The Scientific Revolution and Philosophical Rationalism

views updated

The Scientific Revolution and Philosophical Rationalism

Isaac Newton and the Confirmation of the Case for Science.

Isaac Newton (1642–1727) was the first universally recognized scientific genius. In his Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy), better known as the Principia (1687), he provided the mathematical demonstration necessary to prove his theory of gravity, and in doing so also lent irrefutable support to the Copernican thesis that the earth revolved around the sun. Beyond the Principia, Newton was also the discoverer (along with Gottfried Wilhelm Leibniz) of differential calculus, as well as the physical properties of light. He also invented the reflecting telescope. It was Newton who opened up the universe to scientific investigation by insisting that the physical laws that operate on Earth must also operate everywhere else, and that to discover what works on Earth is to discover what works in the universe. In making and announcing these discoveries Newton supplied the final push that turned European civilization toward the acceptance of science, not religion, as the basis of truth and knowledge. The contest between science and religion had been fiercely fought to a stalemate in the decades before Newton, with the defenders of religion, safe behind university walls, content to simply ignore the scientific challenge. The problem hindering the scientific assault was that advocates of science could not agree upon their own argument. The Copernican thesis was the cutting edge of the case being made for science, yet there was no consensus among the advocates of science that it was correct. Many of the arguments that Galileo advanced in favor of the thesis had been deeply flawed, and it is telling that Bacon chose to ignore the thesis in making his case for science. At the heart of the problem was an inability to explain scientifically the phenomenon that the accumulation of the data had revealed: the fact that the planets revolved around the sun in an elliptical rather than purely circular orbit. Newton's theory of gravity solved these problems by advancing the notion that the sun's pull on a planet was strongest when the planet was closest to it, and weakest when the planet was furthest away. His corollary development of the idea of centrifugal force—that at all times the pull of the sun on a planet was balanced by the pull of all other planets—definitively explained the phenomenon for which scientists had long been searching for an explanation. Newton's theory forced even churchmen to accept the veracity of the Copernican thesis. As Alexander Pope observed in a famous couplet from his "Epitaph intended for Sir Isaac Newton," "Nature and nature's laws lay hid in night; God said "Let Newton be!" and all was light." Contemporary Europeans embraced Newton—much as later twentieth-century Americans would celebrate Albert Einstein—as proof of the notion that through reasoned analysis it was possible to know nature, and, through nature, God. In his Lettres philosophiques (Philosophical Letters; 1734) Voltaire wrote with the aim of convincing Continental Europeans to follow the British cultural lead. Four of the twenty-four letters in the volume were devoted to explaining the work of Newton. Newton was a devout Christian who, it has been observed, wrote several million words of theology. Newton was also so deeply enamored of alchemy that the British economist John Maynard Keynes, who collected many of Newton's alchemical works, once characterized Newton as "the last of the magicians." Yet Voltaire correctly perceived that in the battle between science and religion, Newton was the ultimate weapon to defend science, and Voltaire passed on this awareness of the importance of Newton's discoveries to other Enlightenment thinkers. While the editors of the French Enlightenment Encyclopédie may have pointed out their indebtedness to Francis Bacon for their inspiration, Newton's new mechanistic universe was the justification for their work. His idea of a world held together by mathematical regularity, and by the opposing and counterbalancing forces of gravity and centrifugal force played a role in much of Enlightenment thought; this scientific model became, in other words, one of the dominant metaphors of the age, and its influence found its way into political theory, social criticism, and even the aesthetic writing of the period.

Optics and the Search for a Geometric God.

It was not coincidental that Galileo built his case for the Copernican thesis on the evidence he derived from his telescopic observations, or that when Bacon wanted to convey the idea of the cognitive blinders that inhibit human comprehension he adopted the metaphor of distorting mirrors. The seventeenth century was captivated by optics and all technology that derived from the use of glass lenses, much in the same way that the modern world is obsessed with the possibilities that computers offer. Glass lenses, like modern computer chips, are made from silicon. In both instances it is not silicon itself, but the way it has been mathematically configured that creates its utility for humans. The important role that mathematics played in grinding the lenses that were used in telescopes and microscopes inspired numerous attempts at the time to unearth a "geometric God." Seventeenth-century scientists still took as their departure point the premise that a supreme being had created the universe, and thus intellectuals thought that the geometric theorems that their technologies relied upon might be investigated to reveal the "secret" harmonies, proportions, and mathematical relationships God had used in His Creation. In this way geometry also became an important path of study for seventeenth-century philosophers, for, like scientists, they were convinced that it might reveal something about the attributes of the mind of God.

Rationalism and Mathematics.

The chief exponents of the school of seventeenth-century philosophy known as rationalism were all in some way involved in the application of mathematical principles to technological problems. Both René Descartes (1596–1650) and Baruch Spinoza (1632–1677), the first two proponents of rationalism, had, in fact, made their living through lens grinding at one point or another in their careers. Rationalists like Descartes and Spinoza took as their starting point the notion that philosophy might follow a path to truth similar to that of mathematics, which derived its powerful theorems from axioms. In this way, rationalist philosophers became concerned with developing a way of working out the many logical implications of axiomatic statements concerning the nature of existence. To explain their method, one must first have a clear idea of how axioms and theorems function in mathematics. In geometry, for example, it is an axiom that a triangle is a two-dimensional figure or polygon composed by the intersection of three straight lines. All the theorems that have to do with different types of triangles follow from this axiom. In this sense, it can be said that these theorems are innate—that is, inherent in the axiom—and that it is the task of the mathematician to explicate them by logical deduction. Rationalists approached the study of God from this same perspective. Their goal was to demonstrate that God was the ultimate axiom from which all other axioms are logically derived. As a philosophical perspective, rationalism's origins were ancient, and could be traced back to the ancient Greek mathematician Pythagoras, who noted the mathematical correspondences that occur in nature and concluded as a result that "all is number." What was new in its reappearance in the seventeenth century was its application to the Christian intellectual tradition. To that point Christian thought took as a given that knowledge of God was revealed through the Bible or through visions and miracles. But rationalism rejected such revelation as a source of divine knowledge, and taught instead that true knowledge of God was innate within humans and could be deduced by the application of its rigorous intellectual method. Because they rejected the traditional role that divine revelation had long played in religious teaching, though, many rationalists were attacked as free thinkers and atheists.

RenÉ Descartes.

The work of René Descartes has often been cited as the beginning of modern philosophy. At the time that Descartes began writing, skepticism had a pervasive influence over philosophical debate in Europe. Skepticism rejected the possibility of philosophical certainty. Its proponents argued that human beings were incapable of knowing truth and that they could only instead affirm through faith their own beliefs. Descartes sought to demonstrate that by following his rationalistic method, truth could be ascertained and known. His case for philosophical certainty was the starting point for every discussion of the topic during the Baroque and Enlightenment eras. Descartes was a first-rate mathematician, though his impact is mostly forgotten today. He pioneered the methods followed in analytic geometry, which has to do with the utilization of algebraic procedures to resolve geometric problems and vice-versa. It was Descartes also who introduced the practice still followed in algebra of assigning the letters a, b, c, etc., to known quantities, and the letters x, y, z, etc., to unknown quantities. Descartes' religious sensibilities are the subject of some debate, and the stance taken in this debate dictates one's interpretation of his work. One school of biographers has long emphasized the depths of Descartes' Catholic faith, while another has charged that his display of religiosity was merely intended to ward off possible criticism. Untangling Descartes' religious convictions remains a perilous enterprise. By upbringing, he was a Catholic, and he went to great lengths in his work to show that he was not of a similar mind to Galileo. When he learned that the Roman Church had condemned Galileo's works, he even withdrew a manuscript from his publisher in which he had supported the Copernican thesis. Still other evidence of his insincerity must be admitted. Although a Catholic, for instance, Descartes chose to spend a large portion of his adult life living in Protestant Holland, where he was free to pursue his philosophical work without being forced to practice his religion. Yet Descartes presented his philosophy all the same as a scientific case for the existence of God. Those who see his faith as real appreciated his work as a heart-felt if unsuccessful effort to use mathematics to confirm religion. Those who see his faith as insincere have treated his work as a camouflaged expression of atheism. Whatever the position taken on his religious sensibilities, all commentators agree that Descartes was sincere in his belief that mathematics and the rationalism it might foster provided an antidote to philosophical skepticism, the teaching that ultimate truths could not be established. In his Discourse on Method (1637), Descartes mapped out his objections to existing philosophical approaches. In his Meditations on the First Philosophy: In Which the Existence of God and the Distinction Between Mind and Body are Demonstrated (1641), by far his most influential work, he built his case against philosophical skepticism. In this work Descartes presents his most famous argument against doubt in the immortal words "cogito ergo sum" or "I think, therefore I am." For Descartes, when he used the word "cogito" ("I think"), he had in mind a "clear and distinct" idea whose truth was self-evident in the way the truth of a mathematical axiom is self-evident. Importantly, one ramification of Descartes' notion was that it drew an absolute dichotomy between mind and body. Mind had to do exclusively with cognition, with thought. Body had nothing at all to do with thought. Thus, the mind could learn nothing of truth from the body, that is, through sensory perception and experience. The mind could only draw upon itself, upon the ideas that were innate within it. As a result the proof that Descartes fashioned for the existence of God stressed that since the human mind possessed an idea of perfection that idea must come from someone else. That someone else must be perfect, and since only God is perfect, He must have placed the idea of perfection in the human mind as proof of His existence.


Descartes' ideas resonated among the intellectuals of his era, who were searching to find a way to prove God's existence through a seemingly scientific and ironclad rationalistic approach. While many intellectuals agreed with his starting point, some took exception to the path he suggested. Of those, the most important figure to articulate an alternative path to Descartes' rationalism was the Dutch Jewish thinker Baruch or Benedict Spinoza (1632–1677). Spinoza's case against Descartes derived from two observations. First, Spinoza insisted that Descartes had not pushed his ideas to their logical conclusions, and that second, humankind's spiritual freedom might be attained only if the logical conclusions of Descartes' system were embraced. Descartes, it must be remembered, often backed away from public presentations of arguments that might result in his censure from orthodox forces. By contrast, Spinoza's fate provides a powerful example of the consequences of making plain the theological implications that were inherent in a rationalist philosophical approach. As a young man Spinoza had been condemned and expelled from the Jewish community of Amsterdam. At this point he changed his name from Baruch to Benedict. Although a small group of thinkers recognized his achievements at the time of his death, for the most part Spinoza was reviled within the broader European intellectual community as an atheist. Modern commentators have emphasized that the characterization of Spinoza as an atheist is unfair. He had a strong faith in the Judeo-Christian deity; he just conceptualized that deity in a way that was distasteful to contemporary Jews and Christians. Key to Spinoza's argument for the reality of God was his pantheism, an idea he developed in his Ethics, a work completed in 1675 but not published until after his death in 1677. Spinoza modeled the Ethics on the ancient Elements of Geometry of Euclid, and in it, he sought to demonstrate that all that exists in the universe is God. While Descartes had postulated a dichotomy between mind and body, Spinoza rejected that dichotomy and argued instead that mind and body are parallel expressions of the same thing. The human mind, in other words, has within it an impression of the tree that is physically before its eyes. The tree itself exists as an "extension," a term that Descartes used to describe the physical and mathematical concreteness of things, but it exists all the same as a concept in the mind. In this sense mind and body are parts of the very same substance of which all existence is composed, and Spinoza identified that substance as God. In this way everything in the world is thus composed and contained within the deity.

The Controversy Over Spinoza.

The tragedy for Spinoza was that this argument could be interpreted in various contradictory ways. It could be taken, for instance, as an affirmation of an immanent deity who might be worshipped through his attributes, or it could be interpreted as a rationale for an atheistic materialism. Since God exists in all things, in other words, Spinoza could be seen as reducing God's importance to a superfluous detail. It was this latter interpretation of his work that dominated among the many contemporaries that attacked his ideas in the later seventeenth century. It has always been something of a puzzle as to why Spinoza was expelled from the Jewish community of Amsterdam so early in his life, but it remains plausible that perhaps this thinker's early precocious arguments against a providential God and the immortality of the soul may have had something to do with his excommunication. For Spinoza, beliefs in God's providence and the human soul's immortality were only ideas designed to make the deity appealing to humans. They stood in the way of the appreciation of God's human-dwarfing immensity, and it was only by appreciating this enormity that Spinoza believed humankind might find a path to spiritual freedom. In this regard his ideas concerning the human passions followed a similar logic. The passions made human beings and their affairs seem more important than they actually were when judged against the infinitude of God. Freeing oneself from the human passions was thus for Spinoza the only way to see God, and seeing God was the only way to ultimate freedom.

Gottfried Wilhelm Leibniz.

The last contributor of new ideas to the rationalist school of philosophy was Leibniz (1646–1716). The son of a professor, Leibniz earned a law degree by the age of twenty. Somewhat later he began a career in the employ of German princes, primarily the dukes of Hanover, serving among other things as a librarian, a diplomat, an engineer, and an educational reformer. Along the way Leibniz gained fame for his mathematical genius. Historians grant the honor of the discovery of differential calculus to Isaac Newton, but recognize that Leibniz made the discovery independent of the former. Leibniz also sought to reconcile rationalism with German Protestantism. Descartes had postulated an opposition between mind and body. Leibniz dismissed this opposition by rejecting the notion that the body had some reality beyond the mind. He also argued that time and space, the substance in which the body was captured for Descartes, was illusory. Leibniz reversed the philosophical inclination to define being as static or passive existence. For him, to be was to do, doing being equated with thinking. He could thus treat mind and body as the active and passive, immaterial and material parts of a whole. The idea that matter was composed of atoms was just then beginning to take hold in scientific discourse. Since he rejected the idea that matter has any existence outside the mind, Leibniz developed as an alternative to the idea of the atom, the idea of the monad. The idea of monads can be discerned evolving in Leibniz's work, reaching fruition in his Monadologia (Monadology; 1714), published two years before his death. Monads were the irreducible, indivisible, and metaphysical "things" that made up the world. As Leibniz characterized them, monads were complete concepts; they were self-contained and autonomous. Leibniz was extrapolating from mathematical reasoning


introduction: As the debate over the nature of knowledge heightened in Europe around 1700, thinkers came upon new ways of defining epistemology, the science of mental knowledge. One response was George Berkeley's radical idealism, that is, the notion that the mind and senses shaped all knowledge of the outside world, and without perception, nothing existed. Gottfried Wilhelm Leibniz came to a different conclusion. To explain how the mind apprehended and comprehended the world, he relied on the concept of monads, a concept he himself invented. A monad was, as he observed, "nothing but a simple substance, which enters into compounds." The theory of knowledge that such a theory produced was complex, as this excerpt shows; it did not win many adherents.

  1. The Monad, of which we shall here speak, is nothing but a simple substance, which enters into compounds. By 'simple' is meant "without parts." (Theod. 10)
  2. And there must be simple substances, since there are compounds; for a compound is nothing but a collection or aggregatum of simple things.
  3. Now where there are no parts, there can be neither extension nor form [figure] nor divisibility. These Monads are the real atoms of nature and, in a word, the elements of things.
  4. No dissolution of these elements need be feared, and there is no conceivable way in which a simple substance can be destroyed by natural means. (Theod. 89)
  5. For the same reason there is no conceivable way in which a simple substance can come into being by natural means, since it cannot be formed by the combination of parts [composition].
  6. Thus it may be said that a Monad can only come into being or come to an end all at once; that is to say, it can come into being only by creation and come to an end only by annihilation, while that which is compound comes into being or comes to an end by parts.
  7. Further, there is no way of explaining how a Monad can be altered in quality or internally changed by any other created thing; since it is impossible to change the place of anything in it or to conceive in it any internal motion which could be produced, directed, increased or diminished therein, although all this is possible in the case of compounds, in which there are changes among the parts. The Monads have no windows, through which anything could come in or go out. Accidents cannot separate themselves from substances nor go about outside of them, as the 'sensible species' of the Scholastics used to do. Thus neither substance nor accident can come into a Monad from outside.
  8. Yet the Monads must have some qualities, otherwise they would not even be existing things. And if simple substances did not differ in quality, there would be absolutely no means of perceiving any change in things. For what is in the compound can come only from the simple elements it contains, and the Monads, if they had no qualities, would be indistinguishable from one another, since they do not differ in quantity. Consequently, space being a plenum, each part of space would always receive, in any motion, exactly the equivalent of what it already had, and no one state of things would be discernible from another.
  9. Indeed, each Monad must be different from every other. For in nature there are never two beings which are perfectly alike and in which it is not possible to find an internal difference, or at least a difference founded upon an intrinsic quality [denomination].
  10. I assume also as admitted that every created being, and consequently the created Monad, is subject to change, and further that this change is continuous in each.
  11. It follows from what has just been said, that the natural changes of the Monads come from an internal principle, since an external cause can have no influence upon their inner being. (Theod. 396, 400)
  12. But, besides the principle of the change, there must be a particular series of changes [un detail de ce qui change], which constitutes, so to speak, the specific nature and variety of the simple substances.

source: Gottfried Wilhelm von Leibniz, The Monadology and Other Philosophical Writings. Trans. Robert Latta (London: Oxford University Press, 1898; reprinted 1951): 217–223.

here. What he had in mind was a sentence such as "A is equal to A," a statement that would obviously remain true whatever the moment, whatever the situation. As Leibniz envisioned it, the set of valid predicates for each of these monads were some part immaterial, some part material in a hierarchical progression that stretched from the least active monads, such as those that took on the appearance of stone in the real world, to the most active, such as those that as a collectivity generated the appearance of the most sentient humans. The creator of all these monads was God, who remained the apex of the geometric pyramid favored by the rationalists, but who was now understood to be the monad for whom all other monads were predicates. Because he rejected the reality of material existence, Leibniz rejected the idea of causality, the idea that one thing in the material world caused another. Rather, he insisted that the predicates that exist for a given subject exist as a network of explanation from which it is possible to deduce the connection between events. For example, if one of the predicates for John is that he drives a car, and another of the predicates is that he is a careless driver, it is possible to deduce what Leibniz identified as the "sufficient reason" why John has a car accident. Applying this notion of sufficient reason to the world in which he lived, Leibniz argued that there was a rational explanation for all that occurred. It is in this sense that it is possible to extract from Leibniz's ideas the notion that we live in "the best of all possible worlds," the idea for which the French playwright Voltaire lampooned Leibniz in the figure of Doctor Pangloss, a central character in his satire Candide.

Nicholas Malebranche.

Malebranche (1638–1715) was slightly senior in age to Leibniz, and his writings had their intellectual impact earlier than those of Leibniz. Like Leibniz, he was concerned with reconciling rationalism with Christianity, though in his case the Christianity in question was French Catholicism. He is often left out of discussions on Baroque philosophy because his contemporaries recognized him more as a disciple of Descartes than as the originator of new ideas. Yet in his role as a defender and reformer of the teachings of his master, he was perhaps the most influential of the rationalists after Descartes. Spinoza and Leibniz both used Descartes as the departure point for the development of their own systems of thought. Neither of these systems ever replaced that of Descartes as the definitive notion of rationalism. Malebranche rethought Descartes' ideas in light of the criticisms that had been directed at them in the last part of the seventeenth century. In the eighteenth century, when rival philosophers talked about rationalism, what they inevitably had in mind was Descartes as amended by Malebranche. Male-branche's life and career followed a pattern that recurred often in early-modern French intellectual life. Born with a deformed spine and a sickly constitution, he preferred a life of seclusion and scholarship early on. In 1664 he was ordained a priest, though he never took on any pastoral duties. In the same year, after failed efforts to become a historian, then a biblical scholar, he discovered the writings of Descartes. Descartes' words caused his heart to "palpitate," and he spent the rest of his life studying and explaining Descartes' thoughts. Malebranche's major work on Descartes, De la Recherche de la Verite (The Search After Truth) appeared in three volumes published in 1674 and 1675. In this work he advanced two ideas that shaped the understanding of Cartesianism. First was the notion of "vision in God," the idea that all mental images or ideas exist only in God, and that at his discretion God allows man to see these things. Descartes had argued that ideas were innate within the human mind without working out how those ideas got there or how they were accessed on a moment-to-moment basis. For Descartes, it was sufficient to argue that God implanted ideas in the human mind at the moment of creation. Malebranche went beyond this and, fusing the ideas of Descartes with those of Saint Augustine, presented an image of an omnipresent God who continuously interacts with the human mind. Seemingly anticipating the assault on rationalist assumptions that was soon to come from empiricists, Malebranche rejected the argument that ideas came into the mind directly through the senses. The senses can reveal pain and pleasure. They cannot reveal what is causing pain or pleasure. Knowledge of what is outside the mind can only enter the mind through the representations placed there by God. What is perceived when one looks at a tree is not the tree as it really is, but the representation of the tree placed there by God. The second idea associated with Malebranche is "occasionalism," the argument that God is the ultimate cause of every action. To get a sense of what Malebranche was striving to express here, think of a soccer game where in the closing minutes a player gives the ball a kick that sends the ball through the goal for a winning score. As Malebranche would explain it, the player in question would be the occasional or incidental cause of the winning kick. The real source of the kick was God, who used the player as an instrument of his will.


A. Donagan, Spinoza (New York: Harvester, 1988).

L. Pearl, Descartes (Boston: Twayne, 1977).

D. Radner, Malebranche: A Study of a Cartesian System (Assen, Germany: Van Gorcum, 1978).

N. Rescher, Leibniz (Totowa, N.J.: Rowman and Littlefield, 1979).

W. R. Shea, The Magic of Numbers and Motion: The Scientific Career of René Descartes (Canton, Mass.: Scientific History Publications, 1991).

R. M. Silverman, Baruch Spinoza: Outcast Jew, Universal Sage (Northwood, England: Symposium Press, 1995).

R. S. Woolhouse, Descartes, Spinoza, Leibniz: The Concept of Substance in Seventeenth-Century Metaphysics (London: Routledge, 1993).

About this article

The Scientific Revolution and Philosophical Rationalism

Updated About content Print Article