On Leibniz: Expanded Edition

9. The Epistemology of Inductive Reasoning in Leibniz

170  9 The Epistemology of Inductive Reasoning in Leibniz 1. Introduction Philosophers naturally think of Leibniz as first and foremost a metaphysician : the author of the Monadology and the founder of the “new system of preestablished harmony.” From this perspective, Leibniz’s ideas regarding the theory of knowledge fade into the background. In the common way of thinking among philosophers, Leibniz is not a substantial contributor to the theory of knowledge. Nevertheless, it is in this somewhat unaccustomed role that he will be presented in this present discussion. Epistemology is—to be sure—negligible if we assume the standpoint that is standard in the articulation of Leibniz’s metaphysics. Everything here turns on the monads and their complete individual notions as apprehended by God from all eternity sub ratione possibilitatis. Once the world has come into existence, truth becomes a matter of agreement “with the actual facts” (adaequatio ad rem). At this level, everything is worked out from a God’s eye point of view. But, of course, from the angle of human rather than divine epistemology— from that of the question of how we are to find out about how things go in the world—this does not help much. We humans do not know the complete individual notions of any existing substances—not even that of our own self or spirit. Unlike God, we cannot penetrate the realm of contingent fact by means of calculation and reasoning from general principles. Our only route into the issue of how things actually stand in this world is through experi­­ the epistemology of inductive reasoning in leibniz 171 ence. (Reasoning alone cannot carry us beyond the sphere of the necessary truths.) From the angle of the practicalities of the human situation, Leibniz is—so I shall argue—as rigid an empiricist as any. And this leads squarely to the issue of the empirical epistemology of the contingent realm—of how we humans are to extract truths from our experience . This issue, which does not even arise in the metaphysics of Leibniz, must nevertheless play a significant part in his philosophy. 2. The Extraction of Particular Truths from Experience Let us begin with perceptual knowledge, knowledge as it is to be extracted from particular experiences. The problem now is not the theocentric one of which ontological possibility is to be actualized, but the homocentric one of which epistemological possibility in the phenomenal sphere is to be recognized as actual—that is, veridical. Leibniz treats this epistemological issue in one of his most powerfully seminal works, the little tract De modo distinguendi phaenomena realia ab imaginariis which was probably written in the late 1670s. How does the golden mountain I imagine differ from the real, earthen, rocky, and wooded mountain I see yonder? Primarily in two respects: internal detail and general conformity to the course of our experience of nature. Regarding the internal detail of vividness and complexity Leibniz says: We conclude it from the phenomenon itself if it is vivid, complex, and internally coherent [congruum]. It will be vivid if its qualities, such as light, color, and warmth, appear intense enough. It will be complex if these qualities are varied and support us in undertaking many experiments and new observations; for example, if we experience in a phenomenon not merely colors but also sounds, odors, and qualities of taste and touch, and this both in the phenomenon as a whole and in its various parts which we can further treat according to causes. Such a long chain of observations is usually begun by design and selectively and usually occurs neither in dreams nor in those imaginings which memory or fantasy present, in which the image is mostly vague and disappears while we are examining it.1 Regarding the second aspect of coherence, Leibniz says: 172 the epistemology of inductive reasoning in leibniz A phenomenon will be coherent when it consists of many phenomena, for which a reason can be given either within themselves or by some sufficiently simply hypothesis common to them; next, it is coherent if it conforms to the customary nature of other phenomena which have repeatedly occurred to us, so that its parts have the same position, order, and outcome in relation to the phenomenon which similar phenomena have had. Otherwise phenomena will be suspect, for if we were to see men moving through the air astride the hippogryphs of Ariostus, it would, I believe...