Isaac Newton (4 January 1643 – 20 March 1727) was an English mathematician, astronomer, and physicist/natural philosopher who is widely recognized as one of the most influential scientists of all time. Newton’s most notable contributions were made to the fields of physics, mathematics, and scientific method, which were so groundbreaking that he is currently considered to be one of the most important physicists in modern Western history.1 Philosophers of science credit Newton’s revolutionary theory of gravity and his experimental approach to conducting natural philosophy as outlined in his major work, Philosophiæ Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy or simply the Principia), whose principles became central to the mosaic of late 18th and 19th century science.1 Some consider the Principia to be the work that initially created physics as its own scientific field separate from the umbrella of metaphysics and philosophy. 1
When Isaac Newton began his studies at Cambridge University's prestigious Trinity College in 1661, more than a century had passed since Nicolaus Copernicus (1473-1543) had proposed a heliocentric cosmology in 1543. It had been fifty years since Galileo Galilei (1564-1642) published his observations with the telescope in 1610, which uncovered dramatic evidence for the Copernican system. At about the same time, Johannes Kepler (1571-1630) published his laws of planetary motion, indicating that the planets revolved around the sun on elliptical paths, replacing the circular motion and complex epicycles of Copernicus and Claudius Ptolemy (c. 100-170).2 According to Westfall, "by 1661 the debate on the heliocentric universe had been settled; those who mattered had surrendered to the irresistible elegance of Kepler's unencumbered ellipses, supported by the striking testimony of the telescope, whatever the ambiguities might be. For Newton, the heliocentric universe was never a matter in question".2 A planetary Earth that rotated on its axis and revolved around the sun was incompatible with the accepted physics of Aristotle (384-322 BCE). The community of the time was engaged with the question of how it could be that the Earth itself was in motion through space, and with the question of how one could hope to gain reliable knowledge in the face of the failure of Aristotelian scholastic knowledge accepted for centuries.
Newton’s education at Cambridge was classical, focusing on Aristotelian rhetoric, logic, ethics, and physics. Bound to Aristotelian scholasticism by statutory rules,the curriculum had changed little in decades.324 Like many of the more ambitious students, Newton distanced himself from classical metaphysics and instead studied the works of the French natural philosopher René Descartes(1596-1650) on his own. By 1664, Newton is known to have read the 1656 Latin edition of Descartes' Opera Philosophica, a one volume compilation of Descartes' major works.4 Newton is known to have been profoundly influenced by Descartes views of space, matter, and God, and by commentaries on Descartes by Henry More (1614-1687). 1 Descartes had died just over a decade earlier, and his works had first been published within the preceding thirty years. They were gaining in popularity and by about 1680 would become the accepted centerpiece of the Cambridge curriculum, as they also would in Paris by 1700.5 When Newton published his magnum opus, the Principia in 1687, he was challenging a Cartesian orthodoxy. The full title of Newton's work suggests he intended it to be in dialog with Descartes' Principia Philosophiae (Principles of Philosophy) published in 1644.1
Descartes was the most prominent member of a community of corpuscularist thinkers, who maintained that visible objects were made of unobservably tiny particles, whose relations and arrangement were responsible for the properties of visible bodies. In this mechanical natural philosophy, particles influenced one another only by direct physical contact, which was the cause of all motion, and ultimately all change.6 One of the attractions of these ideas is that, unlike Aristotle's, they allowed for a movable planetary Earth, and celestial motions weren't different in kind from terrestrial motions. They explained gravity, in qualitative terms, as due to a swirling vortex of particles around the Earth, which pushed things towards its centre. In accord with Copernican heliocentrism, Descartes posited that a larger vortex surrounded the sun, with the smaller planetary vorticies caught in a larger solar vortex.76 In Newton's time, major champions of the mechanical natural philosophy included Christiaan Huygens (1629-1695) and Gottfried Wilhelm Leibniz (1646-1716), who was to become a major rival of Newton's.
For Descartes, the ultimate justification of knowledge claims lie with human reason and the absence of doubt. He relied on classical methods of theorizing and conjectured hypotheses in order to construct scientific propositions.1 Such a rationalist approach to knowledge was also championed by Baruch Spinoza (1632-1677), Nicolas Malebranche (1638-1715), and Leibniz.8 But, by the early 17th century, experimental researchers like Galileo and Robert Boyle (1627-1691) had begun to elaborate and practice a very different approach to knowledge based on experimentation and extensive use of mathematics. Following the inductive methodology advocated by Francis Bacon(1561-1626), they maintained that theoretical principles emerged from experimental data by a process of inductive generalization. However, there were also dissenters like Newton's contemporary Christiaan Huygens, who believed that most experimental work involved formulating hypotheses about unobservable entities, which were tested by their observable consequences. This was an early form of hypothetico-deductivism.
Newton on Mathematics and Natural Philosophy
Newton's two most important works of natural philosophy were the Principia, published in 1687 9, which dealt with his theories of motion and universal gravitation, and Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions, and Colours of Light 10 which was published in 1704 and dealt with his theories of light and color. 11 Newton made mathematics much more central to the conduct of natural philosophy than Descartes, by producing a general mathematical theory of the motion of bodies. 1 He posited three mathematical laws of motion, together with a law of universal gravitation. Changes in the state of motion of objects were caused by forces acting on them. Quantities of force and amounts of matter were measurable. The laws specified the mathematical relationship between the acceleration experienced by an object, the quantity of matter composing it, and the magnitude of the forces acting on it. 4
In contrast with the Cartesian mechanical philosophy, in Newton’s physics, material objects were not required to be in direct contact in order to influence each other's motion. Forces could act at a distance. To explain both falling bodies on Earth and the motions of the moon and planets, Newton posited a gravitational force that acted as the inverse square of the distance between objects. He claimed to have derived this relationship from Kepler's observational laws of planetary motion. The works of Ptolemy, Copernicus, and Kepler used the mathematical language of geometry in their descriptive accounts of celestial motions. In the Principia Newton likewise presented his arguments geometrically. Unlike his predecessors, Newton sought to do more than simply describe celestial motions. He sought to explain them in terms of gravitational forces acting between bodies. In order to do this, Newton invented a new branch of mathematics, integral and differential calculus. Calculus deals with mathematical quantities that are continuously changing, such as the magnitude and direction of gravitational forces acting on an orbiting body. 124 Newton developed the basic concept of calculus during 1665-6, while Cambridge University was closed due to a plague, but didn't publish it until the first decade of the eighteenth century. He is thus co-credited with inventing calculus with his contemporary and rival Gottfried Wilhelm Leibniz (1646-1716).13
Newton on Methodology
Prior to the publication of The Principia, the philosophy of motion and change in the universe was largely a theoretical and non-mathematical enterprise. The dominating methodological approach both in the Aristotelian-scholastic and Cartesian natural philosophy, was one in which truths about the natural world were proposed as conjectural hypotheses. Cartesian rationalismsought to deduce such hypotheses from fundamental metaphysical principles that were deemed evidently true by human reason. 18 Influenced by the more experimental and mathematically oriented methodologies of Bacon, Galileo, and Boyle, Newton drew a distinction between a conclusion drawn from observation or experimental evidence and one that was merely a speculative 'hypothesis'. He explicitly rejected the method of hypotheses, and instead demanded that all propositions be deduced from the observed phenomena and then converted into general principles via induction. 14115 In the second edition of the Principia, Newton states:
I have not as yet been able to deduce from phenomena the reason for these properties of gravity, and I do not feign hypotheses. For whatever is not deduced from the phenomena must be called a hypothesis; and hypotheses, whether metaphysical or physical, or based on occult qualities, or mechanical, have no place in experimental philosophy. In this experimental philosophy, propositions are deduced from the phenomena and are made general by induction. The impenetrability, mobility, and impetus of bodies and the laws of motion and law of gravity have been found by this method. And it is enough that gravity should really exist and should act according to the laws that we have set forth and should suffice for all the motions of the heavenly bodies and of our sea.16
The generality of Newton's rejection of hypotheses in natural philosophy is unclear since, in the Opticks he did discuss hypotheses about light, and did raise the possibility of an invisible aether responsible for gravitational attraction. 1 His epistemological beliefs were similar to those of his contemporary and friend, John Locke (1632-1704) who maintained that all knowledge came from experience. 17 Newton called his methodology the experimental philosophy, because theories about the behavior of empirical objects can only be refuted via experimental procedures.15 He expressed its core beliefs in a set of four “rules for the study of natural philosophy,” which he stated in book III of The Principia as follows:
- No more causes of natural things should be admitted than are both true and sufficient to explain their phenomena
- Therefore, the causes assigned to natural effects of the same kind must be, so far as possible, the same
- Those qualities of bodies that cannot be intended and remitted (i.e. qualities that cannot be increased and diminished) and that belong to all bodies on which experiments can be made should be taken as qualities of all bodies universally
- In experimental philosophy, propositions gathered from phenomena by induction should be considered either exactly or very nearly true notwithstanding any contrary hypothesis, until yet other phenomena make such propositions either more exact or liable to exceptions.16
Out of these four rules a new, engaged method for conducting science emerged that stood in stark contrast to the previous passive and theoretical Cartesian and Aristotelian-scholastic methods. Propositions formulated based on observations of the natural world and placed back into the natural world to be tested empirically.15 The calculus became deeply incorporated into the experimental method, as it was used to mathematically calculate empirical predictions from natural laws, and then evaluate how exactly the prediction matched the observed reality. Newton claimed to have derived his law of universal gravitation using this method as applied to Kepler's laws of planetary motion. In the Cartesian natural philosophy, centripetal force had already been defined as the agent that pulled the moon towards the Earth, keeping its orbit circular rather than linear. Newton appealed to rules 1) and 2) to claim that the centripetal force, and the force that compelled objects to move downwards towards the Earth, were merely two different expressions of the same thing. Newton then went on to apply the third rule, and argue that this force, which he called gravity, must be a universal property of all material objects. From here, he went on to argue for the unification of superlunary and sublunary phenomena, which Aristotle had deemed to be distinct realms.18
Newton's theories provoked immediate and wide interest in Britain, and became accepted there by the first decade of the eighteenth century. 45 In continental Europe, acceptance came more slowly. To proponents of the mechanical philosophy, it was methodologically necessary that all motion be given a cause involving direct physical contact of bodies. Many of Newton's continental contemporaries, in particular Leibniz and Huygens, strongly objected to the idea that forces could act at a distance. Leibniz regarded the theory of gravitation as a regression in natural philosophy and accused Newton of treating gravity as an 'occult quality' beyond philosophical understanding. After an intense debate, Newtonian gravitation theory became accepted through much of continental Europe by the middle of the eighteenth century. 1 51920
More than two centuries after Newton published the Principia, a new theory of motion and gravitation was formulated by Albert Einstein (1879-1955), who was inspired by new developments in non-Euclidean geometry and by problems with James Clerk Maxwell's (1831-1879) theory of electromagnetic radiation. The new theory replaced Newton's theory as the accepted theory of motion and gravitation by about 1920. Einstein's General Theory of Relativity explained the success of its predecessor by showing that its equations reduce to those of Newton in the limit of weak gravitational fields and velocities that are an insignificant fraction of that of light. Einstein's theory eliminated the problem of action at a distance by postulating that the mass of an object warps space-time, and that the local manifestation of this curvature influences distant bodies. 521
Newton's experimental philosophy shaped accepted claims about scientific methodology, influencing the methodological pronouncements of George Berkeley (1685-1753), David Hume, Thomas Reid (1710-1796), and Immanuel Kant (1724-1804). 14 However, according to McMullin, Newton's methodology ran contrary to the consensus that had been emerging among natural philosophers of his time, in favor of what we now recognize as the hypothetico-deductive method. 14 Historical research shows that the scientific community did not use Newton's own criteria in evaluating his work. His theories did not become accepted outside of England until after their prediction of the oblate spheroid shape of the Earth was confirmed by expeditions to Lapland and Peru. Newton's own theories became accepted based on confirmed novel predictions that distinguished them from the rival theory of Cartesian vortices, rather than by Newton's own inductive methodology. Further, Newton's theory, in fact, posited unobservable hypothetical entities, including gravitational attraction, absolute space, and absolute time.52214
By the mid-eighteenth century natural philosophers were beginning to realize that many successful theories violated the strictures of Newton's inductive experimental philosophy. The eighteenth century saw the acceptance of a variety of theories that posited unobservable entities, including Benjamin Franklin's (1706-1790) theory of electricity, which posited the existence of an unobservable electric fluid, the phlogiston theory of combustion and rust, which likewise posited an unobservable substance, and Augustin-Jean Fresnel's (1788-1827) wave theory of light which posited an unobservable fluid ether as the medium of light, and Herman Boerhaave's (1668-1738) vibratory theory of heat. 235 The methodologists of the early nineteenth century, William Whewell (1794-1866) and John Hershel (1792-1871) recognized that the actual practice of science did not conform to the prescribed Newtonian methodology and openly advocated the hypothetico-deductive method. 23
Here are the works of Newton included in the bibliographic records of this encyclopedia:
- Newton (1687): Newton, Isaac. (1687) Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). Pepys, London.
- Newton (1704): Newton, Isaac. (1704) Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions and Colours of Light. Prince's Arms in St. Paul's Churchyard. Retrieved from https://archive.org/details/opticksortreatis00newt.
- Newton (1952): Newton, Isaac. (1952) Opticks or A Treatise of the Reflections, Refractions, Inflections & Colors of Light. Dover Publications.
- Newton (1999): Newton, Isaac. (1999) The Principia: Mathematical Principles of Natural Philosophy. University of California Press.
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Citation keys normally include author names followed by the publication year in brackets. E.g. Aristotle (1984), Einstein, Podolsky, Rosen (1935), Musgrave and Pigden (2016), Kuhn (1970a), Lakatos and Musgrave (Eds.) (1970). If a record with that citation key already exists, you will be sent to a form to edit that page.
- Janiak, Andrew. (2016) Newton's Philosophy. In Zalta (Ed.) (2016). Retrieved from https://plato.stanford.edu/entries/newton-philosophy/.
- Westfall, Richard. (1980) Never at Rest: A Biography of Issac Newton. Cambridge University Press.
- Christianson, Gale. (1984) In the Presence of the Creator: Isaac Newton and his Times. The Free Press, Macmillan Inc..
- Smith, George. (2009) Newton's Philosophiae Naturalis Principia Mathmatica. In Zalta (Ed.) (2016). Retrieved from http://plato.stanford.edu/archives/spr2009/entries/newton-principia/.
- Barseghyan, Hakob. (2015) The Laws of Scientific Change. Springer.
- Disalle, Robert. (2004) Newton’s Philosophical Analysis of Space and Time. In Cohen and Smith (Eds.) (2002), 33-56.
- Garber, Daniel. (1992) Descartes' Physics. In Cottingham (Ed.) (1992), 286-334.
- Lennon, Thomas and Dea, Shannon. (2014) Continental Rationalism. In Zalta (Ed.) (2016). Retrieved from http://plato.stanford.edu/archives/spr2014/entries/continental-rationalism/.
- Newton, Isaac. (1687) Philosophiae Naturalis Principia Mathematica (Mathematical Principles of Natural Philosophy). Pepys, London.
- Newton, Isaac. (1704) Opticks: or, A Treatise of the Reflexions, Refractions, Inflexions and Colours of Light. Prince's Arms in St. Paul's Churchyard. Retrieved from https://archive.org/details/opticksortreatis00newt.
- Westfall, Richard. (1999) Sir Isaac Newton. In Encyclopedia Britannica (2016). Retrieved from https://www.britannica.com/biography/Isaac-Newton.
- Friedman, Michael. (2002) Kant, Kuhn and the Rationality of Science. Philosophy of Science 69 (2), 171-190.
- Cohen, Bernard I. and Smith, George. (Eds.). (2002) The Cambridge Companion to Newton. Cambridge University Press.
- McMullin, Ernan. (2001) The Impact of Newton's Principia on the Philosophy of Science. Philosophy of Science 68 (3), 279-310.
- Smith, George. (2002) The Methodology of the Principia. In Cohen and Smith (Eds.) (2002), 138-173.
- Newton, Isaac. (1999) The Principia: Mathematical Principles of Natural Philosophy. University of California Press.
- Rogers, John. (1982) The System of Locke and Newton. In Bechler (1982), 215-238.
- Harper, William. (2002) Newton’s Argument for Universal Gravitation. In Cohen and Smith (Eds.) (2002), 174-201.
- Aiton, Eric J. (1958) The Vortex Theory of Planetary Motion. Annals of Science 14, 157-172.
- Frangsmyr, Tore. (1974) Swedish Science in the Eighteenth Century. History of Science 7, 29-42.
- Isaacson, Walter. (2005) Einstein: His Life and Universe. Simon and Schuster.
- Terrall, Mary. (1992) Representing the Earth's Shape: The Polemics Surrounding Maupertuis's Expedition to Lapland. Isis 83 (2), 218-237.
- Laudan, Larry. (1984) Science and Values. University of California Press.