Historical Background. Over the centuries a doctrine developed in the Roman Catholic and Eastern Orthodox churches known as “Apostolic
Succession.” According to this belief, as taught by the Roman and Orthodox Churches, all bishops can trace their line of succession back to one of the
apostles. This is to say that a bishop is only a valid bishop if he (the masculine gender is used here because neither of these churches accepts the
ordination of women) has been consecrated by another bishop.
Present Roman and Orthodox Teaching. Following from this is the obvious: only a validly
consecrated bishop (one having been consecrated by another validly consecrated bishop)
celebrate valid sacraments. If the bishop is not validly consecrated (in apostolic succession)
then the priests and deacons he ordains are not valid priests and deacons and the
sacraments they celebrate are not really sacraments.