In 18th- and 19th-century German philosophy, a Zeitgeist (ˈtsaɪtɡaɪst) ("spirit of the age") is an invisible agent, force, or daemon dominating the characteristics of a given epoch in world history. The term is usually associated with Georg W. F. Hegel, contrasting with Hegel's use of Volksgeist "national spirit" and Weltgeist "world-spirit". Its coinage and popularization precedes Hegel, and is mostly due to Herder and Goethe. Other philosophers who were associated with such concepts include Spencer and Voltaire. Contemporary use of the term sometimes, more colloquially, refers to a schema of fashions or fads that prescribes what is considered to be acceptable or tasteful for an era: e.g., in the field of architecture. Hegel in Phenomenology of the Spirit (1807) uses both Weltgeist and Volksgeist, but prefers the phrase Geist der Zeiten "spirit of the times" over the compound Zeitgeist. The Hegelian concept is in contrast to the Great Man theory propounded by Thomas Carlyle, which sees history as the result of the actions of heroes and geniuses. Contradistinct Hegel perceived such "great men", specifically Napoleon, as the "embodiment of the world-spirit" (Die Weltseele zu Pferde "the world-soul on horseback"). Carlyle stresses that leaders do not become leaders by fate or accident. Instead, these individuals possess characteristics of great leaders and these characteristics allow them to obtain positions of power. According to Hegel biographer D. R. Forsyth, Leo Tolstoy disagreed with Carlyle's perspective, instead believing that leadership, like other things, was a product of the "zeitgeist", the social circumstances at the time. Great Man theory and zeitgeist theory may be included in two main areas of thought in psychology. For instance, Great Man theory is very similar to the trait approach. Trait researchers are interested in identifying the various personality traits that underline human behaviors such as conformity, leadership, or other social behaviors.