for comments on dra s of the paper that led to corrections and improvements. Any errors remaining are, of course, mine. Work for this chapter was partially supported by a Philip Leverhulme Prize and MICINN project FI-C-, which I gratefully acknowledge. Finally, special thanks are due to the editor for his forbearance.

No abstract

First dra : July ; this dra : December Even if we are able to decide on a canonical formulation of our theory, there is the further problem of metaphysical underdetermination with respect to, for example, whether the entities postulated by a theory are individuals or not. . .We need to recognise the failure of our best theories to determine even the most fundamental ontological characteristic of the purported entities they feature. . . What is required is a shi to a di erent ontological basis altogether, one for which questions of individuality simply do not arise. Perhaps we should view the individuals and nonindividuals packages, like particle and eld pictures, as di erent representations of the same structure.ere is an analogy here with the debate about substantivalism in general relativity. (Ladyman )In his paper "What is Structural Realism?" ( ) James Ladyman drew a distinction between epistemological structural realism (ESR) and metaphysical (or ontic) structural realism (OSR). In recent years this distinction has set much of the agenda for philosophers of science interested in scienti c realism. It has also led to the emergence of a related discussion in the philosophy of physics that concerns the alleged di culties of interpreting general relativity that revolve around the question of the ontological status of spacetime points. Ladyman drew a suggestive analogy between the perennial debate between substantivalist and relationalist interpretations of spacetime on the one hand, and the debate about whether quantum mechanics treats identical particles as individuals or as 'non-individuals' on A version of this paper will appear in Rickles, French and Saatsi (eds), e Structural Foundations of Quantum Gravity, Oxford University Press. Please quote from and cite the published version.

Diffeomorphism invariance is sometimes taken to be a criterion of background independence. This claim is commonly accompanied by a second, that the genuine physical magnitudes (the "observables") of background-independent theories and those of background-dependent (nondiffeomorphism-invariant) theories are essentially different in nature. I argue against both claims. Background-dependent theories can be formulated in a diffeomorphism-invariant manner. This suggests that the nature of the physical magnitudes of relevantly analogous theories (one background free, the other background dependent) is essentially the same. The temptation to think otherwise stems from a misunderstanding of the meaning of spacetime coordinates in background-dependent theories.

The purpose of this paper is to evaluate the 'Lorentzian pedagogy' defended by J.S. Bell in his essay "How to teach special relativity", and to explore its consistency with Einstein's thinking from 1905 to 1952. Some remarks are also made in this context on Weyl's philosophy of relativity and his 1918 gauge theory. Finally, it is argued that the Lorentzian pedagogy-which stresses the important connection between kinematics and dynamics-clarifies the role of rods and clocks in general relativity. *