Apostolic Succession, and How a Line Is Traced

In the episcopal understanding the succession is physical. A bishop is consecrated by the laying on of hands by other bishops, customarily three, each of whom was consecrated the same way, and the chain is understood to run back to the apostles. That is why episcopal churches keep consecration records with the care other institutions keep title deeds, and why the identity of the consecrating bishops is recorded rather than only the fact of the consecration.

Two distinctions do a great deal of work here. Validity concerns whether the act was effective; liceity concerns whether it was permitted. An ordination performed irregularly, in defiance of church law, may be illicit and still valid, which is how episcopal churches can recognise the orders of bodies they are not in communion with, and it is why bishops who ordain without authorisation are disciplined rather than treated as having done nothing.

The clearest modern case is the Roman judgement on Anglican orders. Rome recognises Eastern Orthodox and Oriental Orthodox orders without qualification. In the bull Apostolicae Curae of 1896 it declared Anglican ordinations null, on the ground that the Edwardine ordinal had a defect of form and of intention, and the archbishops of Canterbury and York replied the following year in Saepius Officio, disputing both grounds and observing that the same reasoning would invalidate several ancient rites. Neither side has moved, and the ecumenical conversations since have worked around the question rather than through it.