Historically, "philosophy" encompassed any body of knowledge. From the time of Ancient Greek philosopher Aristotle to the 19th century, "natural philosophy" encompassed astronomy, medicine, and physics. For example, Newton's 1687 Mathematical Principles of Natural Philosophy later became classified as a book of physics. In the 19th century, the growth of modern research universities led academic philosophy and other disciplines to professionalize and specialize. In the modern era, some investigations that were traditionally part of philosophy became separate academic disciplines, including psychology, sociology, linguistics, and economics.
Other investigations closely related to art, science, politics, or other pursuits remained part of philosophy. For example, is beauty objective or subjective? Are there many scientific methods or just one? Is political utopia a hopeful dream or hopeless fantasy? Major sub-fields of academic philosophy include metaphysics ("concerned with the fundamental nature of reality and being"), epistemology (about the "nature and grounds of knowledge ...its limits and validity" ), ethics, aesthetics, political philosophy, logic, philosophy of science, and the history of Western philosophy.
Since the 20th century, professional philosophers contribute to society primarily as professors. However, many of those who study philosophy in undergraduate or graduate programs contribute in the fields of law, journalism, politics, religion, science, business and various art and entertainment activities.
Traditionally, the term "philosophy" referred to any body of knowledge. In this sense, philosophy is closely related to religion, mathematics, natural science, education and politics. Newton's 1687 "Mathematical Principles of Natural Philosophy" is classified in the 2000s as a book of physics; he used the term "natural philosophy" because it used to encompass disciplines that later became associated with sciences such as astronomy, medicine and physics.
In Classical antiquity, Philosophy was traditionally divided into three major branches:
This division is not obsolete but has changed. Natural philosophy has split into the various natural sciences, especially astronomy, physics, chemistry, biology, and cosmology. Moral philosophy has birthed the social sciences, but still includes value theory (including aesthetics, ethics, political philosophy, etc.). Metaphysical philosophy has birthed formal sciences such as logic, mathematics and philosophy of science, but still includes epistemology, cosmology and others.
Many philosophical debates that began in ancient times are still debated today. Colin McGinn and others claim that no philosophical progress has occurred during that interval. Chalmers and others, by contrast, see progress in philosophy similar to that in science, while Talbot Brewer argued that "progress" is the wrong standard by which to judge philosophical activity.