Age of Enlightenment Louis XV until the French Revolution. If taken back to the mid-17th century, the Enlightenment would trace its origins to Descartes' "Discourse on the Method", published in 1637. In France, many cited the publication of Isaac Newton's "Principia Mathematica" in 1687. It is argued by several historians and philosophers that the beginning of the Enlightenment is when Descartes shifted the epistemological basis from external authority to internal certainty by his "cogito ergo sum" published in 1637. As to its end, most scholars use the last years of the century, often choosing the French Revolution of 1789 or the beginning of
Cogito, ergo sum "Meditations", Descartes phrases the conclusion of the argument as "that the proposition, "I am, I exist," is necessarily true whenever it is put forward by me or conceived in my mind." ("Meditation" II) At the beginning of the second meditation, having reached what he considers to be the ultimate level of doubt—his argument from the existence of a deceiving god—Descartes examines his beliefs to see if any have survived the doubt. In his belief in his own existence, he finds that it is impossible to doubt that he exists. Even if there were a deceiving god (or an evil demon),