A pope is
said to speak ex cathedra
the chair” when he solemnly puts forward some teaching in a manner intended to
be definitive and absolutely binding.
This is also known as an exercise of the pope’s extraordinary magisterium
, and its point is to settle once and for
all disputed matters concerning faith or morals. The First Vatican Council taught that such ex cathedra
doctrinal definitions are
infallible and thus irreformable. The ordinary magisterium
of the Church too
(whether in the person of the pope or some other bishop or body of bishops) can
sometimes teach infallibly, when it simply reiterates some doctrine that has
always and everywhere been taught.
does not hold, however, that popes always
teach infallibly when not speaking ex
cathedra. The First Vatican Council
deliberately stopped short of making that claim. One reason for this is that there have been a
few popes (though only a few) who erred when not exercising their extraordinary
magisterium. The most spectacular case
is that of Pope Honorius I (pope from 625-638 A.D.), who taught a Christological
error that facilitated the spread of the Monothelite heresy, and was formally
condemned for it by several Church councils and later popes.