the greatest care, by direction of His Holiness Leo XIII, P. M.; together with a syllabus of books to be avoided, there are published also the Constitutions of the Apostolic Chair by which the examination and proscription of bad books are at present governed: viz.: the Constitution ‘of Offices and Duties,’ promulgated by Leo, Jan. 25, 1897, and the Constitution ‘_Solicita ac Provida_’ by which Benedict XIV, on July 9, 1753, established clear and firm rules for the use of the Roman and universal Inquisition, and also of the Holy Congregation of the Index, in examining and judging books. “As to the Constitution of Benedict XIV, it does not apply so much to the faithful in general as to those who are entrusted by the Holy See with the task of examining books. The Constitution of the present Pope has another object, since, revoking the rules of the holy Synod of Trent, ‘it sets forth certain new general Decretals, which are to be obeyed religiously by Catholics everywhere.’ Furthermore, these general Decretals and the Index have this in common, that both exist for the purpose of teaching what books to avoid reading and owning. The Decretals, however, serve this end in one way, the Index in another. For the Decretals prohibit the greatest possible number, indeed almost all, of noxious and tainted books, the reading of which is strongly forbidden by the natural law itself; while the Index reviews and notes but a small part of these. By the Decretals, _genera_ and classes only of bad books are proscribed; by the Index, individual books, each with its title and even the author’s name. Hence it is plain how greatly they err who suppose the whole question of improper books to be decided by the Index alone, as though of the innumerable perverse and pernicious books which have appeared in the course of centuries, those only are prohibited which have been condemned by special decrees and noticed in the catalogue of prohibited books. In fact, any given book can only be safely declared lawful reading when these two conditions are satisfied: it must not occur in the Index nor be contained in any of those classes which are as a whole reprobated and condemned by the Decretals.