Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. Not merely in the present lecture on the unity of social science, but throughout the course on the more general subject, The Meaning of Social Science, I shall virtually elaborate the thought which I suggested in a paper entitled The Sociological Stage in Social Science. It was published in the American Journal of Soci ology for March, 1910.