854. The kinds of printed matter forbidden by the Code (Canon 1399) are as follows: (a) the prohibition extends to books, to other published matter (such as magazines and newspapers), and to illustrations that attack religion and what are called “holy pictures” (i.e., images of our Lord and the Saints), if opposed to the mind of the Church; (b) the prohibition extends to published matter dangerous to faith, and therefore to the following; to writings or caricatures that attack the existence of God, miracles or other foundations of natural or revealed religion, Catholic dogma, worship or discipline, the ecclesiastical hierarchy as such, or the clerical or religious state; to those that defend heresy, schism, superstition, condemned errors, subversive societies, or suicide, duelling, divorce; to non-Catholic publications of the Bible and to non-Catholic works on religion that are not clearly free from opposition to Catholic faith; to liturgical works that do not agree with the authentic texts; to books that publish apocryphal indulgences and to printed images of holy persons that would be the occasion of error (e.g., the representation of the Holy Ghost in human form).
855. The mere presence, however, of condemned matter in a writing does not cause it to fall under prohibition.
(a) Some works are not forbidden unless the author’s purpose to teach error or attack the truth is known. Hence, books on religion written by non-Catholics which contain errors against the Catholic Faith are not forbidden, unless they deal with religion _ex professo_ (i.e., not incidentally or cursorily, but clearly for the purpose of teaching). It is not necessary, however, that religion be the main theme of the book, Similarly, books that attack religion are forbidden, not when attacks are casual or by the way, but when they are made purposely; and the same is true as regards books that insult the clerical state. The purpose is recognized from the declaration of the author, from the nature of the work, from the systematic treatment, length or frequency of argumentation or attack, etc.
(b) Other works are not forbidden, unless they contain not only agreement with error, but also argument in defense of error. Thus, books in favor of heresy, schism, suicide, duelling, divorce, Freemasonry, etc., are forbidden when they champion wrong causes by disputing in their behalf.
(c) Other works are forbidden, not because they state, but because they approve of error. Such are books that attack or ridicule the foundations of religion or the dogmas of faith, those that disparage worship, those that are subversive of discipline, those that defend proscribed propositions, those that teach and favor superstition, etc.
856. Books that deal with religion _ex professo_ (i.e., of set purpose), or _obiter_ (i.e., incidentally), are as follows: (a) Books that are _ex professo_ religious are manuals of theology, works of sermons, treatises on the Bible, instructions on religious duties, works of piety, text-books of church history. Works of a profane character, such as scientific books, may also teach religion _ex professo_, but it is not easy as a rule to perceive the intention of teaching religion in works of this kind. (b) Books that deal with religion only _obiter_ are works of a profane character, in which the subject of religion is introduced only briefly (e.g., by way of illustration).
857. Books dealing _ex professo_ with religion and written by non-Catholics are: (a) forbidden, if they contain matter contrary to Catholic faith; (b) not forbidden, if it is clear to one (e.g., from a competent review) that they contain nothing contrary to Catholic faith.
858. How is one to know in a particular case whether a book falls under one of the foregoing classes forbidden by the Code? (a) If the Holy See has made a declaration, the matter is of course clear; (b) if no declaration has been made, and one is competent to judge for oneself, one may read as much as is necessary to decide whether the book is one of those proscribed by the Code; but if a person has not received the education that would fit him for judging, he should consult some person more skilled than himself, such as his parish priest or confessor.
859. Is it lawful to read newspapers, magazines, or reference works (such as encyclopedias), which contain some articles contrary to faith, and others that are good or indifferent, if these papers or books have not been condemned? (a) If the reading or consultation, on account of one’s individual character, will subject one to grave temptations, then according to natural law it should be avoided. (b) If there is no serious danger or temptation, but the policy of the works or journals in question is anti-religious or anti-Catholic, as appears from the space given to hostile attack, their frequency or bitterness of spirit, then, according to the law of the Code just mentioned, one should avoid such reading matter. Examples of this kind of literature are papers devoted to atheistic or bolshevistic propaganda, anti-Catholic sheets, etc. (c) If there is no danger to the individual, and the editorial policy is not hostile, one may use such matter as is good and useful, while passing over any elaborate or systematic attack on truth or defense of error.
860. Individual books are forbidden by name to all Catholics by the Holy See and to their own subjects by Ordinaries and other local or particular councils (Canon 1395). Books condemned by the Apostolic See must be considered as forbidden everywhere and in whatsoever language they may be translated into (Canon 1396).