Epistemology (ἐπιστήμη, episteme = science: the knowledge of, understanding - and λόγος, logos = the logical study of) is the branch of philosophy concerned with the nature, scope and the application of scientific knowledge (specific/natural sciences and social studies). Generally speaking, epistemology is also referred to as the 'theory of knowledge'. It questions what knowledge is and how it can be acquired and/or applied. To this extent, knowledge is pertinent to any given subject or entity. Much of the debate in this field has focused on the philosophical analysis of the nature of knowledge and how it relates to connected notions such as truth, belief, and justification. It has also been established that this theory of the method and the grounds of knowledge, is that branch of metaphysics which deals with the nature and validity of knowledge. 1.2 PHILOSOPHYThe subject of philosophy is for the use of reason and argument in the search for truth and the nature of reality, especially of the causes and nature of things and of the principles governing existence, perception, human behaviour, and the material universe.Philosophical activities can also be directed at understanding and clarifying the concepts, methods, and doctrines of other disciplines, or at reasoning itself and the concepts, methods, and doctrines of such general notions as truth, possibility, knowledge (epistemology), necessity, existence (ontology and metaphysics), and proof. Philosophy has many different areas, classified according to the subject-matter of the problems being addressed; thus, philosophy of mind is concerned with questions such as: 'How do the mental interact with the physical?'Philosophy of mathematics with questions such as 'what constitutes a proof?'Of religion ('does God exist?')Of science ('what constitutes good evidence for a hypothesis?')Of ethics; of politics; and indeed of any other discipline. The first philosophers were also the first scientists, people who asked questions about the physical world and who attempted to answer them by observation and reasoning rather than by appealing to magic or to a God of some kind. These people, known as the pre-Socratics, were the precursors of Socrates, Plato, and Aristotle, the three great philosophers who set the agenda for many of the philosophical questions debated today. Philosophy regularly gives birth to new disciplines as one group of the questions it is trying to answer become amenable to study by the physical sciences. Psychology, for example, is a discipline that is still in the process of separating itself from philosophy. Great advances in scientific thinking have usually been accompanied by great advances in philosophical thinking. For example, Galileo's work on the mechanics of planetary motion in the late 16th century was a motivating force in Descartes' work on knowledge and justification, while the physicist Albert Einstein (1879-1955) paid tribute to Hume as one of the philosophers whose work inspired his theory of relativity.In the 20th century, the principal schools of philosophy are continental philosophy and logico-analytic philosophy. Within these principal schools, however, there are major divisions according to sides taken in the various great disputes of philosophy. For example, until fairly recently it was a matter of great concern whether someone was a dualist or a monist--whether they believed that there are two different sorts of substance (the physical and the mental), or only one sort--either the physical (materialism) or the mental.There are also major disputes about whether or not there are such things as 'innate ideas', concepts that are inborn rather than acquired through experience, and whether we can make sense of a world that is independent of us and our minds (realism) or whether the mind is in fact more fundamental than some extra-mental reality (idealism)