A philosopher, in a broad sense, is someone who studies philosophy. The word “philosopher” comes from the Ancient Greek (philosophos), which means “lover of wisdom”. The introduction of the terms “philosopher” and “philosophy” has been ascribed to the Greek thinker Pythagoras. A philosopher, in the more narrow and common usage, is any intellectual who has made contributions in one or more current fields of philosophy, such as aesthetics, ethics, epistemology, logic, metaphysics, social theory, and political philosophy. A philosopher may also be one who worked in the humanities or other sciences which have since split from philosophy proper over the centuries, such as the arts, history, economics, sociology, psychology, linguistics, anthropology, theology, and politics. They may relate this knowledge to the discussion of philosophical problems. In the classical sense, a philosopher is someone who lives according to a way of life, whose focus is upon resolving existential questions about the human condition. Typically, these particular brands of philosophy are Hellenistic ones and those who most arduously commit themselves to this lifestyle may be considered a philosopher. An example of the expected standards of this definition is Marcus Aurelius, who is widely regarded as a philosopher in the modern sense, but personally refuses to call himself by such a title, since he had a duty to live as an emperor. In both definitions, philosophers address these questions through critical, systematic and reasoned approaches.