Roger Bacon (c. 1220–1292) and his System of Laws of Nature: Classification, Hierarchy and Significance Yael Kedar Tel Hai College Giora Hon University of Haifa Bacon discussed three different types of laws of nature: (1) particular laws governing one element or phenomenon (such as the law of the gravity of water); (2) the laws of the multiplication of species; and, (3) the universal law of nature. Each set of laws has its own explanatory function: (1) the particular laws account for the unique features of individuals and species; (2) the laws of multiplication explain the common features of matter and how individuals affect one another physically; and (3) the law of universal nature regulates these interactions and keep them in balance. Bacon’s laws share common fea- tures with early modern conception of laws. For example, they can be restated as if/then sentences and cover future events; some support counterfactuals; and all are endowed with explanatory power and free from space-time limitations. When considered together, they form a system, ordered in hierarchical relations. The different levels of laws cover three aspects of Aristotelian causality: formal, efficient, and final. The law of universal nature is a metaphysical axiom, necessary for upholding the very idea of a nature governed by laws. This indicates that Bacon conceived of nature as orderly and predictable; he presented a conception of a lawful nature and showed an understanding of what it takes to be lawful to a degree that had not been seen before. 1. Introduction The idea that nature is governed by laws and that the goal of science is to discover and formulate these laws, rose to prominence during the Scientific This research was supported by the Israel Science Foundation (grant no. 1622/13): “Roger Bacon (c.1220–1292) and the Making of the Concept of Law of Nature.” Perspectives on Science 2017, vol. 25, no. 6 © 2017 by The Massachusetts Institute of Technology doi:10.1162/POSC_a_00263 719 Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/POSC_a_00263 by guest on 26 September 2021 720 Roger Bacon’s System of Laws Revolution of the seventeenth century. It was manifestly held by the most significant actors of that revolution such as Galileo, Descartes, Kepler, Boyle, and Newton. But this idea was not new. In fact, it made an appear- ance in the Middle Ages, and it is likely to have emerged already in Antiquity (Ruby 1986; Lehoux 2012; Kedar and Hon 2017).1 In this paper we pay close attention to the concept of law of nature in the writings of Roger Bacon, the outspoken Franciscan who promoted ex- perimental science. We will be using Bacon as a test case to show that long before the Early Modern period scholars were working toward the idea of law of nature. Some historians of science hold that even if the concept of law of nature can be found prior to Descartes, its content was significantly different from the seventeenth-century concept (for example, Henry (2004, 2009)). We do not question this claim. Rather, our goal is to find, de- scribe, and characterize any usage which Bacon made of the term lex in connection with natural processes in the physical world. Typically, the term lex would refer to a description of regularities in nature, play an explanatory role, and be linked to mathematical concepts.2 Upon reading Bacon’s corpus, one cannot but notice the pronounced and broad use of the term lex in several contexts. We examine the various kinds of laws which Bacon introduced, describe their applications in the contexts they are found, and interpret their meanings. We classify the laws, identify the relations among them and the hierarchy they form. Fi- nally, we ask, what did Bacon mean when he appealed to this concept and whether this meaning is like the early modern one? To be sure, Bacon’s appeal to the concept of law of nature was noted in several earlier studies, such as Crombie’s (1959, 1996), Schramm’s (1981) and Ruby’s(1986). However, none of these studies offer a comprehensive description, nor an analysis of the specific laws which Bacon prescribed. Crombie provided a few quotations referring to Bacon’s optical laws and claimed that they demonstrate a shift in inquiry, but he did not investigate them any further; Schramm commented only on the law of universal nature; and Ruby ad- dressed the origins of the concept of law of nature in Bacon’s optical works and analyzed the relations between the terms regula and lex in his thought. She referred to Schramm’s treatment of the law of universal nature, but 1. Ruby argues that the modern concept of law of nature appeared in three different processes at different times in different fields all prior to the time of Copernicus. Lehoux maintains that a concept of law of nature, similar to the early modern one, can be found in premodern sources such as Ptolemy. Kedar and Hon claim that Robert Grosseteste and Roger Bacon facilitated a coherent conception of both “natures” and “laws.” 2. Expressions including the phrase “natural law,” which in most cases appear in moral and political contexts, do not fall under this category. Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/POSC_a_00263 by guest on 26 September 2021 Perspectives on Science 721 dismissed this law as resulting from a different motivation and as irrelevant to Bacon’s set of optical laws. Lindberg (1968), Smith (2015), and a few other scholars discussed Bacon’s treatment of the optical phenomena of reflection and refraction, but have not paid attention to his use of the term lex in these contexts. Above all, Bacon’s laws of particular natures have not yet been investigated, nor is there a study of the linkage between the various kinds of laws which sets them into a hierarchical system of signif- icance. With this paper we seek to address this lacuna. We begin with a classification of the various laws of nature invoked in Bacon’s writings and we set them in their order of generality. We suggest three categories, namely, (1) laws of particular natures, (2) laws of the multiplication of species, and (3) the law of universal nature. In the second section we examine the relations between the various laws and determine whether they constitute a coherent system. In the third section we address the meaning of the phrase “laws of nature” in the way Bacon used it, and suggest insights as to its historical significance. This last section builds on the comprehensive study by Weinert (1995) in which he maps various types of laws of nature and provides criteria for distinguishing laws of nature from accidental regularities. Weinert sums up effectively most of the literature on this subject prior to 1995 which makes his mapping most helpful. Bacon developed the concept of law of nature in De multiplicatione spe- cierum and De speculis comburentibus from the late 1250s or the early 1260s, the Opus majus and Opus tertium from 1267–1268, and the Communia nat- uralium and Communia mathematica from the late 1260s and early 1270s (Easton 1952). These texts are assumed to comprise the most mature expressions of many of Bacon’s theories. All of them belong to the period after Bacon’s supposedly crucial encounter with the writings of Robert Grosseteste (c. 1168–1253) and various Arabic sources. Despite Ruby’s claim (1986) that Bacon appeared to have discarded the universal law in the Opus majus and considered it foolish, we show that Bacon addressed the law of universal nature several times in the Communia naturalium and used it to explain not only the impossibility of vacuum, but other phenomena as well. It is therefore an inseparable part of the scheme of laws which he constructed. In sum, the thrust of our paper is that Bacon did not intro- duce the concept of lex in isolation; rather, it was part of a hierarchical lawful scheme with a novel explanatory power projecting a new image of nature—a nomological image. 2. Laws of Nature: A Classification We list the three types of laws which we have found in Bacon’s writings. We set the three types in an order of generality, that is, from the particular to the general. We begin with particular laws governing only one element Downloaded from http://www.mitpressjournals.org/doi/pdf/10.1162/POSC_a_00263 by guest on 26 September 2021 722 Roger Bacon’s System of Laws or phenomenon (§ 2.1); we then move on to laws governing a larger set of natural elements (§ 2.2); and, finally, we address the one law that encom- passes nature as a whole, namely, the universal law of nature (§ 2.3). 2.1. Laws of Particular Natures The laws of particular natures apply to either one element, one species, or an individual. It is defined as “a reigning power of the species with its individuals … that is, the power reigning the species and the power reigning the individual” (Bacon CN 1.2.3, p. 93).3 (1) The law of the gravity of water According to “the law of the gravity of water” (legem gravitatis aquae), water always runs to the lower place so that their surface is always equally distant from the center of the universe (Bacon OM 4.4.11, p. 158). The lower the position of the water is, the more they will contract (Bacon OM 4.4.11, p. 159). The water’s surface must form a sphere around the center of the world: If lines be drawn everywhere to the surface of the water from the centre of the earth … and if one of those lines will be shorter than the others, the water will run to the end of that line until equality is established.