Volume 4 of the complete edition contains essays, speeches, prefaces, and letters on science and philosophy. This collection of texts documents Valéry's engagement with philosophers and theorists such as Descartes and Pascal, whose ideas were foundational to his thinking. Furthermore, Valéry's writings present his own philosophical approaches. As in his prose works, these observations are characterized by the attempt to reconstruct the process of sensory perception and to subject understanding and creative processes to rational scrutiny. They reveal an intertwining of individual (natural) scientific disciplines with the world of literature and with questions of aesthetics.