Philosophy is a field of study that includes diverse subfields such as aesthetics, epistemology, ethics, logic, and metaphysics, in which people ask questions such as whether God exists, what is the nature of reality, whether knowledge is possible, and what makes actions right or wrong. The fundamental method of philosophy is the use of reasoning to evaluate arguments concerning these questions. However, the exact scope and methodology of philosophy is not rigid. What counts as philosophy is itself debated, and it varies across philosophical traditions.

The term philosophy comes from the Greek word "Φιλοσοφία" (philo-sophia), which means "love of wisdom" or less commonly "friend of wisdom". Many ancient Greek philosophers made the distinction between the desire for wisdom, as opposed to the desire for material things, vices, and the satisfaction of bodily desires. The definition of wisdom for many ancient Greeks would have been about virtue and the desire for knowledge and not false opinions. However, the term is notoriously difficult to define today (see definition of philosophy) because of the diverse range of ideas that have been labeled as 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.