Trial of Galileo (1633): The Inquisition and Heliocentrism

The trial of Galileo was the 1633 prosecution of the Italian scientist Galileo Galilei by the Roman Inquisition for defending the theory that the Earth moves around the Sun. Held in Rome between April and June 1633, it ended with Galileo being found “vehemently suspect of heresy”, forced to renounce his views and confined to house arrest for the rest of his life. The case has become the most famous episode in the history of relations between science and religion, and its meaning is still debated.

Background: Copernicus, the telescope and Scripture

In 1543 Nicolaus Copernicus had proposed that the Sun, not the Earth, lies at the centre of the planetary system. For decades this was treated mainly as a mathematical model. Most scholars still followed Aristotle and Ptolemy, and several passages of the Bible, read literally, seemed to describe a moving Sun and a fixed Earth.

Galileo’s telescopic discoveries of 1609–1610, including the moons of Jupiter and the phases of Venus, made him famous and turned him into an open advocate of Copernicus. This drew opposition from university philosophers and some clergy. In his Letter to the Grand Duchess Christina (1615) Galileo argued that the Bible teaches salvation, not astronomy, quoting a cardinal’s remark that the Bible shows how to go to heaven, not how the heavens go.

The Catholic Church after the Council of Trent was especially sensitive to lay people interpreting Scripture, a central issue in its conflict with Protestantism. Galileo’s foray into biblical interpretation therefore alarmed the authorities.

The 1616 warning

In February 1616 theological consultants of the Holy Office declared that the claim that the Sun is motionless at the centre of the world was “foolish and absurd in philosophy” and formally heretical. On 26 February Cardinal Robert Bellarmine, on the pope’s instructions, informed Galileo that he must abandon the opinion.

What exactly happened at that meeting became the crux of the later trial. A note in the Inquisition’s files records that the Commissary General then ordered Galileo not to “hold, teach or defend” the doctrine “in any way whatever, verbally or in writing”. This note was not signed by Galileo or by witnesses. Bellarmine later gave Galileo a certificate stating only that he had been told the doctrine could not be held or defended.

On 5 March 1616 the Congregation of the Index suspended Copernicus’s book “until corrected” and banned works that argued Copernicanism agreed with Scripture. Galileo was not named.

The Dialogue (1632)

In 1623 Cardinal Maffeo Barberini, an admirer of Galileo, became Pope Urban VIII. Galileo visited Rome in 1624 and had several audiences with him. He understood that he could discuss Copernicanism as a hypothesis, provided he did not claim it was proven.

The result, after years of work, was the Dialogue Concerning the Two Chief World Systems, published in Florence in February 1632 with licences from Church censors in Rome and Florence. Written in Italian for a wide audience, it presented a conversation over four days between three characters: Salviati, who argued for Copernicus; Simplicio, a defender of Aristotle; and Sagredo, an intelligent layman.

Although framed as an impartial discussion, the book clearly favoured Copernicus, and Galileo’s argument from the tides, which he considered decisive, was in fact mistaken. Worse, the pope’s own favourite argument, that God could produce the same effects in ways humans cannot know, was placed at the end in the mouth of Simplicio, whose name could be read as “simpleton”. Urban VIII felt betrayed, and he was also under political pressure during the Thirty Years’ War to appear firm in defence of the faith.

The trial

In the summer of 1632 sales of the Dialogue were stopped and a special commission examined it. Galileo, now 68 and in poor health, was summoned to Rome. He arrived on 13 February 1633 and stayed at the Tuscan ambassador’s residence, the Villa Medici.

At his first interrogation on 12 April 1633 he was confronted with the unsigned 1616 note forbidding him to teach Copernicanism in any way. Galileo said he did not recall such an order and produced Bellarmine’s certificate. He claimed, implausibly, that his book had not defended Copernicus but shown the weakness of his arguments. During the proceedings he was lodged in a comfortable apartment in the Holy Office building rather than a prison cell.

The Commissary General, Vincenzo Maculano, arranged an informal meeting to persuade Galileo to admit some fault in return for leniency. At his second deposition on 30 April Galileo conceded that, rereading the book, he saw he had made the Copernican arguments stronger than intended, out of vanity. On 10 May he submitted a written defence.

The pope, however, decided that Galileo should be questioned about his intentions under the threat of torture. At this final examination on 21 June Galileo repeated that he had not held the Copernican opinion since 1616. The threat was a formal procedure; there is no evidence that torture was used.

Verdict and abjuration

On 22 June 1633, in a hall of the Dominican convent of Santa Maria sopra Minerva in Rome, Galileo heard the sentence. He was declared “vehemently suspect of heresy” for having held and defended a doctrine contrary to Scripture after being told it could not be held. The Dialogue was prohibited, and he was sentenced to imprisonment at the Inquisition’s pleasure and to recite the seven penitential psalms once a week for three years.

Kneeling, Galileo read a formal abjuration in which he cursed and detested his errors and promised never again to assert them. Of the ten cardinals who served as judges, seven signed the sentence; three, including the pope’s nephew Francesco Barberini, did not.

The imprisonment was immediately commuted. Galileo spent several months in Siena as the guest of Archbishop Ascanio Piccolomini, and from December 1633 lived under house arrest at his villa at Arcetri, near Florence, forbidden to publish or to receive visitors freely.

Key people

Galileo Galilei (1564–1642), mathematician and philosopher to the Grand Duke of Tuscany, was brilliant, combative and confident of his ability to win arguments, qualities that both made his reputation and created enemies.

Pope Urban VIII (Maffeo Barberini, pope 1623–1644) was a cultured former patron of Galileo whose personal sense of betrayal shaped the severity of the case.

Cardinal Robert Bellarmine (1542–1621), the leading Jesuit theologian of the day, delivered the 1616 warning. His certificate was Galileo’s main defence document, although Bellarmine himself had died before the trial.

Vincenzo Maculano, a Dominican and Commissary General of the Holy Office, conducted the interrogations and sought a negotiated outcome.

Aftermath, myths and legacy

At Arcetri Galileo completed Discourses and Mathematical Demonstrations Relating to Two New Sciences, on the strength of materials and the motion of bodies, which was smuggled out and published by the Elzevir firm in Leiden in 1638. He went blind around 1637–1638 and died on 8 January 1642.

Myth: Galileo said “And yet it moves” to his judges. The phrase “Eppur si muove” first appears in print in Giuseppe Baretti’s Italian Library of 1757. A seventeenth-century Spanish painting discovered in the twentieth century contains the words, suggesting the legend circulated earlier, but there is no evidence he said them at the trial.

Myth: Galileo was condemned for saying the Earth is round. Educated Europeans had known the Earth was a sphere since antiquity. The issue was whether the Earth moves around the Sun.

Myth: the trial was simply science against religion. Historians stress the role of personal relations, Church politics, the disputed 1616 document and the fact that, in 1633, the motion of the Earth was not yet proven. Many churchmen, including Jesuit astronomers, were active in science.

The Church dropped its general ban on books teaching the Earth’s motion in 1758, and in 1822 permitted the printing of books presenting it as fact; the Dialogue disappeared from the Index of Prohibited Books in the 1835 edition. In 1981 Pope John Paul II set up a commission to study the case, and on 31 October 1992 he acknowledged that Galileo’s theological judges had erred. In popular memory Galileo is often linked with the earlier execution of Giordano Bruno in 1600, although the two cases differed greatly in charges and outcome.

Timeline

• 1610, March: Galileo publishes Sidereus Nuncius.
• 1616, 26 February: Bellarmine warns Galileo to abandon Copernicanism.
• 1616, 5 March: Copernicus’s book is suspended until corrected.
• 1632, February: Dialogue Concerning the Two Chief World Systems published in Florence.
• 1633, 12 April: First interrogation of Galileo in Rome.
• 1633, 30 April: Galileo admits he overstated the Copernican case.
• 1633, 22 June: Sentence and abjuration at Santa Maria sopra Minerva.
• 1638: Two New Sciences published in Leiden.
• 1642, 8 January: Galileo dies at Arcetri.
• 1992, 31 October: John Paul II acknowledges the Church’s errors in the case.

Why it matters

The trial of Galileo became a symbol of the clash between free inquiry and authority, and it shaped how the Scientific Revolution was remembered. It also had practical effects: scientific work on Copernicanism in Catholic Italy became cautious, while the centre of gravity of new science shifted increasingly towards northern Europe.