Through an analogy whose nature escapes physics's confines but whose existence is imposed on the physicist's mind, we surmise that it [i.e., the ordering of physical phenomena that constitutes physical theory] corresponds to a certain supremely eminent order. In a word, the physicist is forced to recognize that it would be unreasonable to work for physical theory's progress were this theory not the increasingly better defined and more precise reflection of a metaphysics - the belief in an order transcending physics is the sole justification of physical theory.
Duhem says this somewhere in La théorie physique, son objet, sa structure (1906); but I'd have to look up precisely where.
