Philosophy is a study that includes various diverse subfields such as aesthetics, epistemology, ethics, logic, and metaphysics. Various philosophical traditions use different methods and include different topics in their study. Some, for example, include politics, physics, or religion. The fundamental method of philosophy involves the systematic use of critical reasoning to evaluate arguments in defence of assertions of belief or opinion.

The term philosophy comes from the Greek word "Φιλοσοφία" (philo-sophia), which means "love of wisdom". The term is notoriously difficult to define (see definition of philosophy) because of the diverse range of ideas that have been labeled as a philosophy. The Penguin Dictionary of Philosophy defines it as the study of "the most fundamental and general concepts and principles involved in thought, action, and reality". The Penguin Encyclopedia says that philosophy differs from science in that philosophy's questions cannot be answered empirically, and from religion in that philosophy allows no place for faith or revelation. However, these points are called into question by the Oxford Dictionary of Philosophy, which states: "the late 20th-century... prefers to see philosophical reflection as continuous with the best practice of any field of intellectual enquiry." Indeed, many of the speculations of early philosophers in the field of natural philosophy eventually formed the basis for modern scientific explanations on a variety of subjects.
Informally, a "philosophy" may refer to a general world view or to a specific ethic or belief.