Causation and Modern Philosophy

Keith Allen, Tom Stoneham

• Publisher: Routledge
• Year: 2011
• ISBN:
  9781136820052
• Edition: 1
• Topic: Philosophy
• Subtopic: Modern Philosophy

This volume brings together a collection of new essays by leading scholars on the subject of causation in the early modern period, from Descartes to Lady Mary Shepherd. Aimed at researchers, graduate students and advanced undergraduates, the volume advances the understanding of early modern discussions of causation, and situates these discussions in the wider context of early modern philosophy and science. Specifically, the volume contains essays on key early modern thinkers, such as Descartes, Hobbes, Spinoza, Leibniz, Hume, Kant. It also contains essays that examine the important contributions to the causation debate of less widely discussed figures, including Louis la Forge, Thomas Brown and Lady Mary Shepherd.

1 Galileo

Reflections on Failure

David Wootton

I. Galileo’s Theory of the Tides

Galileo was one of the greatest scientists of all time.¹ As a result of his determination to publish his results, he faced trial by the Inquisition and condemnation. It is scarcely surprising that most accounts of Galileo are fundamentally uncritical. An older literature—from Duhem to Koestler—which argued that he had achieved much less than he claimed now receives little support.² A newer literature—from Feyerabend to Biagioli—insists that his work consisted of a series of public performances, that it was geared to obtaining patronage and status; but this literature insists that this is true of science in general, and so blunts its critique of Galileo—a critique which is, in any case, largely misconceived.³ My argument here is that understanding Galileo requires us to think about his failures, and that those failures are evidence of his confused thinking on the subject of causation. My conclusion is a cautionary one: consistency alone would not have rescued Galileo. But it is clear from the responses of his peers that Galileo’s mistakes were unforced. They resulted from a commitment to Copernicanism that went beyond reason—as interesting commitments often do.

Very early in his career, in 1592, Galileo became a Copernican.⁴ At the time (roughly fifty years after the publication of De Revolutionibus), a public commitment to Copernicanism was extremely rare. Only one competent mathematician—Thomas Digges—had published in defence of the Copernican system. Tables which employed Copernican mathematical techniques were not uncommon—but the astronomers who produced them, such as Giovanni Magini, were usually firmly opposed to heliocentrism. Galileo’s conversion, which was to have a determining influence on his intellectual activities throughout the rest of his life, was grounded in a basic discovery. In collaboration with his patron, Guidobaldo del Monte, he had carried out an experiment which established the parabolic path of projectiles.⁵ Armed with this new knowledge, Galileo was convinced that he could rebut the standard arguments against Copernicanism, which were physical not astronomical: why, if the earth is moving under our feet, do we not fall over? Why, if an object is dropped from a high tower, does it not land to the west of the tower’s base? Why does a cannon shot not travel further if fired to the west than if fired to the east? Galileo’s project for a new physics, which culminated in the Two New Sciences of 1638, was designed to destroy the physical arguments against Copernicanism; his new astronomy—the discovery of the mountains on the moon, of the moons of Jupiter, of sunspots, and of the phases of Venus in a few brief months between the winter of 1609/10 and the winter of 1610/11—decisively refuted Ptolemaic astronomy, but left the alternative system of Tycho Brahe relatively undamaged. What Galileo lacked, in order to prove Tycho wrong, was proof that the earth moved. Attempts to prove this by, for example, measuring stellar parallax had proved uniformly unsuccessful.

This brief summary enables us to place Galileo’s two great failures in context. The first is well known. From an early date (our earliest evidence dates to 1595), Galileo decided that the only possible explanation of the tides must be that they were a consequence of the motion of the earth.⁶ According to Copernicus, the earth both orbits the sun in the course of a year and rotates on its axis in the course of a day. The combination of these two movements means that any point on the surface of the globe (apart from the North and South poles) speeds up and slows down in the course of every twenty-four hours—for twelve hours its speed is the result of rotation being added to orbital motion; while for twelve hours its speed is the result of rotation being subtracted from orbital motion.

Galileo’s theory of the tides faced substantial difficulties. Galileo developed and adapted it to try to explain why there are two tides a day, not one; and why the heights of tides vary on an annual and on a lunar cycle. He published his final version of the theory in his Dialogue Concerning the Two Chief World Systems of 1632.⁷ His original intention—thwarted by the Roman censors—was that his book should be entitled Dialogue on the Tides, and his fundamental argument in that book was that, since only the double movement of the earth can account for the tides, the Copernican account of the universe must be correct. Since any explicit defence of Copernicanism had been banned by the Catholic Church in 1616, Galileo’s argument laid him open to the charges that rapidly followed publication and that inexorably led to his trial and condemnation.

The crux of the matter is this: Galileo dismisses all alternative accounts of the tides (accounts, for example, which explained them in terms of some sort of attraction exercised by the moon) as fantastical—only a mechanical explanation will do. Indeed, he sought to construct a machine which would replicate the earth’s movement and cause tidal movement in a miniaturised ocean. Unfortunately, Galileo was wrong—no mechanical system can adequately account for the movement of the tides as they occur on this planet.⁸ Despite the great sophistication of Galileo’s theory, he had no explanation for the fact that the time of high and low tide changes in a regular fashion from day to day—as was immediately pointed out by his friend and rival Giovanni Battista Baliani.⁹

There is no evidence that Galileo’s tidal theory ever convinced anybody. It is worth pausing to consider what would have happened if he had not committed himself to it and had not decided to pursue it in the face of every obstacle. Had he chosen to go on debating Copernicanism after the condemnation of 1616, but had not introduced his theory of the tides, he would have been able to argue that the Ptolemaic system had been destroyed by the discovery of the phases of Venus.¹⁰ And he would have been able to argue that the Copernican system was in certain respects more plausible than the Tychonic system—the earth, for example, shines by reflected light, and all the other bodies that shine by reflected light are in movement; the sun shines by its own light, and all the other bodies that shine by their own light appear to be fixed.¹¹ But he would not have been able to claim that he could prove the truth of Copernicanism. There would have been no trial in 1633, no condemnation of Galileo, and no formal judgement that Copernicanism was heretical. As a result, there would have been far greater intellectual freedom in Catholic countries over the course of the subsequent two centuries (Copernicanism was not officially permitted by the Catholic Church until 1835). The scientific revolution, which flourished primarily in northern Europe, out of reach of the Inquisition, might well have advanced more rapidly and more generally. There might have been an Italian or even a Spanish Newton.

Galileo’s commitment to his theory of the tides was a major intellectual error. It appears to have resulted first from an overenthusiastic determination to find arguments in favour of Copernicanism, and second from a dogmatic insistence that in physics causal explanations have to be mechanical explanations and cannot involve action over a distance. This insistence flew in the face of the acknowledged difficulty of providing, for example, a mechanical account of magnetism—a subject Galileo had studied with great care over many years.¹²

II. Galileo and the Horror Vacui

The story I have told so far appears straightforward. Galileo was committed to a mechanistic physics, and this commitment led him astray. It was, indeed, responsible for his greatest failure. But I want now to argue that Galileo’s lack of commitment to mechanistic explanations becomes apparent as soon as we look at Galileo’s other great failure, his failure to resolve basic questions about the production of a vacuum. I hope to convince you of a basic paradox: Galileo was too committed to mechanism, and at the very same time, he was insufficiently committed to mechanism. Resolving this paradox will not be easy.

Even before Galileo became a Copernican, he was opposed to the Aristotelian view that some substances are heavy and descend towards the centre of the earth, and others are light and rise towards the heavens.¹³ Galileo, whose early science was modelled on Archimedes, insisted that heaviness and lightness were relative and not absolute terms—light objects float upwards not because they are light but because they are less dense than heavier objects which crowd them out. Relative density (or specific gravity) thus explains why bubbles of air rise in water, or why wooden sticks descend when released in air. In 1611 Galileo defended this Archimedean account against his Aristotelian opponents, who argued that it is shape not relative density that determines whether objects float—they held that ice is denser than water but floats because of its flat shape; while Galileo argued that the fact that ice floats is proof that it is less dense than water.¹⁴

Galileo was thus committed to the view that air has weight; that we live in an ocean of air; and that it presses on us from all sides. He carried out experiments to determine the weight of air by measuring containers with more or less air in them.¹⁵ Galileo’s study of flotation had led him to explain how, within a confined space, a small weight of displaced water could support the far greater weight of a floating body—a version of the principle of the lever, which provides the theoretical foundation of the hydraulic press. In the Arsenal at Venice he had seen ships which were robust when floating in the water, but which had to be supported by shoring when on dry land—when floating they were held together by the pressure of the water, while on dry land they would have broken under their own weight.¹⁶ Galileo was thus an expert on how pressure works.

Moreover, even before Galileo became a Copernican, he had been prepared to accept the possibility of a vacuum—in contrast to the Aristotelians, who argued that there could be no such thing. By 1630, if not earlier, Galileo reasoned that a pump cannot raise water more than approximately thirty-four feet because if the column of water is higher than that it breaks and a vacuum appears. He thus held that there was nothing mechanically difficult about producing a vacuum; all one needed was a well where the water level was more than thirty feet below the surface, and a pump.¹⁷ Moreover, his friend Sagredo had pointed out to him that there was a vacuum in the top of every thermometer—Sagredo’s thermometers were made out of wide tubes, so that the vacuum space was substantial enough for him to conduct simple experiments, and to conclude that sound did not cross the vacuum.¹⁸

Yet Galileo—who had conducted extensive experiments with pendulums, floating bodies, magnets, and projectiles—never conducted any vacuum experiments. He did not explain the limit on how high a pump could raise water in terms of air pressure; instead, he related it to theories regarding the breaking strength of materials. Take a rope: if you lift it higher and higher into the air, eventually it will break under its own weight. This, Galileo argued, is what happens in a high-rise pump. Normally some force holds the water together; but when the weight of the water passes a certain limit, that force is overcome. What force is this? It is obvious that anything can cut through water, and that the fluidity of water implies that its parts slip past each other. So water cannot be held together as a rope is. Rather, it is held together in the same way that two polished slabs of marble are held together if one is placed on top of the other—lift the top one and the bottom one comes up with it. The force holding the column of water together and holding the two marble slabs together is the resistance to the production of a vacuum—Galileo maintained that it was easy to produce a vacuum, but to do so one had to overcome a measurable horror vacui, a mysterious force that acted to prevent vacuums from coming into existence. Since this force was rather powerful, much of the strength of materials, Galileo reasoned, derived from it.¹⁹

It is important to see what has happened here. Galileo had to hand all the intellectual tools required to account for the failure of suction pumps in terms of air pressure. This would have been a mechanical Archimedean explanation. Indeed, such an explanation was carefully laid out for him by Baliani in a letter of 1630—there, Baliani seems to be tactfully suggesting that such an explanation would work better than the explanation Galileo is proposing, although he acknowledges that he would expect the force of air pressure to be greater than it appears to be (this for the simple reason that Boyle’s law had yet to be discovered—it would not have occurred to Baliani that the weight of air in a given volume diminishes as one rises through the atmosphere).²⁰ But instead, Galileo adopted a nonmechanical explanation in terms of an occult force, the horror vacui. This explanation required an appeal not to mechanically efficient causes, such as weight, but to an Aristotelian final cause—when it comes to the vacuum (and only when it comes to the vacuum), nature appears to be purposive. It is true that this explanation seems to have been a placeholder for a more sophisticated explanation—Galileo went on to argue that all material objects contain infinitesimal vacua, so we do not need to assume that the cause of the horror vacui is a vacuum that does not yet exist.²¹ But he never explained how these infinitesimal vacua might act to prevent the creation of a substantial vacuum.

Within a year or so of Galileo’s death in 1642, Roman philosophers set out to prove that he had been wrong to claim that it was easy to make a vacuum. They created a tube sealed at one end which was more than thirty-four feet long, filled it with water, and upended it, open end down, in a butt of water; to their astonishment it turned out that there appeared to be a void at the top of the tube. Galileo had been vindicated. Galileo’s disciple Torricelli suggested conducting the same experiment with mercury rather than air, thus creating an apparatus which was much easier to manipulate. In the resulting Torricellian space at the top of the tube it was possible to include another mercury-filled tube, and to show that no column of mercury could be supported within a void. Thus it was apparent that the presence of air was the precondition for supporting a column of water or mercury within a container sealed at one end—which convincingly showed that air pressure was the cause of the phenomenon. Pascal went on to show with the Puy de Dôme experiment (in 1648) that there was further good evidence to support this hypothesis. Thus Torricelli’s tube was transformed into a barometer.²²

Torri...

Table of contents

• Cover
• Halftitle
• Title Page
• Copyright
• Contents
• Acknowledgements
• Introduction
• 1. Galileo: Reflections on Failure
• 2. Primary and Secondary Causes in Descartes’ Physics
• 3. Causation and the Cartesian Reduction of Motion: God’s Role in Grinding the Gears
• 4. Spinoza’s Conatus as an Essence-Preserving, Attribute-Neutral Immanent Cause: Toward a New Interpretation of Attributes and Modes
• 5. Are Mind-Body Relations Natural and Intelligible? Some Early Modern Perspectives
• 6. Hobbes’s Redefinition of the Commonwealth
• 7. Hume, Causal Realism, and Free Will
• 8. Pouring New Wine into Old Skin: The Meaning of Hume’s Necessary Connexions
• 9. Is Causation a Relation?
• 10. Kant on Causal Knowledge: Causality, Mechanism, and Reflective Judgment
• 11. Regularities All the Way Down: Thomas Brown’s Philosophy of Causation
• 12. Causality and Causal Induction: The Necessitarian Theory of Lady Mary Shepherd
• List of Contributors
• Index