The Catholic Church, the most hierarchical of all Christian traditions, maintains a complex system of clergy and laity. Deacons, priests, and bishops comprise the ordained clergy, who are members of the diaconate, the presbyterate, and the episcopate. Among the hierarchy of bishops, there are metropolitans, archbishops, patriarchs, and the pope, who is the bishop of Rome. Cardinals are nearly always bishops, but that was not always the case. Some cardinals in the past were nonordained prelates. Unless they originally received Holy Orders to the diaconate, they were not part of the clergy and could not administer the sacraments of the church. Among those typically nonordained and considered to be part of the laity are nuns, friars, and religious brothers and sisters. As part of the reforms handed down by the Second Vatican Council (1963 to 1965), the laity has took a more active role in church activities and worship services (Mass). Before being ordained a priest, canon law currently requires education of two years of scholastic philosophy and four years of theology. Dogmatic and moral theology, the Holy Scriptures, and canon law must be studied at a seminary. As more stringent adherence to Catholic doctrine began to be required, the once-sanctioned, peculiar practices within monasteries and convents became limited. In contrast to others in the liturgical family, the Catholic clergy are not allowed to marry.
