(Presented at the Mellon Conference on Hylomorphism, Caltech, May, 2008)
In his Will to Power fragments, Nietzsche mocks Kant's reverence for the eternal and unchanging as follows: 'When … Kant says: "Two things remain forever worthy of reverence,"' that is, the starry heaven and the moral law, 'today we should sooner say: "Digestion is more venerable."' KSA, XII, 317. And in Thus Spake Zarathustra, he puts it even more succinctly: "For verily, my brethren, the spirit is a stomach! " (KSA, IV, pp. 257–8).
There is another, ancient view, one Leibniz identifies as Jewish, according to which "spirit is a bone." This bone is the Luz in Hebrew or the ajb in the Islamic tradition, and has been identified by some historians of medicine with the coccyx. Thus Leibniz writes in a letter to Johann Friedrich, 21 May 1671 that "even the Jews relate the story that in a certain little bone they call the Luz, the soul survives intact together with the flower of substance' (A II i 116). On this view, “every body, both man and beast, plants and minerals have a kernel of substance." This kernel consists "in a physical point (which is the proximate instrument and as it were the vehicle of the soul, which is located in a mathematical point) [and] endures forever." Now the coccyx is somewhat larger than a mathematical point, but we get the idea: Leibniz believes early on that there must be some special bit of the body that is immortal, that is, as he writes, "not diminished by teeth or by stomach acid” and that is “so subtle that it even remains in the ashes when the thing is burned.”
In a later text however, a note from February 1676, Leibniz conceives the flower of substance somewhat differently: “I think that the flower of substance is our body," he writes. "This flower… subsists perpetually in all changes … It is easily seen from this why cannibals, devouring a man, have no power over the flower of substance. This flower of substance is diffused through the whole body, and in a way it alone contains form.” For him, at this point, the flower is not identified with some particular part or other, but rather with the entire body, which is, nonetheless, admitted to be in perpetual flux.
Now an aggregate for Leibniz has whatever low degree of reality it has in virtue of the very relative stability of the cohesion of its parts. A corporeal substance, in contrast, has no such cohesion; there is constant flux between it and its environment. And yet it is precisely this capacity to endure throughout the flux that wins for it the status of true substance as opposed to mere aggregate. The corporeal substance is what is in constant communication with its environment, what has its being only through its environment, to the extent that it takes in material from its environment and transforms that material into itself. The soul or dominant monad has appetite, to be sure, but this is an appetite for ever more perceptions, not for calories.
Probably unknowingly, Nietzsche's identification of the stomach with the spirit takes up one strand of a venerable tradition of medical and philosophical thinking about the corporeal duties of the animal soul. For Paracelsus, to cite one prominent example, digestion is an alchemical process par excellence, and the stomach is nature's supreme alchemist, to the extent that it skillfully separates the good from the bad, and incorporates the food into the body. It is for him the archaeus itself that is in charge of digestion and so of the preservation of life. The Paracelsus scholar Ernst Wilhelm Kämmerer argues that the Spagyrite's idea of archaeus is itself a later descendent of the 'archonten' or 'daimon of digestion' introduced by Proclus and Iamblichus. We do not have time to pursue this ancient pedigree here, but bring it up only to show how importantly linked, traditionally, were the problems of nutrition on the one hand and that of bodily life on the other. For Paracelsus, to live is just to eat --nur das ist, was isst--, to endure in existence by substantially transforming the world into the self. The various theories of immaterial principles in nature that would emerge in the late 17th century, moreover, such as More's archaeus, Cudworth's plastic natures, or Georg Ernst Stahl's body-preserving soul, emerge directly out of this long tradition of explaining the process of nutrition within the context of a corporeal-substance metaphysics.
In this paper, I would like to argue that Leibniz's move from 'spirit is a bone' to 'spirit is a stomach' brings us to the very heart of his metaphysics of corporeal substance. For him, the focus on digestion is by no means a rejection of what is eternal and unchanging, as it would later be for Nietzsche. Rather, a sophisticated account of digestion --or 'change of stuff', to adapt the revealing German term for the process-- offers a key as to how to conceive of corporeal substances as real, without for that being forced to revert to the naïve and mythological view according to which the soul remains permanently attached to some inexplicably favored part of the body or parcel of matter.
Nutrition, or more precisely self-nutrition, is a deeply important factor both in Leibniz's description of the machine as a machine of perpetual motion, as well as in his description of it as a pyrotechnic machine. Perhaps the most significant idea introduced in the Corpus hominis of the early 1680s, and one that will remain important to Leibniz up through the polemic against Stahl in 1709-10, is that animal bodies, as well as human bodies, are, as he puts it, not so much hydraulic-pneumatic machines (as Borelli and other earlier mechanists may have imagined), but rather pyrotechnic or 'pyriac' machines, to the extent that their functioning is maintained by the conversion of fuel (i.e., food), into a vital heat analogous to fire. Leibniz asserts in Section IV of the Corpus hominis that "the first mover in this machine is something analogous to a flame or to the Sun or a fixed star, from which there arises an ebullition which feeds itself."
Now of course the analogy between the celestial bodies and the heart is very ancient. But Leibniz hopes to transpose this ancient theory into a distinctly mechanistic framework, arguing not that the animal body derives its vitality from a celestial source, but that it is literally a machine that harnesses the very same powers that make the celestial bodies hot and bright. For Leibniz, something literally similar to celestial burning happens when the excocted chyle mixes with the blood and produces fermentation. In any animal, Leibniz thinks, "a moderate and enduring boiling endures, which is fed by a circulating matter that grows more and more rarefied and is also restored little by little… We will thus rightly assert that an animal is not only a Hydraulico-Pneumatic machine, but also in a certain respect a Pyrotechnic one."
To the extent that Leibniz is engaged in the study of what he calls 'animal economy', the animal is no less a machine than it had been for Descartes, but there are a number of differences between the two philosophers' respective analyses of this machine. For one thing, Leibniz is willing to speak of animal machines in terms of their functional, as opposed to merely dispositional, unity. Machines of nature, for Leibniz, like the machines that we construct for our own reasons, have ends, and these ends may be understood in entirely mechanical terms, as rooted in the structure and motion of the mechanical body. Another difference lies in Leibniz's ascription of species membership to animal machines, whereas, as we saw in the previous chapter, Descartes remains entirely silent on how it is that a particular animal machine is the kind of machine that it is. Yet another difference is the motivation each thinker had for studying animal economy: for Descartes, again, a complete account of the animal in mechanical terms was a necessary, if otiose, step in the comprehensive case he spent his life seeking to make for a mechanized natural philosophy. For Leibniz on the other hand the initial interest in animal economy grows out of a prior interest, not in mechanical natural philosophy, but in the advancement of the institution of medicine. Finally, whereas for Descartes the analysis of the animal qua machine constitutes an exhaustive analysis of the animal, for Leibniz it is just the beginning. In the study of animal economy, Leibniz's model of the animal is fairly independent of the one familiar to most students of Leibniz from his broader metaphysical concern with organic bodies and corporeal substances. [See handout; summarize].
In Leibniz's science of animal economy, nutrition, or self-nutrition, is importantly wrapped up with the animal's 'quasi-perpetuity' or eternity in kind. It is on a par with reproduction as one of the two functions that raises the animal to the status of a sort of perpetual-motion machine. Of course, an animal differs from the ideal perpetual-motion machine both in that it has a species, and in that it requires constant refueling in order to exist. It differs from ordinary machines or 'organica artificialia' in that it is both self-sustaining and self-reproducing. Leibniz berates other mechanists who dream in vain of a perpetual motion machine in the stricter sense of a machine that requires no fuel at all:
[I]n order that men should obtain this durability of action in their machines, they now add to them a quasi-perpetual machine that is made by nature, which is of course man himself, the pilot, who repairs what is weakened or broken down in time, who applies an external force, bringing agents together with patients… or in some other way conserves the power of the Machine.
In other words, artificial machines are only able to continue running because a certain kind of natural machine --a human being-- tends to them by bringing them new fuel. But natural machines themselves require no such attendance:
Nature… brings it about that her Machine is able to do this very thing on its own, that is, that it be able now to be nourished, whereby worn-down parts and forces are renewed.
And even if the individual animal will eventually cease functioning, in death, it is still capable of a sort of perpetuity to the extent that it is capable of reproduction: "Machines of this sort are able to produce others similar to themselves [Machinae huiusmodi alias sibi similes producere possent]." Animals are thus perpetual-motion machines not just to the extent that they are self-nourishing machines but also, and more fully, to the extent that they are reproductive machines. Put two clocks in a room together, and you will never get a third, little clock out of them. Put two (appropriately selected) dogs together, and you might. The dog needs something exterior to it in order to reproduce 'itself' in its offspring, namely, another dog of the opposite sex. But it also needs something exterior to it in order to sustain it in its own individual life, namely, food. Again, Leibniz believes that this is as close as nature ever comes to a perpetual-motion machine, and mechanists are deluding themselves if they hope for something both self-contained and perpetual. Eventually, the individual machine breaks down, but if all goes well it will not break down before transmitting its likeness to another machine; and even before it breaks down it requires constant sustenance from the outside. But it still qualifies as 'a sort of' perpetual-motion machine to the extent that it moves itself so as to obtain its own sustenance and see to its own reproduction through the transmission of its species or special office to its offspring.
This parallelism between nutrition and generation is certainly not original in Leibniz. Leibniz seems, whether by a direct or indirect route, to have appropriated the idea of a special science of 'animal economy' from the English Gassendist Walter Charleton, who himself writes in 1659 of the “Oeconomy of Nature in the body of Man; a System of innumerable smaller Machines or Engines, by infinite Wisdom fram’d and compacted into one most beautiful machine." Charleton sees the question of nutrition as the natural starting point of the science of animal economy,
not only because the Stomach, Gutts and other parts principally inservient thereto, being, by reason of impurities contain’d in them, more prone to putrefaction, ought therefore first to be taken out of the cavity of the Abdomen, to prevent noisomness; but because Nutrition seems to be, if not one and the same thing with, yet at least equal or contemporary to Generation it self.
He goes on to explicitly identify nutrition and generation as two aspects of one and the same process: "To nourish, what is it but to substitute such, and so much of matter, as is, by reason of exhaustion, wanting to the solid parts of the body, namely flesh, nerves, veins, arteries, &c.?… Nutrition is nothing else but Generation continued." Both of these aspects are governed by what Charleton calls a 'Plastic Spirit,' which works
within us through the whole course of our life, from our very first formation to our death; doth in the same manner perpetually regenerate us, out of a liquor analogous to the white of an Egg, by transmuting the same into the substance of the solid parts of our body. For, as I said before, Nutrition is necessary to all Animals, not only in respect of the Augmentation of their parts, while they are little Embryons; but also in respect of their Conservation after during life: because their bodies being in a natural consumption or exhaustion, would inevitably be soon resolv’d into their first elements, unless the providence of Nature had ordain’d a continual renovation or reparation of the parts, by substitution and assimilation of fresh matter.
Charleton suggests that "the Human Embryo perhaps is nourish’t before the Empsychosis." Descartes, too, had seen the formation of the fetus as explicable in terms of nutrition, a view of fetal development that Gaukroger has identified as “about as mechanist a route as is possible." But whether it is mechanist or not depends on the metaphysics of nutrition of the author in question. For a late Aristotelian such as Agostino Nifo or, as we will see, for G. E. Stahl, nutrition is by no means a merely mechanical process: the preservation of the unitary body throughout the perpetual flow of the new material that it takes in is the work of the soul, indeed it is the soul's principal function. Charleton and Leibniz both align themselves with Descartes, as it happens: the fact that nutrition occurs before empsychosis means that nutrition cannot itself be a soul-driven process. As Leibniz repeatedly emphasizes, nutrition is a more basic process in the study of animal economy than is sense or voluntary motion, since sense requires the prior possession of organs formed through nutrition. But for a Stahl or a Nifo, there is nothing at all 'mechanical' about the grounding of physiological processes, even fetal development, in nutrition.
Certainly, the most common view of nutrition in the decades preceding Leibniz and Charleton's interventions was that it involves the substantial transformation of food. To cite one useful reference work, Goclenius's Lexicon Philosophicum defines "nutrimentum" or "alimentum" in both the proper and metaphorical senses. This latter includes odors and other signals of nutrition that do not actually nutrify. In the proper sense, nutrition may be either potential or actual, potential when the aliment is brought to the mouth and delected, and actual, when this aliment has been "decocted" and is incorporated into the substance of the living thing [ut in rei viventis substantiam concedat]." Goclenius cites Thomas Aquinas, for whom "to be nourished means, properly speaking, that in oneself something is received toward ones own bodily conservation." Here the substantiality of the body is not explicitly mentioned, but in the context of Thomist metaphysics there is no reason why it should have to be.
Leibniz appropriates most of the ideas regarding nutrition that we have heard from his predecessors. He agrees with Charleton that it precedes --if not temporally in the development of the fetus, then at least in the order of explanation-- the capacities for voluntary motion and sense. Indeed, the study of nutrition is the foundation of the science of animal economy, as nutrition gives rise to those organs that are required for sensation. He explains in the De scribendis novis Medicinae elementis:
In truth with our Medicine more is [learned] concerning Nutrition than voluntary motion, and more concerning this Motion than the functions of Sense, and it may be supposed that the Machine is capable of Nutrition, and sense free from animal motion, easier moreover to be explained, in what way we are nourished than in what way we perceive and act; indeed from aliments those parts are also generated which we require for the functions of the sensitive soul, it will be preferable to inquire into those parts first which are seen by a certain reason to be held in common with plants, than those that are characteristic of animals [alone].
What, though, is the precise mechanism of nutrition? By what means is food transformed into bodily matter? We have seen that Leibniz agrees with most other moderns in holding that it is not a variety of corruption, and in holding that whatever it is, it must be entirely mechanical. In his view, nutrition is an instance of fermentation. Fermentation had been a central concept of chemical medicine since Paracelsus, and more noticeably with the transportation of Paracelsianism into the Anglo-Dutch sphere by Jean-Baptiste van Helmont and Franciscus Sylvius in the early 17th century. For these iatrochemical thinkers, fermentation occupies a central place in natural philosophy, as it makes possible an account of the origination of forms from --in the case of van Helmont-- the universal empty matter of water. As Betty Jo Dobbs explains, "[t]he ferment originates [for van Helmont] in a divine idea and, as it operates upon the 'empty' matter, the ferment itself is internalized and becomes the archeus, the internal governing principle of the created being that insures the working out of God's plan for its existence."
Fermentation remains by far the most important process in Cartesian, and, by extension, mechanist physiology. By appeal to fermentation, Descartes believes himself able to account not just for the heat of the heart, but also digestion and a number of other bodily processes. This is the same basic process, Descartes believes that we witness in many, seemingly distinct natural phenomena, including the production of heat in moist hay and the preparation of beer and wine. In all of its manifestations, fermentation is the production of heat from corruption, and Descartes believes it responsible for digestion, respiration, conception, and certain components of fetal development.
In Dobbs's view, Descartes's incorporation of the concept of fermentation into his physiology is a prime example of the habit of early mechanists to restate common cultural assumptions "in terms of corpuscularian mechanisms that disguised but by no means eliminated their vitalistic components." Yet this criticism may not be entirely fair. While there is no doubt some truth in the general point that the mechanists gained nothing in explanatory force by substituting 'microstructure' for 'form' or 'virtue', it is clear that Descartes conceived fermentation as a straightforwardly thermomechanical process, and that he conceived the changes it brought about not in terms of the emergence of new forms, but in terms of the quantitative alteration of preexisting corpuscles. If he could not account for the details of these changes at the microlevel, that does not mean that in granting to fermentation a central place in physiological phenomena, he did not have reason to hope that someday it might be explained in entirely mechanical terms. The same certainly holds true for Leibniz.
Another important figure in the background of Leibniz's contribution to animal economy --including his eventual adherence to the view that the animal is a fermenting or pyrotechnical machine-- is Thomas Willis, a physician and founding member of the Royal Society who published the treatise De anima brutorum in 1672, a treatise that is in many important respects an important contrast to Charleton's Gassendian physiology. Willis believes that fermentation is an inorganic process, indeed defining it as the "inorganic motion of natural bodies." He also believes that it can happen, however, in any number of kinds of body, including animate ones: "Bodies that are susceptible to fermenting are of diverse consistencies and conditions, as fine or course, liquid or solid, animate or inanimate, natural or artificial" (ibid). While he conceives fermentation as a strictly physical process, Willis nonetheless thinks that it can serve to propel a body along the course of development proper to it: "Fermentation is the motion of internal particles, or of the principles of any given body, as the tendency towards perfection of the same body, and even by means of its transformation into another."
Willis clearly sees fermentation as spreading across the different natural kingdoms or 'families', and thus as a basic explanatory principle of geology, botany, and animal physiology:
And fermentation is said to be a thing of nature in three families: mineral, vegetable, and animal… Minerals, though in the viscera of the earth fermentation is less conspicuous than on the surface, nevertheless it is easy to establish the elementary particles or the fermentative principles enclosed in the depths of the earth, just as in a given pregnant uterus...
In vegetables,
fermentation has to this point been more widely discerned: provided namely that they are germinating, growing flowering, bearing fruit, maturing, declining and perishing, it is possible to observe the diverse motions of the particles or principles, their various conditions and adjustments.
In animals, finally,
the first beginnings of life, from the spirit in the heart, just as from some small fermenting point, are derived. Their motion is not, as in vegetables, slow and insensible, nor so great as to be discerned in increments, but rather at once rapid and apparent to the eyes: as you see, the spirit is set in motion by a moving point (just as at the starting barriers at a race course), and by the vehicle of the blood extends out more and faster.
Again, Willis believes that in the end fermentation is always the same across kingdoms: it is the motion of internal particles. But depending upon the sort of body in which it happens, it will contribute to transformation in a different way. For Leibniz as well, fermentation is a strictly chemical process, but each kingdom of nature has a chemistry specific to it:
There is so to speak a chemistry proper to animals, and the transformations that occur in the animal humors arise from chemistry no less than do vegetable liquors. Consequently, all bodies arise from chemistry, when we consider them not as structures but as masses, and when we apply to them physical operations consisting in an insensible process.
This last point is key to understanding the role of fermentation in Leibniz's conception of animal economy. For him, fermentation is a fundamental principle governing a number of processes in animal bodies, as it is also in plants and in minerals. But it operates in the animal body not as an integrated structure of interconnected organs, but rather as a mass of fluids. Fermentation is the process that yields organs with functions out of a mass, and it is in this respect that for the study of animal economy fermentation is more basic or primitive than the study of voluntary motion or sense. It is also in this sense that an animal can be the object of study of chemistry and biology at once.
For Willis as for Descartes, fermentation is fundamentally a thermal process, responsible for the production of heat in the body. Thus Willis maintains that the souls of animals are at once 'corporeal' and 'igneous [igneam]':
And even Brutes, make use of a material and divisible soul inferior to that of man, [which is] coextensive with the whole body, as it is seen to be constituted from several [parts],… seeing therefore that between the soul and the body there is no intermediate, but rather the members and parts of the body are organs of the soul.
While Willis presents much of his work in opposition to Charleton, this is not because he objects to the revival of Epicurean philosophy with which Charleton was associated, but because he believes that he is the superior interpreter of it. He calls upon Epicurus as ancient authority for the view of the soul-body relationship he defends:
With this agrees the teaching of Epicurus passed on from antiquity, and revived again in our century, which introduces the clearly corporeal Soul, [and] which consists in the texture of subtle atoms, and asserts,… that from the mind of Gassendi there resounds this same, that the animal is a sort of loom, in which the body is the warp, while the soul is the woof.
Leibniz for his part takes up the view that with respect to animal economy the principle of life is 'igneous', but he denies strongly that this principle is a soul.
For Leibniz, it is the body-machine itself that is igneous, and the full account of this igneous body-machine requires no mention of the soul at all. One may of course doubt that there is much difference between saying that there is an igneous and corporeal soul, on the one hand (Willis's view), and on the other that the body is moved by a vital, igneous principle while the soul is something to be invoked only quite apart from any corporeal function (Leibniz's view). But Leibniz's insistence that the body-machine itself, and not the soul, is the igneous principle behind vital phenomena, shows the extent to which he remains in his theory of animal economy true to the Cartesian view of the animal-machine, and to the Cartesian view --to which Willis assents, while nonetheless adopting the very un-Cartesian idea of a corporeal soul in animals-- that there can be no subtle or rarefied substance that serves to mediate between the soul and the body.
Now I have already mentioned that for Leibniz nutrition sustains the body machine entirely independently of the soul. The body and the soul are both very different kinds of automata, and both have very different appetites: the one for food, the other for a succession of perceptions. In the Animadversiones against Stahl of 1709-10, as we shall shortly see, Leibniz repeatedly accounts for the cohesion of the organic body, and its simultaneous dependence on constant influx of material from the environment surrounding it, not by appeal to the cohesive force of the soul, but by comparison to a flame's constant consumption of fuel. In short, if a body needs a soul to account for its cohesion over time, then so does a flame. The image of a flame burning wood or oil is a common theme in early modern accounts of nutrition. For example, Gassendi believes that sensation arises when the soul is 'kindled' in the body as fire is kindled in a log. "Food such as bread or herbs," he writes,
is no more distant from living and sensing flesh than a log is form a light-giving and burning flame… Just as… particles can be disentangled from a log, which particles will have a new power of lighting and heating once they move and arrange and dispose themselves in a new way --so spirituous particles can be obtained from dissociated food, which particles will possess an energeia of sensing once they are divided in a certain manner and disposed in a new way.
For Leibniz, it is because the body is like a flame that Leibniz believes that it is sustained or held together not by the soul but by the constant incorporation and transformation of new matter. This argument is developed at great length in the Animadversiones. As in the Corpus hominis, in his polemic against Stahl Leibniz explicitly distinguishes the natural machine from the 'hydraulico-pneumatic machine' in that it is also an 'igneous [pyria]' or 'pyrotechnical' machine. "Et dici potest corpus nostrum non tantum machinam hydraulico-pneumaticam, sed et pyriam esse." Leibniz writes that "there are in animals eruptions and explosions similar to those of a cannon [pyriis similes]," and again that "the animal body is a hydraulico-pneumatico-igneous machine; the force of impulsion [in animals] is born from explosions that arise in it like canons." Also as in the Corpus hominis, Leibniz compares the animal moved by the beating of the heart, or first motor, to the alchemical furnace whose heat is modulated by bellows and other implements: "We can easily conceive that the motive principle can augment or alter the energy in the body of an animal, in the same way that registers, bellows, or combustibles intensify or diminish the force of a stove."
The point of contention around which the entire polemic rotates is the question whether or not the soul need be invoked in order to account for the structural unity of the animal body. Unlike in earlier texts, notably the Machina animalis of 1677, in which Leibniz maintains that the study of animal economy ultimately serves to unravel the nature of life, here Leibniz seeks to radically separate animal economy and philosophy. An animal is alive, but none of the phenomena treated by animal economy can reveal this. An animal is alive in virtue of its capacity to perceive, which is a soul-based and not a machine-based activity. The polemic against Stahl, then, is Leibniz's first attempt to treat the subject of animal economy and at the same time to clearly demarcate it from the subject matter of philosophy, with which, he believes, Stahl himself has conflated it.
Leibniz is optimistic about the possibility of deducing the vegetative force that preserves the body "from the structure of the machine itself." For him, life could not possibly consist in the preservation of the body, since the nutrition, metabolism, and excretion of wastes through which this preservation is effected is fundamentally little different from the manner in which a flame avoids extinction by burning up surrounding matter. And a flame, Leibniz insists, is patently not a living thing. The comparison with the flame is central to Leibniz's polemic against Stahl, for in Leibniz's view it shows that there is no sound reason for cordoning living beings off from mechanistic explanation on the grounds that their capacity for self-preservation cannot, as Stahl would have it, be explained without appeal to the inherence of a soul: "That life preserves itself in casting off alien substances and in conserving the substances that it appropriates to itself does not rule out mechanism any more than the fact that the flame attracts air and sends off smoke." Leibniz cites experiments by Boyle to corroborate his view that an animal, like a flame, is in perpetual flux, and is nothing in itself without the constant appropriation of materials from the surrounding environment. The animal, in contrast with the flame, is constituted from fundamentally liquid parts, whose solidity arises only from the "cohesion that is produced by the conspiring movements of the fluid bodies."
For Leibniz, every living thing is ensouled, but it is not the soul's function to hold the body together, as it is for Stahl. In Leibniz's view, this function can be taken care of by the 'vegetative force' alone. Leibniz mocks Stahl's view of the soul as having a body-preserving function, comparing its role here to that of salt in cured ham: "The very celebrated author identifies [the role of the soul] with the power of preserving the body from its own tending towards death, since otherwise the bodies of living things would decompose, so that future life would have the value of salt, as was said in jest of the soul of a pig."
So the soul is neither associated with some particular bit of matter, nor is it responsible for holding all of the matter of the body together. What is its role, then, in the organization of the body? The short answer is that it does not have a role, as the body is for Leibniz an automaton. Nonetheless the soul will always be associated with some bit of organized matter or other. While this association will ultimately be explicated in terms of the preestablished harmony that is first mentioned by name only in the 1690s, in my view the picture of the soul as constantly associated with some bit of organized matter or other --rather than with some particular favored bit of matter-- is one that begins to take shape already in the early 1670s. Already in the Theoria motus abstracti of 1671, Leibniz seems to hold the view that there are indestructible bodies not because there is some particular bit of matter to which a mind is attached for all eternity, but because mind is always attached to some bit of organized matter or other; e.g.: "Body is as incorruptible as mind, but the various organs around it are changed in various ways" (A VI iii 521). Indeed, even in the letter to Duke Johann Friedrich of the same year, in which we have already seen Leibniz promoting the 'Jewish' doctrine according to which 'spirit is a bone', we also find Leibniz offering an account of soul as something much more difficult to pinpoint. He writes:
I hold first to the opinion that every body --people as well as animals, herbs, plants, and minerals-- has a kernel of its substance which, distinct from the Caput mortuum, is understood to be just like what the chymists take "from the damned and phlegmatic earth" This kernel is so subtle that it even remains left over in th ashes of things that have been burnt, and can, as it were, draw itself together into an invisible centre. As one can, to a certain extent, use the ashes of plants as seeds, and as the salient point in the foetus or fruit of a plant or animal already encompasses in itself the kernel of the whole body. Now as this kernel of substance consisting in a physical point (the proximate instrument, and as it were the vehicle of the soul constituted in a mathematical point) remains always, so it is of little consequence whether all gross matter is so in us.
The particular alchemical reference to the extraction of a kernel of substance from the Terra Damnata is to the process of tincture, in which a plant --say-- is burned down into a residue so that its soul essence (in the case of plants, its essential oils) can be separated from its physical body, which is thought to arise entirely from salt crystals. The essential oil ("essential" in the sense that it contains the individual essence of the plant whose body has been reduced to "damned earth" or a "death's head") has nothing hard or bone-like or atomic about it, and it seems very unlikely that Leibniz would invoke this alchemical comparison if what he had in mind was a Gassendian view (as Ric Arthur describes it) of material soul-atoms.
This suggests to me that, in spite of the concession to the view according to which 'spirit is a bone', already as early as 1671 Leibniz is already working towards the formulation of the idea that 'spirit is a stomach', that is, that it is not some particular bit of matter that remains forever attached to a soul, but rather that it is itself the power of rendering newly incorporated matter into the organized body of the corporeal substance associated with the soul. Later, Leibniz will develop the doctrine of preestabished harmony --according to which this associated matter comes to be associated with the soul not as a result of any causal power of the soul, but only as a result of God's plan at the Creation-- as well as the doctrine of the dominant monad --according to which the soul serves as the organizing principle of the body not through any causal influence upon the body but only through the relatively greater perception it enjoys of the particular body it dominates--. But as early as 1671 Leibniz is already uncomfortable with the idea of some arbitrarily bit of matter endowed with some special spiritual, and even immortal, properties. This discomfort becomes apparent, in my view, only when we pay attention to the alchemical background of Leibniz's writings of the early 1670s, and to his intense preoccupation with the metaphysics of nutrition that had been of such great interest to natural philosophers from Paracelsus to van Helmont and beyond.
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