  Jeffers advances criticisms of Du Bois’s definition of race and, unlike most other philosopher commentators, of his causal explanation of the existence of spiritually and culturally distinct races. Regarding the latter, he questions the reliability of Du Bois’s general, historical account of the genesis of the social factors to which Du Bois attributes the existence of these races (Jeffers, 2013, 417). Regarding the former, he adduces an important conceptual point: namely, that Du Bois neglects to justify the assumption that the historical and social facts that define and distinguish the spiritually distinct groups that the historian and the sociologist identify as races should be thought to constitute (constitutively to construct) those groups as races.  Perhaps they serve simply to constitute them as cultural entities, or, as Du Bois himself sometimes writes, as nations (Jeffers, 2013, 416). Absent that assumption, neither the historian nor the sociologist is entitled to identify the clearly defined, spiritually distinct groups he or she observes as races. And, absent that assumption, Du Bois is hardly entitled to present the definition that he bases on what the historian and the sociologist observe as answering the question, “What, then, is a  race?”[20]