The idea of Masonic brotherhood probably descends from a 16th-century legal definition of a brother as one who has taken an oath of mutual support to another. Accordingly, Masons swear at each degree to keep the contents of that degree secret, and to support and protect their brethren unless they have broken the law. In most Lodges the oath or obligation is taken on a Volume of Sacred Law, whichever book of divine revelation is appropriate to the religious beliefs of the individual brother (usually the Bible in the Anglo-American tradition). In Progressive continental Freemasonry, books other than scripture are permissible, a cause of rupture between Grand Lodges.