Pascendi Dominici Gregis §51

⁵¹ To give you some more general directions, Venerable Brethren, in a matter of such moment, We bid you do everything in your power to drive out of your dioceses, even by solemn interdict, any pernicious books that may be in circulation there. The Holy See neglects no means to put down writings of this kind, but the number of them has now grown to such an extent that it is impossible to censure them all. Hence it happens that the medicine sometimes arrives too late, for the disease has taken root during the delay. We will, therefore, that the Bishops, putting aside all fear and the prudence of the flesh, despising the outcries of the wicked, gently by all means but constantly, do each his own share of this work, remembering the injunctions of Leo XIII. in the Apostolic Constitution Officiorum : Let the Ordinaries, acting in this also as Delegates of the Apostolic See, exert themselves to prescribe and to put out of reach of the faithful injurious books or other writings printed or circulated in their dioceses . In this passage the Bishops, it is true, receive a right, but they have also a duty imposed on them. Let no Bishop think that he fulfils this duty by denouncing to us one or two books, while a great many others of the same kind are being published and circulated. Nor are you to be deterred by the fact that a book has obtained the Imprimatur elsewhere, both because this may be merely simulated, and because it may have been granted through carelessness or easiness or excessive confidence in the author as may sometimes happen in religious Orders. Besides, just as the same food does not agree equally with everybody, it may happen that a book harmless in one may, on account of the different circumstances, be hurtful in another. Should a Bishop, therefore, after having taken the advice of prudent persons, deem it right to condemn any of such books in his diocese, We not only give him ample faculty to do so but We impose it upon him as a duty to do so. Of course, it is Our wish that in such action proper regard be used, and sometimes it will suffice to restrict the prohibition to the clergy; but even in such cases it will be obligatory on Catholic booksellers not to put on sale books condemned by the Bishop. And while We are on this subject of booksellers, We wish the Bishops to see to it that they do not, through desire for gain, put on sale unsound books. It is certain that in the catalogues of some of them the books of the Modernists are not unfrequently announced with no small praise. If they refuse obedience let the Bishops have no hesitation in depriving them of the title of Catholic booksellers; so too, and with more reason, if they have the title of Episcopal booksellers, and if they have that of Pontifical, let them be denounced to the Apostolic See. Finally, We remind all of the XXVI. article of the abovementioned Constitution Officiorum : All those who have obtained an apostolic faculty to read and keep forbidden books, are not thereby authorised to read books and periodicals forbidden by the local Ordinaries, unless the apostolic faculty expressly concedes permission to read and keep books condemned by anybody . IV. - Censorship