Descartes published in 1637 the Discours de la méthode as a preface to three scientific essays. He formulates four rules of method: accept nothing as true that is not self-evident, divide each problem into parts as small as necessary, proceed from the simplest to the most complex, and make complete enumerations to omit nothing. The starting point is methodic doubt: suspending judgment on anything admitting the slightest doubt, until finding an indubitable truth on which to build knowledge. The cogito ergo sum — the first certainty to survive radical doubt — founds the thinking subject as the epistemological basis. The Cartesian method introduces analytic reductionism as a tool: breaking complex phenomena into simple elements, solving the simple elements, and recomposing them. This program structures Western scientific thought until the 20th century and is the methodological basis for Leibniz's calculus, Newton's mechanics, and the later formalization of logic by Boole and Frege.