Draft paper, presented at: XII Conference of the Italian Association for the History of Economic Thought "FACTS AND THOUGHT IN ECONOMIC HISTORY AND HISTORY OF ECONOMIC THOUGHT", February 21st-23rd 2013, University of Florence Final version published in: Poettinger/ Tusset (eds.), Economic Thought and History London, New York: Routledge, 2016, pp. 43-57 Economic facts, theoretical beliefs and the ‘double movement’ Claus Thomasberger * 1 Introduction The vision of the relation between facts and thought which prevails in economic theory and historical research does not only influence the answers to the question of how fruitful the introduction of economic history into the study of the history of economic thought and vice versa is. It also has a history of its own. This paper focuses on a range of interpretations of this relationship that are underlying economic theories in the nineteenth and twentieth century. * University of Applied Sciences, Treskowallee 8, 10313 Berlin, Claus.Thomasberger@HTW-Berlin.de. This paper was originally presented at the XII Conference of the Italian Association for the History of Economic Thought, “Facts and Thought in Economic History and History of Economics”, University of Florence, February 21-23, 2013.