Jus Canonicum by the Rev F X Wernz S.J. and the Rev P Vidal S.J. (1938) Chapter VII
De Summo Pontifice
translated by J.S. Daly
[The power of the Roman Pontiff ceases...]
453. By heresy which is notorious and openly made known. The Roman Pontiff should he fall into it is by that very fact even before any declaratory sentence of the Church deprived of his power of jurisdiction. Concerning this matter there are five Opinions of which the first denies the hypothesis upon which the entire question is based, namely that a Pope even as a private doctor can fall into heresy. This opinion although pious and probable cannot be said to be certain and common. For this reason the hypothesis is to be accepted and the question resolved.
A second opinion holds that the Roman Pontiff forfeits his power automatically even on account of occult heresy. This opinion is rightly said by Bellarmine to be based upon a false supposition, namely that even occult heretics are completely separated from the body of the Church... The third opinion thinks that the Roman Pontiff does not automatically forfeit his power and cannot be deprived of it by deposition even for manifest heresy. This assertion is very rightly said by Bellarmine to be "extremely improbable".
The fourth opinion, with Suarez, Cajetan and others, contends that a Pope is not automatically deposed even for manifest heresy, but that he can and must be deposed by at least a declaratory sentence of the crime. "Which opinion in my judgment is indefensible" as Bellarmine teaches.
Finally, there is the fifth opinion - that of Bellarmine himself - which was expressed initially and is rightly defended by Tanner and others as the best proven and the most common. For he who is no longer a member of the body of the Church, i.e. the Church as a visible society, cannot be the head of the Universal Church. But a Pope who fell into public heresy would cease by that very fact to be a member of the Church. Therefore he would also cease by that very fact to be the head of the Church.
Indeed, a publicly heretical Pope, who, by the commandment of Christ and the Apostle must even be avoided because of the danger to the Church, must be deprived of his power as almost all admit. But he cannot be deprived by a merely declaratory sentence...
Wherefore, it must be firmly stated that a heretical Roman Pontiff would by that very fact forfeit his power. Although a declaratory sentence of the crime which is not to be rejected in so far as it is merely declaratory would be such that the heretical Pope would not be judged, but would rather be shown to have been judged.