 That final claim – that the mathematical units of space and time must be defined by appeal to infinitesimals – follows for Cohen from the principle of continuity. This is the Leibnizian principle that Cohen glosses as “there are no jumps in consciousness” (Cohen 1883, §42), which for him means that mathematical and scientific theories must represent objects as continuous. Recent commentators have emphasized that, for Cohen, the principle of continuity is a requirement of reason, and thus an expression of his methodological rationalism (see Damböck 2017, 4.4.1 and Edgar forthcoming). At the same time, that the principle of continuity serves this function for mathematical natural science is, for Cohen, a fact of science revealed by his historical investigation of the development of calculus.