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 the "I" from the thinking thing. Here, the "cogito" has already assumed the "I"'s existence as that which thinks. For Kierkegaard, Descartes is merely "developing the content of a concept", namely that the "I", which already exists, thinks. As Kierkegaard argues, the proper logical flow of argument is that existence is already assumed or presupposed in order for thinking to occur, not that existence is concluded from that thinking. Bernard Williams claims that what we are dealing with when we talk of thought, or when we say "I am thinking," is something conceivable from a third-person perspective; namely objective "thought-events"