The author has carried out the analysis of Kazimierz Twardowski’s arguments concerning the solution to the major ethical problems: the problem of ethical criterion and the problem of the truth. The problem of social ethics identity in Polish philosopher’s scientific works has been examined in the paper. It was found out that the creator of Lwiw-Warsaw school defined social ethics as a science of methods and techniques of maximum harmonization the interests of individuals with social interests. Scientist’s tendency to harmonize the interests of individuals with social interests through the principle of justice has been found.