Karl Marx expressed the Entfremdung theory, of estrangement from the self, in the Economic and Philosophic Manuscripts of 1844 (1927). Philosophically, the theory of Entfremdung relies upon The Essence of Christianity (1841), by Ludwig Feuerbach, which states that the idea of a supernatural god has alienated the natural characteristics of the human being. Moreover, in The Ego and its Own (1845), Max Stirner extended Feuerbach's analysis that even the idea of "humanity" is an alienating concept for individuals to intellectually consider in its full philosophic implication; Marx and Engels responded to these philosophic propositions in The German Ideology (1845).