Since each and every religious institute has its own unique aim, or charism, it has to adhere to a particular way of religious living that is conducive to it, whether "contemplative", "enclosed", mendicant, or apostolic. Thus some religious institutes – especially of nuns who are subject to "Papal Enclosure" – strictly isolate their members from the outside world, of which the "grilles" in their parlours and churches are tangible evidence. Other religious institutes have apostolates that require their members to interact practically with the secular world, such as teaching, medical work, producing religious artworks and texts, designing and making vestments and writing religious instruction books, while maintaining their distinctiveness in communal living. Several founders, in view of their aim, require the members of their institute not only to profess the three Evangelical Counsels of chastity, poverty, obedience, but also to vow or promise stability or loyalty, and maybe certain disciplines, such as self-denial, fasting, silence.