1. Butterfield, J. and C. J. Isham, C. J. (2001). Spacetime and the philosophical challenge of quantum gravity. In Physics Meets Philosophy at the Planck Scale. Craig Callender and Nick Huggett, eds. Cambridge University Press, Cambridge. Preprint cited here, gr-qc/9903072.
2. Callender, Craig and Huggett, Nick, eds. (2001), Physics Meets Philosophy at the Planck Scale, Cambridge University Press, Cambridge, pp. 1–30.
3. Eppley, K. and Hannah, E. (1977). The Necessity of Quantizing the Gravitational Field. Foundations of Physics
7, 51–65.
4. Friedman, M. (1983). Foundations of Spacetime Theories. Princeton University Press, Princeton.
5. Hacking, I. (1996). The Disunities of Science. In: The Disunity of Science. P. Galison and D. Stump, eds. Stanford University Press, Stanford.