Who was Siger of Brabant? What did he really think? What I’m going to do in this paper is thoroughly investigate the figure and the thought of one of the most important medieval philosophers. Firstly I’ll show all the the different thesis supported by Renan, Mandonnet, Van Steenberghen, Wéber, Gauthier and many others scholars about Siger’s thought. Then I’ll focus all my attention on this question: did Siger ever support the so called “double truth” thesis? Trying to answer this question I’ll show why according to my opinion Sigier was an original thinker and why we can argue that he really was one of the most important magistri artium in the University of Paris in the thirteenth century.