First principle foundationalist system of philosophy. He used the "method of doubt", now called Cartesian doubt, to systematically doubt everything he could possibly doubt, until he was left with what he saw as purely indubitable truths. Using these self-evident propositions as his axioms, or foundations, he went on to deduce his entire body of knowledge from them. The foundations are also called "a priori" truths. His most famous proposition is "Je pense, donc je suis." ("I think, therefore I am", or "Cogito ergo sum") Descartes describes the concept of a first principle in the following excerpt from the preface to the "Principles
Mr. Cogito Cogito and Pure Thought"), "Pan Cogito czyta gazetę" ("Mr. Cogito Reads A Newspaper"), "Pan Cogito a ruch myśli" (" Mr. Cogito and the Motion of Thought"), "Domy przedmieścia" ("Houses On The Outskirts Of The City"), "Alienacje Pana Cogito" ("Mr. Cogito's Alienations"), "Pan Cogito obserwuje zmarłego przyjaciela" ("Mr. Cogito Watches a Deceased Friend"), "Późnojesienny wiersz Pana Cogito przeznaczony dla kobiecych pism" ("Mr. Cogito's Late Autumn Poem For Women's Magazines"), "Pan Cogito rozważa różnice między głosem ludzkim a głosem przyrody" ("Mr. Cogito Considers the Difference Between the Human Voice And The Voice of Nature"), "Pan Cogito biada nad małością snów" (Mr. Cogito