The work of Theodor Waitz is an important but hitherto unnoticed source of Dilthey’s concept of ‘human sciences’. Waitz was an outstanding philosopher and psychologist who, in the late 1850s, devoted himself wholeheartedly to empirical anthropology. In this field Waitz distinguished himself for his defence of the unity of humankind against mainstream polygenic and racial doctrines. Waitz inspired Dilthey’s articulation of psychology into two branches: the ‘descriptive’ one and the ‘explanative’ one. Even more remarkably, in a work reviewed by Dilthey (...) in warmly favourable terms, Waitz explicitly mentioned and defined the ‘sciences which treat of the spirit ’. Some of Dilthey's most interesting ideas are thus prefigured in Waitz’s long underrated work. (shrink)