Questions of existence, rationality, knowledge, values, mind, and language are just some of the topics systematically explored in philosophy. These inquiries are typically framed as issues that must be investigated or solved. Some say the term was first used by Pythagoras (570–495 BCE), while others say the Pythagoreans appropriated the term. The philosophical process involves inquiry, critique, argument, and presentation. In the past, philosophers were those who practiced a broad conception of philosophy that included all branches of study. Natural philosophy, as it was known from the time of the Greek philosopher Aristotle until the 19th century, included such diverse fields as astronomy, medicine, and physics. The rise of modern research universities in the 19th century prompted the professionalization and specialization of academic philosophy and other disciplines. Since then, many fields of study that were once part of philosophy—including the social sciences like psychology, sociology, linguistics, and economics—have split off to form their fields of study.

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