Since the draft of the manuscript reviewed by Clark is not available, we do not know in how far Kapp modified his critique. In this context it is of interest that Kapp's letter to Clark on December 12,1945 referred to a working title that differs from the later book publication: “I am very grateful to you for having read parts of my manuscript on Social Costs and Returns which I submitted to you” We do not know whether Clark's influence was decisive on Kapp's decision not to publish roughly half of his original book manuscript, which contained a discussion of planning for social returns of untilities which diffuse themselves among all members of society.