Most definitions of philosophy are contentious, due to the nature of the study having changed so dramatically in scope over the ages. Famous philosophers often quote philosophy as being "thinking about thinking". This is a useful metaphor, as, reflective thought about specific kinds of thinking - belief policy, claims to knowledge - are part of it.

A more detailed definition is philosophy as 'systematic rationally critical thinking' of the nature of reality (Metaphysics), the theory of knowledge and how we achieve it (Epistemology) and how one 'ought' to conduct oneself (Ethics).

Western philosophy refers to ideas in the Occidental world - the two main traditions of which are Analytic and Continental - as opposed to Oriental/Eastern philosophy.