 This kind of attitude was captured by Pierre Duhem’s (1906) distinction between two parts of a scientific theory: the representative part, which classifies a set of experimental laws; and the explanatory part, which “takes hold of the reality underlying the phenomena” (1906 [1954: 32]). Duhem understood the representative part of a theory as comprising the empirical laws and the mathematical formalism, which is used to represent, systematize and correlate these laws, while he thought that the explanatory part relates to the construction of physical (and in particular, mechanical) models and explanatory hypotheses about the nature of physical processes which purport to reveal underlying unobservable causes of the phenomena. For him, the explanatory part is parasitic on the representative. To support this view, he turned to the history of science, especially the history of optical theories and of mechanics. He argued that when a theory is abandoned because it fails to cover new experimental facts and laws, its representative part is retained, partially or fully, in its successor theory, while the attempted explanations offered by the theory get abandoned. He spoke of the “constant breaking-out of explanations which arise to be quelled” (1906 [1954: 33]).