Laws of nature, natural properties, and the robustly best system

This paper addresses a famous objection against David Lewis’ Best System Analysis (BSA) of laws of nature. The objection—anticipated and discussed by Lewis (1994)—focuses on the standards of simplicity and strength being (in part) a matter of psychology. Lewis’ answer to the objection relies on his metaphysics of natural properties and its ability to single out the robustly best system, a system that is expected to come out far ahead of its rivals under any standard of simplicity and strength. The main task of this paper is to argue that Lewis’ reply to the objection in terms of nature being kind to us does not succeed, if nature’s kindness is understood in terms of the naturalness of the properties composing the Humean mosaic. For epistemic access to natural properties is downstream to any previous identification of the best system. A possible Lewisian rejoinder in terms of cross-world Humean mosaic of natural properties is considered and rebutted. The paper concludes by suggesting that Lewis could instead avail himself of a better answer to the objection, if the standards of simplicity and strength were re- interpreted along perspectivalist lines.