According to Nagel (1961), reduction is a species of covering-law explanation: one theory is reduced to another when it is possible to identify the theoretical terms of the first with those of the second and to literally derive the first from the second. On the assumption that scientific disciplines and theories correspond to one another, reduction serves as a model of interdisciplinary integration as well. Mechanist’s objections to the covering-law model of constitutive explanation (i.e., micro-reduction) are discussed above (see Section 3.1); here the focus is rather on how distinct disciplines of science are integrated.