by Thomas Dixon
How do we know anything?
We generally derive our knowledge of the world from four sources: our senses, our powers of rational thought, the testimony of others, and our memory. The first obvious thing to note about all these sources is that they are fallible. Our senses can deceive us, our reasoning can be faulty, other people can knowingly or accidentally mislead us, and most of us know only too well (and increasingly with age) how partial and distorted our memories can be. The whole project of modern science could be summarized as the attempt to weave these individually relatively feeble threads into a more resilient web of knowledge. So the sense experience of one person must be witnessed, corroborated, and repeated by many others before it is accepted. Simple observations of the properties of things must be supplemented by carefully designed experiments which test more precisely how they behave in different circumstances. Human powers of perception on their own may be limited, but the invention of the telescope and the microscope in the early 17th century, and of many other even more sophisticated devices since then, has enormously increased the scope and accuracy of the observations and measurements that can be made. But experiments could not be designed, and observations would not make any sense, without the use of reason. Theoretical hypotheses about the nature of reality, and reasoning about what experimental evidence is needed to support or refute them, are prerequisites of scientific knowledge. Finally, scientific experts must cite the sources of their knowledge and explain the chain of their reasoning if their testimony is to be accepted. And the publication of scientific results in treatises, books, specialist journals, and, now, electronic databases provides us with a collective and well-documented memory greater than anything that would be possible by relying on one person’s memory alone.
The knowledge thus produced is a highly prized possession in human societies. It bestows on us the ability to manipulate not only the natural world but also each other. One of the most important advocates of science in 17th-century England, Francis Bacon, wrote that ‘human knowledge and human power meet in one; for where the cause is not known the effect cannot be produced’. In other words, an understanding of the secret workings of nature would allow people to produce machines and medicines to improve the human condition. Bacon also wrote, to justify the new knowledge of the period, that ‘all knowledge appeareth to be a plant of God’s own planting’, whose spread and flourishing at that time had been divinely ordained.
Natural philosophers in 17th-century England such as Robert Boyle and Robert Hooke – the new ‘virtuosi’ of the experimental method, the founders of the Royal Society – were perceived by some as a threat to orthodoxy. Their claims to be able both to discover and to manipulate hidden forces in nature seemed to verge on usurping the role of God. That was why it was important to reassure their readers that in reaping this knowledge they were collecting a harvest which was, in Bacon’s words, ‘of God’s own planting’. In this image, God planted the seed of knowledge and natural philosophers harvested its fruit. According to another popular metaphor, God was imagined not as a kind of cosmic farmer but, as we have noted, as an author of two books – the book of nature and the book of scripture. This metaphor was based on the same idea – that the ultimate source of knowledge was God and that humans had to adopt certain techniques to acquire that knowledge.
One of the useful things about these metaphors of agriculture and of reading is that they draw attention to the fact that human knowledge (at least of the natural kind) is made rather than simply found. Seeds do not become plants and bear fruit unless they are sown in the right conditions, are watered and fed, and are harvested in the right way. Texts do not generally have obvious meanings, but rather these must be teased out through the collective efforts of many readers using different historical and literary techniques. Even if one decides to approach a text in search of its ‘literal’ meaning, that is by no means a simple matter. It is also well known among literary scholars that the project of discerning an author’s intentions in a text is a difficult and controversial one. The histories of science and religion reveal that these difficulties have been experienced in full measure in relation to both of God’s books. Neither nature nor scripture offers a transparent account of its author’s intentions. Some have gone further, of course, and denied that either is a work of divine authorship at all. Some read the book of nature as an autobiography and the scriptures as purely human works.
This brings us to the question of whether, in addition to the four sources of knowledge already mentioned – sense, reason, testimony, and memory – a fifth needs to be added, namely revelation. It is a belief shared by Jews, Christians, and Muslims that God’s authorship can be detected both in nature and in scripture (the Torah, the Bible, or the Quran, respectively). While the natural world reveals the power, intelligence, and goodness of its Creator, the scriptures reveal God’s plans for his chosen people and the legal and moral basis according to which they should live. Corresponding to this idea is the subtly different distinction between natural and revealed forms of knowledge. Natural knowledge is produced by the exercise of the natural human faculties of sense and reason (these faculties can be engaged in reasoning about scripture as well as about the natural world). Revealed knowledge is produced by a supernatural uncovering of the truth – either through the medium of scripture or by a direct revelation of God to the individual believer. Natural theology, then, as opposed to revealed theology, is a form of discourse about God based on human reason rather than on revelation. This includes theological works making inferences about God from the design apparent in the natural world – as in William Paley’s famous Natural Theology (1802) – but it also includes more purely philosophical works about God’s existence and attributes. Modern books arguing for belief in ‘Intelligent Design’ on the basis of the ‘irreducible complexity’ of nature are within this same tradition, as we will see in Chapter 5.
Debates about science and religion virtually always involve disagreements about the relative authority of different sources of knowledge. This is true of debates about the relative weight to be given to testimony and to experience when considering claims about miracles, as we will see in Chapter 3. It is also true of the 18th-century clash between Deism and Christianity. Thomas Paine’s objection to Christian philosophers was not that they found God in nature – he did too – but that they thought they could also find God through his self-revelation in the Bible. For Paine, the only possible kind of revelation was from God directly to an individual. If God ever did act in this way, it was revelation ‘to the first person only, and hearsay to every other’. The scriptures were therefore no more than mere human testimony and the rational reader was not obliged to believe them. Advocates of creationism in the 20th century took the opposite approach to Paine’s. For them, the word of God as revealed in the Bible was the most reliable form of knowledge and anything that seemed to contradict their interpretation of scripture had to be rejected. This included mainstream scientific theories of evolution. Some creationists were even moved to re-read the book of nature and produce their own ‘Creation Science’ which harmonized geology with Genesis. While rationalists have rejected revelation altogether, and fundamentalists have insisted that all forms of knowledge be tested against the Bible, many more have looked for ways to reconcile their readings of God’s two books without doing violence to either.
The rise and fall of Galileo
Galileo belonged to this last category of believers seeking harmony between the Bible and knowledge of nature. He endorsed the view that the Bible is about how to go to heaven and not about how the heavens go. In other words, if you wanted to know about matters pertaining to salvation you should consult scripture, but if you were interested in the detailed workings of the natural world, then there were better starting points – namely empirical observations and reasoned demonstrations. This was not a particularly unorthodox view in itself, but Galileo failed to persuade the authorities that it was a principle that could be applied to h
is case. Although the church was certainly not opposed in general to the study of mathematics, astronomy, and the other sciences, there were limits to how far the authority of the Bible and of the church could be challenged by an individual layman like Galileo. He went beyond those limits. There were three central characters in the story of how he did so – the telescope, the Bible, and Pope Urban VIII.
At the beginning of the 17th century, Galileo was one of only a tiny handful of natural philosophers who thought it likely that the Copernican astronomy was an accurate description of the universe. The majority of those who took an interest in such questions, including the mathematicians and astronomers working within the Roman Catholic Church, held to the system of physics and cosmology associated with the ancient Greek philosopher Aristotle. There were two elements in this existing Aristotelian science which would be challenged by Galileo. First, there was the earth-centred model of the cosmos produced by the 2nd-century Greek astronomer Ptolemy. This was the standard astronomical model and, despite certain complexities and technical problems, it worked as well as the Copernican model as a device for calculating the positions of the stars and planets, and had the considerable advantage of according with the common-sense intuition that the earth was not in motion. The second Aristotelian principle that would come under attack was the division of the cosmos into two regions – the sublunary and the superlunary. The sublunary region consisted of everything within the orbit of the moon. This was the region of corruption and imperfection and of the four elements of earth, water, air, and fire. In the superlunary region, the domain of all the celestial bodies, everything was composed of a fifth element, ether, and was characterized by perfect circular motion.
2. A 16th-century illustration of Ptolemy’s earth-centred astronomical system. At the centre is the world, composed of the four elements of earth, water, air, and fire, surrounded by the spheres of the moon, Mercury, Venus, the sun, Mars, Jupiter, Saturn, and finally the sphere of the fixed stars. This Ptolemaic system had been endorsed by Aristotle and was still accepted by almost all natural philosophers at the start of the 17th century.
Galileo’s great contribution to astronomy was to use a newly invented optical instrument – named the ‘telescope’ in 1611 – to provide observations with which to challenge this Aristotelian and Ptolemaic theory. Galileo did not invent the telescope himself, but as soon as he heard of its invention he set about making his own superior version. The earliest telescopes, made in the Netherlands, magnified only by a factor of three. Galileo developed an instrument with magnifying power of about twenty times, which he turned towards the heavens with spectacular results. These results were published in two books, The Starry Messenger in 1610 and his Letters on Sunspots in 1613, which established his reputation as a brilliant observational astronomer and as one of the leading natural philosophers in Europe. These works also made it clear that Galileo favoured the Copernican astronomy.
Just a couple of examples will give a sense of how Galileo wielded his telescope against Aristotelian science. Perhaps the most telling single discovery made by Galileo was that Venus, when viewed through the telescope, could be seen to display phases. In other words, like the moon, its apparent shape varied between a small crescent and a full disc. This strongly suggested that Venus orbited the sun. If the Ptolemaic system had been true and Venus, which was known always to be close to the sun in the sky, described an orbit closer to the earth than the sun’s, then it should have appeared always as a thin crescent. Secondly, Galileo was able to deploy a number of key observations against the strong commitment of the Aristotelians to the division of the cosmos into distinct sublunary and superlunary regions. His telescope revealed that the moon was a rocky satellite with craters and mountains – more like the earth than like an ethereal and perfect heavenly body. He also showed that Jupiter had four satellites or moons. This helped defeat a common objection to the Copernican theory. On the Ptolemaic theory, the earth’s moon was treated as the closest of several planets, all of whose orbits centred on the earth. If Copernicus were right, then the moon would have to orbit the earth, while the earth in turn went around the sun. Was it possible that a celestial body could move in an orbit with a centre other than the centre of the cosmos? The discovery that Jupiter was accompanied in its orbit (whether that was around the earth or around the sun) by four satellites established that such motion was indeed possible. Finally, Galileo’s discovery of sunspots further undermined the Aristotelian distinction between perfect heavenly bodies and a changeable and imperfect earth.
It was largely thanks to Galileo’s publications that Copernicanism became such a live issue in the 1610s. Galileo was aware that his advocacy of the new astronomy was arousing both theological and scientific objections. One of the reasons for the former was the apparent inconsistency between Copernican astronomy and the Bible. Several Old Testament passages referred to the movement of the sun through the heavens and the immobility of the earth. An often-quoted passage was from the Book of Joshua, which referred to God stopping the sun and the moon in the sky to light the earth while the Israelites took vengeance on the Amorites. Seeking to forestall biblical objections to the view that the earth moves, Galileo wrote his Letter to the Grand Duchess Christina in 1615 in which he articulated his views about how to deal with apparent conflicts between natural and revealed knowledge. He relied heavily on the views of the Fathers of the Catholic Church, especially St Augustine. The central idea was the principle of accommodation. This stated that the Bible was written in language accommodated to the limited knowledge of the relatively uneducated people to whom it was initially revealed. Since the readers of the Book of Joshua believed that the earth was stationary and the sun moved around it, God’s word was couched in terms that they would understand. All agreed that biblical references to God’s ‘right hand’ or to God’s experience of human passions such as anger should not be taken literally but were accommodations to common understanding. Galileo argued that the same attitude should be taken to biblical passages referring to the movement of the sun. The other general principle Galileo adopted, mentioned above, was that the Bible should only be given priority in matters relating to salvation. In matters of natural knowledge, if the text seemed to contradict the best available science, then it would need to be reinterpreted.
All of this was indeed in tune with St Augustine’s 4th-century approach to scripture. However, Galileo was writing at a time when more conservative views were in the ascendancy thanks to the crisis of the Protestant Reformation, which had started in the early decades of the 16th century in Germany and England, and continued to divide Europe both politically and religiously in the 17th century. One of the central tenets of Protestant forms of Christianity was the importance of scripture and the right of each individual to read the Bible in their own language, rather than encountering Christian teaching only through the mediation of priests and the doctrinal pronouncements of Church Councils. The Catholic Church’s principal response to the Reformation came in the form of a series of meetings which comprised the Council of Trent (1545–63). One of the declarations of that Council was that, in matters of faith and morals,
no one, relying on his own judgement and distorting the Sacred Scriptures according to his own conceptions, shall dare to interpret them contrary to that sense which Holy Mother Church, to whom it belongs to judge their true sense and meaning, has held and does hold, or even contrary to the unanimous agreement of the Fathers.
In the context of these Counter-Reformation teachings, Galileo’s suggestion in his Letter to the Grand Duchess Christina that he, an individual layman, had the authority to tell the ‘Holy Mother Church’ which parts of scripture needed to be reinterpreted, and how, smacked both of arrogance and of dangerous Protestant leanings. The fact that in 1632 he would publish his Dialogue in vernacular Italian rather than scholarly Latin would add further to that impression.
When a committee was asked to report on the question of Copernicanism to the Inquisition
in 1616, it declared it to be both false and absurd as scientific doctrine, and additionally to be contrary to the teachings of scripture and thus formally heretical. Galileo was personally summoned into the presence of Cardinal Robert Bellarmine, who instructed him that he must not hold or defend the Copernican astronomy. At the same time, Copernicus’s On the Revolutions of the Heavenly Spheres, which had been largely ignored since its appearance in print, was now suspended from publication, pending ‘correction’. By drawing new attention to Copernicanism and to the Church’s attitude to scripture, Galileo had succeeded in having the former declared heretical and in seeing the latter hardened and entrenched in a more conservative position.
The election in 1623 of Cardinal Maffeo Barberini as Pope Urban VIII must have seemed to Galileo like the answer to his prayers. Barberini was an educated and cultured Florentine. Even better, since 1611 he had been an admirer and active supporter of Galileo’s work, even composing a poem, Adulatio Perniciosa (‘In Dangerous Adulation’) in 1620, expressing his admiration for Galileo’s telescopic discoveries. In 1624, Galileo had several meetings with Urban VIII, during which he was assured that he could discuss the Copernican theory in his work but only as one hypothesis among others. Urban argued that God, in his omnipotence, could make the heavens move in any way he wished, and so it would be presumptuous to claim to have discovered the precise manner in which this end was achieved by the divine will. Galileo nevertheless left Rome reassured and was soon at work on the book that would be published in 1632 as his Dialogue Concerning the Two Chief World Systems.