This work explores the extension of papal infallibility with regard to its object (doctrine of faith and morals) and with regard to its act (ordinary teaching and extraordinary or solemn definition). Two main questions are taken up in the first part: whether it is certain that the pope is able to speak infallibly about doctrines pertaining to faith or morals which are not directly included in the deposit of faith (e.g. the canonization of saints); and secondly, whether this secondary object of infallibility extends to everything pertaining to faith and morals (so as to include, for example, every particular moral norm of the natural law). The second part is then primarily concerned with the question as to whether the pope is infallible only in the exercise of his extraordinary magisterium or whether the ordinary papal magisterium might also be infallible in some cases.