The FIRST TRUTH,  : "Ac proinde hæc cognitio, ego cogito, ergo sum, est omnium prima & certissima, quæ cuilibet ordine philosophanti occurrat." (English: "This proposition, I think, therefore I am, is the first and the most certain which presents itself to whoever conducts his thoughts in order)  Principles of Philosophy (1644), Part 1, article 7:  


René Descartes.