1 Empiricism vs. Rationalism: on the context of Several Renowned Philosophers of Mediaeval Europe Dr. Debashri Banerjee Abstract: In the medieval Europe there arises a significant controversy regarding the source of the attainment of the object of knowledge. From there took birth two different philosophical theories, namely existentialism and rationalism. Now let me state about them in details. Rationalists convey that the object of knowledge has to be dependent only upon the reasoning power. They never admit the external existence of substance as the object of knowledge. Thus their thesis never considered as realism, rather as idealism. They are ardent believer of the internal existence of substance. According to them, substance never exists in reality, but only inside the human mind. The substance, as viewed by them, is the object of our mental states. Without the use of reasoning power of human beings the existence of substance cannot be touched at all. Existentialism is another important philosophical doctrine of medieval Europe. Existentialists claimed that the object of knowledge is dependent solely upon existence. They admitted only the external existence of substance as the object of knowledge. Their theory is considered as idealism; instead of realism. They are ardent believers of the external existence of the substance. According to the existentialists, substance must exist in reality. It cannot exist in human mind. As they said that if the object of knowledge, i.e. the substance, exists only in the internal world. Then we will never verify them. However the verification of the substance, as the object of knowledge, seemed mandatory to them. In this article I try to focus on the uniqueness of the theory of contemporary empiricists, like John Locke, Berkeley and Hume along with rationalists, like Descartes, Spinoza and Leibnitz in brief. Keyword: Empiricism, Rationalism, Medieval Europe, reasoning, experience, object of knowledge. Introduction: In the medieval Europe there arises a significant controversy regarding the source of the attainment of the object of knowledge. From there took birth two different philosophical theories, namely existentialism and rationalism. Their difference lies only in their perception of substance as the object of knowledge. For rationalists the object of knowledge is the human