Covenant-breaking is the faith's only form of expulsion and it is narrowly defined: it is not doubt, disagreement, criticism, moral failure or leaving the faith, all of which carry no such penalty. It applies to someone who accepts Bahá'u'lláh's authority and then actively opposes the appointed successor. The principal cases were Mírzá Yahyá, Bahá'u'lláh's half-brother, who contested his claim in the 1860s, and Mírzá Muhammad 'Alí, Bahá'u'lláh's son, who contested 'Abdu'l-Bahá's appointment and litigated over the shrines. Shoghi Effendi declared a number of relatives Covenant-breakers, including in some cases for marrying into such families. The requirement on ordinary Bahá'ís is complete avoidance, including of relatives, which is the harshest rule in the faith and is defended as protecting the Covenant that has kept the religion whole. Only the head of the faith may make the declaration, and the total number over a hundred and eighty years is a few dozen. The resulting near-absence of schism in a religion of eight million is genuinely unusual.