The modern leading rationalist is René Descartes. He was the founder of modern rationalism. He was born in a noble family. He was a brilliant person since his childhood. His father called the little Descartes as a philosopher. In his early days he served in the arm-force. Descartes was a rationalist. He attempted to understand the world through rational thinking. There was not much place for rational thinking in the medieval period before Descartes.

• He was the first person who identified “rationalism”. He invented/developed this kind of philosophy. He did not face many problems, unlike the other people who tried to refute or proof the ideas.
  
  

Because medieval thinking was based on the concept of God, faith and devotion that were considered as the path reaching the God. Medieval philosophers argued that the existence of God cannot be understood through rational thinking.

Descartes held the view that the truth can be understood only by rational thinking. Therefore, he was doubtful about everything that would come without a rational basis. For him, the first rule was to accept nothing as truth what he would not recognize clearly as a truth, to accept nothing more than what was presented to his mind clearly and so he would not have occasion to doubt. The second rule was to divide each problem or difficulty into as many parts as possible, analyzing a problem to have a clear understanding. The third rule was to commence one's own reflection with objects that are as simple and as easy as possible to understand the particular problem ; rise them little by little to knowledge, up to the most complex knowledge. The fourth rule was to make observations so complete and general and one should be certain that one has omitted nothing. This includes the influence of mathematical knowledge of Descartes in his philosophical thinking.

• Sometimes if there is a problem, it may be understood better after being divided into several parts.
  
• “Discourse of methods” - using mathematical knowledge of Descates he tried to understand the philosophical problems. Thus he realized, that by dividing a problem into several smaller problems one can solve it easier.
  
  

Descates' view was, that there is nothing real in the external world. Descates doubted/suspected his own experience. He thought that everything man experiences might not be real. Descates determined to doubt everything until the doubt becomes impossible to be pushed. Descartes said:

“Everything I saw was false. There is nothing in the world that would be certain/permanent. ”

To explain this, he further brings the argument of wax. It has its own characteristics. It has a shape. If we take a flame near to the wax, it starts to melt. Then all characteristics that it had before, disappeared. After the piece of wax is fully melted, how can one say that it is the piece of wax that one has seen before, in order to grasp the nature of wax. One cannot use their senses, but one must use their mind.

Dualism in the philosophy of Descates

• Dualism means body and mind.
  
  

According to Descartes, body works like a machine. It is out of a certain material, it extends and moves. This follows the law of physics. On the other hand, the mind is described as a momentary entity. Descartes argued, that only human beings have mind and the mind interacts with the body. This is a form of Buddhism, that the mind controls the body or otherwise body controls the mind. The question is who makes the combination. According to Descartes, it is the God.