A philosophical study of the nature of knowledge, its types, and its conditions, which are belief, truthfulness, and justification. It discusses the most prominent theories presented by contemporary philosophers in analyzing these conditions. It answers questions related to understanding, interpretation, and scientific knowledge. It delves into the most important branches of contemporary epistemology, such as natural epistemology and social epistemology. In addition, the author addresses the concepts of knowledge through linguistic and logical analysis. He advocates a view of philosophy as conceptual clarification as well as naturalism. He presents an epistemological doctrine that he calls moderate naturalism, which comes within the framework of a moderate form of scientific tendency.