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 whose presence is introduced by a poem entitled "Dusza Pana Cogito" (Mr. Cogito's Soul). It brings to our attention Mr Cogito's soul leading a life of its own. In contrast with the souls of the ancient world, it tends to leave him unexpectedly, wandering here and there, oblivious of the owner's well-being. The soul always returns, though, making it possible for Mr. Cogito to adore the world's beauty and diversity in the next poem – "Modlitwa Pana Cogito – podróżnika" ("A Prayer Of Mr. Cogito The Traveller"). This is followed by "Pan Cogito – powrót" ("Mr. Cogito – A Return"),