Philosophy involves the rational investigation of concepts and beliefs through logical argumentation. It examines the nature of reality, knowledge, and morality. There are several branches of philosophy including metaphysics, epistemology, and ethics. Philosophy can also refer to the specific doctrines of influential philosophers like Descartes or philosophical approaches within disciplines like law. A philosopher is someone who studies or teaches philosophy through investigating fundamental questions about human existence, knowledge, and morality using reason and intellectual inquiry.