This article develops a critical evaluation of the theoretical foundations of the Common Core of European Private Law Project, in particular, of the theory of Rodolfo Sacco. The overall aim of this exercise is to test to what extent the common core project can truly provide an accurate and relatively neutral description of European Private Law. First, it describes the comparative law theory of Rodolfo Sacco and describes briefly how this method is applied practically in the Common Core of European Private Law Project. Second, it describes a number of criticisms that can be raised against this method. In doing so, it defends the thesis that law has a multi-faceted character and that there is not one single method for the study of comparative law that is able to cover all of these different facets. Rather, in order to provide an accurate and precise description of a different legal system, one has to apply different comparative methods.