In the 18th century, the most important French scientists and philosophers, led by Diderot and d'Alambert, undertake the writing of an ambitious scientific and educational work, the Encyclopedia. D'Alambert takes on the task of writing the "Introductory Discourse" and formulating the guiding principles that govern the entire project. The result far exceeds the initial goals. We have in our hands the iconic text of the French Enlightenment, this philosophical and political movement that decisively influenced modernity.