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Theological heresy

In his Lectures on the History of Philosophy, Hegel writes that Bruno's life represented "a bold rejection of all Catholic beliefs resting on mere authority."

Alfonso Ingegno states that Bruno's philosophy "challenges the developments of the Reformation, calls into question the truth-value of the whole of Christianity, and claims that Christ perpetrated a deceit on mankind... Bruno suggests that we can now recognize the universal law which controls the perpetual becoming of all things in an infinite universe." A. M. Paterson says that, while we no longer have a copy of the official papal condemnation of Bruno, his heresies included "the doctrine of the infinite universe and the innumerable worlds" and his beliefs "on the movement of the earth".

Michael White notes that the Inquisition may have pursued Bruno early in his life on the basis of his opposition to Aristotle, interest in Arianism, reading of Erasmus, and possession of banned texts. White considers that Bruno's later heresy was "multifaceted" and may have rested on his conception of infinite worlds. "This was perhaps the most dangerous notion of all... If other worlds existed with intelligent beings living there, did they too have their visitations? The idea was quite unthinkable."

Frances Yates rejects what she describes as the "legend that Bruno was prosecuted as a philosophical thinker, was burned for his daring views on innumerable worlds or on the movement of the earth." Yates however writes that "the Church was... perfectly within its rights if it included philosophical points in its condemnation of Bruno's heresies" because "the philosophical points were quite inseparable from the heresies."

According to the Stanford Encyclopedia of Philosophy, "in 1600 there was no official Catholic position on the Copernican system, and it was certainly not a heresy. When Bruno was burned at the stake as a heretic, it had nothing to do with his writings in support of Copernican cosmology."

The website of the Vatican Apostolic Archive, discussing a summary of legal proceedings against Bruno in Rome, states:

In the same rooms where Giordano Bruno was questioned, for the same important reasons of the relationship between science and faith, at the dawning of the new astronomy and at the decline of Aristotle's philosophy, sixteen years later, Cardinal Bellarmino, who then contested Bruno's heretical theses, summoned Galileo Galilei, who also faced a famous inquisitorial trial, which, luckily for him, ended with a simple abjuration.