Marcelo Dascal

The main thesis of this paper is that Leibniz’s encompassing rationalism, as expressed by the Principle of Sufficient Reason (as in the formula nihil est sine ratione: Grua 13, 267, 268, etc.), requires a substantial modification of the conception of Reason usually attributed to Leibniz. This modification consists in a shift from a conception that views deductive logic as the paradigm of Reason to a conception that acknowledges also the need and legitimacy of non-conclusive forms of reasoning as essential components of rationality (as in the formula blandior ratio: C, 34). I will first survey how extensive, albeit usually overlooked, is Leibniz’s concern with these “weaker” forms of reasoning, and how crucial they are for many of his practical and theoretical endeavors. I will then trace back this acute need of Leibniz´s brand of rationalism to the peculiar nature of the Principle of Sufficient Reason (PSR), as opposed to the other basic principle of his philosophy, the Principle of Contradiction (PC). I will present here only the bare bones of the argument, in a sort of extended summary, omitting the textual support as well the references to the relevant secondary literature.

Leibniz the jurist and the counsel needs “soft reason” both for theoretical and for practical purposes. To be sure, Leibniz often defines rigorously the principles of justice and draws strictly deductive conclusions from them, thus presenting the theory of justice in quasi-mathematical terms. And yet, jurisprudence is the art of transforming these abstract principles into a corpus of organized law, providing the guidelines for interpreting and applying the law, and actually using them and critically evaluating such uses. On all these counts, “juridical logic” makes use, essentially, of at least two (in fact, many more) “soft” components: presumptions and hermeneutics. The former are, most typically, procedural rules that distribute asymmetrically the onus probandi – the best known of such rules being the presumption of innocence. A presumption explicitly favors a certain conclusion, but only insofar as no stronger reasons against such a conclusion are produced. The “default” conclusion, therefore, is not logically entailed, since it can be overruled. It is, nevertheless, the conclusion the system embedding such a presumption allows one to draw in the absence of contrary reasons. This is, admittedly, a weak kind of inference, if compared with entailment, and yet a widespread and seemingly indispensable one for a judicial system to function. Legal hermeneutics, on the other hand, which is always required when the issue is to decide how to match laws with specific cases, is “soft” insofar as it consists in a non-formalizable process of interpreting a text under varying contextual conditions.

Leibniz the political advisor and self-appointed politician needs “soft reason” because politics is always Realpolitik, i.e., the art of the realistically possible rather than of the logically possible. As such, it has to do with a realistic assessment of the circumstances, forces, tendencies, and psychological dispositions of the rulers of the world. This assessment requires one, among other things, to undertake the difficult and imprecise task of putting oneself “in the place of the other”. Once the various factors are assessed and weighed, a course of action best serving the interests of one’s employer, one’s country, one’s nation, one’s faith (pick up your choice) can be chosen. The next step is to deploy one’s persuasive talents to get the relevant persons to do the relevant things according to the chosen course of action. All of these steps are, to be sure, rational – for we are speaking about rational, not emotional persuasion.. But they are surely not demonstrative. The use of the genre or title demonstratio for resolving demonstratively (and, of course, in a favorable way) the issue of the election of the King of Poland should not mislead us in this respect, for it is nothing but a rhetorical device. In this, as well as in its remarkable well-informedness, it does not differ from the quite persuasive argumentation exhorting the most Christian king to divert his belligerent appetite from his European neighbors to Egypt, an argumentation that soon makes room for the not less persuasive but much more inflamed rhetoric used against the same “most Christian Commander”.

Leibniz the church politician needs “soft reason” because the achievement of his irenical efforts – he soon realizes – is not just a matter of formulating a doctrinal basis acceptable to all Christian factions. The doctrinal issues turn out to be, in fact, only a small part of the questions under contention, and perhaps the easiest ones to resolve. The rest requires endless negotiations, with an intricate and subtle “methodology” whose variants Leibniz analyzes in detail. Instead of the “hard logic” of simple dichotomies, that leads to the “method of exclusion” (e.g., excommunication), the appropriate method requires the acknowledgment by each party of the special sensitivities and fears of the other, as well as of their asymmetrical positions in the struggle for power and recognition. A give-and-take of mutual concessions that takes into account these factors, so as not to threaten too much anyone, is the best that can be done, given the circumstances – and in spite of its softer logic, not even this much was achieved by Leibniz and his partners, as we know..

Leibniz the theologian who, in spite of their practical irrelevance for church politics, must address doctrinal issues, both as a sincere Lutheran and especially as a believer in the compatibility of faith with reason, soon gave up his attempts to solve these issues in a demonstrative way, as he had dreamed of in his Demonstrationes catholicae. For he realized that, for that purpose, he would have to admit the complete explicitation of the meaning of the sentences expressing the mysteries of faith. In addition to running against the doctrine of the essential unintelligibility of the mysteries, this would inevitably privilege one or another interpretation thereof, thus endorsing the position of one Christian faction against the others. It seems, then, that Reason is either completely impotent to support Christian doctrine or else, worse, it is incompatible with it, as skeptics like Bayle argued. The ingenious solution Leibniz found for this dilemma, which he elaborated upon in the Theodcy, is a wonderful example of making Reason “softer”. Instead of demonstrability as the sole halmark of rational support for a position, Leibniz suggests that defensibility is also good enough, at least in those cases where demonstration is not attainable. The believer in the mysteries cannot be called irrational nor asked to believe just on faith as long as for any given objection against the mysteries appropriate refutations – i.e., an appropriate logical defense – can be provided. Clearly, this concept of defensibility is based on the rules governing traditional disputationes, where the burden of proof does not fall upon the party that proposes a thesis, whose only task is to refute the objections raised by the opponent against his thesis. Rules such as these, however, are, strictly speaking, not “logical” but “dialectical”, insofar as other dialogical or dialectical games might well adopt quite different rules. Leibniz the Lutheran theologian, furthermore, was well aware of the untenability of Luther’s “semantic naivete”, which assumed that divine grace alone would enable every reader of the scriptures to fully understand their one and only meaning. As in jurisprudence, an elaborate interpretive labor, guided by an hermeneutics capable of navigating between metaphor and literal meaning, between semantics and pragmatics, was the soft counterpart of Luther’s assumption that Leibniz the theologian undertook to develop.

Leibniz the scientist who took very seriously his often repeated claim that the ultimate aim of science is its application to yield happiness for human beings needs “softness” for various r. First of all, in spite of his efforts, he discovered to his dismay that he could not produce a purely deductive physics. Secondly, applications of science, e.g. in engineering or medicine, like the applications of law, require one to take into account a multiplicity of varying contextual factors not themselves represented in the formulation of the scientific laws. Such applications, therefore, require, in addition to the “calculations” permitted by such laws, the use of judgment and discernment regarding the relative importance or non-importance of the additional factors – judgment being that imponderable human ability not reducible to formal means. Thirdly, the “scientific enterprise” is not a solo affair, as Descartes and others seemed to believe. It is a cooperative enterprise that requires a scientific policy and appropriate scientific institutions. The appropriate policy and institutions must respect and foster diversity of views rather than dogmatism and sectarianism, if they are to promote the growth of knowledge. All this requires a rather flexible, “soft” way of handling apparent conflicts between scientists and schools (which were not unusual in the République des Lettres in Leibniz’s time), for different scientists and different schools may contribute to “the truth” in different, albeit complementary ways. Leibniz’s reputation as an anti-sectarian and as an eclectic capable of reconciling, for example, the science (and metaphysics) of the “ancients” with that of the “moderns”, no doubt was grounded in his having achieved the ability to use the “method of reformulation”, whereby apparently conflicting theories could be shown to be in fact in agreement, at some appropriate level of analysis.

Leibniz the epistemologist needs “soft reason”, first and foremost in his struggle against skepticism. Those rationalists who equate knowledge with certainty and thus admit only “hard” reasons are in fact relatively easy prey for Pyrrhonians. The latter boast a not entirely unproven ability to produce “hard” arguments of equal weight to those that support any claim of certain knowledge, thus bringing the “Balance of Reason” to paralysis, i.e., to a total inability to decide. It is this state of isostheneia that has to be feared above all by the rationalist, for it would imply either death by lack of any rational ground to decide (as in the case of Buridan’s ass) or entirely arbitrary, i.e., irrational, action. An essential piece in Leibniz’s strategy against the skeptics is to fight this dilemma by introducing a tertium, namely “soft” reasons, i.e., reasons that are not conclusive and nevertheless are sufficient to incline the balance of reason towards one pan or the other. Instead of a balance that only admits either equilibrium or a conclusive decision towards one or the other side, as the confrontation between the skeptic and the hard rationalist would have it, a large variety of gradations becomes now available, the two extremes being the exception rather than the rule. “Reasons” – says Leibniz – “are to be weighed, not counted”, implying that weighing, unlike counting, is a much more complex and delicate process, whose outcome is most of the time tentative, not final. Ruling out the existence of indiscernible things or states is just the radical metaphysical counterpart of the epistemological softening of the reasons the Balance of Reason is supposed to weigh.

But Leibniz the metaphysician badly needs “soft” reason too. Otherwise, how would he be able to make the absolutely essential (for him) metaphysical distinction between contingency and necessity? According to the Monadology, contingent truths are those whose “resolution into particular reasons could proceed into unlimited detail” (par. 36) and, “since all this detail involves nothing but other prior or more detailed contingents, each of which requires a similar analysis in order to give its reasons, we do not make progress in this way” (par. 37). If we cannot advance in understanding contingency through the way of analysis, which is the way of “hard” reason, what is the alternative? Obviously, it is not by accident that, in the Discours de Metaphysique, Leibniz employs the phrase “inclines without necessitating”, clearly evoking the image of the balance mentioned in the preceding paragraph, in order to describe the most characteristic feature of contingency. It pertains to the very essence of contingency (if one may say so) to result from the infinite complexity of infinitely embedded infinite details, each inclining, however small its weight, the ontological balance one way or another. It is because this non-analytical “soft” process of comparing unequal weights lies at the ontological heart of contingency that, at the epistemic level, contingent truths cannot be known via demonstrations, requiring instead observation, experience, approximation, hypothetical generalization, probability, and other “weak” forms of reasoning.

Leibniz the metaphysician-theologian-moral philosopher of course follows suit. In order not to blame God for actually causing our evil actions and in order to bear responsibility for what we choose to do, our actions cannot be necessitated neither by logic nor by God’s perfect design of the world. We must, therefore, be endowed with some measure of liberty to decide by ourselves and act as we decide. But Leibniz also rules out the possibility of a “freedom of indifference”, which would amount to nothing but acting without reasons, i.e., arbitrarily and therefore irrationally. Leibniz followed very attentively the controversy between Hobbes and Bramhall on liberty and free will, and was quite sympathetic towards Hobbes’s quasi-necessitarian account of freedom (cf. GP VI 388-399). His own solution, however, again relies on the notion of “inclination”. There is no action, he argues, without an “inclining reason”, even if such a reason is just “the caprice to show one’s liberty, the pleasure or the advantage one believes to find in such an affectation” (Theodicy, par. 45; GP VI 128). And again, it is because the choice motivated by such an inclination is not necessary that it is free (ibid.). In other words, “soft” reason is essential for Leibniz’s concept of liberty.

In the light of his massive need for “soft” reason, it is not surprising that Leibniz sought to develop both its theory and its tools. Such tools include those mentioned above and many others, belonging to dialectics, the calculus of probabilities, juridical logic, hermeneutics, semiotics, and other relevant disciplines. Such means, along with the strictly deductive ones (which he did not neglect to improve), would yield a new and comprehensive “true logic”, capable of providing Reason with all the tools required for implementing Leibniz’s ambitious rationalistic program. This other, “soft” side of Leibniz’s logic certainly deserves the attention it has not received so far. But this is not our task here. Rather, we should now return to the suggestions made in the opening paragraph, and inquire whether and how the various manifestations of the leibnizian need for “soft” reason can be directly related to the Principle of Sufficient Reason.

In spite of occasional suggestions that either the PSR can be deduced from the PC or vice-versa, on the main Leibniz maintains the logical independence of these principles, which he calls the two great principles of reasoning (Monadology par. 31). He also maintains the different scope of the jurisdiction of each principle. The PC rules over the domain of the possibles or essences, whereas the PSR rules over the domain of the existents. Accordingly, there are two types of truths, each accounted for by one of the principles: the PC accounts for truths of reasoning or necessary truths, whereas the PSR accounts for truths of fact or contingent truths (Monadology par. 33). He insists that “contingent truths cannot be reduced to the principle of contradiction” (Grua 303) and that, if there were no PRS, there would be no “principle of truth” regarding contingent things, for the PC does not account for contingent truths (Grua 305). To be sure, both kinds of trut share their “analytic” character and both principles provide “reasons” for the truth of a proposition, be it necessary or contingent. And yet these reasons are of two kinds: “in necessary propositions, the reason necessitates; in contingent propositions, it inclines” (Grua 303).

The nature, scope and modus operandi of the two principles are thus markedly different, and the difference clearly underscores the difference between a “hard” and a “soft” conception of reason. If we further inquire why the PSR is necessarily associated with the latter, we fall back in other central tenets of his metaphysics, particularly the idea of “global comparison” or “global perfection”. The reason for “existence” (in a broad sense, applied to both necessary and contingent “things”), he claims, is always a comparative matter, a matter of the existing thing having “more reason” to exist than other things that might exist instead of it (Grua 303). And yet, in the strict sense in which all existing things are contingent except God (Grua 288), the relevant comparison of reasons cannot be made on the basis of the (real) definitions of things (i.e., their “essences”) alone – as must be the case regarding necessary truths (ibid.). Contingent truths, Leibniz says, depend upon an “extrinsic principle”, namely the comparison of their degree of perfection with that of other things (ibid.). Such a comparison cannot be restricted to a particular individual or group of things, given the leibnizian assumption that every individual substance is related to every other individual substance in the possible world to which they both belong. Up to this point, the somewhat intermediate (as between “hard” and “soft” reason) notion of “compossibility” seems to comply with the requirement of global comparison also in the domain of the possibles. However, insofar as the issue is which of the possible worlds will be chosen as the only existing one, the comparison must consist in a global weighing of the degrees of perfection of entire possible worlds. As such, it involves an extremely complex assessment of infinite sets of properties. Only God’s unlimited calculating capacity is capable to perform conclusively such an elaborate weighing, and even then – Leibniz insists – God’s conclusion does not become a necessitating reason, remaining a reason that inclines without necessitating. This is obviously not the case with conclusions derived through the PC, which are such that incline by necessitating, even from God’s perspective.

If transposed to the human level, the contrast is even more remarkable. Humans, like God, are perfectly capable to apply PC-related logic in order to demonstrate necessary truths. But they are intrinsically unable, unlike God, to perform the PSR-related global comparisons that would yield a conclusive verdict about contingent truths. They are thus condemned to be unable “to know the true formal reason for existence” (Grua 304). In dealing with contingent truths, then, humans are forced to know them only a posteriori, through appearances and experience, and resorting to a variety of forms of inference that fall short of strict deduction.

Although commentators have noticed that the term ‘reason’, as employed in connection with the PSR, often means “cause” rather than, say, “proof”, they have not noticed – as far as I know – that there is another ambiguity of the term ‘reason’ in Leibniz, of much deeper significance, which I have tried to highlight here. If indeed, as I have tried to show, the PSR is intrinsically related to the idea of a blandior ratio in order to ensure that indeed everything in the world is rational, and if indeed it is not a corollary of the PC, one should ask what exactly is its status. Insofar as it can be justified at all, might it not be the case that it can only be justified through “soft” reasons? For example, from a human point of view, shouldn’t it be granted only the status of, say, a “general presumption of rationality”? At times Leibniz seems to come close to such a view, as when, after affirming that the PSR is a principle “divinely implanted in our mind and confirmed by both reason and experience”, he adds the ominous cautionary phrase: “to the extent that we can penetrate things” (Grua 304). Presumably Candide was not acquainted with this text, isn’t it, Monsieur Voltaire?