At the University of Jena the philosopher Erhard Weigel (1625–99) was one of the most influential German proponents of the new “geometric method.”34 His students included two of the most famous thinkers of the early German Enlightenment, Wolff’s later patron Gottfried Wilhelm Leibniz, and the jurist, historian, and philosopher Samuel von Pufendorf (1632–94). Weigel’s influence prompted Pufendorf to write his 1660 treatise on natural jurisprudence, Two Books of the Elements of Universal Jurisprudence,35 in the geometric style, though he later more or less abandoned this in his better known work, On the Law of Nature and Nations of 1672.36 An important figure in Christian Wolff’s intellectual development, even before he became acquainted with Leibniz, was Ehrenfried Walther von Tschirnhaus (1657–1708). Tschirnhaus was a nobleman from Upper Lusatia who studied law and medicine at the University of Leiden from 1668, at a time when Cartesian philosophy was the subject of considerable controversy there.37 In 1674 he was introduced to the circle around Spinoza, who gave Tschirnhaus a manuscript copy of his Ethics, Demonstrated according to the Geometric Method. Following travels to London, Paris, and Italy, Tschirnhaus returned to the Netherlands in 1679 and completed the manuscript of
[print edition page xx]
his treatise Medicine of the Mind, or an Attempt at a Genuine Logic, in Which the Method of Finding Unknown Truths Is Discussed,38 in which he expressed his great admiration for the “incomparable” Descartes.39 Wolff had heard of Medicine of the Mind when he was still at school, but failed to obtain a copy. He certainly read it at university, however, and in 1705 met Tschirnhaus himself to discuss Medicine of the Mind, an event he thought sufficiently memorable to record in his autobiography.40
The importance of mathematics for Wolff’s philosophy is already evident from the title of his 1703 dissertation, Universal Practical Philosophy, Written according to the Mathematical Method. In the preface, Wolff summed up the significance of recent progress in mathematics for philosophy. Over the past century, he said, mathematics had flourished, and
the other disciplines derived the great splendour, with which they now shine, from the fact, that their scholars now philosophize according to mathematical principles, that is, they are now used to distinguish accurately the concepts of the understanding from the perceptions of the imagination; examining first the nature of things, and deducing everything else from that; and finally progressing from universal and simple principles to more specific and complex conclusions, according to the laws of the genuine method for finding the truth.41
[print edition page xxi]
Although mathematics and philosophy were different types of knowledge—philosophy was concerned with causal explanation, mathematics with measurement and quantification—the standards of mathematical and philosophical demonstration were essentially the same. For in mathematical argument
terms are explained by accurate definitions …; propositions, that are accurately defined as regards the subject and predicate, are rigorously proved on the basis of definitions and propositions that have been demonstrated previously.… At all times careful attention is paid to the rule that those things are stated first which are used to understand and to prove subsequent statements.42
In philosophical argument, too,
one must not use terms unless they have been defined precisely.… [N]othing may be accepted as true, unless it has been sufficiently demonstrated.… [I]n propositions the subject as well as the predicate are accurately determined … and everything is arranged in such a way, that all that is necessary to understanding the subsequent argument and for providing its foundation is stated first.43
“Who does not see,” Wolff concluded, “that the rules of the mathematical method are the same as those of the philosophical method?”44
[print edition page xxii]
The aim of both mathematical and philosophical reasoning was to develop a chain of rigorous, syllogistic argument. The principles that were the starting point of this argument varied. They could be definitions, empirical matters of fact that were absolutely certain, axioms, or propositions that had already been demonstrated.45 It was also possible to construct an argument from uncertain principles, but in that case the conclusions lacked certainty too. Only when the principles were unquestionably true, and each step in the argument followed necessarily from the previous ones, was the conclusion also reliable. Like Wolff’s other works, The Law of Nations according to the Scientific Method was intended as an application of this kind of argument. A paragraph typically begins with a hypothesis, followed by a definition, which is used to develop a demonstration. This leads to a proof of the initial hypothesis, which is restated at the end of the paragraph to conclude the argument.
Wolff’s influence on the teaching of philosophy at German, Dutch, and Scandinavian universities was profound. In the second half of the eighteenth century Wolffians occupied academic positions all over the Protestant territories of the Holy Roman Empire.46 Faithful disciples, such as Daniel Nettelbladt (1719–91) in Halle and Joachim Georg Darjes (1714–91) in Frankfurt an der Oder, lectured to generations of students, many of whom later pursued successful careers in the Prussian state bureaucracy.47 Wolff’s system was also popular at Catholic universities in Germany, Austria, and Italy, where his philosophy was often welcomed as a modernized, updated version of the scholastic philosophy that had been taught there before.48 His views on international law were also of great significance for the ideas of the Swiss jurist Emer de Vattel (1714–67), author of the classic The Law of Nations of 1758. There Vattel
[print edition page xxiii]
remarked that had he “every-where pointed out what I have borrowed [from Wolff], my pages would be crowded with quotations equally useless and disagreeable to the reader.”49 Yet Vattel also emphasized his disagreements with “[t]hat great philosopher.”50
One of the most important of these concerned Wolff’s idea of a civitas maxima. Like other philosophers, Wolff regarded the law of nations as a direct extension of the law of nature.51 Nations, he wrote in The Law of Nations, were considered as “individual free persons living in a state of nature” (§16). But he also believed that all states together formed a “supreme state” (civitas maxima), which was analogous to a political community of ordinary citizens. That “supreme state” had “a kind of democratic form of government,” mainly because no particular state or group of states exercised sovereignty over all other members of that “supreme state” (§19). It was not feasible, however, for nations to assemble in one place and reach collective decisions, as the citizens of an ordinary democratic state did. Therefore the law of that supreme state had to be “the will of all nations which they are bound to agree upon, if following the leadership of nature they use right reason” (§20); it was not the actual common will of the assembled nations of the world, but the will they all ought to have concerning their mutual relations if they followed the guidance of reason.52
Vattel regarded the idea of a civitas maxima as irrelevant to the conduct of relations between states. Although the different states of Europe, for example, were more than a “confused heap of detached pieces, each of which thought herself very little concerned in the fate of the others,”53 they did not form a state comparable to a political community
[print edition page xxiv]
of ordinary citizens. Modern Europe, Vattel wrote, was “a kind of republic,” but its members, unlike those of Wolff’s civitas maxima, were ruled by “that famous scheme of the political balance, or the equilibrium of power; by which is understood such a disposition of things, as that no one potentate be able absolutely to predominate, and prescribe laws to the others.”54 Although Wolff in §§642–51 of The Law of Nations discussed the question
