Bruno entered the Roman Catholic church’s Dominican order in Italy at the age of eighteen. As his thinking developed, it deviated from the norm. In 1576 he was indicted for heresy, but he escaped and spent sixteen years traveling throughout Europe. Meanwhile, he attracted wide attention for his philosophical positions. Bruno was an original thinker, capable of influencing in later years not only Baruch Spinoza but also German philosophers, such as Friedrich Jacobi, Friedrich Schelling, and Georg Wilhelm Friedrich Hegel.

Bruno was a philosopher of nature, part of the movement away from the domination of Aristotle. He embraced the Copernican system and developed it in metaphysical terms. For example, he held that God is infinite and unitary substance, while the effects of this substance (like people) are merely accidents. In this view, he anticipated Spinoza. Bruno concluded that there is an infinite number of worlds. Bruno’s hylomorphism was seen, variously, as pantheism and as materialism. Bruno was also fascinated by magical matters and the Hermetic cult of ancient Egypt. For example, he was famous for his mnemonics, which incorporated the mysticism and magic of Raymond Lull.

During the sixteenth century the Roman Catholic church was under attack by the growing Protestant Reformation. In 1591 Bruno was arrested by the church’s Venetian Inquisition. The burden was on him to prove his innocence, with no right to cross-examine witnesses. Some charges against Bruno were doctrinal, such as his alleged denial of transubstantiation; others concerned philosophical positions. In 1593 he was transferred to the Roman Inquisition. Fragmentary records make it impossible to know how Bruno was treated during his imprisonment, but by 1599 he had ceased to be cooperative. He denied that his opinions were heretical.

Part of Bruno’s defence before the Inquisition was his appeal to the doctrine of the Two Truths, a doctrine advanced by William of Ockham and John Duns Scotus that had not yet been condemned by the church. Bruno argued that he was a philosopher, and that he could follow philosophical truth wherever it leads, so long as he did not contradict any of the truths of theology. There were, he held, two sets of truths— those of philosophy and those of theology. The Inquisition disagreed. When he was sentenced to death, Bruno told his judges that perhaps they had greater fear in passing the sentence than he had in hearing it. His judges refused the reduced severity of garroting before he was burned to death in Rome and his ashes were thrown to the winds. In 1603 his books were added to the Index Librorum Prohibitorum.

In 1889 a statue to Bruno’s martyrdom was erected in the same Roman marketplace where he was burned. It still stands as silent testimony to Bruno’s courage in his convictions.