Critical examination of the rational grounds of our most fundamental beliefs and logical analysis of the basic concepts employed in the expression of such beliefs. Philosophy may also be defined as reflection on the varieties of human experience, or as the rational, methodical, and systematic consideration of the topics that are of greatest concern to humanity. Philosophical inquiry is a central element in the intellectual history of many civilizations. Difficulty in achieving a consensus about the definition of the discipline partly reflects the fact that philosophers have frequently come to it from different fields and have preferred to reflect on different areas of experience. All the world's great religions have produced significant allied philosophical schools.