Philosophy of Science in the Scientific Revolution

The Scientific Revolution was not only a matter of new discoveries. It was a transformation in the basic categories by which natural philosophers understood nature, the methods they used to investigate it, and the standards by which they judged their results. This section examines the philosophical core of that transformation: the rejection of Aristotelian final causes, the rise of the mechanical philosophy, the increasing role of mathematics, and the growth of new methods for the investigation of nature. The three articles treat the most important themes in more detail: empiricism, the scientific method, and the rationalism vs. empiricism debate.

From Final Causes to Mechanical Laws

The single most important philosophical change of the Scientific Revolution was the rejection of Aristotelian final causes. Aristotelian science explained motion, change, and biological growth in terms of purposes — the ends or goals for which things happen. A heavy body falls because it is seeking its natural place at the center of the cosmos. An acorn grows into an oak because that is its telos, its end. A flame rises because the natural place of fire is above the natural place of air. The natural philosophers of the seventeenth century, in a slow and contested process, abandoned this framework. They sought efficient causes — the mechanical interactions of matter in motion that produced observable effects. The decisive move was the construction of what is often called the mechanical philosophy: the doctrine that the natural world is a system of particles in motion, governed by laws of motion and contact action, with no purposes and no teleology. Descartes, Hobbes, Boyle, and Huygens all defended versions of the mechanical philosophy; Newton accepted it in principle but accepted also the existence of universal gravitational attraction, which seemed difficult to explain by contact action. The rejection of final causes was not complete in the seventeenth century. It was a slow process, with many natural philosophers — including Newton himself — retaining a place for the divine purposes in the economy of nature. The full rejection of teleology is, in fact, a feature of the late-nineteenth-century scientific worldview rather than of the Scientific Revolution itself. But the move away from Aristotelian final causes, and toward mechanical efficient causation, was one of the defining features of the revolution.

The Role of Mathematics

A second feature of the new philosophy of nature was the increasing centrality of mathematics. Aristotelian natural philosophy had been largely qualitative, treating nature in terms of the categories of substance, form, quality, and purpose. The new natural philosophy was increasingly quantitative, treating nature in terms of measurable quantities related by mathematical laws. The Pythagorean and Neoplatonic traditions of the Renaissance had emphasized the mathematical structure of the cosmos; the recovery of Archimedes in the sixteenth century had made it possible to imagine a mathematics of mechanics. Galileo, in the Assayer (1623), famously declared that the book of nature is written in mathematical characters, and that its letters are triangles, circles, and other geometric figures. Descartes, in the Discourse on Method and the Meditations, sought to make the whole of natural philosophy into a deductive system modeled on mathematics. Newton’s Principia was the most ambitious attempt yet to construct a mathematical natural philosophy, and its success helped to establish the model of mathematical physics that would dominate the next two centuries. The role of mathematics in the Scientific Revolution is examined in detail in the article on What Is the Scientific Method? and in the page on Bacon and Descartes.

The Rise of Empiricism

A third feature of the new philosophy of nature was the increasing emphasis on empirical observation and experiment. The Aristotelian tradition had valued empirical observation but had not made experiment central. The new natural philosophers insisted that natural philosophy must be grounded in the testimony of the senses, properly controlled and interpreted. The empirical approach was defended most famously by Francis Bacon in his Novum Organum (1620). Bacon argued that the Aristotelian tradition had been too ready to construct theories on the basis of inadequate observation, and he proposed a new method based on the systematic tabulation of instances of natural phenomena, the gradual ascent from particular observations to general axioms, and the careful exclusion of error. Bacon’s method was inductive, in contrast to Descartes’s deductive approach, and the two together defined the principal methodological orientations of the early-modern period. The empirical approach was extended in the work of the Royal Society, whose motto — Nullius in verba (On no one’s word) — expressed the commitment to direct investigation of nature rather than reliance on ancient authority. Robert Boyle’s experimental work on the vacuum, the air pump, and the chemistry of acids and alkalis exemplified the new method. Isaac Newton’s “Rules of Reasoning in Philosophy,” prefixed to the Principia and the Opticks, articulated a sophisticated form of empiricism that combined careful observation with a willingness to construct mathematical laws on the basis of that observation. The story of empiricism is told in the article on What Is Empiricism and Why Did It Matter?.

The Rise of Rationalism

The new natural philosophy was not only empirical; it was also, in important ways, rationalist. René Descartes is the most important figure on the rationalist side. In his Discourse on Method (1637) and Meditations (1641), Descartes argued that genuine knowledge must be grounded in clear and distinct ideas, perceived by the mind, rather than in the testimony of the senses, which can be deceiving. The method of doubt — a systematic doubt of all beliefs that admit of any doubt — was to be followed by the construction of a new natural philosophy on the secure foundation of the cogito (the famous “I think, therefore I am”) and the clear and distinct ideas of mathematics. Descartes’s rationalism was the most ambitious philosophical program of the seventeenth century. He sought to derive the laws of nature from the clear and distinct idea of extension — the property of bodies in space — and to explain the entire physical world as a system of corpuscles in motion governed by mechanical laws. His influence on the growth of physics, physiology, and philosophy was immense, especially in continental Europe. The rationalist tradition was continued by Nicolas Malebranche, by Gottfried Wilhelm Leibniz (who also invented the calculus, independently of Newton), and by the early Spinoza. The contrast between the rationalism of Descartes and the empiricism of Bacon defined the principal philosophical opposition of the early-modern period, and the way in which the two traditions interacted and developed is one of the great stories of the history of philosophy. The comparison is examined in detail in the article on Rationalism vs Empiricism.

The Methodological Synthesis: Newton

The most important philosophical achievement of the late seventeenth century was the synthesis of the rationalist and empiricist traditions in the work of Isaac Newton. Newton’s method, as articulated in the Principia and the Opticks, was neither pure deduction from first principles nor naive inductive generalization from observations. It was a combination of the two: mathematical deduction from empirically established laws, and empirical confirmation of the mathematical consequences of those laws. Newton’s Rules of Reasoning in Philosophy, which he formulated in the Principia and elaborated in the Opticks, were four:

1. We are to admit no more causes of natural things than such as are both true and sufficient to explain their appearances.
2. Therefore to the same natural effects we must, as far as possible, assign the same causes.
3. The qualities of bodies, which admit neither intensification nor remission of degree, and which are found to belong to all bodies within the reach of our experiments, are to be esteemed the universal qualities of all bodies whatsoever.
4. In experimental philosophy we are to look upon propositions inferred by general induction from phenomena as accurately or very nearly true, notwithstanding any contrary hypotheses that may be imagined, till such time as other phenomena occur, by which they may either be made more accurate, or liable to exceptions. These rules defined a middle path between Cartesian rationalism and Baconian empiricism. They were an important part of the philosophical legacy of the Scientific Revolution, and they shaped the practice of natural philosophy for the next two centuries. The story of Newton’s method is told in the article on What Is the Scientific Method? and in the article on the Principia Mathematica.

Bacon, Descartes, and the New Method

The methodological writings of Bacon and Descartes were among the most important philosophical works of the seventeenth century. Bacon’s Novum Organum and Descartes’s Discourse on Method were both published within a few years of each other, and they defined the principal orientations of the new natural philosophy. The two writers also had enormous personal influence: Bacon as a kind of patron saint of the new experimental science in England, and Descartes as the founder of the most influential philosophical school in continental Europe. The two figures are treated together in the page on Bacon and Descartes.

The Experimental Method

The experimental method — the deliberate intervention in nature, with controlled variation of conditions, to test hypotheses about the behavior of natural things — was a defining feature of the new natural philosophy. The experiment became a kind of artificial experience, in which the natural philosopher asked a specific question of nature and received a specific answer. The experimental method was developed in many hands: in Galileo’s inclined-plane experiments on motion, in Torricelli’s barometer experiment, in Pascal’s experiments on atmospheric pressure at different altitudes, in Boyle’s work with the air pump, in Huygens’s experiments on the pendulum clock. The Royal Society and the Académie des Sciences institutionalized the new method, with regular meetings, publication of experiments, and replication by independent observers. The story is told in more detail in the article on What Is the Scientific Method?.

The Limits of the Mechanical Philosophy

The mechanical philosophy was extraordinarily successful, but it was not universally accepted, and it left a number of important phenomena unexplained. The most conspicuous was gravitation. Newton accepted the law of universal gravitation, by which every particle of matter in the universe attracts every other particle with a force inversely proportional to the square of the distance between them. Yet the mechanical philosophy — committed to contact action and the impossibility of action at a distance — could not explain how this force was transmitted. Newton himself famously declined to “feign hypotheses” about the cause of gravitation, accepting the law as a description of the phenomena without offering a mechanical explanation. This was a profound philosophical difficulty, and it generated a long debate in the eighteenth and nineteenth centuries. The discovery of the gravitational field concept in the nineteenth century, and the work of Faraday and Maxwell on electromagnetism, eventually dissolved the difficulty, but in a way that went beyond the original mechanical philosophy. The history of these debates is part of the longer history of philosophy of science.

The Religious and Moral Context

The new philosophy of nature was deeply entangled with religious and moral concerns. Many of the major figures of the Scientific Revolution — Newton, Descartes, Boyle, Kepler, Bacon — were deeply religious, and they often saw the new natural philosophy as a way of understanding the works of God. The “intelligent design” of the cosmos was a recurring theme, especially in England. Yet the new science also posed a serious challenge to traditional religious understandings, especially when its results were taken to imply that nature operates entirely by natural causes. The story is examined in detail in the page on Religion and the Church.

The Legacy

The philosophy of science that emerged from the Scientific Revolution — the commitment to mathematical description, the reliance on experiment, the rejection of teleology, the construction of natural laws — became the dominant framework for the natural sciences in the eighteenth, nineteenth, and twentieth centuries. The philosophical problems generated by the revolution — the problem of induction, the problem of the relationship between mathematics and nature, the problem of the limits of mechanism — are still with us today, and they are part of the active agenda of contemporary philosophy of science. The story of these developments is told in the page on Bacon and Descartes and in the broader Scientific Revolution overview.

Related Articles

• The Scientific Revolution: A Complete Overview
• What Is Empiricism and Why Did It Matter?
• What Is the Scientific Method?
• Rationalism vs Empiricism: How Did They Differ?
• The Mechanical Philosophy: How the World Became a Machine
• Bacon and Descartes