ABSTRACTThis paper elaborates a conception of the unity of science that emerges in the context of Dilthey’s well-known treatment of the distinction between the Naturwissenschaften and the Geisteswissenschaften. Dilthey’s account of the epistemological foundations of the Geisteswissenschaften presupposes, this paper argues, their continuity with the natural sciences. The unity of the two domains has both a psychological and a biological basis. Whereas the psychological functions at work in scientific thinking, the articulation of which is the task of Dilthey’s proposed science (...) of ‘descriptive and analytic psychology’, are common to both kinds of sciences, their ontological ground consists in the embodied and environmentally situated context of human beings, and is expressed in Dilthey’s central concept of ‘life’. Accordingly, this paper develops the shared biopsychological foundations of the epistemology of the natural and human sciences from Dilthey’s writings in the 1880s and 1890s. Dilthey’s conception of unity, furthermore, has implications for philosophy’s orientation towards the special sciences. Thus, in conclusion, this paper applies the biopsychological account to sketch an outline of Dilthey’s historicist method in the philosophy of science, and considers its similarities and differences with a contemporary approach in ‘historical epistemology’. (shrink)