This concept was introduced into economics from philosophy by Karl Marx, in his youthful Economic and Philosophic Manuscripts, written in 1844 but appearing in print only in 1932. Prior to the 1844 Manuscripts, alienation constituted a topic of purely philosophical speculation. Marx studied it in Hegel and Feuerbach, while present-day research claims to have observed anticipations of the idea in authors as old and as various as Jean-Jacques Rousseau, Calvin, Cicero and even Plato.