The infallibility of the pope was not defined until 1870 at the Vatican Council; this definition does not constitute, strictly speaking, a dogmatic innovation, as if the pope had not hitherto enjoyed this privilege, or as if the Church, as a whole, had admitted the contrary; it is the newly formulated definition of a dogma which, like all those defined by the Councils,continued to grow into an ever more definite form, ripening, as it were, in the always living community of the Church.
Pastor aeternus, cap. iv.); " we teach and define as a divinely revealed dogma, that the Roman Pontiff, when he speaks ex cathedra - i.e.
This explains the late date at which the dogma was defined, and the assertion that the dogma was already contained in that of the papal primacy established by our Lord himself in the person of St Peter.
(d) Infallibility is the guarantee against error, not in all matters, but only in the matter of dogma and morality; everything else is beyond its power, not only truths of another order, but even discipline and the ecclesiastical laws, government and administration, &c.
For the theological aspects of the dogma of infallibility, see, among many others, L.