Toleration of What Is above Reason: The Impact of Leibniz’s View on Religious Belief on Experiential Matters

Abstract

The aim of this paper is to show how the understanding of Leibniz’s notion of toleration in matters of faith should be considered not merely as a pragmatic, but also as an epistemologically and metaphysically relevant concept. Following Maria Rosa Antognazza’s account, I will argue that Leibniz’s view on the belief of mysteries is ‘above reason’ and the relation between faith and experience plays an important role in his discussion of transubstantiation with Des Bosses, but also that Leibniz allows for presumptions based on faith to enter metaphysical discussions. Doing so, despite the fact that we cannot achieve certainty in these matters and have to accept a variety of different beliefs regarding the same objects, enriches our understanding of the world and of God—and also gives us reason to take seriously Leibniz’s engagement with corporeal substances, albeit only as presumptions rather than as necessary consequences of his basic metaphysical system. Finally, I will illustrate this point by showing how it is also in play in Leibniz’s response to Tournemine regarding the mind-body-union.

1. Introduction

It is not obvious that Leibniz can be counted among the most modest of thinkers. After all, he puts forward his own metaphysical system that sets out to solve more or less all problems that have been plaguing philosophers for millennia, while at the same time aiming to reconcile the Catholic and Protestant factions, participating in some of the most important political debates of his time, inventing or improving upon several machines and apparatuses, composing a history of the house of Brunswick, presenting his infinitesimal calculus to the world, among many other important or at least notable achievements.1 At the same time, there is a certain humility expressed in his own words, first and foremost in his affirmation that what he is doing is not revolutionizing philosophy. Rather, according to his own words, his works are supposed to unearth the correct assumptions and hypotheses that are already found in all the preceding philosophical traditions and systems, because “we find in most philosophical sects more good sense than we had realized” (Leibniz 1997, p. 85) as they “are right in a good part of what they propose, but not so much in what they deny” (Leibniz 1969, p. 655; Leibniz 1875–1890, III, p. 607). Of course, even here there are limits. What the Cartesian ‘sect’ has to say about extended substance and motion, for example, does not exhibit too much sense.2 Something similar can be said about his attitude towards doctrinal differences, although it is here a bit more difficult to gauge the exact extent or import of his attitude. It has been suggested that his push for toleration3 in this arena is first and foremost a means to reconcile unnecessary divides in the Christian church (see Lærke 2019a, pp. 269–72). According to this understanding of his position, Leibniz’s tolerant attitude should be regarded more as a pragmatic or ecumenical tool, rather than a deeply held epistemological conviction that is based on genuinely held beliefs about the limits of our knowledge and the certainty we can achieve in important aspects of our religious life. But others have defended that the latter should be considered to be Leibniz’s true position. In particular, Maria Rosa Antognazza has argued that Leibniz’s commitment to toleration is much stronger and not merely comprises pragmatic, but also, and importantly so, epistemological and theological grounds (Antognazza 2002, 2013, 2018). In the following, I will not assess this dispute directly but will show how Maria Rosa Antognazza’s position gains some traction by the analysis of a concrete example, namely Leibniz’s correspondence with Bartholomew Des Bosses. Here we see how his epistemological urge for toleration is extended from doctrinal or more narrowly conceived theological questions to issues considered to belong to genuine philosophical inquiry. I will do so by, first, introducing Leibniz’s notion of ‘truth above reason’ and his discussion of the similarity between faith and reason. I will argue how and why further support not only can, but also should, be given to the claim that the nature of religious belief is of fundamental importance to Leibniz’ philosophical outlook in general. I will then take a closer look at how these concepts are in play in the discussion of transubstantiation in Leibniz’s correspondence with Des Bosses. Here, the relation between religious belief (change in substance) and experience (endurance of appearances or sensible properties) is especially pronounced. I will argue that in particular the introduction of the ‘vinculum substantiale’, but also the discussion of corporeal substance in this correspondence should be viewed as being motivated by presumptions based on faith and thus should be approached with the same attitude as truths above reason are. I will conclude with another example where we can see Leibniz employing this tactic, this time with regard to the question of the mind–body union. The aim of this paper is to show that a tolerant attitude, on the one hand, is built into Leibniz’s view of the nature of belief given the world is infinitely plentiful, but is also, on the other hand, a means to get a better grasp of and deeper love for God by engaging seriously with all the possible meanings our experiences can have.

2. Knowledge, Limitation, and Toleration: Leibniz’s Notion of ‘above Reason’

For Leibniz, not every belief that is related to religious issues raises the question as to whether it should be tolerated, because he employs the traditional distinction between natural theology, which is for him that “which could be acquired from the nature of things by the power of man’s natural abilities” (Leibniz 2016, p. 199), and revealed theology. Thus, what falls under natural theology is what is susceptible to proof, such as the existence of God, the immortality of the soul, and to some extent even preestablished harmony, and we can have genuine knowledge of these things (For a detailed account, see Lærke 2019a, pp. 252–58). But there are, in addition, certain theological doctrines that are “received from miracles and martyrs, and passed on to us by the unbroken tradition and writings” (Leibniz 2016, p. 104; Leibniz 1923–, VI.vi, p. 2323)4. Among these are the so-called mysteries of faith, which cannot be proven in a strict sense, in part because we do not even fully know how they are to be understood—if they were fully understood or even just fully understandable, they would not be true mysteries at all (Leibniz 1923–, VI.iv, pp. 800–1)5, but rather something we simply have not understood yet. Most commonly counted among them, and treated extensively by Leibniz, are the Trinity (God as Father, Son, and Holy Spirit), Incarnation (Jesus Christ’s becoming flesh) as well as the Eucharist (bread and wine becoming flesh and blood).6 This notion of mysteries as essentially mysterious puts Leibniz prima facie in an awkward position. After all, it is generally held that he is committed to the intelligibility of the world, which rules out that the mysteries could be treated as absolutely incomprehensible or that he could allow for them to be accepted on faith alone, independent of their being in accordance with reason. Such a view would, furthermore, be irreconcilable with the claim that we can form genuine beliefs about them in the sense that we assent to them. The solution he proposes is to distinguish that which is ‘above reason’ from that which is ‘against reason’. True mysteries are of always the former kind, but never of the latter. They follow the universal order of the world, even if we limited beings do not grasp this universal order well enough to be able to see how they fit into it. After all, there is nothing, not even true miracles, that can go against the decreed divine order. As Leibniz states in the Discourse on Metaphysics: Whatever happens in the world is “always in conformity with the universal law of the general order, even though [it] may be above the subordinate maxims” (Leibniz 1989, p. 48; Leibniz 1923–, VI iv, p. 1554) and this is true as much for mysteries as it is for individual miracles.

But what precisely is this notion of a ‘truth above reason’?7 In the Theodicy, Leibniz introduces it in distinction from ‘contrary to reason’ and as following from the fact that there are different kinds of necessity, namely logical or metaphysical necessity on the one hand and physical necessity on the other. He continues: “For what is contrary to reason is contrary to the absolutely certain and inevitable truths; and what is above reason is in opposition only to what one is wont to experience or to understand” (Leibniz 1985, Preliminary Discourse, §23). Later in the text, he emphasizes again that the crucial point is the lack of understanding we have, which makes mysteries appear to us as violations of the natural order, but not that the mysteries introduce any kind of irregularity into the preestablished harmonious order of the world. Therefore, above reason is “that which one cannot comprehend and which one cannot account for” (Leibniz 1985, Preliminary Discourse, §60). It is important to note that this characterization of ‘above reason’ is not supposed to merely point out that something is beyond our current grasp, but that there is a general epistemic limitation that finite minds are subjected to.

That Leibniz has not just some kind of coincidental ignorance in mind, but a more fundamental constraint imposed on our knowledge, becomes clear when we refer to the discussion of this terminology in the New Essays, where Leibniz sets out to criticize Locke’s way of defining ‘above reason’ along with ‘according to reason’ and ‘in opposition to reason’. To be fair, it is less Locke’s own words that gives rise to this discussion, but rather the misleading phrasing in the French translation that Leibniz uses. While Locke himself introduces propositions above reason as “Propositions, whose Truth or Probability we cannot by Reason derive from those Principles [i.e., ideas we have from sensation and reflection]” (Locke 1975, p. 687; Essay IV xvii, §23), the French translation renders it as referring to propositions whose truth or probability we do not see as derivable by reason rather than as propositions whose truth we simply cannot derive by reason.8 This misleading translation is then expanded upon by Leibniz and he ascribes to Locke the following view: under ‘above reason’ falls “every view whose truth or probability we do not see to be derivable by reason from sensation or from reflection” (Leibniz 1981, p. 492). It is this characterization of ‘above reason’ that Leibniz objects to when he worries that, for Locke, too much and at the same time nothing at all will be ‘above reason’. It is too much because everything “we do not know and lack the capacity to know in our present state” (Leibniz 1981, p. 493) is thereby rendered ‘above reason’. This includes also the knowledge of all those facts that we simply do not yet have the right means to acquire or whose acquisition is hindered by the imperfection of our senses rather than by any insufficiency of our reason. This turns ‘above reason’ into little more than a misleading way of referring to what is presently, but merely coincidentally, outside our stock of knowledge. And while this seems too broad an extension for a theologically useful notion of ‘above reason’, it removes, at the same time, also the possibility of a narrower and more profitable notion. After all, so Leibniz, God could always supply us with the means to obtain any truth whatsoever through sensation and reflection. Taking this possibility into account, then, strictly speaking, nothing would be truly above reason. And,

[i]ndeed, the greatest mysteries are made known to us by God’s testimony, which we recognize through those rational grounds for belief on which our religion rests—grounds which unquestionably depend on sensation and reflection. The question, then, seems to be not whether the existence of a fact or the truth of a proposition can be deduced from the sources which reason employs (from sensation and reflection, that is, or rather from the outer and inner senses), but whether a created mind is capable of knowing the wherefore of this fact or the a priori ‘reason’ for this truth. Thus we can say that what is ‘above reason’ can indeed be learned but cannot be understood by the methods and powers of created reason, of however great and exalted a kind.

(Leibniz 1981, p. 493)

What does this discussion mean for religious beliefs? Leibniz establishes here the distinction between what falls under natural theology as distinct from what falls under revealed theology and from this distinction follows that there are several kinds of propositions relating to faith. Some of these propositions are not up for debate because they are according to reason such that we can prove them and attain absolute certainty regarding their truth, i.e., they can be ‘understood by the methods and powers of created reason’. Because we can gain absolute certainty regarding their truth, we do not need to accept that others hold opposing views—as we know and can provide necessary and sufficient reasons that show how any opposing view is necessarily false and therefore should not be assented to. But there are others, in particular the mysteries, that do not allow for such a proof of their truth. This is not to say that the mysteries are unintelligible or unreasonable, since if they were unintelligible, we could not believe them in the first place and if they were unreasonable, we would be misguided if we were to accept them. However, this just answers the question of why we believe them, namely because we understand them, and our reasons for believing them are enough for us to assent to them. It is a different question to ask whether we should believe them. Leibniz holds that the reasons we can provide in favor of such truths above reason justify our belief without certainty of their truth. It should be noted that the requirement he provides seems to be intended for the philosopher rather than for anyone who assents to a particular belief,9 because what needs to be established in order for someone to be entitled to accept such a belief is in fact quite onerous: it must be shown that the belief in question is not contrary to reason, i.e., that it is possible (because if it were contrary to reason, it would be impossible and indefensible). Naturally, this is not sufficient to account for any belief, as we do not assent to anything simply because it does not contradict what we regard with reason to be true. Therefore, there must also be positive reasons for adopting it, but according to Leibniz these reasons can vary from person to person, even when we consider beliefs regarding the same object. Some of those reasons we have already encountered above: they are received from history, witnesses, and testimony; many others are personal and incommunicable.10 However, since we do not have any absolutely certain knowledge in this area and do not fully understand what those beliefs are about in the first place, what falls under its remit, such as the mysteries, can be interpreted in several ways and have different meanings for different persons. The meaning one ascribes to a specific mystery, and even the acceptance of any particular mystery, will depend on individual reasons such as which witnesses and whose testimony one has encountered or takes to be authoritative, which considerations about the world one has engaged in, or which texts one has read. From this individual character of the meaning of mysteries, several important consequences follow regarding the toleration of the beliefs held about them, namely (a) that the belief in or the rejection of any of the mysteries in any particular understanding of them is not essential to the pious character of the individual, especially in regard to their salvation (in difference to natural theological truths which are a non-negotiable stock of necessary truths that can be known a priori and must be adopted). Thus, there are two kinds of dogmas: necessary ones and indifferent ones. Furthermore, (b) the truth of any possible understanding can be presumed11 and held to be true by any individual who perceives themself to have sufficient reasons to do so. Furthermore, given this analysis of belief in mysteries as justified by the possibility of their truth, the sufficiency of purely personal motivation, and the additional view Leibniz holds, namely that we cannot prescribe certain beliefs and force assent12, Leibniz’s position seems to demand toleration of a variety of different takes on one and the same mystery, and this not only for pragmatic reasons but also for epistemological and metaphysical ones.

If we put what has been said so far in a nutshell, we arrive at the following view of beliefs insofar as they concern mysteries: their object is partly intelligible; they must be shown to be possible (but not to be true); they can be reasonably believed (for explicable or inexplicable reasons); they cannot be known with absolute certainty; they can and do have many meanings. But so far, this has led only to a negative result: we cannot demand anyone assent to any mystery or ascribe any particular meaning to it because they are not fully intelligible and admit many interpretations. But now one might wonder why Leibniz then bothers throughout his life to provide analyses and explanations of various of the mysteries. It might be simply the case that he wants to explicate his own interpretation of them and elaborate on the meaning he ascribes to them, but this does not explain why he also devotes much time and attention to explaining specific understandings of certain mysteries he does not assent to, e.g., transubstantiation. He obviously thinks that there is value in all those different meanings and hypotheses regarding the mysteries, even in those that he himself does not ascribe to, neither as a Protestant nor as an individual believer.

Before we move on to the analysis of the discussion of the specific mystery of the Eucharist, in order to see how this commitment to unearth possible meanings is present in it, there is one last, but very brief point I want to make. Already the summary of the nature of belief might have led some readers to think that it is quite similar to Leibniz’s accounts of our knowledge of matters of fact—apart from the difference in source: in both cases, the source seems to be experience, although in the case of the mysteries this is a very particular kind of revelatory historical source. And Leibniz is in fact very clear that faith and experience are structurally similar. In the opening paragraph of the ‘Preliminary Discourse’ of the Theodicy, he makes this relation explicit:

I begin with the preliminary question of the conformity of faith with reason […] I assume that two truths cannot contradict each other; that the object of faith is the truth God has revealed in an extraordinary way; and that reason is the linking together of truths, but especially (when it is compared with faith) of those whereto the human mind can attain naturally without being aided by the light of faith. […] It is in the same sense that sometimes reason is contrasted with experience. Reason, since it consists in the linking together of truths, is entitled to connect also those wherewith experience has furnished it, in order thence to draw mixed conclusions; but reason pure and simple, as distinct from experience, only has to do with truths independent of the senses. And one may compare faith with experience, since faith (in respect of the motives that give it justification) depends upon the experience of those who have seen the miracles whereon revelation is founded, and upon the trustworthy tradition which has handed them down to us, whether through the Scriptures or by the account of those who have preserved them.

(Leibniz 1985, Preliminary Discourse, § 1)

Let us now see how this analogy between beliefs based on experience and mysteries of faith plays out in one particular case, namely Leibniz’s correspondence with the Jesuit Bartholomew Des Bosses.

3. Faith and Experience, Eucharist and Bodies in the Correspondence with Des Bosses

Given how many volumes are filled with Leibniz’s various correspondences, let me say briefly why I focus here on the one he entertained with Des Bosses rather than on any of the others (or why I do not take recourse to many of them in order to be able to claim that I am providing a fuller picture of Leibniz’s thought): The debate of the Eucharist, that is, of one specific mystery of faith, not only features prominently in this correspondence, but it constitutes a particularly interesting treatment of it. In these letters, the focus is not so much on what is the one way in which this particular mystery must be understood, but it is almost a smorgasbord of possible accounts as to how transubstantiation could be reconstructed in line with theological demands as much as with Leibniz’s own metaphysical system—and this, despite the fact that Leibniz, as a Protestant, is not required to provide any account of transubstantiation at all. That is, when it comes to the mystery of the Eucharist—if we want to call upon the terminology introduced above—the meaning Leibniz ascribes to it is quite different from the one Des Bosses assents to; for Des Bosses, transubstantiation is the true meaning of the Eucharist, whereas for Leibniz “there is no place for either the transubstantiation or consubstantiation of the bread” (Leibniz 2007, p. 153). Nonetheless, Leibniz (with support from Des Bosses) aims to show throughout this correspondence how both of these meanings can be understood in a manner that is not contrary to reason and according to what we know to be true. Furthermore, this correspondence also features the much-maligned notion of a vinculum substantiale, which, for the purpose of this paper, is a feature rather than a bug. This ‘substantial bond’ is among the most puzzling features of Leibniz’s mature philosophy, but it is so for a peculiar reason. It only appears—or seems to appear—in one place, viz. in this very correspondence with Des Bosses.13 Furthermore, its status is unclear: Early commentators have regarded it as a mere diplomatic concession in order to solve a specific theological problem (namely, transubstantiation) (Russell 1937, p. 152). However, more recently, others have pushed back against this solely negative assessment and consider the vinculum substantiale as a hypothetical construct, albeit one that causes more problems than it solves and that is thus ultimately (and rightfully) rejected by Leibniz (Adams 1994, pp. 299–303; see also Garber 2009, pp. 372–82). Brandon Look, who has probably worked more on this correspondence as well as on the vinculum substantiale than anyone else, argues that the fact that Leibniz does not adopt this substantial bond in the end as a genuine metaphysical item should not lead us to overlook the fact that its failure as a metaphysical tool can serve as a helpful means to understand his mature metaphysics (Look 1999). I think this is right, but here I want to argue that it is, in addition, a helpful means to understand not how there are bodies (for which the vinculum is supposed to provide the means) but why Leibniz sometimes seems to accept such ‘bonded’ substances and sometimes not, and how this is related to this view on beliefs we hold due to our faith. What I aim to show in the following is that if we keep in mind the attitude of toleration as it follows from the status of beliefs above reason, we find that this very same attitude enters also into more classically philosophical matters, e.g., when it forms the background to the question if there are corporeal substances. What I do not aim to do here is to solve the hotly debated question as to whether Leibniz in fact assents to the proposition that there are corporeal substances or not14, but rather to show that there might be reasons why Leibniz seems to vacillate between the two positons and that these reasons stem from his view on religious belief and the tolerant attitude prescribed by them.

Before we get to the heart of the matter, let me first locate the correspondence in the context of the life and works of Leibniz. It takes place between 1706 and 1716 and when put in relation to other important philosophical writings of his, we can say that it begins roughly ten years after the publication of the Système nouveau de la nature (1695), which marks the first publication of his metaphysical system of preestablished harmony as well as the beginning of an increasing use of the notion of simple substance (Antognazza 2009, p. 352), and two years after abandoning work on the New Essays (1704), from which I have drawn above. In addition, the most notorious expositions of his metaphysical system emerged during this time: The Monadology and the Principles of Nature and Grace (both 1714); it is furthermore the period in which the Theodicy (1710) was published (and translated into Latin by none other than Des Bosses). We are, therefore, in the time period where Leibniz is committed to monads, i.e., simple substances characterized by perception and appetite, whose perceptions of the whole universe explain the phenomena and their harmony.

The correspondence itself covers a wide variety of topics15, but because they are frequently addressed in a roundabout way, not always related to each other and sometimes only of interest to those with an inclination for the machinations of church politics, it is tempting to view also the question of the Eucharist in isolation and treat it as if it were independent of the general discussions regarding metaphysics, faith and belief that we find in these letters. The first reason why we should refrain from doing so is found in the motivation for the exchange itself, which Des Bosses states in the first letter: “my plan, such as it is: namely, that with your notions preserved so far as possible, I may accommodate the substance of them with the doctrines of Aristotle, or rather, accommodate the former with the latter and both with the dogmas of the Church” (Leibniz 2007, p. 7). The discussions of dogmas, in these letters predominately regarding the Eucharist, are not discussions that simply happen to happen besides others. Rather, they are from the outset an integral part of the program of the exchange, part and parcel of the more general philosophical discussions. It is therefore unsurprising that the question of the explanation of transubstantiation is first introduced not as a problem of its own, but in the context of the relation between monads and matter, that is, between metaphysically fundamental items and bodies such as bread and wine. Leibniz immediately understands Des Bosses’ request for an elucidation of this issue as an invitation to hypothesize about how transubstantiation could be explained given the parameters of his own metaphysical system. The answer he gives is not a straightforward explanation, but phrased as a conditional, based on an assumption of what Des Bosses’ belief in transubstantiation requires, i.e., what meaning he attaches to the mystery of the Eucharist. Leibniz assumes, correctly, that for the Jesuit Des Bosses the general meaning of transubstantiation is the destruction of one set of substances that are the bread and wine, and its replacement by another set, which encompasses different substances, while retaining the perceptible properties of the bread and wine. This first attempt at an explanation runs as follows:

If you wish to hold real accidents that remain without a subject, it must be said that when the monads constituting the bread are destroyed with respect to their primitive active and passive powers, and the presence of the monads constituting Christ’s body is substituted for them, there remain only the derivative forces that were in the bread exhibiting the same phenomena that the monads of the bread had exhibited.

(Leibniz 2007, p. 153)

Surprisingly, it is Des Bosses who concedes that this explanation would agree with the beliefs of his order and of himself, but most unfortunately does not seem to align too well with Leibniz’s own metaphysical assumptions, because derivative forces are modifications of primitive forces, and if the latter are destroyed, then so must be the former (Leibniz 2007, p. 159). In the following letters, both exchange a few more—and radically different ideas—as to how transubstantiation and monadological metaphysics might be compatible before the topic is drowned out by more general discussions of politics and metaphysical issues. It is Leibniz—rather than Des Bosses—who revives the topic, this time in the context of Des Bosses’ announcement that he plans to write a treatise about corporeal substance. Rather than giving an exposition of his view on this matter or rather than either confirming or denying the existence of such substances, Leibniz phrases his suggestion again in the form of a conditional:

If corporeal substance is something real over and above monads, as a line is taken to be something over and above points, we shall have to say that corporeal substance consists in a certain union, or rather in a real unifier superadded to monads by God, and that from the union of the passive powers of monads there in fact arises primary matter, which is to say, that which is required for extension and antitypy, or for diffusion and resistance.

(Leibniz 2007, p. 225)

An interpreter would be hard-pressed to find reasons here to read this either as an affirmation or as a rejection of corporeal substances on Leibniz’s part, as he explicitly states the reason for these musings about the possibility of corporeal substance. The reason he provides is that the basis for introducing corporeal substances at this point is found not so much in his own metaphysical assumptions, but rather in what is above reason: in faith. He is in this passage quite explicit that a sufficient reason for introducing corporeal substances into our discourse can be found in one’s individual belief, while our knowledge of metaphysics supplies us with the means to furnish this assumption with clearer meaning: “if faith drives us to corporeal substances, this substance consists in that unifying reality, which adds something absolute (and therefore substantial), albeit impermanent, to the things to be unified” (Leibniz 2007, p. 227). Here, beliefs above reason and reason come together in Leibniz’s consideration: What our best available theory tells us to be the case and about which we can thus be at least morally certain, i.e., what is in accordance with preestablished harmony and monadological metaphysics (see Leibniz 1997, p. 20), is called upon to account for what we are entitled to presume to be true, given that it does not contradict these principles and is possible. In this correspondence, we thus see Leibniz adopting a two-pronged strategy:

(1) We can deliberate on what the best metaphysical account of the phenomena is and according to this deliberation, it is only monads or simple substances that we need in order to explain all of them.16 Furthermore, if we operate in this manner, we do not need to invoke any proposition that is not proven and merely presumed: “The hypothesis of mere monads has this distinction, that, with it assumed, nothing remains unexplained, nor is anything assumed except what is proven and what must be assumed necessarily.” (Notes on Des Bosses’s letter of 12 December 1712; Leibniz 2007, p. 307).

(2) We can entertain presumptions that are based on grounds other than strictly monadological ones. It is in this context that Leibniz introduces the vinculum substantiale into the discussion with Des Bosses. On the one hand, this bond serves to account for transubstantiation as it is a “unifying reality” (Leibniz 2007, p. 227) that allows for the monads that ground the appearance of the bread to remain while the substance they, qua superadded vinculum substantiale, constitute changes into the body of Christ. Transubstantiation is then the imposing of the substantial bond of Christ onto the body that is the bread. But more importantly, it can only fulfil this explanatory role because it is, more generally, an account of corporeal substance, which requires such a unifier that renders it substantial by giving it a genuine unity, if it is to exist in a monadological system. Accordingly, we can also see what the status of the vinculum substantiale is: it is an attempt to accommodate a religious commitment of one corporeal substance changing into another within a monadological metaphysics, which is, as it happens, at the same time an accommodation of our everyday metaphysical commitment to corporeal substances. In this sense, it is neither something that Leibniz himself is committed to nor is it a mere concession to Des Bosses. Rather, it should be understood as a genuine attempt to provide a meaningful account of a possibility that is entertained based on reasons of faith. Therefore, the question as to whether Leibniz truly believes, at least for a time, that there is such a bond or not, is the wrong question to ask. According to what we have seen, it might very well be one of the manifold ways in which an attempt to give meaning to an assumption based on faith could proceed: by entertaining it as an option among many which, as long as it is not contrary to monadological principles, can be presumed and should be investigated—even by those who do not presume it themselves.

We have to tread carefully here: Leibniz does not want to say that if faith drives us to the assumption of corporeal substance, then any account of it or any meaning ascribed to it will do. The limits imposed by reason still stand—unfortunately for Cartesians, whose conception is therefore still not a candidate for what it possibly means to be corporeal substance. But here, metaphysics and faith meet rather than diverge: While the assumption of corporeal substances does not enjoy certainty, there are reasons that can be drawn from faith that entitle us to presume their existence. Leibniz himself invokes, as we have seen, in particular the idea that a certain belief in mysteries, such as in transubstantiation, can supply such a reason. What this exchange shows is that the belief in corporeal substances can proceed in tandem with the belief in the mysteries: as long as there is nothing that precludes them, i.e., as long as they are possible, we can, provided we have reason to do so, presume their existence and try to deepen our understanding of them by figuring out how they might be accounted for. Furthermore, I do not see that there are grounds to restrict this to being a prerogative of beliefs based on faith. We might have plenty of reasons to presume the existence of bodies, such as our daily experience or our dabbling in physics. In fact, the correspondence supplies another, almost universal reason why we presume the existence of material unities, even though it is Des Bosses who introduces it: it is innate to us that we attribute reality to corporeal substances (Leibniz 2007, pp. 237; see also p. 329). Accordingly, to regard Leibniz’s view on belief based on faith and the toleration that follows from it because its object cannot be fully grasped as irrelevant to his general philosophical outlook might very well be mistaken. I do not want to claim that it is obvious that Leibniz holds that the meaning of corporeal substance is in part and essentially beyond our grasp, and thus that it belongs to the essence of corporeal substance to remain at least partially unclear and hidden to us. I merely want to suggest that this would be a possible explanation as to why he sometimes seems to endorse their existence and sometimes seems to reject it, namely that he merely presumes their existence or makes room for their analysis even if he does not feel compelled to accept their existence. Thus, to treat them as either existing or non-existing would both permissible, as long as neither option is against reason. Another reasons to think that this is a viable view for Leibniz might also be found in a fact that is at the intersection of metaphysical and religious belief: the infinite plenitude of the wonderful thing that is the whole of creation. In a short commentary on John Toland’s Christianity Not Mysterious, he writes:

[T]he divine nature itself, which is infinite, is necessarily incomprehensible. In the same way, there is something of infinity in all substances too, which is why we can perfectly understand only incomplete notions, like those of numbers, shapes and other such modes that are abstracted from things by the mind. I admit that we have, as the author quite rightly observes, some distinct notion of the infinite (namely the infinite in itself, or absolute infinite), but through the finite intellect given to us there is no distinct consideration of infinite varieties, yet this would very often be needed in the comprehension of divine matters.

(‘Hasty comments on the book Christianity not Mysterious, written 8 August 1701’ Leibniz 2016, p. 212)

Engaging with all the different meanings that this creation opens to us might not bring us metaphysical certainty, but it can lead us to a better and deeper understanding of God and his creation, thus maybe not moving faith closer to metaphysics or metaphysics to faith, but making us see how both together move us, for Leibniz, to a deeper love of God. It is this positive role of the mysteries, namely that they open up a variety of different understandings, that thereby grounds Leibniz’s toleration for different understandings of them, not merely as something to be accepted because we cannot prove it to be otherwise, but as something to be embraced and to be endorsed.

4. When Metaphysics and Faith Meet: Leibniz’s Answer to Tournemine

According to the picture presented here, there are certain parameters that Leibniz assumes we not only can take for granted but must assent to. Among them are the validity or truth of certain assumptions (i.e., next to his favorite principles of sufficient reason, contradiction and plenitude, preestablished harmony, and the grounding function of monads), but also further propositions that are of concern for us as finite individuals. We can know that God exists and created the best or that our soul is immortal. But we are also limited creatures confronted with an infinite and thus in part incomprehensible world. This means that there are various ways to understand and account for these only partially accessible aspects of it and we have to accept that what we presume and hold to be true regarding them falls outside of what we can know with reason. This further entails that, within the parameters set by our knowledge, we have to tolerate that others might hold quite different beliefs regarding the same objects or aspects, simply because they differ in the reasons that motivate their assent or because they lack reasons to assent at all. This does not mean that we do not think, maybe even rightfully so, that our reasons are the better ones. But since we cannot prove the necessary truth of these beliefs, we cannot force others to assent to them. Taken in such a general manner, it matters little if we talk about toleration of religious assumptions or about assumptions about the kinds of items we should allow access into our ontology beyond those that our metaphysics absolutely requires.

According to the view proposed here, what Leibniz does when he entertains the position of one of his correspondents is not so much a concession that merely aims at converting them to his own point of view or placating them by pretending that their view somehow aligns with what he himself holds, but it is the application of a genuinely held belief that different motivating reasons lead to different views and that there is something valuable in understanding those views—not only for the correspondent but for Leibniz himself. Take, for example, the general problem of the mind–body union as pointed out by Tournemine, who responds to Leibniz’s presentation of the preestablished harmony in the New System by highlighting that mere harmony between bodies and perceiving simple substances, no matter how perfect, is not a genuine unity. Far from opposing this assessment, Leibniz concedes its truth but does not consider it to be a rejection of a possible union—simply because this union is akin to the mysteries and thus there are, at least for Leibniz, reasons to assent its existence regardless of the fact that his own metaphysical system does not require it. The reasoning for this follows the lines we have just partly observed, partly unearthed in the correspondence with Des Bosses. Leibniz writes in response to Tournemine’s criticism:

But since this metaphysical union, which is added on to that, is not a phenomenon, and as we have not even been given any intelligible notion of it, I have not taken it upon myself to look for an explanation of it. […]

That is, the union between mind and body is not something that is accessible to an a priori proof. From the system of preestablished harmony, no immediate explanation of this union follows nor is this union something we even understand clearly enough to expect such a proof. Rather, the system of preestablished harmony by itself can explain the phenomena while remaining neutral on the status, and even the existence, of such a union.

However, I do not deny that there may be something of this kind; it would be something like presence, which is also something whose notion has not been explained as it is applied to incorporeal things, and is distinguished from the relations of harmony which go along with it. […]

That this union is not demanded by preestablished harmony is not a sufficient reason to exclude it as a possible existent. Rather, the parameters according to which an explanation of this union can be given, are dependent on a monadological account insofar as the meaning ascribed to this union must not be contrary to it, that is, as long as such a union is possible and can be explained in a way that is not contrary to reason.

When we see that there is union and presence in material things, we think there must be something somehow analogous in immaterial things; but since there is nothing more that we can understand about these things, we have only obscure notions of them. […]

Leibniz reiterates that the assumption of such a union is not without any reason, albeit it lacks the strong kinds of reason that we demand of our strictly metaphysical explanations. But given that we see something analogous in the phenomena we perceive and therefore have grounds to presume something similar in the case of mind and body, we can legitimately presume such a union without having a full and clear comprehension of it. The union of mind and body thus presents itself as the mysteries do and hence must be treated in a similar fashion, viz. that we cannot ask for and expect conclusive proof. Nor can we demand universal agreement that such a union in fact exists:

It is the same with mysteries, where again we try to elevate what we understand in the normal course of created things into something more sublime which would correspond to them with respect to nature or the divine power; but we cannot understand in such things anything sufficiently distinct to be suitable for making a fully intelligible definition.

(Leibniz 1997, p. 250)

The point that can be extracted from of Leibniz’s answer to Tournemine is again a limited one: it does not explicitly commit Leibniz to there being (or there not being) a genuine union between mind and body. What is important here is rather that the way we have seen Leibniz justify the presumption of and explain the status of belief in matters that are above reason seems to be extended now to other questions like the union of mind and body. It is in the correspondence with Des Bosses that it becomes clear that Leibniz himself accepts that there are reasons that stem from faith, which lead us to presume propositions of which we cannot be certain to the same degree we are when it comes to strictly metaphysical assumptions. Here, in response to Tournemine, he adds reasons from common experience and extends the domain of presumptive items even further. Rather than this being an epistemological failure, because it leads us to varying accounts of the same issue between which we cannot decide, it seems that Leibniz embraces it as a consequence of the richness of the world to which we only have a very limited access. Maybe sometimes it is not so much about being absolutely right about many things and more about not being wrong about them. Once we have ascertained that the manifold ways in which creation presents itself to each of us are possible, we can marvel at these numerous ways of finding meaning in it. It is then up to the philosopher to investigate all these meanings, thereby deepening the infinite wonder that we feel for this best of all possible worlds and the mystery it is.17