Cosmogony is the theory of the origin and development of the universe. In ancient Greek philosophy, such theories usually combined scientific with theological and metaphysical speculation. For example, Plato expounds a cosmogony in his Timaeus.

Empiricism is the philosophy that all knowledge derives from experience, particularly sense experience. Empiricism was particularly popular in Britain, where it was the dominant philosophy in the 17th and 18th centuries. Russell contrasts it with idealism (see entry below).

Idealism refers to the philosophical theory that something nonmaterial (such as mind or spirit) is the ultimate basis of reality, or that the object of external perception consists of ideas. Russell characterizes idealism as the dominant philosophy in Germany during the modern period and as, to a certain extent, opposed to empiricism. He considers empiricism and idealism as the two major strands of philosophy influencing modern thought.