In this paper, we show that, in 1961 and before he had read "The Problem of Social Cost", Calabresi reached exactly the same conclusions as the one reached by Coase and summarized by Stigler as the "Coase theorem" but he believed that this result was valid only in the theoretical world of the economists. We also analyze how Calabresi's thought evolved, in particular including transaction costs in his reasoning, but nonetheless remained faithful to his conclusions about the practical validity of the Coase theorem. Calabresi's conclusions remained ignored by economists and by most of legal scholars until the early 1970s. It was only when scholars started to emphasize the unrealistic assumptions upon which rest the Coase theorem that they also started to pay attention to Calabresi. His works were quoted and essentially used to emphasize the limits of the Coase theorem. Calabresi and Coase were then put on the same footing; the works of the former presented as more complete and more practical than the works of the later.