The fatuous simplicity and the worldly blindness which Bruno displayed, in ever setting foot inside of Italian or papal territory after the delivery of this Oratio Consolatoria, may in one way be appreciated but never understood or explained. Moreover he had made himself persona non grata as well to the Protestants, who were scarcely more liberal than the Catholics. It appears that the great Boethius, superintendent of the Church at Helmstadt, had acted both as judge and executioner, and publicly excommunicated Bruno without a hearing, since there is extant a letter appealing from his arbitrary judgment and malice. The grounds for this judgment were never made clear, since no attention was ever paid to the appeal; but inasmuch as Bruno never really joined the Protestant profession it must have been meant to inflict some species of social ostracism. Boethius had himself to be suppressed later. But Bruno, finding too many enemies, left for Frankfort in 1590, "in order to get two books printed."
These were his two great Latin Works, "De Minimo" and "De Immenso," the introduction to the latter being the "De Monade." He worked at these with his own hands. In the introduction to the former his publisher stated that before its final revision Bruno had been hurriedly called away by an unforseen chance. This sudden departure may have been due to a refusal of the town Council to permit his residence there, or it may have been a call to Zürich, where he spent a few months with one Hainzel, who had a leaning toward the Black Arts. Bruno wrote for him "De Imaginum Compositione," a manual of his Art of Memory. In this Swiss city he also dictated a work "Summa Terminorum Metaphysicorum," which was not published until 1609, and then in Marburg. But Bruno returned to Frankfort in 1591, where he obtained permission to publish his De Minimo. This work was on the "three fold minimum and measurement, being the elements of three speculative and several practical sciences." This like the two next mentioned was a Latin poem, after the fashion of Lucretius. The De Monade, Numero et Figura dealt with the Monad, and with the elements of a more esoteric science, while in the De Immenso et Innumerabilibus, the Immeasurable and Innumerable, he dealt with the Universe and the worlds. These three poems contain Bruno's complete philosophy of God and Nature.
While thus staying in Frankfort for the second time Bruno was invited by a young Venetian patrician to pay him a visit, and become his tutor in those arts in which the philosopher excelled. It was the most unfortunate event in Bruno's unhappy life when he accepted this apparently tempting invitation. Mocenigo, his host, was of good family, but shallow, vain, weak-minded and dishonest, with the fashionable taste of his day for the black arts. It is quite possible that he was moreover the tool of the Inquisition, which had long desired to entrap Bruno. It is probable moreover that the latter quite failed to appreciate how unenviably he was regarded by that Church to which he still felt that he belonged. Furthermore Venice was then a Republic and free, and he longed for his beloved Italy again.
En route to Venice he spent three months in Padua, teaching there and gathering around himself pupils, even in that short time. He had barely left it when Galileo was invited there to teach; as Riehl has said, "the creator of modern science following in the steps of its prophet."
Early in 1592 Bruno went to live in Mocenigo's house. Trouble soon began. Entirely apart in temperament and characteristics, they soon disagreed. The pupil was deeply disappointed at not acquiring that mastery over the secrets of nature for which he had hoped, and found that there was no quick way to acquire a retentive and replete memory. And so Mocenigo announced to his friend Ciotto, the bookseller, his intent to gain from Bruno all he could and then denounce him to the Holy Office. While others were thus conspiring against him Bruno was writing a work on "The Seven Liberal Arts" and on "Seven Other Inventive Arts," intending to present it to the Pope, hoping thus to obtain absolution and be released from the ban of excommunication.
When Bruno at last appreciated the dangers by which he was surrounded he announced his intent to go again to Frankfort to have some of his books printed, and so took his leave of Mocenigo. On the following day, in May, 1592, Bruno was seized by six men, using force, who locked him in an upper story of Mocenigo's house. The next day he was transferred to an underground cellar, and the following night to the prison of the Inquisition. May 23rd his former host denounced him, with a cunning and lying statement concerning some of his views and teachings. Thus he was reported as stating that Christ's miracles were only apparent, that He and the apostles were magicians, that the Catholic faith was full of blasphemies against God, that the Friars befouled the world and should not be allowed to preach, that they were asses, and the doctrines of the Church were asses' beliefs, etc. (McIntyre). This was followed two days later by a second denunciation in which Mocenigo went to a diabolical extreme of deceit and hypocrisy; stating that all the time he was entertaining Bruno he was promising himself to bring him before the Holy Office. Within forty-eight hours the Holy Tribunal met to consider the matter; before them appeared the book-sellers who had known Bruno in Zürich and Frankfort, and before them came Bruno in his own behalf, professing his entire willingness to tell the whole truth. Within a few days Mocenigo made yet another deposition, denouncing Bruno's statements about the infallible Church. On the following day Bruno was again heard in his own defense, and appealed to the famous and fallacious doctrine of two-fold truth, acknowledging that he had taught too much as a philosopher rather than as an honest man and Christian, and that he had based his teachings too much on sense and reason and not enough on faith;—so specious had become his argument with the terrors of the Inquisition before him. He further claimed that his intent had been not to impugn the faith but to exalt philosophy. He then beautifully epitomized his own views, claiming that he believed in an infinite universe, in an infinite divine potency, holding it unworthy of an infinite power to create a finite world, when he could produce so vast an infinity; with Pythagoras he regarded this world as one of many stars,—innumerable worlds. This universe he held to be governed by a universal providence, existent in two forms;—one nature, the shadow or footprint of deity, the other the ineffable essence of God, always inexplicable. Concerning the triune Godhead he confessed certain philosophic doubts as well as concerning the use of the term "persons" in these distinctions, while he quoted St. Augustine to the same effect. The miracles he had always believed to be divine and genuine; concerning the Holy Mass and the Transubstantiation he agreed with the Church. As the days went by he became the more insistent upon his orthodoxy. He condemned the heretic writings of Melancthon, Luther and Calvin, expressed respect for the writings of Lulli because of their philosophical bearings, while for St. Thomas Aquinas he had the most profound regard.
Other counts in the indictment which he had to face were his doubts concerning the miracles, the sacraments and the incarnation, his praise of heretics and heretic princes and his familiarity with the magic arts. He finally made a formal solemn abjuration of all the errors he had ever committed, and the heresies he had ever uttered, or doubts expressed or believed, praying only that the Holy Office would receive him back into the Church where he might rest in peace. Further examinations were held and the earlier processes against him in Naples and Rome recalled. After this there was a period of apparent quiet save that he remained in prison. It is not known to what tortures he may have been subjected, but it is recorded that he knelt before his judges asking their pardon, and God's, for all his faults, and professed himself ready for any penance, apparently not yet realizing the fate in store for him.
A little later it transpired that the Sacred Congregation of the Supreme Tribunal of the Holy Office, in Rome, desired to assume all further responsibility for the process against so distinguished a heretic. Accordingly the machinery of the Church was put in motion to this end. Negotiations with the Venetian Republic, somewhat tedious and complicated, which need not detain us now, were at last concluded. January 7, 1603, the Venetian procurator reported of Bruno that "his faults were exceedingly grave in respect of heresies, though in other respects he was one of the most excellent and rarest natures, and of exquisite learning and knowledge," (McIntyre) but that the case was of unusual gravity, Bruno not a Venetian subject, the Pope most anxious, etc. It was then decided to remit him to the Tribunal of the Inquisition at Rome; whereat it is duly reported, the Pope was deeply gratified.
To Rome then he went and here he was lost, so far as documentary records go, for a period of six years. How to explain this fact and this apparent clemency has bothered the biographers not a little. Whether this time was spent in an examination of his voluminous writings, which would seem incredible, or whether the Dominicans labored so long to procure his more absolute recantation in order to prevent scandal in and reflection on their order, or whether Pope Clement himself regarded kindly—in some degree— the great scholar who was so anxious to dedicate to him a magnum opus;—to these queries history answereth not. The Dominicans pretended—years later—to doubt if he ever had been put to death, or whether he had ever really belonged to their order. These statements are too characteristic to provoke more than a sad smile.
Finally matters were hastened to an end by the efforts of Fathers Commisario and Bellarmino; the latter being the zealous bigot who decided that Copernicanism was a heresy, who later laid the indictment against Galileo. Through their machinations Bruno was, in February, 1599, decreed on eight counts as a dangerous heretic, who might still admit his heresies, and he was to be granted forty days in which to recant and repent. But this period was stretched out some ten months, until December, when it was reported that Bruno refused to recant, having nothing to take back. Among the Tribunal at this time was San Severino, fanatical, bitter because of his failure to secure the papacy, who had declared that St. Bartholomew's was "a glorious day, a day of joy for Catholics." It was decided that the high officers of the Dominicans should make one last effort to compel or coax Bruno to abjure. This he declined to do, Whereupon, January 20th, 1600, it was decreed that "further measures be proceeded to, servatis servandis, that sentence be passed, and that the said Friar Giordano be handed over to the secular authority." A few days later Bruno was degraded, excommunicated and handed over to the Governor of Rome, with the usual hypocritical recommendation to "mercy," and that he be punished "without effusion of blood," which meant of course burning at the stake.