Philosophy is the oldest academic discipline, having given birth over two millennia to logic, ethics, physics, psychology, computer science, the last two in the last century alone. While philosophers themselves quarrel about the nature of the subject, this is because it is the discipline that must ask foundational questions concerning all forms of knowledge, including itself.
Philosophy has disparate branches; to name a few: ethics, political philosophy, logic, philosophy of language and of mind, epistemology, metaphysics, philosophy of the natural and social sciences, aesthetics. What seems to unite them is their concern with questions not normally answerable by science or empirical investigation alone; hence their reliance on abstract thought, and emphasis on conceptual and logical clarity.