This paper examines how economists from David Hume to Irving Fisher have struggled with the applicability of their analyses to those who differed from them in gender, ethnicity, class, or race. Particular attention is paid to how Fisher's discussion of racial and ethnic differences in capital accumulation and time preference changed between The Rate of Interest (1907) and The Theory of Interest (1930), and how it drew on earlier work by John Rae (to whom Fisher dedicated both those books).