Descartes is well known as the Father of modern European or Western Philosophy. He was born in France. His three discourses, which contain the Discourse on Method, published in 1637 are considered as the first great philosophical work to be written in French. In 1641, he published his Meditations. Descartes was not only a philosopher but also a natural scientist who was interested in physics and physiology. Above all he was a great mathematician. He treated mathematics as an instrument of science. This thought profoundly influenced Descartesâ€™ philosophical thinking. He thought that mathematics gave a paradigm or model of certain knowledge and of the method of attaining such knowledge. What is the reason of certainty in mathematical knowledge? Mathematical knowledge is based on self-evident axioms, or first principles. They are clearly and distinctly pursued as self-evident truths. In other words, they are indubitable. That is to say that it is hard to doubt them. They are intrinsically valid or self-certifying. Once we have such self-evident first principle or truths, then with the rules of reasoning or logic, theorems can be validly deduced from them. If axioms are characterised by certainty, then the theorems validly deduced from axioms are also characterised by certainty. Descartes wanted to apply this method to philosophy. In mathematics, there is no appeal to the sense-experiences or the reports of sense-experiences. Human reasoning is the sole source of mathematical knowledge. In this sense, Descartes claimed that by pure reasoning, we can achieve knowledge. Rationalism thus is a philosophical theory which claims that reason, and not empirical experiences, are the source of human knowledge. Rationalism is therefore opposed to Empiricism, which believes sense experience is a necessary basis to all human knowledge. Descartes accepted mathematics as the model of his philosophical method and tried to construct a system of thought which would possess…