The World Philosophy Made

by Scott Soames

  The alleged elimination of “real relations” is supposed to be an example of the use of Ockham’s razor, Don’t postulate entities beyond necessity, which may be paraphrased, Don’t posit entities beyond those needed to explain evident truths. So understood, it can hardly be denied. One might be able to use it more directly to eliminate properties and relations, if the only truths one had to explain were particular truths like ‘Scott Soames is a philosopher’ and ‘Greg and Brian Soames are his sons’, which logically entail the existence of Scott, Greg, and Brian, but don’t logically entail the existence of the property being a philosopher or the relation being a son of. But if we also need explanations of truths about the meanings of general terms, or the cognitions of agents who believe the contents of the thoughts we express by using such sentences, then it’s not clear that Ockham’s razor can be used to eliminate properties and relations.28

  Ockham put it to better use in understanding causation. He refuses to recognize any combination of features in a prior event A as the cause of a later event B, unless events with precisely that combination of features never fail to be followed by an event of the same type as B. He thus tends to identify causation with constant conjunction of items of the same sort, which, he argues, can be known only by empirical observation. In this way, he avoids positing an unobserved necessary connection between cause and effect. Since science is concerned with causes, this was rightly understood to be a blow against assuming in advance that the natural world must conform to any preconceived picture, and in favor of observation-based investigations.

  Ockham was also parsimonious with traditional proofs of the existence of God. He rejected the final-cause (purpose) version of the first-cause argument as presupposing a divine purpose the existence of which it is supposed to prove. He rejected the efficient-cause version of the argument because we can’t rule out an infinite sequence of prior causes. But he did accept an argument based on the idea that every contingent being—i.e., every being which, although it does exist, could have failed to exist—has, at each moment at which it exists, something that conserves its existence. Although the conserver could be another contingent being, the chain of conservers couldn’t, he thought, be infinite, because that would require infinitely many conservers existing at one time, which he judged to be impossible. However, he didn’t take his conclusion to establish the existence of a single, unconserved conserver of all things, or a conserver with any of the attributes usually attributed to God. For Ockham, the Christian belief in God and knowledge of his nature had to be founded on revelation.

  His message about the human soul was similar.

  Understanding by intellectual soul an immaterial and incorruptible form … it cannot be known evidently either by arguments or experience that there is such a form in us or that the activity of understanding belongs to a substance of this kind in us, or that a soul of this kind is the form of the body. I do not care what Aristotle thought about this.… [T]hese three things we hold only by faith.29

  In short, Ockham rejected Aristotelian metaphysics, the Aristotelian distinction between essence and accident, and the use of philosophy to prove central Christian doctrines. But he didn’t reject either Christianity or philosophy itself; on the contrary, he was both a fervent believer and an ardent philosopher. He was also an innovator, whose non-metaphysical, “nominalist” theory of language formed the basis of detailed logical studies. He was followed in this in the last half of the fourteenth and the first half of the fifteenth century by a vigorous Ockhamist movement of Christian thinkers whose theology coexisted with a philosophical tendency to restrict necessary truths provable by unaided reason to those the negations of which could be shown to be logically contradictory—a tendency that led them to emphasize the importance of observation-based methods of acquiring worldly knowledge. This potent combination of theological conservatism with philosophically mandated empirical investigations won many adherents in European universities, encouraging the development of fourteenth- and fifteenth-century science.30

  In sum, the period investigated here was one in which Greek philosophy was given a new start, relieved of the burden of discovering either the meaning of life or a practical path leading to the highest personal fulfillment. Its assigned task, to which it was so well suited, was simply to further the acquisition of knowledge of the world and ourselves. This new lease on life was granted by a religion that was, for a time, confident it could accommodate whatever was discovered by reason and empirical observation. At first, the accommodation took the form of a grand synthesis in which the doctrines of medieval philosophers—whether adapting, modifying, or superseding those of their Greek predecessors—complemented Christianity, while modifying it in the process. But as time wore on, philosophy asserted its natural critical autonomy, the synthesis eroded, and philosophers created the intellectual space they needed to begin laying the foundations for the spectacular growth of mathematics and natural science that was to come.

  CHAPTER 3

  THE BEGINNINGS OF MODERN SCIENCE

  The interpenetration of philosophy, mathematics, and science in the late Renaissance and the early modern period; Copernicus, Kepler, Galileo, Descartes, Newton, Boyle, Locke, Leibniz, Berkeley, Hume, and Kant.

  The remarkable development in western philosophy from the late sixteenth through the eighteenth century was intertwined with great advances in natural science and mathematics. Building on the contributions made by medieval and Renaissance thinkers in advancing observation-based knowledge independent of Aristotelian metaphysics, natural theology, and revealed religion, philosophers in the early modern period made notable contributions to the science and mathematics of their day. Two of those earlier thinkers, Roger Bacon in the thirteenth century and William of Ockham in the fourteenth, were notable for emphasizing the role of mathematics and logic in formulating and testing hypotheses about the natural world. The fourteenth century also saw the beginnings of sustained attacks on Aristotelian physics, which had separated terrestrial from celestial motion. Ockham decisively rejected the Aristotelian account of terrestrial projectiles, while the philosopher, physicist, and rector of the University of Paris John Buridan (died 1360) rejected Aristotelian physics as being incapable of explaining the motion of a spinning top. Nicholas Oresme (died 1382), who also taught at Paris, argued that the hypothesis that the earth rotates can’t be disproved by observation, and, although he didn’t endorse the idea, he did suggest that there are some grounds for taking it to be true. He also questioned the geocentric conception of the universe by taking seriously the idea that there might be more than one world.

  Retrograde motion. Courtesy of Tunç Tezel.

  The independent study of nature continued in the fifteenth and sixteenth centuries, as physics became more heavily mathematical and more focused on precise observation. The first major step was taken by the clergyman, physician, and astronomer Nicolaus Copernicus (1473–1543). Recognizing that the Ptolemaic system had evolved piecemeal—with predictions about one celestial body’s point of occlusion by another being calculated on an individual planet-by-planet basis—he sought systematic integration. In so doing, he addressed the so-called “retrograde” motions of certain planets, when they appear to change direction and move backward in relation to the fixed stars. To explain this, the geocentric system posited bizarre planetary movements—halting, reversing, halting, and advancing again. By contrast, the heliocentric picture put us on a path to explaining why, if the earth moves around the sun, the position of its orbit in relation to those of other circling planets sometimes makes it appear that they change direction, when in fact they don’t.1

  Heliocentric explanation.

  The Copernican model in the second figure illustrates how an observer’s position on an inner planet (the earth) in its orbit around the sun together with the position of a planet in an outer orbit will, at certain times, create the illusion that the outer planet has temporarily changed direction in relation to the fixed stars (A1–A5)
. However, in part because Copernicus didn’t question the dogma that the planets moved in circles, he still needed some ad hoc epicycles to accommodate a few puzzling appearances. Thus, it wasn’t until Kepler discovered the elliptical form of planetary orbits that the remaining observational illusions were explained and the need for epicycles was eliminated. Even then, the causes of celestial motion—about which Copernicus said nothing—remained to be identified and precisely measured. Partly for these reasons, Copernicus is better seen as the last great natural philosopher, charting the geometry of physical space, rather than the first modern celestial physicist offering causal explanations supported by mathematically precise observations.

  That honor goes to Johannes Kepler (1571–1630), who, after eight years of precise and exhaustive observation of the orbit of Mars, announced in 1609 (i) that the planets move in elliptical, not circular, orbits, with the sun as one focus of each ellipse, and (ii) that the area covered by the sweep of the vector connecting the sun to a planet remains constant across equal units of time. Nine years later he announced his third law, that for any two planets, the ratio of the squares of the time taken to complete a single revolution is equal to the ratio of the cubes of their mean distances from the sun. With these discoveries, the epicycles of Copernicus were gone and the movements of the planets were seen as caused by an active force emanating from the sun.

  At first Kepler analogized the sun to God the Father and the force emanating from it to the Holy Ghost. But he also observed something that eventually led him to think of this force in physical terms. Finding that the planets closest to the sun moved more quickly in their revolutions around it than those further away, he concluded that the sun’s power to move the planets diminished with distance, and so the force it exerted must be something like light, which is emitted from a physical source. He described this force, gravity, as being one which, like light, is something that is emitted and somehow travels through empty space without having any substantial existence there, until it is received by a body which is then moved, in the case of gravity, or illuminated, in the case of light.

  Although Kepler’s dramatic findings about gravity were on the mark, he found himself in a quandary. As illustrated by the following remarks, he knew a lot about this universal force, including the fact that the force exerted by one thing on another is in proportion to its mass, while being inversely proportional to the distance between the two.

  Gravity is the mutual bodily tendency between cognate [material] bodies toward unity or contact … so that the earth draws a stone much more than the stone draws the earth.

  If the earth and the moon were not kept in their respective orbits by a spiritual or some equivalent force, the earth would ascend toward the moon) of the distance, and the moon would descend the remaining 53 parts of the interval, and thus they would unite.

  If two stones were placed anywhere in space near to each other, and outside the reach of the force of a third cognate body, then they would come together, after the manner of magnetic bodies, at an intermediate point, each approaching the other in proportion to the other’s mass.2

  Nevertheless, he didn’t know how to think about this mysterious force. How could a body A exert a force on a body B across (presumably) empty space, which provides no medium by which the force exerted by A might be transmitted to B? Astoundingly, his inability to answer this question led him to drop the notion of gravity in subsequent writings. Equally astoundingly, it led both Galileo and Descartes, who studied Kepler, also to reject the notion of force acting at a distance.3

  Despite this puzzle about gravity, Kepler’s advance swept aside the role of Aristotelian final causes (purposes) in explaining nature, the Aristotelian bifurcation of celestial and terrestrial physics, and the need to appeal to the active operation of a divine mind in understanding natural law. As Kepler wrote to a friend in 1605:

  My aim is to show that the heavenly machine is not a kind of divine, live being, but a kind of clockwork … insofar as nearly all the manifold motions are caused by a most simple, magnetic, and material force, just as all motions of the clock are caused by a simple weight. And I also show how these physical causes are to be given numerical and geometrical expression.4

  Despite this testament to what now seems to be commonplace scientific objectivity, Kepler was as much of a mystic as he was a scientist. In addition to being a believing Christian, he was a sometime astrologist and numerologist. He was also obsessed with ancient Pythagorean doctrine about what musical harmonies can tell us about planetary movements and what we can learn about the structure of the solar system from studying so-called perfect geometrical solids. Despite this, his commitment to careful, systematic empirical observation, and his belief in the power of mathematics as an essential scientific tool, allowed him to make great progress.

  The Italian Galileo Galilei (1564–1642) was a contemporary of Kepler. A talented mathematician and professor of mathematics, first at Pisa and then at Padua, he was also an experimental physicist, a natural philosopher, and an astronomer whose technical improvements on the telescope (invented in Holland in the first decade of the seventeenth century) made possible his impressive observations of the sun, the moon, and the planets.5 Well versed in the works of Aristotle, he was highly critical of Aristotelian physics, both terrestrial and celestial. For example, in defending the Archimedean view that it is the density of a body that determines whether it will float in water against the Aristotelian view that it is the shape of the body that matters, Galileo offered experimental evidence that the determining factor is the relative density of the body to the fluid in which it is placed that matters. He also provided experimental evidence confirming Simon Stevin’s observation that bodies of different weight fall at the same rate, which refuted the Aristotelian view that the heavier the object, the faster it falls.6 With this as his starting point, Galileo sought to empirically establish the law of uniform acceleration that the speed of a falling body increases at a constant rate over time (which had been anticipated by earlier investigators). He sought also to support the thesis that a moving body not acted upon by external forces—e.g., friction, wind resistance, etc.—will continue to move in the same direction at a uniform speed (again in opposition to Aristotle).

  Galileo’s contributions to astronomy stemmed in substantial part from observations made possible by his improved telescope, which he started using around 1610. With it, he could clearly observe the mountains on the moon, which led him to conclude that it is made out of material like the earth, contrary to Aristotle’s dichotomy between celestial and terrestrial beings. He also observed sunspots—which a Jesuit priest, Christoph Scheiner, had observed slightly earlier using a telescope of his own construction that incorporated an improvement suggested by Kepler. Like the mountains on the moon, the existence of sunspots further disconfirmed Aristotelian celestial physics by suggesting that the sun (like everything else) consists of changeable matter. In addition, Galileo observed the satellites of Jupiter and the phases of Venus, both of which fit Copernicus and Kepler’s heliocentric conception much better than the geocentric conception of the universe.

  The phases of Venus were especially interesting. Like the moon, Venus, as seen from earth, presents a regular sequence of appearances—full, half, crescent, etc. Because it is closer to the sun than we are, its full orbit is visible to us. When it is on the side of the sun opposite us, it appears full, and small because it is far away. When it is at either end of its elliptical orbit its face is half visible. Because it orbits more quickly than we do, its orbital position gradually catches ours. Now on the same side of the sun as we are, it begins to approach the point at which it will be directly between us and the sun. As it moves closer and closer to this point, it is seen as a gradually thinning crescent—much larger because it is now so close to us. This continues until it disappears (because it is directly between us and the sun), after which it appears again, as a thin crescent on the other side that gradually thickens as the planet
speeds ahead of us in its orbit. It is hard to imagine more convincing observational confirmation of the superiority of the heliocentric conception of the solar system over its geocentric competitor.7

  Finally, it should be noted that Galileo’s firmly grounded scientific results and observations existed side by side with his speculative philosophy of nature. A central part of that philosophy was his version of ancient metaphysical atomism—the belief, unconfirmed by experience or observation, that nature is nothing more than a grand system of some definite number of tiny bits of matter in motion, each with objective properties of having shape, size, position, and velocity in a certain direction. According to this picture, all change is the repositioning of atoms. Moreover, any change could, in principle, be predicted if one had a complete inventory of atoms, their sizes, shapes, positions, velocities, spatiotemporal coordinates, and the forces acting on them.

  Since Galileo took the forces to be mechanical—basically the result of the movements and collisions of atoms—he could not accept the idea of force at a distance (with no intervening medium). Nor could he accept the idea that other, more familiar, properties of macroscopic things—e.g., the color of an object—are truly objective. Like many natural philosophers of the time, he took them to be subjective qualities in observers rather than objective qualities in things observed. His mathematical physics made this seem natural, since things like colors and sounds played no role in it. According to this doctrine—which found many adherents—insofar as the redness of a rose could be considered to be in the rose itself, it is merely the rose’s disposition (due to its atomic structure) to cause certain (red) sensations in us.