Abstract
The quotation above is taken out of context. What Leibniz says in full is that motion, considered “just so” (précisément) and “formally” (formellement), that is, considered as “change of place” (changement de place), is “something not entirely real” (entièrement réelle). What this claim means is that motion considered kinematically, as change of position of points in space through intervals of time, is not quite “real” motion. Leibniz is highlighting an issue on which physicists will take different stands for decades: what constitutes real motion? How to distinguish real from merely apparent motion? He is also expressing his growing dissatisfaction with the Cartesian program for physics, especially the idea that extension (magnitude and figure) is the essence of body, and the idea that in all physical interactions the same quantity of motion is conserved.
‘Le mouvement...n’est pas une chose entièrement réelle’ Leibniz, Discours de Métaphysique (§ 18)
A shorter version of this paper was read at the Colloquium in Honor of Nicholas Rescher, University of Pittsburgh, November 15, 1991. Over the years Nicholas Rescher has taught us so much about Leibniz that it may seem presumptuous of me to offer him this modest study of some aspects of Leibniz’s thought. The offer comes with much good will and with immense admiration for the efforts of one of this century’s most gifted and important philosophers. Leibniz thought that perfection was measured with reference to variety and order, two hallmarks of Rescher’s writings and of his kind and accommodating treatment of his friends and colleagues.
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Notes
I will cite translations by Loemker (1969) as L, with selection number and (where applicable) page number; and by Ariew and Garber (1989) as A&G, with part number, selection number and (where applicable) page number.
For a detailed analysis of this essay see my 1985, slightly revised as 1986, Ch. II.
In brief, the view is that we have nearly perfect understanding of our own perceptual (intentional) mental states, and since every monad is (to some degree) always perceiving, we have insight into the reality of mentality or perception expressive of all being.
See the letters to Arnauld of 1671 (L #10) and to François de la Chaise of (perhaps) 1680 (L #31, III).
See Butts (1986), pp. 7-11, Chs. I & II. For a clear statement of Leibniz’s view, see L #42, 409-10.
See the references in note 5, and A&G, II, A, 3, 4.
The deductive (or perhaps transcendental) hierarchy of concepts Leibniz introduces here is neatly encapsulated in Kant’s brief comment in his discussion of causality in the Second Analogy: “Causality leads to the concept of action, this in turn to the concept of force, and thereby to the concept of substance” [Critique of pure reason, A204/B249]. The crucial difference is that for Kant the only substances are physical forces (centers of resistance); for Leibniz, force (in its metaphysical form, as appetition) pervades the entire universe of the monads, and is ultimately to be identified with the creative activity of God.
The argument (and other statements of Leibniz) seems to commit him to acceptance of this assumption. As we will see, Leibniz, in keeping with his identification of motion as a relation, in fact conventionalizes local motion, as indeed does Descartes.
I employ the translation of Descartes’s Principles of philosophy of Valentine Rodger Miller (Valentine Watson Rodger) and Reese P. Miller, Dordrecht: D. Reidel (1983). The reference here is to p. 50.
It is interesting to note, although the point cannot here be developed in any detail, that both Descartes and Leibniz begin their analyses of many important concepts by attention to ordinary linguistic usage. Given the approved stereotypes, one would not expect such empiricist nit picking from rationalist philosophers!.
He does deliver it, however, in a slightly different context, his attempted rebuttal of Johann Christopher Sturm’s view that a motive force is not necessary in order to explain motion, construed as “the successive existence of the moving thing in different places.” Leibniz’s rebuttal concludes, “From this view it would also follow, finally, that absolutely nothing would change in bodies, and that everything would always remain the same.” “On nature itself, or on the inherent force and actions of created things”, Acta eruditorum, 1689. A&G, I, 21, § 13; L#53, § 13.
As Nicholas Rescher demonstrated years ago in his elegant study of the problem of Buridan’s ass (Rescher, 1960), the only way to choose rationally between two such identical alternatives is to choose randomly. To be rational in such a situation is to have no reason for one’s choice, to have no preference.
What we will now hear from Leibniz sounds much like Nelson Goodman. In a different age familiar with a slightly different idiom, Leibniz might well have written the following
...[F]or to say that something ‘moves relative to’ something else is not to impute any motion to it at all. To say that the moon rotates relative to the sun is entirely compatible with saying that the sun revolves around a fixed moon. And to say that the moon does not rotate relative to the earth is entirely compatible with the earth’s revolving around a rotating moon, as well as with saying that both the earth and moon remain at rest. So perhaps, to avoid giving a false impression, one should say simply that different aspects of the moon face the sun at different times; and that the same aspect of the moon faces the earth at all times. No more about rotation, rest, revolution; no more indeed about motion. Motion disappears from the realm of fact. And that should have been expected from the start, when the question ‘Does the moon rotate or not?’ is answered by ‘That depends upon what we take as frame of reference’. It depends upon what we do; we make the moon rotate or stand still. Motion is optional, a matter of convention, of fabrication imposed upon what we find (Goodman & Elgin, 1988, pp. 94-95).
See A & G, Pt. I, #10, pp. 93-94; and Tentamen de motuum coelestium causis, Gerhardt (1849–55), VI, pp. 144-87. Here Leibniz provides a mechanical model (a vortex around the sun carrying all of the planets) for Kepler’s law of the elliptical paths of planetary bodies and his law of areas. In the first work cited, after praising the simplicity of Copernicus’s system, Leibniz claims that Copernicus’s system does “itself one better” in that of Kepler, apparently because the latter can be provided with a physical model, whereas none is available for the theory of Copernicus.
Here Leibniz is surely right. Recall that in support of Joshua’s army Yahweh was throwing hailstones at the Amorite kings and their armies, and that “more died from the hailstones than the Israelites slew by the sword.” What was needed was more sunlight to make hitting targets easier; an early sunset might have spoiled the Lord’s aim!.
For more of my own views on Leibniz’s methodological writings, see Chapter II of my 1986.
Emphasis supplied. Compare this passage with [L #39, p. 364] where Leibniz praises success in prediction as “sufficient even by itself” to accept the reality of a phenomenon.
A reminder: (L #18, #32, #39).
See the classic expression of this distinction in Leibniz’s “On the ultimate origination of things” (L #51, p. 488; A&G I, 20, p. 151).
I will refer to the four letters by their dates.
That is, about a year and one-half before his death on 14 November 1716; thus we may take these letters to be definitive of Leibniz’s mature view.
I do not think that Leibniz understood the full force of Wolff’s perplexity. Wolff had written: “For I foresee that among the things worthy of observation one must include the things that follow in any way from the assumed state of the thing.” [February 1715] Two points: First, Wolff is surely right that any disease that strikes an individual body does indeed follow from the assumed state of the thing, if by that we mean the body (with its obvious propensity to get the disease), and the body’s situation with respect to the cause of the disease. If the individuality of anything (including I would think a body) consists in its “containing” everything that will ever happen to it, then Wolff is correct in thinking that the course of a disease contains things worthy of observation. Second, a disease is not so much an aberration or, as Leibniz says, an “exception,” as it is, in medical terms, an insult. It is important to note, however, that the insult is not gratuitous, but is, by nature, well thought out. Diseases are themselves identifiable by reference to quite regular symptoms and quite systematic development. If this were not so, there would be no point to trying to cure them. Successful medical practice seems to involve attention to two kinds of general rules: those characteristic of and hence descriptive of healthy bodies, and those characteristic of and hence descriptive of sick ones.
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Butts, R.E. (1993). Leibniz on Choosing Between Rival Scientific Hypotheses. In: Historical Pragmatics. Boston Studies in the Philosophy of Science, vol 155. Springer, Dordrecht. https://doi.org/10.1007/978-94-015-8188-2_2
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