Epistemology briefly means the study of origins that helps us to understand the nature of our knowledge. It comes from Greek words episteme (knowing, knowledge) and logy (study, science). Epistemology deals with the nature, the source and the reliability of knowledge. Epistemology tries to separate true knowledge from false one by analyzing their grounds. The history of epistemology starts in ancient Greek with Socrates, Plato, Aristotle and nearly all philosophers in history made some contributions to this branch of science. We can simplify epistemology by defining it “how do we know what to know”. There are two major views conflicting according to epistemological thinking: empiricism and rationalism. Empiricists such as John Locke and Francis Bacon claim that the all knowledge comes from observation and experiment and they believe in Tabula Rasa. Tabula Rasa means that the human mind is passive from the birth and there should be an authority to teach people in order to save them from conventional thinking and replace it by scientific knowledge. Empiricism only deals with hard sciences, not social ones. Contrary to empirical idea, rationalists believe that human mind is active starting from the birth and the source of knowledge is reason. According to rationalist view defended by philosopher like Rene Descartes, Baruch Spinoza, and Gottfried von Leibniz all questions can be answered by human reasoning in other words by using our minds. Later German philosopher Immanuel Kant tried to solve this conflict by combining two major views. While epistemology is looking for the grounds and the nature of knowledge, ontology deals with beings and existences. For instance the ontology of social sciences is the society. Ontology is briefly the study, science of beings. Ontology refers to the subject of the study whereas epistemology refers to the nature of the subject to be studied.