section_path: Historiography/Time span
section_name: Time span
paragraph_text: Time span
  
  There is little consensus on the precise beginning of the Age of Enlightenment, though several historians and philosophers argue that it was marked by Descartes' 1637 philosophy of Cogito, ergo sum ("I think, therefore I am"), which shifted the epistemological basis from external authority to internal certainty. In France, many cited the publication of Newton's Principia Mathematica (1687), which built upon the work of earlier scientists and formulated the laws of motion and universal gravitation. French historians usually place the Siècle des Lumières ("Century of Enlightenments") between 1715 and 1789: from the beginning of the reign of Louis XV until the French Revolution. Most scholars use the last years of the century, often choosing the French Revolution or the beginning of the Napoleonic Wars (1804) as a convenient point in time with which to date the end of the Enlightenment.
  
  In recent years, scholars have expanded the time span and global perspective of the Enlightenment by examining: (1) how European intellectuals did not work alone and other people helped spread and adapt Enlightenment ideas, (2) how Enlightenment ideas were "a response to cross-border interaction and global integration," and (3) how the Enlightenment "continued throughout the nineteenth century and beyond." The Enlightenment "was not merely a history of diffusion " and "was the work of historical actors around the world... who invoked the term... for their own specific purposes."