Prolegomenon to the articles on "Esse" following this advertance by John Paul II.
"To clarify the problem better, it is necessary to go back to the period before the Enlightenment and, specifically, to the revolution that presupposed the thought of Descartes in philosophy. The "cogito, ergo sum" - I think, therefore I am - involved an inversion in the way of doing philosophy. In the pre-Cartesian period, philosophy, and therefore the "cogito", or better "I know," was subordinated to "esse," which was considered primordial. For Descartes, on the other hand, "esse" appeared secondary to him, while he considered the "cogito" primary. In this way, not only was there a change in the direction in the way of doing philosophy, but also there was a decisive abandonment of what philosophy had been up to that moment, and particularly, for St. Thomas Aquinas: the philosophy of "esse." He (St. Thomas) interpreted everything from the prism of "esse" and from this perspective, he sought an explanation of everything. God, as fully self-sufficient Being ("Ens subsistens), was considered the indispensable foundation of every "ens non subsistens, ens participatum," of all created beings, and therefore, also man. The "cogito, ergo sum" produced the rupture with this way of thinking. The primordial point now was the "ens cogitans." So that, from Descartes on, philosophy converted into the science of pure thought: everything that had been "esse" - the created world as well as the Creator - was assumed into the world of thought - the "cogito" - as the content of human consciousness. Philosophy was concerned about beings in the measure that they are contained in conscience and not in so far as they exist outside of it" (My translation from the Spanish edition: "Memoria and Identity" 21-22).