Leibniz on Natural Teleology and the Laws of Optics

This essay examines one of the cornerstones of Leibniz’s defense of teleology within the order of nature. The first section explores Leibniz’s contributions to the study of geometrical optics, and argues that his introduction of the “Most Determined Path Principle” or “MDPP” allows him to bring to the fore philosophical issues concerning the legitimacy of teleological explanations by addressing two technical objections raised by Cartesians to non-mechanistic derivations of the laws of optics. The second section argues that, by drawing on laws such as the MDPP, Leibniz is able to introduce a thin notion of teleology that gives him the resources to respond to the most pressing charges of his day against teleological explanations within natural philosophy. Finally, the third section argues that contemporary philosophers have been overly hasty in their dismissal of Leibniz’s account of natural teleology, and indeed that their own generally thin conceptions of teleology have left them with few well-motivated resources for resisting his elegant position. Introduction At a first pass, a teleological explanation is an explanation that attempts to explain a behavior or event by appealing to an outcome or consequence of that behavior or event. “Betty is going to law school in order to get rich;” “The bear is swatting at the beehive in 1 order to get honey;” “The heat-seeking missile swerved left in order to hit its target;” and “Stones fall in order to reach their natural resting place at the center of the earth” are thus all at least candidates for teleological explanations. The likely or expected outcomes appealed to in putatively teleological explanations such as these are often called “goals,” “ends,” and, although less commonly today, “final causes.” It is well known that the use of teleological explanations in the domain of physics underwent a massive reevaluation during the early modern period. Prior to the scientific revolution, explanations in terms of final causes were widely accepted, and even thought to be necessary for an adequate account of the natural world. After the scientific revolution, teleological explanations were generally shunned in the practice of physics, and eventually became viewed with suspicion even in relation to biological phenomena. Understandably curious about this dramatic shift in explanatory mores, scholars of the early modern period have devoted a great deal of attention to Cartesian and Spinozistic critiques of the use of final causes, and have significantly increased our understanding of the grounds, implications, and limitations of those criticisms. It is also well-known that Leibniz was one of the most important early modern opponents of the wholesale rejection of teleology and teleological explanations as applied to the physical world. Although committed at least in broad terms to the project of the new science, Leibniz insists that final causes may be “useful not only for admiring the ingenuity of the great workman, but also for discovering something useful in physics and 1 See, for example, Bennett (1983; 1984, 213-230; 1990), Curley (1990), Della Rocca (1996, 252-257), Gabbey (1980), Garrett (1999), Rice (1985), and Simmons (2001).