ke physical theories unfalsifiable and thereby traps them in a process of infinite regression. For him, the unfalsifiable character of physical theories and the process of infinite regression are real obstacles to seeing scientific progress as rational and continuous. The continuous development of physical theory is shown, for Duhem, by the development of abstract theories. Abstract theories are mathematical structures (Lagrangian, Hamiltonian formalism) which form the mold to systematize and organize the empirical laws discovered by the experimental method. Duhem clearly states his predisposition for the abstract aspect of physical theory as an element of continuity between physical theories. At the same time, he blames the use of atomistic theories of matter as unifying frameworks for the discontinuity of physical theory. He says: He [the physicist who is not content with knowing physics through the gossip of the moment] will see abstract theory, matured through patient labor, take possession of the new lands the experimenters have explored, organize these conquests, annex them to its old domains, and make a perfectly coordinated empire of their union. It will appear clearly to him that the physics of atomism, condemned to perpetual fresh starts, does not tend by continued progress to the ideal form of physical theory (Duhem 1974, 304). Thus, the continuity of scientific progress is accounted for by viewing the nature of physical theory as representational structures (Chiappin 1989). The historical continuity of scientific development is shown by the increasing generalization and abstraction of these mathematical structures with which we organize our set of empirical laws. This view of the nature of physical theories operationalizes the idea of progress as the increasing comprehensiveness of physical theories, where the idea of increasing comprehensiveness accounts for the idea of continuity. The principle of continuity states that new theories contain the acquired knowledge and are systematized by the old theo