Physics and Leibniz’s Principles

Leibnizs principles made for an elegant and coherent philosophy. In part meta-physical, in part methodological, they addressed fundamental questions- in the treatment of symmetry, in the relationship of physics to mathematics, in logic-that are if anything even more pressing today than they were in Leibnizs time. As I shall read them, they also expressed a distinctive and uncompromising form of realism, a commitment to the adequacy of purely descriptive concepts. This doctrine has been called semantic universalismby van Fraassen (1991), and the generalist pictureby OLeary-Hawthorne and Cover (1996): it will become clearer in due course just what it entails. The principles that I shall consider are the Principle of Su ¢ cient Reason (PSR) and the Principle of Identity of Indiscernibles (PII). In the \u85rst instance I shall take them both to be methodological principles. The former I shall read as requiring that the concepts of physics be entirely transparent. Analysis and explanation are to proceed without any limits. The perspective is impersonal: any epistemological limitation, to do with our human situation or perceptual ap