Was William of Ockham the first sedevacantist?

[Geremia]

Ockham (cf. this article on him by the Catholic logician Paul V. Spade) invented his dead-end nominalist philosophy in order to justify his being against the papacy (cf. Thomist John Deely's Four Ages of Understanding p. 394 ff., which shows how the Great Western "Schism" lead to the adoption of Ockham's nominalism, despite its weakness).

But was Ockham really a sedevacantist (i.e., one not explicitly against the papacy per se but against a particular pope claimant)?

The following quote from Salza & Siscoe's True or False Pope?: Refuting Sedevacantism and Other Modern Errors p. 210 is quite convincing.

Ockham wrote—"at the end of his letter to the General Chapter in Assisi in the spring of 1334" (cf. Tractatus de Successivis translation p. 12), defending his opposition to Pope John XXII, who opposed the (then-material) dogma that the souls of the deceased destined to heaven behold the Beatific Vision immediately after death, defined by John XXII's successor Benedict XII in Benedictus Deus—that:

Because of the errors and the heresies mentioned above and countless others, I turned away from the obedience of the false Pope and all who were his friends to the prejudice of the orthodox faith. For men of great learning showed me that because of his errors and heresies the same pseudo-Pope is heretical, deprived of his papacy, and excommunicated by Canon Law itself, without need of further sentence. ... In proof thereof several volumes have been published. ... For against the errors of this pseudo-Pope I have turned my face like the hardest rock, so that neither lies nor calumnies nor any persecution (which cannot touch my innermost self in any bodily fashion), nor great numbers of men who believe in him or favor him or even defend him, shall be able to prevent me from attacking or reproving his errors, as long as I shall have hand, paper, pen, and ink. ...

If anyone should like to recall me or anyone else who has turned away from the obedience of the false Pope and his friends, let him try to defend his Constitutions and sermons, and show that they agree with Holy Scripture, or that a Pope cannot fall into the wickedness of heresy, or let him show by holy authorities or manifest reasons that one who knows the Pope to be a notorious heretic is obliged to obey him. Let him not, however, adduce the great number of his adherents, nor base his arguments on reproaches, because those who try to arm themselves with great numbers of lies, reproaches, threats, and false calumnies, show that they are void of truth and reason. Therefore let none believe that I mean to turn away from the recognized truth because of the great number of those in favor of the pseudo-Pope, or because of proofs that are common to heretics and to orthodox men, because I prefer Holy Scripture to a man unlearned in holy science, and I have a higher esteem for the doctrine of the Fathers who reign with Christ than for the tradition of men dwelling in this mortal life.

The Church never condemned Ockham's theories, although Ockham was excommunicated for leaving Avignon without permission.

W. Turner writes in the old Catholic Encyclopedia "Ockham" entry:

Ockham's attitude towards the established order in the Church and towards the recognized system of philosophy in the academic world of his day was one of protest. He has, indeed, been called "the first Protestant". Nevertheless, he recognized in his polemical writings the authority of the Church in spiritual matters, and did not diminish that authority in any respect.

This is sedevacantism.

[Luc]

When I saw Ockham's proto-sedevacantist argument in True or False Pope, I immediately wondered whether it could possibly be a coincidence that the same man who is known for denying that we can know the essences of things by abstracting their intelligible species from their sensual 'vicars' was also, apparently, the first to deny the validity of the putative Vicar of Christ. If his nominalism was indeed intended as a philosophical justification of his sedevcantism, then it surely is no coincidence. Ironically, the same sedevacantist who revived Ockham's argument, Rama Coomaraswamy (in The Destruction of the Christian Tradition, credited in True or False Pope), also bitterly criticized, in his essay on "The Fundamental Nature of the Conflict Between Modern and Traditional Man", Ockham's influence on Western philosophy:

Born in 1290, Ockham is one of the earliest of those who misunderstood the nature of the soul. He not only denied free will, he also denied that the Intellect was capable of forming universal concepts. He and his followers — usually labeled "nominalists" — claimed that all ideas were really images, that is, impressions on the imagination originating in sensual perception. The error — it is one shared by virtually all modern "philosophers" and psychologists — is that nominalists confound the individualized image of the imagination with the concept or idea which resides in the Intellect. According to St. Thomas, the difference between images and ideas consists in the fact that images are representations of things in their singularity, particularity and concreteness, whereas ideas are representations of things in their universality. Despite his denial of "universals", Ockham continued to believe in God. But he held such belief to have no objective character and the nature of his faith was "blind". I would ask you to remember that Faith requires our assent to what the intellect tells us is Truth, and it is the nature of this faculty to "see". The acceptance of nominalism precludes such "vision" and inevitably results in a bifurcation between what can be observed and measured, and what is believed. It is but a short step to envisioning the measurable as the totality of reality, and the relegating of concepts such as the "good" and the "beautiful" — to say nothing of Revelation — concepts beyond measurement and hence seen as having no objective measurable reality — to the realm of private and subjective convictions where they become whatever we feel or want them to be. It is not surprising that Ockham lived his life in rebellion against the Church and died, as far as we know, without the consolation of her sacraments.

If Coomaraswamy disapproved of Ockham's "rebellion against the Church", it is presumably because he thought that Ockham was wrong about John XXII, even though a heretic pope was always possible and is now actually the case with the Vatican II popes.

[Geremia]

I immediately wondered whether it could possibly be a coincidence that the same man who is known for denying that we can know the essences of things by abstracting their intelligible species from their sensual 'vicars' was also, apparently, the first to deny the validity of the putative Vicar of Christ. If his nominalism was indeed intended as a philosophical justification of his sedevcantism, then it surely is no coincidence.

Thomist semiotician John N. Deely's shows the relation between Ockham's nominalism and papal politics in Four Ages of Understanding pp. 385-402:

William of Ockham (c.1285–1349)
    The Second Florescence of Nominalism
    Ockham's Problem with a Doctrine of Signs: There Are No "Generals"
    "The Only Difficulty There Is in Understanding Ockham"
        A Terminological Advance Marred by Conceptual Incoherence
        How Politics Lent to Nominalism a Factitious Following
The Thicket (i.1349/1529)
    A Thicket within the Thicket, 1309–1417: the Papacy, First at Avignon and Then in Schism
        The Papacy at Avignon, 1309–1377
        The Papacy in Schism, 1378–1417

The error — it is one shared by virtually all modern "philosophers" and psychologists — is that nominalists confound the individualized image of the imagination [phantasm?] with the concept or idea which resides in the Intellect.

CP 1.19:

19. In short, there was a tidal wave of nominalism. Descartes was a nominalist. Locke and all his following, Berkeley, Hartley, Hume, and even Reid, were nominalists. Leibniz was an extreme nominalist, and Rémusat [C. F. M.?] who has lately made an attempt to repair the edifice of Leibnizian monadology, does so by cutting away every part which leans at all toward realism. Kant was a nominalist; although his philosophy would have been rendered compacter, more consistent, and stronger if its author had taken up realism, as he certainly would have done if he had read Scotus. Hegel was a nominalist of realistic yearnings. I might continue the list much further. Thus, in one word, all modern philosophy of every sect has been nominalistic.

[Geremia]

According to sedeprivationism, does a material pope have temporal authority?

Update: John of St. Thomas (CURSUS THEOLOGICUS In Summa Thelologicam D. Thomas, Tomus VII, IN SECUNDAM SECUNDÆ DIVI THOMÆ, Quæstio I, DE FIDE, DE AUCTORITATE SUMMI PONTIFICIS, Parisiis Ludovixus Vivês, Editor, 1886, p. 207, sq.) seems to think a heretical pope can exercise (albeit illegitimately/tyrannically) temporal power:

[The Church] may defend itself, not by deposing him [a heretical pope], but by repelling him with force if he proceeds with violence or tyrannically, if, for example, he wished to do something against justice by the force of arms, one could repulse him with arms ; and similarly, if he were to establish something against good morals he is not to be obeyed, because an unjust law does not oblige.