Rene Descartes has often been called the father of modern philosophy, and it is certainly true that his influence has pervaded western thought at least until the present century. The "Discourse" is the exposition of the famous "Method" by which this brilliant mathematician tried to apply mathematical methods to - and thus to discover mathematical certainties in - all fields of human inquiry. Starting from universal doubt he passes, via the celebrated phrase "cogito ergo sum" to the certainty of the existence of God and hence of the reality of created nature.