The Principles of Nature and Grace Founded on Reason
 1. Asubstance is a being capable of action. It is either simple or composite. A simple substance is one that has no parts. Acomposite substance is a collection2 of simple substances, or monads.3Monas is a Greek word that means unity, or that which is one. Composites, or bodies, are multiplicities; simple substances, lives, souls, minds, are unities. And there must be simple substances everywhere, because without simples there would be no composites. And so, the whole of nature is full of life.
2. Monads, having no parts, can be neither formed nor destroyed. They can neither begin nor end naturally and so last as long as the universe, which will change, but won’t be destroyed. They can’t have shapes,4 since then they’d have parts. From which it follows that a monad, in itself and at any given moment, can only be distinguished from another through its internal qualities and actions, which can only be its perceptions (that is, the representations of composites, or of what’s outside, in the simple) and its appetitions (that is, its transitions or its tendencies to move from one perception to another), which are the principles of change. For the simplicity of substance in no way rules out the multiplicity of modifications that have to be found together in this same simple substance, and these have to consist in the variety of relations to things outside it. It’s like in a centre or a point, wholly simple though it is, in which we find an infinity of angles formed by the lines that meet there.
3. In nature, everything is replete, a plenum.5 There are simple substances everywhere, actually separated from one another by their own actions, which continually change their relations. And each distinct simple substance or  monad which forms the centre of a composite substance (an animal, for example) and the principle of its unity,6is surrounded by a mass composed of an infinity of other monads that constitute this central monad’s body proper, through the affections of which this monad represents, as in a kind of centre, the things that lie outside it. This body is organic when it forms a kind of natural automaton or machine, a machine not only as a whole, but also right down to its smallest observable parts. And since, through the plenitude of the world, everything is linked, and since each body acts on and is in turn acted on by every other body to a greater or lesser degree in proportion to the distance between them, it follows that every monad is a living mirror or a mirror endowed with internal action, representative of the universe according to its own point of view, and as orderly as the universe itself. The perceptions in the monad arise out of one another through the laws of appetite or through the laws of the final causes of good and evil, which consist in orderly or disorderly observable perceptions, just as changes in bodies and external phenomena are born from one another through the laws of efficient causes or of motion. Hence there’s a perfect harmony, pre-established from the start, between the perceptions of the monad and the motions of bodies, between the system of efficient causes and that of final causes. And therein lie the agreement and the physical union of body and soul, without either of them being able to change the laws of the other.
4. Each monad, along with its particular body, makes up a living substance. So not only is there life everywhere, joined to limbs or organs, but there are also infinite degree of it in monads, some of which are more or less dominant over others. But when a monad has organs that are adjusted in such a way that, through them, there’s clarity and distinctiveness in the impressions that they receive and so in the perceptions that represent them (as, for example, when rays of light are focussed and act with greater force through the shape of the eye’s humours), this can amount to a feeling, that is, to a perception accompanied by a memory, namely a perception of which a certain echo still remains long it after and which, on occasion, makes itself heard. This kind of living being is what’s called an animal, just as its monad is called a soul. And when this soul is raised to  the level of reason, it’s something more sublime and counted among minds, as I’ll explain in a moment. True, animals do sometimes attain the level of simple living beings, and their souls the level of simple monads, namely when their perceptions aren’t distinct enough to be remembered, as happens in a deep and dreamless sleep or when they fall into a stupor. But perceptions that have become entirely confused have to develop again in animals for reasons that I’ll come to in a moment (§12). Hence it’s just as well to distinguish between perception, which is the internal state of a monad representing external things, and apperception, which is consciousness or reflective knowledge of this internal state, a consciousness that’s given neither to all souls nor to any particular soul all the time. And it’s for lack of this distinction that the Cartesians got things wrong, making the mistake of disregarding perceptions of which we’re not conscious,7 just as people tend to disregard imperceptible bodies. It’s this, too, that lead those same Cartesians to believe that minds alone are monads and that beasts don’t have souls, still less any other principles of life. And just as they flew in the face of people’s ordinary opinions by refusing any feeling to animals, so they curried too much favour with popular prejudice by confusing a long stupor that stems from a great confusion of perceptions with death in the strict sense, in which all perception cease. This has confirmed the ill-founded opinion of the destruction of certain souls and the pernicious view of certain so-called free thinkers, who have denied the immortality of our own.
5. There is connection between the perceptions of animals which has some passing resemblance to reason, but which is founded on the memory of facts or effects alone and not on the knowledge of causes. Hence a dog runs away from a stick with which he’s been beaten because memory represents to him the pain which the stick has caused him. And men, too, insofar as they’re empirical, which is to say in three quarters of their actions, act just like animals. For example, we expect day will dawn tomorrow because we’ve always experienced it that way; only an astronomer predicts it through reason, and even this prediction will one day prove to be wrong when the cause of daylight, which is in no way eternal, ceases. But reasoning in the true sense depends on necessary or eternal truths like those of logic, number and geometry,  which make indubitable connections between ideas and lead to inevitable conclusions. Animals in which such conclusions go unnoticed are called beasts, whereas those know these necessary truths are those who are rightly called rational animals, and their souls are called minds. These souls are capable of acts of reflection, and of considering what we call myself, substance, soul, mind,8 in a word, immaterial things and truths. And this is what makes us capable of science or of demonstrative knowledge.
6. The researches of the moderns have shown, and reason has confirmed, that the living things whose organs we know, i.e. plants and animals, do not come from putrefaction or from chaos, as the ancients believed, but from pre-formed seeds and so from the transformation of pre-existing living things. There are little animals in the seeds of large ones and, through the means of conception, these adopt a new look,9 a look that they make their own and which gives them the means to feed and to grow in order to pass onto a larger stage and thereby bring about the propagation of the large animal. True, the souls of human spermatic animals aren’t rational and only become so when conception determines a human nature for these animals. And just as animals in general are not entirely born through conception or generation, so they do not entirely perish in what we call death, since it’s reasonable to assume that what does not begin naturally does not come to an end in the order of nature either. So, throwing off their mask or their tattered cloak, they simply return to a smaller stage on which they can just as perceptual10 and well-ordered as they were on the larger. And what we’ve just said about large animals equally applies to the generation and death of spermatic animals themselves: they are the offshoots of other, smaller spermatic animals, in comparison to which they would pass as large, for in nature, everything goes on to infinity. Not only souls, then, but animals, too, are ingenerable and imperishable; they are merely developed, enveloped, covered up and stripped bare, transformed. Souls never leave their whole body, and never pass from one body into another that’s entirely new to them. There is no metempsychosis,11 but there is metamorphosis. Animals change, taking on and leaving behind parts alone. In nutrition, this happens  continually, albeit little by little and through tiny, imperceptible steps; visibly, but rarely, in conception and in death, where they gain or lose a great deal all at once, it happens with one fell swoop.
7. Up until this point we’ve been speaking only at the level of simple physicists. Now we need to lift ourselves to the level of the metaphysical by making use of the great, but little used, principle that says that nothing happens without a sufficient reason; that is, nothing happens without it being possible for someone who understands things well enough to provide a reason sufficient to determine why things are as they are and not otherwise. Given this principle, the first question we can legitimately ask will be: Why is there something rather than nothing? After all, nothing is simple and easier than something. Moreover, even if we assume that things have to exist, we need to be able to give a reason why they have to exist as they as they do and not otherwise.
8. Now, this sufficient reason for the existence of the universe cannot be found in the series of contingent things, in bodies, and their representations in souls, since matter is indifferent in itself to motion or rest and to one motion rather than another; as such, we cannot find in matter a reason for motion, still less for any particular motion. And although the present motion in matter stems from a previous one, and that in turn from one previous to it, we get no further forward however far we may want to go back; the same question will still remain. So, the sufficient reason, which has no need of any other reason, has to be outside of this series of contingent things, and has to be found in a substance which is the cause of this series, a necessary being, which carries the reason for its existence within itself. Anything different, and we would still have no sufficient reason at which we could stop. And this final reason for things is called God.
9. This primary simple substance12 must include eminently the perfections contained in the derivative substances that are its effects. Thus, it will have perfect power, knowledge and will; in other words, it will have omnipotence, omniscience and sovereign goodness. And since justice, taken in a very general sense, is nothing other than goodness in conformity with wisdom, God clearly has to contain sovereign justice. The reason through which  things exist is also that on which they depend for their existence and operation, and whatever perfection they have they are continually receiving from it. Whatever imperfection they have, however, stems from the essential and original limitation of the created thing.
10. It follows from the supreme power of God that, in producing the universe, he has chosen the best possible plan, one that combines the greatest variety with the greatest order; one in which ground, place and time are combined in the best possible way; one that produces the maximum effect through the simplest means; one that gives created things the greatest power, the greatest knowledge, the greatest happiness and goodness that the universe can allow. Just as all possible things have a claim to existence in proportion to their perfections in the understanding of God, so the result of all these claims has to be the most perfect actual world that is possible. Without this, it would not be possible to give a reason for why things have gone the way they have, rather than otherwise.
11. The supreme wisdom of God led him to choose, above all, the most appropriate laws of motion and those most suitable to abstract or metaphysical reasoning. The same quantity of total and absolute force or of action, the same quantity of respective force or of reaction, and finally the same quantity of directive force, is always conserved. Moreover, action is always equal to reaction, and the whole effect always equivalent to its total cause. Surprisingly, the laws of motion that have been discovered in our own time, some of which were discovered by myself, cannot be accounted for by the consideration of efficient causes or of matter alone. I’ve found that we have to turn here to final causes, and that these laws, unlike logical, arithmetical and geometric truths, depend less on the principle of necessity and more on the principle of fitness,13 that is, on the choice of wisdom. For anyone who ponders these things more deeply, this is one of the most successful and obvious proofs of the existence of God.
12. From the perfection of the supreme author it follows not only that the order of the entire universe is the most perfect that can be, but also that each living mirror that represents the universe according to its own point of view, each monad, in other words, each substantial centre, has to have its perceptions and its appetites ordered in the way that’s most compatible with all the rest. From which it also follows that souls, that is, the most dominant monads, or, rather, the animals themselves, cannot but awaken from that state of stupor into which death or some other accident can put them.
13. For everything in things is ordered once and for all with as much regularity and correspondence as possible, since supreme wisdom and goodness can only act with perfect harmony. The present is pregnant with the future, the future can be read in the past, what’s distant expressed in what’s close by. We could know the beauty of the universe through every soul if only we could unfold all its folds,14 folds that only open up over time. But just as every distinct perception of the soul includes an infinity of confused impressions that embrace the whole universe, so the soul itself only knows the things that it perceives insofar as it has distinct and elevated perceptions of them. And the soul has some measure of perfection only to the extent that it has distinct perceptions. Each soul knows the infinite, knows everything, but only confusedly. It’s like when I walk along the shore and, hearing the vast noise of the sea, hear the individual noises of each and every wave that makes up the whole, although without ever distinguishing them. But [our] confused perceptions are the result of the impressions that the universe makes on us. It is the same with each monad. God alone has distinct knowledge of everything, because he is the source of it. It’s rightly said that it’s as if God is at the centre of everything;15 but his circumference is nowhere, because to him everything is immediately present, at no distance from the centre.
14. So far as the rational soul or the mind is concerned, this is something more than a [mere] monad or simple soul. The rational mind isn’t only a mirror of the universe of created things, it’s also an image of the divine. Not only does the mind have a perception of the works of God, it is even capable of producing something that resembles them, albeit on a smaller scale. For even if we leave to one side the wonders of dreams, in which we effortlessly (but also involuntarily) invent things that would require a great deal of thought were we to be awake, our soul is architechtonic in its voluntary actions, and in discovering the sciences in terms of which God has ordered things (weight, measure, number, etc.), it imitates in its own realm and in the tiny sphere within which it is allowed to operate, what God does in the wider world.
15. This is why all minds, whether those of men or those of higher beings [genies], entering, by virtue of reason and eternal truths, into a kind of community with God, are members of the City of God; that is to say, they are members of the most perfect state, formed and governed by the greatest and best monarchs, in which there is no crime without punishment, no good act without its appropriate reward, and all in all the highest virtue and goodness possible. AND ALL OF this is achieved, not by a disturbance of nature, as if what God had laid down for souls might interfere with the laws of bodies, but through the very order of natural things itself, in virtue of the harmony which has been pre-established from all time between the kingdoms of nature and grace, between God as architect and God as monarch, in such a way that nature itself leads on to grace, and grace perfects nature while at the same time making use of it.
The Principles of Philosophy or the Elucidation Concerning Monads
1. The monad17 that we’ll be speaking about here is nothing but a simple substance that enters into composites; simple, meaning without parts.
2. And there have to be simple substances since there are composites, because a composite is nothing but a collection18 or an aggregatum of simples.
3. Now, wherever there are no parts, neither extension nor shape nor divisibility is going to be possible. So these monads are the true atoms of nature and, in short, the elements of things.
4. Equally, there’s no need to worry about their being broken up and no conceivable way in which such a simple substance could perish naturally.
5. And, for the same reason, there’s no way a simple substance could begin naturally, since it can’t be formed by composition.
6. We can say, then, that monads can only ever begin or end all at once; that is, they can only ever begin by creation and end by annihilation, whereas what’s composed begins and ends part by part.
7. Equally, there’s no way of explaining how a monad could be altered or changed internally by some other created being because, unlike composites, in which there can always be changes in the relation between parts, in a monad there aren’t any parts to rearrange and no conceivable internal motion that could be excited or directed, augmented or decreased. Monads have no windows through which anything could get in or get out. Accidents can neither detach themselves from substances nor stroll around outside them, as the Scholastics’ “sensible species” used to do.19 So neither substance nor accident can get into a monad from outside.
8. Still, monads have to have some qualities, otherwise they wouldn’t even be beings. And if simple substances didn’t differ in the qualities that they have, there would be no way of detecting any change in things,20 since whatever’s in the composite can only come from its simplest ingredients; and if monads were devoid of qualities, they’d be indistinguishable from one another, given that they don’t differ in quantitative terms. In this case, and assuming a plenum,21 each point would only ever be able to receive through motion the equivalent of what it had before, and so one state of affairs would be indistinguishable from the next.
9. By the same token, every monad has to be different from every other. In nature there can never be two beings that are perfectly alike and between which it’s not possible to find an internal difference or a difference based on an intrinsic denomination.
10. I also take it as read that since every created being is subject to change so, too, is the created monad, and that this change is continuous in each of them.
11. It follows from what we’ve just said that monads’ natural changes come from an internal principle, since no external cause can influence them internally.
12. But as well as this overall principle of change, there also needs to be the detail of the changes,22 and this detail determines, as it were, the specification and the variety of the simple substances.
13. This detail has to include a multiplicity within a unity or within what’s simple. Because every natural change happens gradually, something changes and something stays the same; as such, a simple substance has to have a plurality of affections and relations, even though it has no parts.
14. The transitory state that includes and represents a multiplicity within a unity or within a simple substance is nothing other than what we call perception, which, as we’ll see in what follows, needs to be distinguished from apperception or consciousness. This is where the Cartesians went horribly wrong, since they failed to account for perceptions of which we’re unaware.23 This also lead them to believe that minds [esprits] alone were monads and that there were no animal souls or other entelechies; and they made the common mistake of confusing a prolonged period of unconsciousness with death in the strictest sense, which also exposed them to the Scholastic prejudice of believing in souls that were entirely separable, and even confirmed the opinion of misguided minds that souls are mortal.
15. The action of the internal principle that brings about change, or the transition from one perception to another can be called appetition. True, appetite can’t always attain the entire perception at which it’s aiming, but it always obtains some part of it and arrives at new perceptions.
16. We ourselves experience a multiplicity in a simple substance when we find that the most insignificant thought of which we’re conscious24 includes some variety in its object. As such, everyone who accepts that the soul is a simple substance should accept this multiplicity in the monad. Monsieur Bayle shouldn’t have had the difficulty with it that he had in the ‘Rorarius’ article in his Dictionary.25 17. Besides, we have to admit that perception, and everything that depends on it, is inexplicable in terms of mechanical principles, that is, in terms of shapes and movements. Imagine a machine built in such a way that it could think and feel, in such a way that it could perceive; we can imagine this machine being expanded, while still retaining the same proportions, allowing us to step inside it, just as we walk into a mill. Yet all that we’d see inside would be parts pushing against one another; we’d find nothing that might explain a perception. Accordingly, we should look for perception not in composites or in machines, but in simple substances alone. And that, moreover, is all that we can find in them, perceptions and their changes. And these, again, are the only things making up the internal actions of simple substances.