Rene Descartes 
Discourse on Method and Meditations 

Is it possible to be certain of anything? If so, how? The father of modern philosophy and the founder of rational method in philosophical thought, René Descartes (1596–1650) sought the answers to these questions and in doing so, addressed the most important of methods of thinking and understanding truth. In Discourse on Method, he applies a scientific approach to philosophy that comprises four principles: to accept only what reason recognizes as "clear and distinct"; to analyze complex ideas by dividing them into smaller elements; to reconstruct the ideas; and to make accurate and complete enumerations of the data. His Meditations proceed according to this method, exploring the mind/body distinction, the nature of truth and error, the existence of God, and the essence of material things.