864. When the necessity of reading a forbidden book is urgent, and the opportunity of asking permission from the Holy See or Ordinary is lacking, a person whose duties call for acquaintance with such a book may consider that the law does not bind in his particular case (see 411-417 on _epieikeia_). (a) A professor, editor, critic, etc., who had not yet received permission might read a forbidden book, if, being called upon to criticize it, he could not await the permission; (b) a confessor, pastor, etc., in similar circumstances could read a forbidden book in order to be able to refute it. 865. Those who have received permission to read books forbidden as generally dangerous to faith, may also read papers and periodicals of the same character, and they may use the permission given them anywhere, since it is a personal indult (see 446). The following restrictions, however, are understood in the grant of permission: (a) Permission to read, no matter by whom granted, does not make it lawful to read what is really a danger to one’s faith, for this (as explained above in 849-850) is contrary to natural law. Moreover, those who have received an apostolic indult may not read or retain books proscribed by their Ordinaries, unless the indult extends even to this. (b) Permission to retain does not make it lawful to keep forbidden books in such a way that they will fall into the hands of those who have no right to read them. On the contrary, there is a grave obligation arising from the natural law to prevent such a thing from happening. Hence, those who have permission to keep writings dangerous to faith should not place them on shelves to which there is general access, or else they should label them as dangerous and forbidden (see Canons 1405, Sec.1, and 1403, Sec.2). 866. According to Canon 2318, the following censures are incurred through the use of forbidden books: (a) Excommunication specially reserved to the Apostolic See is incurred _ipso facto_ by those who offer to the public books, even of a non-religious character, written by apostates, schismatics, or heretics in systematic defense of heresy or schism. This censure applies, first, to the chief causes of publicity of the work--i.e., to the author who offers it for publication, and to the publisher and printer (owner or manager of the press) who accept it for that purpose--not, however, to remote cooperators or helpers; secondly, to such chief causes as understand the character of the book, either from the word of the author or from the contents. It is not incurred, if the work is not published (i.e., if it remains in manuscript, or is circulated only privately), or if it is published in other than book form (e.g., as a pamphlet, leaflet or article). Ignorance, if not crass or supine (see 27), excuses from this censure (Canon 2229, Sec.3, n. 1).