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 the first part of the first book of his Academics, Cicero introduced the division of philosophy into logic, physics, and ethics. He was copying Epicurus' division of his doctrine into canon, physics, and ethics. In section thirteen of the first book of his Lives and Opinions of the Eminent Philosophers, the 3rd-century Diogenes Laërtius, the first historian of philosophy, established the traditional division of philosophical inquiry into three parts:
- Natural philosophy ("physics," from ta physika, "things having to do with nature (physis)" was the study of the constitution and processes of transformation in the physical world;
- Moral philosophy ("ethics," from êthika, literally, "having to do with character, disposition, manners") was the study of goodness, right and wrong, justice and virtue.
- Metaphysical philosophy ("logic") was the study of existence, causation, God, logic, forms and other abstract objects ("meta ta physika" lit: "After [the book] the Physics").
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.