Around 300BCE there started a school of Greek philosophy called Skepticism. It continued for centuries, but was more like dogmatic doubt than the modern version. Bertrand Russell put their creed as “Nobody knows, and nobody can know”. They may simply have a bad press. Carneades, one-time head of the skeptical academy, was accused of denying the possibility of all knowledge. In fact he seems to have denied the possibility of certain knowledge, a very different thing.

Religious skepticism started before that. One of the earliest quotations that has survived was by Protagoras, born about 500 BCE:

As to the gods, I know not whether they exist or not, for the obstacles to knowledge are many, both in the difficulty of the question and the shortness of human life.

The historian Robin Briggs places the origins of modern skepticism in the scientific and intellectual revolutions, which culminated in the enlightenment. He sees it as a reaction to the witch craze that swept through Europe during the Renaissance. It seems ironic to place the origins of skepticism in the period when persecution of witches was at its height, but nevertheless some of the earliest expressions of a modern skeptical attitude come from investigations into witchcraft.

In 1588 the Bishop of Angers tested a girl, Martha Brossier, who acted as though possessed by devils. He had two bowls of water brought in, but led her to believe that the one containing ordinary spring water contained holy water and vice versa. When presented with holy water the devils possessing the girl were calm, but when presented with spring water they threw her into convulsions.

John Webster (1677) in The Displaying of Supposed Witchcraft wrote:

There is no greater folly than to be very inquisitive and laborious to find out the causes of such phenomenon as never had any existence, and therefore men ought to be cautious and to be fully assured of the truth of the effect before they adventure to explicate the cause.

(Quoted by John Passmore.) If only the purveyors of modern pseudoscience would take that advice.

Karen Armstrong in A History of God refers to a “classic” French book, The Problem of Unbelief in the Sixteenth Century by Lucien Febvre. This apparently states that vernacular French lacked words for “absolute”, “relative”, “causality”. In consequence, she claims, a skeptical attitude was not possible. However the example of Michel Montaigne (1533-1592) casts doubt on this. Montaigne denied that anything could be known with certainty — a thoroughly modern idea. “It seems to be setting too high a value upon our opinions, to roast people alive for them.” When Montaigne wrote this, his church denied that religious teaching was “mere opinion”.

Yet skeptical ideas predate all this by at least a century. Nicholas of Cusa (1400-1464), a scholar and German churchman, was a cardinal and the church librarian at Rome. Using critical methods to examine church documents, he showed that many of the treasures in the library were forgeries. Nicholas initially attacked the Decretals of Isidore, a mass of documents, supposedly dating from apostolic times to about the 8th century. Many of these justified church policy and doctrine. Internal inconsistency and contradiction coupled with absurd anachronism was his method.

Nicholas of Cusa should be a hero for skeptics. He had no doubts about the central doctrines of Christianity; he merely wanted to clear away the dross. But in doing so he unleashed a new weapon that had a devastating effect. He seems to have been the first to subject sacred writing to scrutiny, but others adopting his methods exposed many of the greatest treasures of the Catholic Church as forgeries.

Lorenzo Valla (1405-1459) took up the new weapon with enthusiasm. He proved the Apostles Creed was written centuries after the last apostle died and the Donations of Constantine was a forgery. This was a sort of will showing that when the Emperor Constantine moved his capital to the East, he had given the Western Roman Empire to the Pope. Voltaire called the Donations, “the boldest and most magnificent forgery which deceived the world for centuries”. The Church fought back by declaring Valla a heretic, but Alfonso of Naples, his patron, protected him. He also benefited in that the ruling pontiff was more interested in scholarship than religion.

Just why the 15th century should have produced this revolution in thought is not clear, but a necessary step had occurred two centuries earlier. Thomas Aquinas (1225-1274) introduced Aristotelian philosophy into Christianity, and with it a “new” definition of truth.

Christian truth had been taken from the bible. For example, 1 John 2.22. “Who is the liar? Who but he that denies Jesus is the Christ?” Or 1 Timothy 1.10 which defines liars as those, “whose behaviour flouts the wholesome teaching which confirms with the gospel”. Or John 14.6, where Jesus says “I am the truth.” This last is a “category mistake”; a person, human or divine does not belong to a class of entities that can be described as “truth”.

Many people today regard Aristotelian truth as common sense, but religious fundamentalists use a different definition. Following a debate with a visiting American creationist, I suggested that he must have known that some of the things he had been saying in public were untrue. He responded by quoting 1 John 2.22, or in other words “Anything I say is true, anything you say is untrue”. This illustrates why such debates are remarkably sterile.

Aristotle held that truth involves correspondence with the facts. Thus, “snow is white” is true if, and only if, snow is white. This may sound obvious, but until this idea had taken hold it was not possible for Nicholas and Valla to question the authenticity of church documents. Such documents were accepted as true simply because they supported church doctrine.

The English Royal Society grew out of a group that met for discussion of various topics including religion, but when the Society gained its Royal charter a rule was instituted that religious matters were not to be discussed at meetings. Instead, they would concentrate on Natural Philosophy, that is science, and they adopted a motto, Nullius in verba. This can be translated variously, but the flavour of the original is maintained by Nothing on authority. In other words, it did not matter what the Church, or the Bible, or Aristotle said, the truth was to be determined by investigation into nature, and it was not to be rejected if it disagreed with those authorities.

The Royal Society held its annual general meeting on the day of St. Andrew. According to John Aubrey (1626-1697), Sir William Petty (a member and a friend of Aubrey) suggested that St Thomas’s day was more suitable. Doubting Thomas was the appropriate patron for a society with the motto There is Nothing in Words (Aubrey’s translation). For the church, faith was a virtue; in a scientist it is a vice if it intrudes into the investigation.

There was still danger in expressing such ideas. Aubrey also tells that the Anglican bishops at this time wanted to burn Thomas Hobbes, the philosopher, at the stake for his heretical views. However, they lacked the power. A quarter of a century earlier, parliament had impeached and beheaded an Archbishop of Canterbury who had too much persecuting zeal. That executed archbishop, Laud, was the last ever to burn a heretic in England. While burning heretics was still a pious duty, it could have unfortunate consequences, particularly for archbishops.

Skepticism and an objective definition of truth were essential for the rise of science, but a third factor was also important: toleration. Free and open (often vigorous; the letters of Isaac Newton are sometimes vitriolic) debate was essential. These factors do not explain the rise of science, but surely they were necessary for its development.

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