Thus historical continuity as a consideration falls outside of pure logic and outside reasons of physics proper, but deals with the relation between physics and metaphysics, what Duhem calls “metaphysical cosmology.” Surprisingly, if one considers him as an instrumentalist, for Duhem, we must judge a physical theory in comparison to an ideal and perfect theory that provides the total and adequate metaphysical explanation of the nature of material things, that is, the natural classification of laws. (For more on Duhem on natural classification and conventionalism, see Dion 2013, Dion 2017, and Ivanova 2015.) For that reason, a coherent physical theory is more perfect than an incoherent set of incompatible theories. Elaborating upon this point and commenting upon the connection between cosmology—that is, metaphysics, natural classification, or the ideal form of physical theory—and physical theory itself, Duhem asserts: