Synthesis Philosophica 12/2
Zagreb, 1997, ISSN 0352-7875
pp. 415-32.

Lorenzo Peña

E-Mail address:


  1. Abstract
  2. §1.-- Roots and Scope of Leibnizian Necessitarianism
  3. §2.-- The Leibnizian Notion of Essence
  4. §3.-- How Are Essence and Existence Linked According to Leibniz?


The several orders of compossibility must be sorted out «before» the divine decision to create this or that universe, since God's decision must be grounded in a sufficient reason, which can only arise from the divine essence itself and the intrinsic qualities of the orders among which He has to make the choice; the greatest perfection of an order of things is mirrored and expressed in every integral component of that order. Consequently, the concept of every real thing does from all eternity contain the unavoidability of its existence before the divine decision. Thus every complete concept of a real thing contains the property of being such that the thing will exist if a created universe exists. Then a thing's existence cannot be external to its concept. There is bound to be more in the concept of something that exists than in that of «something» that does not -- since existence is explained through the quidditative property of being an essence that constitutes an integral part of the most perfect series of things. It is such an essential, quidditative perfection which explains the divine decision, and hence existence. Therefore existence can be deduced from that essential perfection. The essence-as-such, the mere possible, contains something from which existence follows. What Leibniz never manages to explain is what distinguishes existence from that quidditative perfection it unavoidably stems from.

§1.-- Roots and Scope of Leibnizian Necessitarianism

Leibniz's main ontological claim is that essences are possible-entities striving to exist, on each of which existence devolves in accordance with its own essential perfection; however, since there are essences whose existentialization is incompatible with others' -- those which are incompossible with them -- , one single global order of compossible-entities can alone be realized. Which one? The best of all.

That global order, the real world, will encompass only all those essences one of whose quidditative properties is that of belonging to a world that is the best possible one. (For, Leibniz considers all properties essential, and thinks that every individual reflects the whole universe it belongs to, since, among the properties of an individual, one of them is that of belonging to an universe such that ..., where the leaders are to be replaced by any sentence true of the universe in question.) God can create only the best possible world: either He creates nothing, or else He creates the best. Yet, in virtue of the principle of sufficient reason, some suitable reason or other must prompt the divine decision of creating or failing to create; and, if that reason is a divine intention of taking such a decision, that divine intention will also have to have its own sufficient reason. And so on and so forth.

In the last resort the root of all that there is or will be is God's essence. God himself is an entity, a subject, the supreme monad. As happens with any other entity or substance, each predicate which can be truthfully assigned to Him is included in His essence or complete notion. God can constitute no exception to the general rule that praedicatum inest subiecto. Each individual's properties are, all of them, essential to him; an individual's actions stem, all of them, from the agent's essence. Thus God's decision to create is essential to Him and stems from His essence. That's why God, in virtue of His essence, could not help taking the decision to create some world; «once» He had taken such a decision, He could not help taking that of creating the best possible world, i.e. this world; thus, in the end, God could not help creating this world; no other world could be created instead of the best one, and a complete absence of any created world at all was not a real possibility either, since it would run afoul of the divine decision to do what is best (a general decision such that, should God fail to honour it, He would not be necessarily optimal, which assuredly He is for Leibniz). No world can put itself into existence; no possible world can reach existence except through God's creative decision. Accordingly no other world was possible; and since that alone is possible which belongs to a possible world, nothing is possible except what is real. Then everything real is necessarily real.

Thus, such considerations as we were, to start with, putting forward concerning sundry unrealized possible essences turn out, upon reflection, to constitute, for Leibniz, mere heuristic devices, because the outcome of our arguments enforces upon us a necessitarianism not unlike Spinoza's, namely that there are no really possible essences except those of entities which do in fact exist.

Consequently, all truths are necessary, i.e. truths of reason, although the human intellect is not able to grasp every truth as a truth of reason. The only difference which remains between truths of fact and truths of reason proper is a merely epistemologic-human one: a truth of reason, from the human point of view, is one whose predicate is to be found by analysing the notion of the subject through a finite number of steps; whenever, instead, an infinite analysis is to be carried out in order for the notion of the predicate to emerge as one contained in that of the subject, the statement, although on its own, by itself, remaining a truth of reason, is quoad nos, only a truth of fact.

In other words, except as an initial stage, that of a heuristic or explanatory procedure, there is for Leibniz no order of possible non-existent essences (barring the divine ideas corresponding with things). What is possible is what exists only.

I will here refrain from going into the Leibnizian notion of «best-world». Suffice it to say, in that connection, that there are two parameters to compare the degree of goodness of two possible worlds: entitative riches (a world is better if it contains more entities, or a series of entities which taken together amount to more reality, more variety); and simplicity of the ways and means through which such a riches is achieved; although Leibniz does not say how both factors are to be coupled, combined and weighted, he thinks, nevertheless, that the combination does indeed take place, a determinate outcome arising. But, in the end, only a world is possible: the real world. Other worlds are not possible, but imaginable; they are (as Leibniz emphasizes in the famous Tarquinius fable of the Essais de Théodiccée) complete novels. (Leibniz fails to raise the problem of how it is possible for «something» to bear to somebody the relation of being-imagined-by without that something being anything, not even properly a possible entity.)

In order to shun the strict necessitarian conclusion to which the sum of diverse principles of his philosophy commits him, Leibniz could try one of the two following solutions:

1. To maintain that the principle of sufficient reason is contingent. Then this particular application instance thereof may be contingent, namely: that there is a reason why God decides to create, or why God decides not to create; and that there is a reason why, if He decides to create, He decides to create this world rather than any other. Then, even if that reason is necessary, the conditional link between the reason and what it explains would be contingent, and so the explanandum could remain contingent too. But such a «solution» is not Leibnizian; it is appropriate to ask, as regards the principle of sufficient reason itself, what its sufficient or determinant reason is; and -- according to the Leibnizian outlook -- no infinite regression is legitimate. Hence, in the last resort, the divine nature itself, which is necessary, can alone constitute a sufficient reason for the principle of sufficient reason. The latter will thus be non-contingent; unless we claim that it is the link between the divine nature and the principle of sufficient reason which is contingent; but that link will then call for a sufficient reason, which in turn will call for another reason, and so on: to avoid the infinite regress, we must assume that the link is necessary. Moreover, Leibniz takes it as obvious that «x is sufficient reason for y» means that, necessarily, if x exists, y also exists; then the link of sufficient reason, or of grounding, if true, is necessarily true, regardless of whether the principle of sufficient reason itself is necessary or not (although, on the other hand, the principle must be necessary if -- as we have seen -- the link of sufficient reason is non-contingent and if the Leibnizian conception of modality keeps to a pattern not unlike the one which has been nowadays implemented through logical system S5, as has been cogently suggested by Rescher and other interpreters).

2. To maintain that, for Leibniz, an infinite regress can be admitted. Then the decision to create this world has as its own sufficient reason the decision to decide to create it; and this, in turn, has as its sufficient reason the decision of taking the decision to decide to create it; and so on, infinitely. All those decisions (that of creating, that of deciding to create, that of deciding to decide to create, etc.) would be contingent, no decision being the supreme or the first one, no decision directly springing from the divine nature (should a decision directly stem from God's nature, it would be necessary, and then all the links in the chain would turn out to be necessary, too). But it is hard to believe that such an infinite regress could be seriously entertained -- let alone wholeheartedly espoused -- by Leibniz; not because he fails to accept infinity in general, far from it (although late in his life he seems to have become more cautious in that connection); but because, even though Leibniz is inclined to accept an infinite progression, he is apparently reluctant to acquiesce in a regression, i.e. a series each of whose links requires other links, previously given, and so infinitely on; moreover, because Leibniz, with his critical-probing, rationalist turn of mind, would have asked whether all the series has a sufficient reason; and if it has one, and the reason -- whatever it may be -- has another, and so infinitely on, all this new series will be bound to have its own sufficient reason; and the series of series of series of ... of series will be bound to have an ultimate sufficient reason.

But then, what are we to make of Leibniz's tireless reassurances to the effect that a distinction is to be recognized between metaphysical or geometric necessity and merely conditional necessity, necessity ex hypothesi? The difference is epistemological and heuristic, not ontological. Such a difference originates as follows: an assertible content is said to be metaphysically or «geometrically» necessary if, and only if, we humans can prove its logical necessity, through a finite number of demonstrative steps (since there are no infinitely long demonstrations); the necessity of an assertible content is physical, or conditional if we are unable to demonstrate its truth but it can be proved that, if certain antecedent facts are true or real, the content under consideration is also true or real, while we judge those antecedent facts to obtain.

The opposition between Leibniz and Spinoza boils down to the following disagreement: Leibniz emphasizes that, due to its weakness and finiteness, the human intellect cannot demonstrate that all the truths of fact it records are logical truths; but for an infinite intellect, able to understand the complete notion of every thing with the infinitely many determinations it encompasses, and to carry out infinitely long demonstrations it is possible to prove any truth of fact from truths of reason (truths which -- Leibniz mistakenly believes -- can all be deduced from the principle of identity or non-contradiction). On the other hand, Spinoza would be sceptical about such an infinite intellect conceived in what to his mind is an excessively anthropomorphistic way.

For Leibniz, there would be truths irreducibly factual, not only epistemologically quoad nos, but ontologically quoad se -- and, therefore, quoad Deum -- if the divine decision to create was a contingent one, if it lacked any sufficient reason or if whatever bears to that decision the ancestral of the relation of being-sufficient-reason-for was contingent (an entity x bears to an entity z the ancestral of a certain relation, say that of teaching-Latin, if, and only if, either x teaches Latin to z, or x teaches Latin to somebody who teaches Latin to z, or x teaches Latin to somebody who, in turn, teaches Latin to somebody who teaches Latin to z, or..., and so on with any finite number of intermediate links). But, then, God would be the sole entity whose notion would not encompass all its properties, accidents and relations, which would bring in an inexplicable and astounding anomaly, which, to boot, would prevent God from knowing Himself rationally, in so much as He could no longer deduce all his own properties from his own infinite notion.

Nevertheless, desirous as he is of finding some ground to assert that contingent truths are such even, in a certain sense, quoad Deum, or quoad se, Leibniz, in his booklet Generales Inquisitiones de Analysi Notionum et Veritatum (1686), hopes to find it as follows: necessary properties are identical, they are grounded on the principle of identity. Instead, contingent statements cannot be reduced to identical statements, since the complete notion of a monad is not a mere sum of predicates -- those predicates being infinitely many -- but a law generating a sequence of predicates and permitting, once a step in the sequence is given, to carry the sequence on by finding the following step. Moreover a statement such as `Peter denies' can have no concrete sense and no truth-value until the moment and other circumstances are given. But the moment cannot be exhaustively analyzed except by pointing to all entities existent at that moment.

Contingent statements are, so to speak, asymptotic: they can be brought indefinitely nearer to the status of necessary truths. They would be inexhaustible. A contingent statement should be indemonstrable (except from contingent premises), but could be brought indefinitely closer to its demonstration.

Such is, at least, the interpretation put forward by many Leibniz scholars such as Yvon Belaval, in his valuable books on the author of the Monadology (e.g. [B1]). But such interpretation turns out to be mistaken, because God can perfectly understand the law that engenders all the series as well as all the series of predicates itself; and God does not need -- as mistakenly and gratuitously Belaval assumes --, in order to understand a truth as truth of reason, to have «exhausted» the series it enters into, in the sense of having reached the end or the last stage of the series, which is obviously impossible, the series being infinite and thus lacking any end or last stage. But why must we demand such a far-fetched feat? The infinite mind possessing an infinite capacity, it can intellectually see all the infinitely many members or links of the series, and -- since every series of the predicates of an individual encompasses all the truths of the universe that individual belongs to, all the truths of the universe, including all the true existences in the universe. ([K1], pp. 230-1, and references in pp. 254-5.) What is more, Leibniz explicitly says in a paper edited by Couturat: `... Existentiales siue contingentes [propositiones], quarum ueritas a sola Mente infinita a priori intelligitur...' (existential or contingent propositions are those whose truth is understood a priori only by an infinite Mind). And even in the booklet brought forward by Belaval Leibniz says that the truth of true existential propositions is proved `infinitis adhibitis', i.e. by resorting to an infinity of deductive steps -- which is quite possible for an infinite mind, as God's.

It may be objected against my interpretation that Leibniz very often claimed that purely possibles are bound to be there somehow, and that, else, contingency would not exist, the world would be necessary and God would unavoidably do what He in fact does. (See [B1], p. 159; in a similar opinion is subscribed to by what Leibniz says in his letter to Bernouilli of 13 march 1699.) Such pronouncements on Leibniz's part stem: either from an occasional lack of consequence (a sin which is probably committed by every philosopher and human being); or from half-regrets over some consequences of his philosophy, consequences which our author would then understandably try to blunt; or from diplomatic caution, a wariness which was more than justified then as we can see even now, when necessitarianism continues to arouse appalling uproar and turmoil; or (last, not least) from his deep-rooted belief that truth is widely shared and that whenever a philosophical tenet seems hotly debatable, it probably had rather be couched in such as way that people do not balk at it, since such people as were tempted to do so cannot be so unreasonable that they cling to beliefs totally in contradiction with what reason (philosophy) teaches. Moreover, Leibniz genuinely tries to keep some sort of difference between necessary and contingent truths. Preserving such a difference is doubtless one of his main motivations all through his philosophical career. Yet that such a motivation or goal exists is no proof of success.

In the end what Leibniz is able to establish within the framework of his philosophical approach is a merely epistemological cleavage, not an ontological one: God creates necessarily what He creates (should the world be different from the way it is, God would not be God); but such a necessity is so intricate that we cannot demonstrate what it consists is, or why it is necessary for God to create this world; what alone can be proved by us is that, once this world's existence is assumed -- an assumption which we take for granted in virtue of our experience -- , it follows that God was bound to create it.

§2.-- The Leibnizian Notion of Essence

We have seen that every truth of fact quoad nos is a truth of reason quoad se and quoad Deum, and that every property or true predication of a subject is contained in the infinite notion of that subject. Thus, it is contradictory for Plato not to write the Phaedo dialogue. Since we cannot prove that it is contradictory, such truth is, to us (on a merely epistemological level), a mere truth of fact, a contingent truth.

Not unlike other authors belonging to the philosophical tradition -- such as Aquinas and Scotus, with other nuances or qualifications -- Leibniz regards pure essences or possibilia as God's ideas, rationes diuinae. But, thus understood the meaning of `essence', it must be distinguished from what means `essence' when applied to finite entities. A finite entity is, for Leibniz, the same as its existence and also the same as its essence or species infima. But there is an idea or divine notion, which can also be called `essence', and which corresponds to the existing essence of that individual (and Leibniz, as a nominalist philosopher -- or, more exactly perhaps, a reist one --, assigns reality to individual substances only -- although his theory of the substantial bond [uinculum substantiale] opens a breach into such a nominalist reism).

To prevent a confusion I'll call the divine idea the `essence-as-such', so as to distinguish it from the individual, which is the same as its essence or species infima, a species existent as a finite being in the created universe.

The divine substance, although it is simple, is composed of simple perfections. God by knowing himself knows those simple perfections under the form of simple absolute notions. They are co-eternal with God's substance, «preceding» any decision to create. They express the divine substance and through them is God infinitely perfect. Such perfections constitute the quality of essences-as-such; every essence-as-such has a degree of perfection. The essence-as-such is a degree of every perfection combined with degrees of others perfections. The essences-as-such are also co-eternal with the divine substance and they are the proper field of the principle of non-contradiction.

Sometimes (mainly in some of his early essays) Leibniz seems to suggest that, unlike pure essences, complete notions of individuals are not co-eternal with God, since, in addition to the specific differences, they include a reference to time, in virtue of which this or that individual is the one which it in fact is, and no other. Such a temporal reference involves the temporal decree that entails the law of its concrete existence realized under the form of the set of predicates that will make up a substance. Such is Robinet's interpretation ([R1], p.50). Robinet tries to prevent a necessitarian construal of Leibniz as the one I am now proposing.

Nevertheless, such a difference only means that, within the essences-as-such, a distinction is to be made between, on the one hand, complete essences of individuals, and, on the other, essences of species non infimae, i.e. of kinds of greater or smaller generality. Those of individuals are infinite, and entail an infinity of perfections -- on account of which they cannot be intellectually known by man; those of kinds are finite and entail only a finite number of predicates or perfections, owing to which they can often be known intellectually by a human individual. In such a context, `pure essence' designates a generic essence exhaustively intelligible through a finite number of steps. As regards the would-be co-eternality between God and the essences-as-such (or complete notions) of individuals, Leibniz admits that, rigorously speaking, there is a strict co-eternality between God and such notions; still, being infinitely complex, such notions entail, in their content, a reference to time, to succession, to a temporal order and a coordination with an infinite number of other essences-as-such; and, thus, they do not express divine perfections as simply and immediately as incomplete or generic essences do; generic essences do not contain any idea of time, because time appears as an order and coordination of an infinity of things; thus, the very expression of generic essences, what they express, is devoid of temporal structure; whereas what is expressed through the complete notion of an individual involves time, even if the complete notion is not temporal but eternal.

While identifying the divine notions with the essences-as-such of finite entities, Leibniz wants to surmount the controversy between the thomistic view-point (according to which God knows possibilia as they are present in God, since they are God's ideas) and that of Francisco Suárez (according to which God knows possibilia as they are in themselves, with their own being; such a being is, for Suárez, only a mere being-so, not being tout court or existence). Essences-as-such do not have any other being but the one they have in God as God's ideas. But such a reduction runs into difficulties which had already been pointed out by Henry of Gaunt, Alnwick, Poncius, Suárez, and other late Scholastics. Scotus himself had assigned to the uncreated essence in its «diminished» or tiny being (esse diminutum, an intelligible being that is not a mere being of reason, but something in between ideal and real being) a precedence of nature with respect to the divine knowledge thereof, since -- according to the Subtle Doctor -- such essences do not stem from God's thought, but from God's thinking Himself as such. Such a claim gives rise to a problem, namely whether it is God's thinking that man is a rational animal what makes it true; or if conversely it is because such a fact obtains -- because it is a truth -- that God, who is infallible, thinks so. Although Leibniz would try to avoid the problem by denying that one of the two alternative terms might have any priority over the other, the problem remains of whether, when God knows an essence, He knows a mere idea (something whose being reduces to its being thought), or something endowed with an entity in-itself.

Be that as it may, Leibniz certainly identifies God's notions with the pure notions of things in themselves, i.e. with the essences-as-such of things. Those essences are uncreated (see Théod. III 415; Disc. XXX): should God create the essences-as-such, His understanding would be unconstrained by any logical or metaphysical principles, and His will would be blind, as the casting of the dice, the flip of a coin, or a whirling roulette -- the wheel of Fortune. God would then act at whim, in a haphazard, random, fortuitous, way. His decisions would be adventitious, causeless, undetermined.

The essence-as-such of every individual expresses only whatever will be true of that individual if it exists. Leibniz's famous example is that, once Julius Caesar is put into existence, he could not help crossing the Rubicon. Once Adam was put into existence, he could not help sinning. And it is senseless to hanker after more strength or more riches, or to wish one had other parents: that would amount to wanting not to exist. (And, once any entity among those which constitute this world is put into existence, so must be all the others, since every essence-as-such of an individual expresses the whole universe, containing as it does the property of belonging to a world wherein ... exists -- where the ellipsis can be replaced by a designator of any entity which has existed or will exist. In virtue of the principle of identity of indiscernibles, no individual can inhabit two different possible worlds -- let us say so even if, barring the real world, possible worlds are mere fictions.)

That is why Leibniz claims that praedicatum inest subiecto: the essence-as-such of an individual is a law of formation of an infinite series of predicates; every true statement ascribes to one of the predicates contained in that series its membership of the series. The entity once given, all that it will do or undergo follows with necessity; the future necessarily follows from the present, and the present from the past: le présent est gros d'avenir.

Leibniz had suggested that every essence is a complete intersection of previously given predicates, i.e. of predicates which exist in God with some sort of precedence with respect to their combination. But later on (see [B1], p. 162) he changes his mind in that connection: such a combination of predicates or ideas previously given is impossible since every idea is modified when it enters a notion. In other words, ideas are not what they are independently of their being able to be truthfully predicated of this or that individual. And, when they change, the individual notions they enter into change, too. Depending on whether Nero was or not a singer, being a singer will be a particular, determinate property, rather than a different one, the difference spreading not only to Nero but to every singer, and to the entire world.

Since Leibniz realizes that, if Francis I is defeated in Pavia, it is not possible for him not to be defeated in Pavia -- i.e. there is no possible entity identical to Francis I not defeated in Pavia --, he draws the conclusion that every possible individual exists in a possible world only.

On the other hand, in order to preserve a certain independence or invariance of possible individuals through different possible worlds, so as to make the sentence `Francis I could have failed to be defeated in Pavia' true in some sense, Leibniz claims that possibilia can be considered in two ways: (1) sub ratione generalitatis (considering only some of the attributes, not the complete notions); (2) sub ratione indiuiduorum (every substance involves the totality of the system of compossibles of which it is part and parcel).

Such a solution encounters a difficulty: the predicates attributed in the first consideration, viewed, accordingly, regardless of whether the subject in question possesses the remaining properties it in fact possesses, are incomplete: each of them will be different depending on whether the subject possesses or not every other property in the set. Ambition is a different property altogether depending on whether, e.g., Catherine of Medici was ambitious or not; caution is also a different property depending on whether she is cautious or not; but Catherine, in her turn, is not the same regardless of whether she is ambitious or not; so, before caution can be identified by the fact -- among others -- of that queen possessing that quality, she has to be individuated by her possession of other attributes, at least of those which deserve to be taken to constitute her-as-possible sub ratione generalitatis. But each of those attributes, in turn, is bound to have been previously individuated or singled-out, which unavoidably triggers an infinite regress. Thus nothing could apparently be individuated, since, before an individual can be individuated, each «essential» property thereof must have been individuated; before that, every individual endowed with that property has to have been individuated; and, moreover, each of the other essential properties of the individual in question must also have been previously individuated; and so on.

A solution to those difficulties would be the following: every individual is identified by the properties it has, and each property is identified by the individuals endowed with it. But in the same way as no individual can exist in two different worlds, no property can exist in more than one world either. The individuation of individuals and of properties possessed by them would be mutual or reciprocal, and properly speaking two worlds would share nothing at all, neither their inhabitants nor the properties those inhabitants have or lack.

But then, how can an individual be considered merely possible sub ratione generalitatis, i.e. as an entity endowed with a notion constituted by only a few among the properties that do in fact constitute its [complete] notion? Those properties would lose their identity should they be abstracted from the other properties the individual possesses. Thus taken, the properties are no longer those which are in fact present in the real world: we are considering them as if they were invariant through different possible worlds, or perhaps rather as if they were elements of an indefinite pseudo-world which could be concretely realized both as the real world and, alternatively, as a different «possible» world.

Thus a possible world cannot differ from the real only in a single contingent particular fact. Once the smallest atom of the whole world-scheme is changed, everything changes. Two different worlds are thus incommensurable. Talking about pure possibility is fantasy, nothing else.

We can fall back on the following contrivance: suppose there is a world wherein Pizarro does not conquer Peru. But Pizarro is identified by being Peru's conqueror, among other things. Then, let us suppose that Pizarro is identified, not as being the conqueror of Peru tout court, but as being the conqueror-of-Peru-in-the-real-world. Such a view would lead us to properties-as-functions, mapping possible-worlds and individuals into truth values. But then how are possible worlds individuated? Moreover, `The real world' would be a pleonastic expression, if the «real world» is indeed the only world that is real, the others being purely and simply unreal.

Another solution would be to lay down bare individuals, or bare properties, independently identified. But that would be a glaringly anti-Leibnizian solution.

Even though the postulation of bare individuals, or haecceities, is anti-Leibnizian, Leibniz suggests once (N.E. II XXVII 10) that God could, while extraordinarily changing the real identity of an entity, keep its personal identity, provided a certain proprium quid of the entity was retained, which would be constituted by both internal and external appearances. That proprium quid would be over and above the predicates, and beyond them.

Be it as it may, such a solution, going as it does counter to the principle of identity of indiscernibles, is profoundly anti-Leibnizian. What is more, in the rare passages wherein Leibniz suggests the existence of such «overidentitties» of things he speaks about them in terms of appearances, phenomena, and hence without any explanatory role.

§3.-- How Are Essence and Existence Linked According to Leibniz?

But now the thorniest and most serious problem must be brought up: does existence belong to that series of predicates? Or is existence (or, if you want, would-be-existence, or tendential-existence) extrinsic to the essence-as-such? Leibniz's repeated claims favouring the latter alternative -- on the face of them -- are mustered by those who want to view Leibniz as a contingentist philosopher. But we cannot disregard the fact that Leibniz lays down a bridge, a transition, between the order of the essences-as-such and that of existences, namely: the principle of sufficient reason -- a principle which in turn, as we have already seen, cannot be contingent. In accordance with that principle, for something to exist a sufficient reason must be given; and, in the last resort, as the existence of an individual entails that of a particularly determined possible world it belongs to, the ultimate sufficient reason for the existence of an individual is that its essence-as-such, or notion, contains the predicate of belonging to the best possible world. Since such a world is the only one God can in fact create, when God does create it the individual in question is also put into existence -- at least the individual is ascribed the property of existing the moment it is suitable for it to start its career -- even if Leibniz sometimes seems to suggest that every monad exists always. Existence stems unavoidably from a certain purely quidditative property or perfection of the essence-as-such, viz.: that of belonging to the best possible world. And non-existence of whatever, failing to reach existence, seemed to be possible but turns out in the end to be impossible (reducing to a mere fiction) inevitably follows from a quidditative property of its own essence-as-such, namely: that of belonging to a maximal set of entities that not is the best. Either to exist is to belong to the best possible order of things or at least the former property (existence) follows from the latter (that of belonging to the best possible order).

On its own, by itself, every possible entity -- Leibniz says -- has a tendency -- or conatus -- to existence. (If my construal is correct and, in the last resort, all unactualized possible-entities turn out to be mere fictions, according to Leibniz, then that tendency will be fictitious, too; it would be an analogical as if; needless to say, that as if fictionalism also encounters many difficulties: what do such fictions consist in? What is its fictitious conatus or tendency to exist? Problems Leibniz prefers to shrug on.)

The notion of conatus is central to Leibnizianism. Leibniz seems to often regard the conatus towards a motion or a state as the very same motion or state, only in a smaller degree -- perhaps an infinitesimal one. The conatus contains the further course of the thing to which it can truthfully be ascribed. What is in this connection hard to understand is that, if the conatus ad existendum the uncreated essences-as-such are endowed with consists in a smaller degree of existence, such an existence cannot be the divine existence (which is the existence those essences are bound to possess, being as they are God's ideas, while Leibniz rejects any real distinction between God and God's ideas -- or in general God's attributes or properties). Hence such a smaller degree of reality or existence would be a degree of created existence. Then, while still uncreated, the essences-as-such would be possessed of a created existence. Such a conclusion is contradictory. Leibniz would adamantly reject any contradiction. (At this stage we know that systems or theories containing contradictions are perfectly possible and logically admissible, thanks to the existence of paraconsistent logics. Such a perspective was not open to Leibniz. Nor -- unlike other philosophers, such as Nicholas Cusanus -- did he ever have any ever so faint inkling on the possibility of contradictorial but logically admissible theories.)

Yet a still more serious difficulty arises as regards the Leibnizian view of existence: what is existence according to Leibniz? Does it reduce to the property of belonging to the best order of things? Or is it something else, even if it supervenes on the aforementioned property? If the former alternative is chosen, the essences-as-such do exist (with such an existence as befits them qua finite essences or of finite beings). Then nothing except God and his ideas would exist, which would be a pantheism much more radical than Spinoza's. Spinoza admits a real difference -- at least an objectively modal one -- between God and his modes, the latter being entities truly different from God; whereas, as the reist he is, Leibniz does not accept the existence of non-substantial entities, and so is bound to lay down a real identity between God and his ideas, including the notions or essences-as-such of created entities. The irksome and unpalatable outcome of such a line of reasoning would then be not just full-fledged absolute pantheism, but even Parmenidean monism. The outcome can be avoided only if existence does not reduce to the quality of belonging to the best possible order of things, even if it supervenes on it. Even so, if that quality supervenes on the considered property of belonging to the best possible order of things, it will also be possessed or exemplified by the essences-as-such.

More explicitly, Leibniz says in his already quoted booklet Generales Inquisitiones de Analysi Notionum et Veritatum: `Aio igitur Existens esse Ens quod cum plurimis compatibile est'. (`I say, accordingly, that the existent is what is compatible with the most things.') Does that mean that existence is defined through that compatibility with most things, with the greatest ontological riches? Or does it mean that all, and only, those possible-entities that are compatible with the maximal ontic riches receive existence? A strongly extensionalist point of view (according to the which two properties are identical if whatever possesses one of them also possesses the other) should reduce the latter construal to the former, but, then, all contingency would vanish, created existence becoming a constituent note of the divine eternal idea of the created entity; which means that such an existence would not be created. That strongly necessitarian interpretation of existence seems to be borne out by Leibniz's claim (quoted by Knecht in [K1], p.230): `Existere nihil aliud esse quam harmonicum esse...'

On the other hand, Leibniz often says that to every essence its own degree of existence corresponds, and that no two different creatures may have the same degree of existence or reality; otherwise, they would have the same degree of essential perfection, and so they would be indiscernible; which, in virtue of the principle of identity of the indiscernible, would mean that those «two» things would be one and the same thing. (Leibniz seems to assume that no two different things can share the same degree of essential or quidditative perfection, nor accordingly of existence; in other words: that the extent of existence merited by an essence-as-such will be either larger or smaller than that corresponding to any other essence-as-such. Such a claim is stronger than the principle of identity of indiscernibles. What Leibniz seems to take for granted is that two identical degrees of existence are the same existence, and no two different things can have the same existence.) Well and good, but what is that something which is merited by the essence-as-such in proportion to its intrinsic quidditative perfection (provided such an essence belongs to the best possible order of things)? What is existence? Upon receiving it does the essence-as-such undergo some metamorphosis or transmutation? Does it «come out» from God? Otherwise, how can it receive existence, when it already was possessed of divine existence, which was its own being?

Finding no answer to such questions which he does not even dare to bring up openly, Leibniz sometimes seems to want to approach existence by means of purely empirical finding. Thus, in a autobiographic fragment of 1666 (reprinted by Foucher de Careil in Mémoire sur la philosophie de Leibniz, t.I) Leibniz develops his early view of existence: existence is not a predicate, he says in effect. He makes it plain that he drew the conclusion that we men can assert only what we perceive, or, at most, that whose effects we perceive. But, as it cannot be said that only what we perceive exists, Leibniz at that early stage drew the conclusion that for something to exist is for it to be perceived by an infallible spirit of which we would be mere emanations (euius nos tantum effluvia essemus). Solipsism is unthinkable even as a hypothesis, Leibniz tirelessly repeats against Descartes.

Such views can be put against the background of Leibniz's well-known and repeated claim from his early booklet Disputatio Arithmetica de Complexionibus (or rather from the Appendix to that booklet that is a part of his essay De Arte Combinatoria, both of which were written in march of 1666): necessary truths, guaranteed by the law of non-contradiction, must be distinguished from contingent or existential truths.

But such a view would bring us back to a position incompatible with the conclusions Leibniz rightly derives from his own principles, which call for a bridge of sorts between the reign of essences and that of existences, a supervenience of existence on the quality of belonging to the best order of possible things; and even a one-to-one correspondence between degrees of existence and degrees of intrinsic quidditative perfection of the essence-as-such.

In other essays, Leibniz defines existence as the possibility of being perceived (esse nihil aliud esse quam percipi posse, [B1] p. 107). But sensation by itself does not prove anything: a dreamed palace is not a real palace. And there are real things which are not perceived. Thus Leibniz draws the conclusion that to exist is not the same as to be perceived. What makes the difference between our true and our false sensations is that the former alone sunt consentientes.

Now, coherence among sensations must have some cause. Existence is that quality of the perceived objects that makes us have coherent sensations. Then, far from defining existence through an empirical-sensorial content, Leibniz's later views regard existence as something more fundamental, something presupposed by the reliability of sensations.

Let us examine this doctrine in the context of the Leibniz's mature views, according to which sensations are obscure perceptions, while ideas or concepts are clear perceptions. Will we be bound to say that what exist is that which generates perceptions which are obscure but coherent? Why? What privilege is deserved by such a capacity of producing obscure, rather than clear, perceptions? On the other hand, if whatever is clearly conceivable and coherent exists, we would be espousing a strictly Spinozian necessitarianism, despite Leibniz's hopes to keep clear of it.

Yet the former alternative cannot be seriously taken to be Leibniz's considered conception, since then existence would be devalued, becoming an inconceivable remainder, something darkly perceivable only -- so to speak, like irrational and unintelligible dregs. What is more: existence must be the same property for God and for created things, yet God has no obscure perception and He cannot perceive himself obscurely. And Leibniz has said that nihil aliud est realitas quam cogitabilitas. What is only clearly thinkable cannot be bound to lack existence. Yet the essences-as-such are clearly thinkable. What else is «added» in order for them to reach existence?

We could look for a solution through what Leibniz says in his logic booklet «De Organo siue Ars Magna Cogitandi», on the in basis of previous essays devoted to binary arithmetics. Leibniz draws a diadic system that only uses digits 1 and 0: God and Nothingness; it thus symbolizes the origin of creatures and their infinite progression, which owe to God -- the positive fact -- their perfection and to Nothingness -- the negative fact -- their imperfection and their limitations (see [B1] p. 133, and also [K1], p. 244). Thus, the finite existence of creatures results from a certain combination of being (God) and not-being (Nothingness). But such a combinatorial implementation does not seem compatible with the most central theses of Leibniz's approach. The monadologic system allows for no such entity as Nothingness; and furthermore such a solution would entail the presence of two ultimate and mutually irreducible principles of things, which is not acceptable within the framework of Leibniz's theodicy. Most of all, such a solution is contradictory, since for an entity to be Nothingness or not-being means that it both is and is not; but Leibniz's general views cannot be reconciled with any admission of true contradictions.

In summary, for Leibniz, the essence grounds the existence, but the essence itself needs an existential support; yet, Leibniz did not manage to establish that those two theses are compatible with one another. Moreover, within the system of preestablished harmony, all truths of fact quoad nos emerge as truths of reason quoad se; thus in the last resort the whole order of being-there escapes from its apparent factuality, so much so that an infinite intellect sees reality as a coherent set of necessary and transparent connections founded on reason. Within that frame the divide between essentialism and existentialism is blurred, to the point of disappearing, since the order of existences turns out to be the same as the order of essences viewed from a certain angle. It is hard though to find a satisfactory account of the difference between angles.

The internal strain Leibniz's thought suffers from can be put as follows. Leibniz faces this problem: how to conciliate two fundamental intuitions underlying all the system of preestablished harmony, that according to which, existence being a perfection, the concept of an existing entity must contain more than that of a non-existing entity (see [S1], p. 127) and that according to which existence is extrinsic to essence, and thus the essence of a real thing would not differ from that of the same thing considered solely sub ratione possibilitatis (as Leibniz suggests in its booklet De Veritatibus Primis).

In other words, it seems to be no final, satisfactory answer to the question of what existence is and how, according to Leibniz, it is not included in the essence of the thing, although it follows from it, and how nevertheless the existent thing in created reality is not the same as the essence-as-such, but a different entity which «mirrors» the essence-as-such or which «corresponds to it». What is then the difference between the idea-of-existence (created or finite), that is in the essence-as-such, and the created or finite existence itself?

Oddly some authors claim that according to Leibniz existence is the sole predicate God bestows or withholds freely, i.e. haphazardly or just-because (because he pleases to do so, as the only or the ultimate «explanation»!). (Such is J. Skosnik's opinion, [S2], p. 690.) That is not so. The argument Skosnik backs up that interpretation with is that, occasionally (e.g. in a letter to Arnauld) Leibniz says that every existent can be conceived as a mere possible. But Leibniz proceeds to add that, thus conceived, the existent is a complete notion containing predicates which correspond to all its actions and relations -- Skosnik grants it; and, thus, it contains the quality of belonging to the sole order God is going to create, the only one He can create (should He create a different one, He would betray himself, and He would not be God, since He would be creating a world less good that the best possible one). Then, as God cannot but create this world, He cannot refrain from creating every integral component of the world, since, one of them once removed, not this world but a different one would exist (in virtue of the principle of identity of indiscernibles).

But Skosnik rightly points out a difficulty: if the existence of finite entities is necessary for Leibniz -- as it indeed is -- , how can God consider such an entity «independently of its existence»? (That sounds as considering gold «leaving aside» its being a metal: does that make any sense? What such an «abstraction» or «leaving-aside» could consist in?) Moreover, Leibniz tirelessly repeats that, in all true statement, the predicate inest subiecto, that the concept of the predicate is included in that of the subject. Such a principle applies unrestrictedly, and so is bound to apply to existential statements, too, despite Leibniz's occasional misgivings. What Leibniz cannot offer is a compelling, cogent, clear reason why the principle fails to apply to existential statements. The principle means that any statement is true if, and only if, it can be proved (we know that truths of fact quoad nos cannot be proved by us because the proof would need infinitely many steps). Then an existential statement is true if, and only if, it can be proved -- i.e. if, and only if, it is a necessary truth.

An amazing feature of Skosnik's construal is his claim -- upon which his whole interpretation hinges -- to the effect that, for Leibniz, there is no link between an individual and the world it inhabits. To the contrary! Although Leibniz asserts -- as Skosnik emphasizes -- that every individual is a world apart, that means only that nothing enters monads and nothing comes out of them, each monad being closed; yet every monad mirrors the whole universe, and a monad is the particular entity it is, rather than another, depending on the universe it inhabits. Thus, pace Skosnik, it is true for Leibniz that, had Erasmus failed to exist in this world, he would not have written the Praise of folly. A different «entity», however similar to Erasmus, but not Erasmus himself, might have written such a book (well, not that book, but another if very similar one) in some other possible world; but, in the end, not even that is true for Leibniz, since that other world would be possible only if God could create it; its possibility calls for God to break the principle of creating (only) the best; and that in turn calls for God himself to be less than optimal, which is impossible.

Skosnik proposes a «free logic» (it would be less inaccurate to call it `logic free from actual-existence assumptions', since it contains presuppositions of possible-existence) and asserts -- erroneously, to my mind -- that such a logic reflects Leibniz's conceptions. But it is worthwhile to remark that, although he admits that sundry Leibnizian texts uphold the PPE principle (namely, the principle that what is possible can exist), i.e. the principle according to which, whenever an entity with certain characteristics is possible, it is possible for there to be such an entity -- i.e. it is possible that there exist an entity with those characteristics --, Skosnik is bound to reject that principle. He even claims that PPE is not is a principle Leibniz should want to espouse ([S2], p. 715). However Leibniz clearly advocates PPE -- as most people do. Admittedly, when combined with other Leibnizian principles, PPE entails that, if a predicate can be attributed to something, that something exists. What Skosnik concludes is that «therefore» Leibniz is bound to reject PPE, and to assert that some possibilia cannot exist, i.e. that some possible «entities» are such that it is impossible for them to exist.

To sum up, construals such as Skosnik's (one among the swarming legion of fashionable contingentist interpretations Leibniz's philosophy has undergone of late) seem to be doomed. According to Leibniz existence, every existence, is necessary. That is why he defines (see [C1], p. 349) `ens' as `possibile'. If to be an Ens, to be something which is, is the same as to be possible, then whatever can be is. In the in end, all things considered, when everything is taken account of, real, existing entities alone turn out to be possible at all. That is why Leibniz acquiesces to the saying (ibid. n.) Non-Entis nulla sunt attributa.