In seeking a suitable topic for the address at this annual event of the psychometricians, I tried to keep in mind the motto of our official publication, Psychometrika, to promote “the development of psychology as a quantitative, rational science.” The best that I have been able to do falls short of this ideal in two important respects. Although the material that I am to bring before you pretends to be quantitative, in the sense that measurements have been made, the problem has not been rationalized and the data have thus far yielded only to graphical treatment.