Of course the doctrine's recognition as a theory is separable from its exercise as a fact. Many Roman Catholic writers have not only maintained that during the Age of the Fathers no case occurs of its exercise; but that the principles advocated demonstrate that it was not even recognised as a theory, since by those very principles it is actually excluded. Roman opponents of the doctrine have also pointed out that no profession of belief in the infallibility of the Church can be adduced to prove belief in the infallibility of the Pope for the simple reason that many Roman theologians who believed the former have rejected the latter.
All that can be done in a limited space is to select the chief examples of the Patristic teaching; and then to show how the Ultramontanes and their opponents employed them.
1. A crucial instance is the famous language of St Irenæus:—