"SINCE THE BEGINNING, THE ORDAINED MINISTRY HAS BEEN CONFERRED AND EXERCISED IN THREE DEGREES: THAT OF BISHOPS, THAT OF PRESBYTERS, AND THAT OF DEACONS. THE MINISTRIES CONFERRED BY ORDINATION ARE IRREPLACEABLE FOR THE ORGANIC STRUCTURE OF THE CHURCH: WITHOUT THE BISHOP, PRESBYTERS, AND DEACONS, ONE CANNOT SPEAK OF THE CHURCH (CF. ST. IGNATIUS OF ANTIOCH, 'AD TRALL.' 3,1)."
(Catechism of the Catholic Church ¶ 1593)