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|Summary='''Sir Isaac Newton''' (1642-1727) was a natural philosopher who lived and worked in England in the 17th and 18th century. 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.[[CiteRef::Janiak (2016)]] 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[[Newton (1687)|The Principia]] (''Philosophiæ Naturalis Principia Mathematica''), whose principles became central to be the foundation for the dominant Newtonian mosaic which influenced much of late 18th and 19th century science.[[CiteRef::Janiak (2016)]] 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.[[CiteRef::Janiak (2016)]]
|Historical Context=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 his 1543 ''De revolutionibus orbium coelestium'' (''On the Revolutions of Heavenly Spheres''). It had been fifty years since Galileo Galilei (1564-1642) had published his observations with the telescope in 1610. Galileo had discovered dramatic evidence favoring the Copernican system. His discovery of the phases of the planet Venus indicated that it revolved around the sun and was lit by reflected sunlight. His description of four moons circling Jupiter indicated that Earth, with its own moon, resembled this planet. His studies of sunspots indicated that the sun revolved on its axis, and finally, his discovery of surface features on the moon indicated that the moon was another world, as expected under the Copernican system, but not by Aristotelianism. Around 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 Ptolemy.[[CiteRef::Westfall (1980)|pp. 1-7]] 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".[[CiteRef::Westfall (1980)|p. 6]] A planetary Earth that rotated on its axis and revolved around the sun was incompatible with the accepted Aristotelian physics. 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 can gain reliable knowledge given the evident failure of Aristotelian scholastic knowledge accepted for centuries.
# 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.[[CiteRef::Newton (1999)|pp. 794-796]]</blockquote>
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 are born from natural sources and placed back into the natural world to be tested empirically.[[CiteRef::Smith (2002)]] As the four rules were absorbed into the ensuing mosaic, the calculus became deeply incorporated in 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, the 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.[[CiteRef::Harper (2002)|pp. 183-184]]
