Historism is a philosophical and historiographical theory, founded in 19th-century Germany (as Historismus) and especially influential in 19th- and 20th-century Europe. It pronounces the historicity of humanity and its binding to tradition.
Historist historiography rejects historical teleology and bases its explanations of historical phenomena on sympathy and understanding (see Hermeneutics) for the events, acting persons, and historical periods. The historist approach takes to its extreme limits the common observation that human institutions (language, Art, religion, law, State) are subject to perpetual change.
Historism is not to be confused with historicism, nevertheless the English habits of using both words are very similar. (The term historism is sometimes reserved to identify the specific current called Historismus in the tradition of German philosophy and historiography.)
Because of the power held on the social sciences by logical positivism, historism or historicism is deemed unpopular.
Karl Popper, one of the most distinguished critics of historicism, criticized historism, too. He differentiated between both phenomena as follows: The term historicism is used in his influential books The Poverty of Historicism and The Open Society and Its Enemies to describe “an approach to the social sciences which assumes that historical prediction is their primary aim, and which assumes that this aim is attainable by discovering the 'rhythms' or the 'patterns', the 'laws' or the 'trends' that underlie the evolution of history”. Popper wrote with reference to Hegel's theory of history, which he criticized extensively. By historism on the contrary, he means the tendency to regard every argument or idea as completely accounted for by its historical context, as opposed to assessing it by its merits. Historism does not aim for the 'laws' of history, but premises the individuality of each historical situation.