Newtonianism

A standard definition of Newtonianism or Newtonian philosophy found in early eighteenth-century dictionaries such as John Harris's Lexicon Technicum (5th ed., 1736) is: "The doctrine of the universe, and particularly of the heavenly bodies; their laws, affections, etc., as delivered by Sir Isaac Newton." An almost identical definition appears around thirty years later in the Encyclopédie of Denis Diderot and Jean le Rond d'Alembert: "Newtonianisme ou philosophie Newtonienne: c'est la théorie du méchanisme de l'univers, & particulierement du mouvement des corps célestes, de leur lois, de leur propriétés, telle qu'elle a été enseignée par M. Newton" (Newtonianism or Newtonian philosophy: the theory of the mechanism of the universe, and particularly of the motion of the heavenly bodies, of their laws, their properties, as delivered by Mr. Newton).

The authority of Newtonian philosophy was established through the publication of the two major works of Sir Isaac Newton (1642–1727) in natural philosophy, The Principia (Philosophiae Naturalis Principia Mathematica, 1687) and the Opticks (Opticks; or, A Treatise of the Reflections, Refractions, Inflections & Colours of Light, 1704). The former was a work in rational mechanics where Newton aimed to study "the motion that results from any force whatever and of the forces that are required for any motion whatever." His major stake was to overcome the model of impact that dominated the mechanical philosophy of his time and to introduce the notion of attractive force as a proper dynamic factor of motion. Accordingly, he aimed to explain Kepler's laws through the use of universal attraction and to discard the Cartesian theory of vortices. The latter work was a study in the spirit of mechanical philosophy, where Newton investigated the phenomena of light. He introduced his experimental method and he elaborated the atomistic model of matter. In the successive editions of the work he enriched it with a number of "queries" where he developed his theoretical and metaphysical contemplations about the nature of matter, the various instances of attractive and repulsive force, and the theoretical grounding of experimental induction.

The publication of the Principia clearly marked the establishment of a new spirit in European natural philosophy. It is equally clear, though, that Newton's contemporaries differed significantly in the appreciation of his magnum opus. Followers like Edmond Halley (1656–1742) and Voltaire (1694–1778) were so excited by Newton's achievements that they placed him in the highest position of the philosophical firmament of the time. At the same time, however, Christiaan Huygens (1629–1695) was astonished by the fact that such an elaborate synthesis in mechanics was founded upon the notorious notion of universal attraction. Along a similar line, Gottfried Wilhelm Leibniz (1646–1716) accused Newton of turning the entire operation of Nature into a perpetual miracle. Having been nourished by the Cartesian rationalistic tradition, Huygens and Leibniz found that the adoption of attraction by natural philosophers would bring about a reversion to the "occult qualities" of Scholasticism.

Historians assume that the Principia is one of the least read documents in the history of ideas. Even in the early eighteenth century influential philosophers like John Locke (1632–1704) and Voltaire adopted its message without having read or understood its technical part. The reputation of the Principia was based primarily on the authority of very few competent readers. At the same time, quite a few nonmathematical philosophers made a systematic attempt to bring Newton's message to the general reader. To this purpose, they proceeded with the compilation of comprehensive treatises where they presented an outline of Newtonian mechanics and experimental philosophy.

The Opticks was a far more widely read work. A reason for this was its deceptive accessibility. The Opticks was not a revolutionary work in the sense the Principia was. It was rather a brilliant display of the art of experimentation, and it was often cited as a model of how to approach a difficult problem by experiment and how to conduct precise quantitative experiments. What was important in the Opticks from the point of view of the Newtonian synthesis was that Newton elaborated there the most comprehensive public statement he ever made of his experimental method:

As in Mathematics, so in Natural Philosophy, the Investigation of difficult Things by the Method of Analysis, ought ever to precede the Method of Composition [or Synthesis]. This Analysis consists in making Experiments and Observations, and in drawing general Conclusions from them by Induction, and admitting of no Objections against the conclusions, but such as are taken from Experiments, or other certain Truths. For Hypotheses are not to be regarded in experimental philosophy.… By this way of Analysis we may proceed from Compounds to Ingredients, and from Motions to the Forces producing them; and in general from Effects to their Causes, and from Particular Causes to more general ones, till the Argument end in the most general. (Optics, 1979, p. 404)

Newtonianism, however, is much more than the direct impact of Newton's two major works on European intellectual life. First of all, Newtonian philosophy was neither a given system nor a definitive synthesis in natural philosophy. It was rather a multifaceted current shaped by the interpretations of Newton's works and, to a significant degree, by the adaptations of these works to various intellectual environments all over the European continent. Moreover, throughout the eighteenth century "Newtonianism" meant much more than a physical theory. It was an amalgam of scientific, political, and religious ideas, which only partially went back to Newton's original works. It was quite common for people who endorsed Newtonian philosophy to have only a vague idea of his mathematical and experimental investigations. Nevertheless, Newton became something of an authority people drew upon in order to resolve matters concerning not only nature's interpretation but also the conduct of man, the function of the state, and the doctrines of religion. Thus, in what follows we will briefly examine the many aspects of Newtonianism in a variety of intellectual contexts that assigned an accordingly variable meaning to the term.

The author of the aforementioned article in the Encyclopédie was Jean Le Rond d'Alembert. Being one of the protagonists in the developments that took place in the field of Newtonian natural philosophy in the mid-eighteenth century, he was well aware of the inadequacy of a general definition of Newtonianism. Hence, after the short descriptive definition he gave in the opening of the article, he immediately proceeded with the delineation of a broad spectrum of notions and practices that contributed to the formation of this intellectual current. Some authors, he notes, perceive Newtonian philosophy as a version of "corpuscular philosophy," enriched and corrected by the discoveries of Newton. In this sense, Newtonian philosophy is nothing else than a new philosophy, distinct from the Cartesian, the peripatetic, and the other ancient philosophies of the body. Others perceive Newtonian philosophy as the method Newton employs in his philosophy. This method consists in deriving conclusions directly from the phenomena, without feigning hypotheses, in starting from simple principles, in deducing the primary laws of nature from a small number of selected phenomena, and in using these laws in order to explain all the other natural effects. In this sense, Newtonian philosophy is nothing else than "experimental physics," opposing to the ancient philosophy of the body. Others perceive Newtonian philosophy as the branch of philosophy that examines natural bodies mathematically and applies geometry and mechanics in the resolution of the respective problems. In this sense, Newtonian philosophy is nothing else than "mechanical and mathematical philosophy." It is clear, thus, that for d'Alembert and his contemporaries, even in the narrow field of natural philosophy Newtonianism means at least three different things: a new philosophy of body, experimental philosophy, and rational mechanics. In fact, all these philosophical and mathematical traditions have a bearing on Newton's own work and mark the distinctive research and philosophical directions that stem from the various pieces of the Newtonian synthesis.