 The concepts of classical particle mechanics (henceforth abbreviated by CPM) exemplify well the notions of T-theoreticity and T-non-theoreticity. As has been indicated above, all methods of determining the force acting upon a particle make use of some axiom of classical particle mechanics, such as Newton’s laws of motion or some law about special forces. Hence, force is CPM-theoretical. Measurement of spatial distances, by contrast, is possible without using axioms of CPM. Hence, the concept of spatial distance is CPM-non-theoretical. The concept of mass is less straightforward to classify as we can measure this concept using classical collision mechanics (CCM). Still, it was seen to be CPM-theoretical by the structuralists since CCM appeared reducible to CPM (Balzer et al. 1987: ch. 2).