R.I. Raspe and A. G. Kästner had enjoyed several years of joint examination of Leibnizs manuscripts when, in 1762, Raspe announced the impending publication of a volume of these hertofore suppressed works. The volume was dedicated to Baron Gerlach Adolf von Münchausen.
A. G. Kästner
This is the first English translation of Kästners Preface. Its strategic significance is reported in Leibniz to Franklin on Happiness, in this issue. The author's footnotes are in superscript; editor's footnotes are bracketed; and are supplied by David Shavin. It was translated from the French by Nancy Shavin.
Preface to Leibniz's
New Essays on Human Understanding
That the real universe were something altogether different than the apparent one, is a truth that should no longer be in doubt since Descartes, who maintained, to the great astonishment of the philosophers of his time, that light and colors have no similarity to the ideas that we form of them.1 The metaphysics of Leibniz have always seemed to me to be based on this principle.
Those who accuse him of impenetrable obscurity  would find it quite clear, if only they would rid themselves of certain prejudices similar to the "intentional species" against which Descartes had to battle.  They maintain that the manner in which M. Leibniz has conceived the origin of extension is inexplicable. They prove by geometrical demonstrations, how absurd it is to look at a body as a sum of points. Can one blame for this absurdity, the person to whom the whole continent of Europe is indebted for the infinitesmal calculus? I say this continentin order to let those rejoice in that liberty, of which they are so jealous
Deeply divided from the whole world are the British.
It is not body that M. Leibniz composes from simple beings, but the phenomenon of extension, which he accounts for, by saying that we represent to ourselves, indistinctly, a great number of non-extended beings. The telescope shows us clusters of stars, where the naked eye sees only luminous spots. The spot is not composed of stars as the whole is composed of parts: it is an appearance which offers itself to eyes too weak to distinguish the stars. So, the Elements  of Leibniz.
The representative force, with which Mr. Leibniz has endowed his Elements, seemed dubious even to M. Wolff. Yet, this same Mr. Wolff had brought into the full light of day this truththat the universe is a whole whose parts are so intimately connected, that one could not change the least thing, without changing the whole into a completely different universe; that it holds together the spider's thread with the same force that pushes or pulls the planets around the sun. This is how a French Philosopher and beautiful spirit2 understood what the German Metaphysician  had demonstrated by profound reasoning. Knowning this, could M. Wolff still doubt, that that which happens at each moment to each individual, so affects the universe as a whole, that the infinite mind sees in this, the universe that is, the only one to which an individual, such as he is, could be a part? 
If one were to say to someone who is not so well schooled in the science of numbers, that 23 is the 12th term of an arithmetic progression which starts with 1, he will find, first of all, that this progression is one of odd numbers. You need only put in place of the sequence and its given term, the universe and the individual. It is in this sense that I have always understood those "mirrors of the universe" of Leibniz , which seemed so ridiculous to many Philosophers, because these gentlemen had no idea how to find an entire sequence from one given term. M. Leibniz used the verb "to represent," as he explains it himself in his remarks on the book of M. Locke now being published.3 The relationship of the circular base of a cone and its section is such that, if you know one, you also know the other. It is thus, that we represent in mechanics, velocities and times by straight lines; thus, that a thermometer represents the warmth of the air, a barometer the weight of the atmosphere.
I had hoped that these reflections would not be altogether misplaced at the beginning of a collection of this great man's philosophical writings, extracted from his manuscripts, many of which are still kept at Hanover to this day. It is up to those who will benefit from it, to acknowledge the protection always so graciously accorded the sciences by the enlightened Ministers to whom the King has confided the happiness of his domains , in the care of enriching the republic of letters with these works.
One could not have chosen an editor more worthy than M. Raspe, who combines a solid knowledge with satisfying insights, and who has made every possible effort to make this choice agreeable to the general public. It is for him to instruct the readers concerning some historical circumstances pertinent to this edition. As for me, having had, among many other duties, only a few days to write this Preface, first in Latin as the editor had wished, and then after that to recast it into French, as he thought to ask a little while later, I would hope that I will be pardoned if this Preface is found to be less worthy than the place it holds.
If only I may be permitted to add yet some few more thoughts to which the reading of the following passages has given rise.
In Part II, there is a discussion of the law of continuity in respect to the collision of bodies. M. Euler is of the same mind as M. Leibniz and has, happily, made use of this to calculate the laws of motion.4 
It is also known that M. Leibniz distinguished the species of Ideas more rigorously than anyone before him.5 Hence, one would expect to see him sometimes correct M. Locke, a far less rigorous writer on these matters. Thus, in the investigation of simple Ideas, p. 77 
]. The English Philosopher is as much beneath the German, as the opticians from earlier times, who mistook a ray of sunlight for a simple phenomenon, were beneath Newton. If M. Leibniz had written the history of the human mind, his work would differ from that of M. Locke, as the history of an insect described by Roesel, would differ from a rough draft done by Frisch. 
M. Poley enriched his excellent translation of M. Locke's book  with observations drawn from the Philosophy of Leibniz and of Wolff. It is a shame that these observations were not written in another language. Perhaps they would have been useful for some minds, who were too superficial to understand M. Locke, and who, in order to pass as Philosophers at very little cost, became extreme admirers of hisimagining themselves as having seen all truths, as the pedants of barbarous ages imagined it with respect to Aristotle. 
After the time when the Philosophers were debating the question of the blind man, p. 92 , there was an experiment on this which was reported in the Philosophical Transactions.6 At first glance, it appeared to be more in opposition to M. Leibniz, than it was after a more thorough examination. The blind man, who wishes to recognize by sight the bodies that he had distinguished by touch, must, according to M. Leibniz, compare the effects that the surfaces of the bodies have on his two senses. This is what the blind man seemed to do after having been cured by Cheselden, when he took the cat into his hands, which he had not been able to distinguish well enough from the dog, when he was first beginning to see. The observers imagined that he was merely examing the cat with great intensity, whereas, in fact, he was examining it as much with his hands as with his eyes. No one thought of proposing to this young man an experiment with some surfaces as uniform as those of a sphere, or a cube; and it appears that this singular event lacked the presence of sufficiently philosophical observers. His judgement on the paintings was just as Leibniz had predicted. 
It is not only nowadays that we have begun to ask if all the rotations of the earth around its axis are equal,7 since M. Leibniz had the same doubt, p. 104. 
Are we to believe that, in the most immediately apprehended science , the first notion, that of figure, would yet be not well defined? This is nonetheless what is shown, p. 105. 
The reader will see by these examples, chosen randomly, whether these works by Leibniz merit the public's attention, and whether, as in the already known writings of the same author, they contain the seeds of truths, which will enrich the cultivation of the republic of letters.
Göttingen, September 1764
The Author's Footnotes
1. Rene Descartes's 1637 Dioptrics, Chapter 1.
2. M. de Maupertuis, Essay de Cosmologie, 1750.
3. Book II, chapter 8, section 12, p. 87.
4. Histoire de l'Academie Royale de Berlin, 1745, p. 37, 51.
5. Gottfried Leibniz's "De cognitione, veritate & Ideis," Acta Eruditorum, Leipzig, 1684.
6. Philosophical Transactions of the Royal Society of London, No. 402; Robert Smith's Compleat System of Optiks, Book 1, chapter 5. [Also, Smith's "On Distinct and Indistinct Vision" was the cause of some debate and notoriety.-N-ed.]
7. See the dissertation of M. Paul Frisius on the daily motion of the Earth, which has won the 1756 prize of the Royal Academy of Berlin.
 In particular, Leonhard Euler's 1760/1 Letters to a German Princess and Voltaire's 1759 Candide.
 Medieval, scholastic term. Kästner picks up on Leibniz's attack, that "modern" Newtonians were reviving occultist appeals to innate qualities.
 Latin in text: "Penitus toto divisos orbe Brtiannos."
 I.e., the "Monads."
 I.e., simple beings or Monads.
 Euler's 1739 Tentamen musicae and 1760/1 Letters. Kästner judos Euler's patronizing, "dumbing-down" approach to ladies. The ear and mind of a woman, or man, can distinguish harmonies, without a supercomputer counting vibrations.
 I.e., where both phenomena and cause are in the visible universe.
 I.e., Leibniz.
 Christian Wolff's problem with "representation" included his sensitive theory on the relatedness of the universe, that would not allow him to explain why he himself existed, that is, what God's mission for Wolff was. (Or, to make a business of representing Leibniz, is not to know Leibniz.)
 The "Monads."
12] Such is Kästner's description of the role of Baron Gerlach Adolph von Münchausen, Minister to Hanover from the British Court, and leader of the faction for "happiness" for the body politic. (Pierre Beaudry has located a 1766 work by Kästner, in part on "happiness," entitled Nouvelle Theorie des Plaisirs by Sulzer and Kästner.) Münchausen was key in the liberating of the Leibniz documents they published.
13] Kästner alludes to one of the last works written by Euler prior to Maupertuis' arrival at the Berlin Academy in 1745, after which Euler was instructed by Maupertuis, effectively, that Leibniz was now to be treated as a public enemy. Hence, Kästner's reminder to Euler was likely a jab, not a compliment.
14] See "Of Simple Ideas," Book II, Chapter ii, in Leibniz's New Essays.
15] A.J. Roesel von Rosenhof's Historia naturalis ranarum, a massive work on the German frogs and toads, was noted for the vivid artwork, capturing, e.g., muscles in action. J.L. Frisch's Beschreibung von allerley Insecten in Teutschland, also voluminous, was evidently known for its "just the facts, ma'am" style of drawings.
16] Heinrich Eberhard Poley's 1757 German publication of the 1709 abstract of Locke's Essay.
17] Kästner effectively blasts as medievalists, the English followers of Locke, who had such great pretensions as modern defenders of liberty!
18] Found in Leibniz New Essays, Book II, Chapter ix, section 8.
19] William Molyneux, who was engaged in catty comments with Locke about Leibniz, proposed for public consideration: Would a blind adult, upon first being able to see, recognize by sight objects that he had learned by touch? In 1728, the British surgeon William Cheselden removed the cataracts from a 14-year old, who was observed as described above.
 Found in Leibniz New Essays, Book II, Chapter xiv, section 21.
 Found in Leibniz New Essays, Book II, Chapter xv, section 4.
Leibniz’s Critique of Locke
Preface to the New Essays Concerning Human Understanding
MP, pp. 422-33
I. Introduction (422b)
A. to contrast his philosophy with that of Locke, wrote this work in the form of a dialogue, with one character presenting Locke’s view in the Essay, and the other presenting Leibniz’s response
B. compared himself to Plato and Locke to Aristotle, although he admitted that they both differ from the ancients in several ways
1. for instance, Locke and Aristotle subscribed to the blank slate theory of the mind (423a)
2. while Leibniz and Plato thought that there are innate principles
A. the question is whether all truths depend upon experience and induction
B. Leibniz argued that although the senses may be necessary, they are not sufficient to give us all our knowledge
1. experience gives us only particular instances or individual truths (423a)
2. no number of individual instances will suffice to establish the universal necessity of a general truth (423a-b)
a. for instance, the Greeks and Romans thought that every twenty-four hours day changes to night and night to day (423b)
b. but this does not hold in Nova Zembla
c. there may also be some time in the future when the earth and even the sun no longer exist
C. thus, necessary truths such as we find in mathematics must have some basis other than the senses
1. although it may be that without the senses we would have never thought of them
2. logic, metaphysics, and morals are full of such truths
3. their proofs must arise from internal principles, which are called innate
4. however, we should not imagine that we can read these principles as easily as we read the words of a book – but they can be discovered by dint of attention
5. senses provide occasions for this
D. It is in this way that we differ from animals: animals are purely empirical
1. cannot form necessary truths, while people are capable of demonstrative knowledge (423b)
2. animals, like some people (e.g., empirics), can infer only that what has happened in the past will happen again in similar circumstances, without being able to determine whether the same reasons are at work (424a)
3. why people can easily trap animals and why empirics make mistakes: they do not take into account that the world changes and that people acquire new skills and tricks
4. this is why the wisest people do not simply rely on past experience but seek the reason that something happens. Allows them to find exceptions to uncertain rules.
III. Locke on reflection (424b)
A. Leibniz suggested that Locke may actually have agreed with him on the question of whether the mind is a blank slate since Locke says that there are two sources of ideas: sensation and reflection
B. reflection is nothing but attention to what is in us
C. And Leibniz maintained that there is a great deal within us that does not come to us from the senses: (q.v.)
1. “we are innate to ourselves, so to speak”
2. and that includes being, unity, substance, duration, change, action, perception, pleasure, etc. (424b)
a. these ideas are always present even though they may not be consciously perceived (apperceived)
b. made an analogy with veined marble, rather than a blank tablet
1.) if veins marked out shape of Hercules, then the block of marble would be more determined toward that shape, although it will still take some work to make the statue
2.) this is how ideas and truths are innate in us, that is, as natural inclinations, potentialities, dispositions, or habits
D. Locke appears to have denied that there is anything potential in us, anything we are not consciously perceiving (424b-25a)
1. but Leibniz argued that he could not have meant this in all strictness, since not everything in our memories is always consciously perceived. (425a)
a. Sometimes things are even hard to retrieve when we need them
b. although we may recall them at some other time, like a song
2. elsewhere Locke said that there is nothing in us that we did not at some point consciously perceive (425a)
3. but why should we believe that everything is acquired by apperception of external things and nothing from within ourselves?
4. even Locke recognized reflection as a source of ideas
IV. On whether the mind is always thinking
A. Here Leibniz thought it would be more difficult for him to find agreement with Locke, who argued that the mind is not always thinking
1. dreamless sleep
2. since bodies can be without motion, souls can be without thought
B. First of all, Leibniz denied that there is such a thing as absolute rest: there is never any body without motion
C. Second, he argued that at every moment there are infinite tiny perceptions in us that we do not consciously perceive (425b)
1. we ignore them because they are either too small, too numerous, too homogeneous, lack novelty, etc.
2. for example, the roar of the sea is made up of the many noises of each wave that we do not distinguish
3. we never sleep so soundly that we do not have some weak sensations, and we would never be wakened by the greatest noise if we did not hear its faint beginnings (426a)
4. these tiny perceptions make up complex sensations such as flavors
5. also, they make up the individual, connecting him to his past
6. they also explain pre-established harmony between soul and body and among all the monads or simple substances (426b)
7. and they determine our choices when the alternatives seem to be equivalent
8. in sum, these tiny perceptions are as useful to philosophy of mind as corpuscles are to physics
D. insensible variations among things also explain how it is that no two things are ever exactly alike (427a)
1. hence no such thing as empty tablets of the mind, minds without thought, etc. (q.v.)
2. if we thought that things we cannot consciously perceive do not exist in the soul or the body, we would fail in philosophy and politics, by ignoring imperceptible changes (427a-b)
3. it is okay to use abstractions in philosophy as long as we know what we’re doing: this is what mathematics does (427b)
4. these little perceptions also explain how, no two souls, human or otherwise, ever leave the hands of the Creator perfectly alike (427b, q.v,)
E. Leibniz also argued that souls are never completely separated from bodies – there are only gradual differences in the states of the soul, like caterpillar to butterfly (427b-28a)
V. Physical issues (428b)
A. Locke and Leibniz also disagreed about matter
B. Locke thinks that the void is necessary for motion
1. this assumes that the parts of matter are rigid. If they were, motion in a plenum would be impossible.
2. but Leibniz would not grant this assumption. Rather, he assumed matter to be fluid and infinitely divisible
C. Leibniz agreed with Locke and other mechanical philosophers that one part of matter operates on another only by impulse (429a)
D. However, it seems that Locke retreated from this position in his reply to the Bishop of Worcester, Edward Stillingfleet, where he was trying to defend his claim that matter can think (380b-381a)
1. Locke said that although he used to think that bodies could act on one another only by impulse, he was convinced otherwise by Newton: the existence of gravitational attraction shows that God can put powers into bodies that are inconceivable to us (429a, q.v.)
2. Leibniz agreed that God can do things beyond our understanding (429b)
3. however, he did not think that we should invoke miracles to explain the ordinary course of events in nature (q.v.)
E. Ironically, Locke objected to admitting operations of the soul that are not sensible, yet does not balk at admitting operations in matter that are not even “intelligible”
VI. Whether matter can think (430a)
A. The Bishop of Worcester, Edward Stillingfleet, objected to Locke’s saying that it is possible for matter to think:
1. asked Locke how reflection could assure us of the existence of the mind if matter could think. (q.v.)
2. Locke had said in the Essay that the operations of the soul provide us with the idea of the mind
B. Locke’s reply
1. we know by experience (experiment) that we think
2. thinking cannot exist by itself without being in a substance
3. the power of thinking added to any substance makes it a spirit, (430a, q.v.)
a. regardless what other properties it has, such as whether it is has the additional modification of being solid,
b. just as the property of solidity makes something matter regardless whether it can think
4. if by spirit, Stillingfleet meant an immaterial substance, Locke granted that he could not prove there is such a thing, although he thought it highly probable (430a-b)
5. however, Locke believed that religion and morality depend only on the immortality of the soul, not on its immateriality (430b)
C. In response, Stillingfleet cited passages from the Essay where Locke said that we form the notion of immaterial substance from ideas of thinking, perceiving, liberty, and the power of moving our bodies, and that we have as clear a notion of immaterial substances as we have of material
D. Leibniz said Stillingfleet could have added that from the fact that the idea of substance is contained in both body and mind, it does not follow that they are modifications of one and the same thing
1. Leibniz made two distinctions: (431a)
a. modifications vs. attributes (i.e., “perpetual and principal predicates,” q.v.)
b. real or physical kinds vs. logical kinds
1.) things of the same physical kind, or those which are homogeneous, can be changed into each other by changing their modifications
2.) but two things that are heterogeneous, that is, of different physical kinds, can be of the same logical kind, and then they are not simply modifications of the same stuff
c. example: space and time are heterogeneous things, not modifications of one and the same physical thing, yet both belong to the same logical kind, continuous quantities
2. what Leibniz implied is that substance is only a logical kind that includes mind and body
E. Locke’s third letter to Stillingfleet (431b)
1. Locke said that God can add any properties he pleases to matter without changing its essence. He can:
a. give it motion
b. give vegetation to plants
c. give sensation to animals
2. but even those who agreed with him so far objected when he went a step further and suggested that God could also add thought to matter, as if this would change the essence of matter (431b, q.v.)
3. Locke argued that if adding thought to matter changes its essence from extended solid substance, then why doesn’t adding motion and life do the same?
4. one could object that we cannot conceive how matter could think, but Locke argued that God is not limited by what human beings can or cannot conceive
a. Locke then provided the example of the property of gravitational attraction
b. Here Leibniz objected that gravity represents a return to occult or inexplicable qualities or faculties
1.) compare 433b, where he compared these faculties to little demons or spirits
2.) as if watches told time by their power of clockness, without wheels, etc., or windmills ground grain by their fractive power, without need for a millstone
5. Locke then added that we do not even conceive how the soul thinks and maintained that since we can conceive both material and spiritual substance without any activity, it is up to God to give thinking to one or the other (431b)
F. Leibniz’s reply (432a)
1. agreed with Locke that we should not deny what we do not understand
2. however, he argued that we can deny what is absolutely unintelligible and inexplicable
3. also, denied that matter or spirit can be conceived without any activity, as activity is the essence of substance in general
G. however, Leibniz explained that he does not entirely agree with Stillingfleet, either
H. According to Leibniz, God does not just arbitrarily give this or that property to substances, but only those that are natural to them
1. that is, those properties that can be explained by the nature of the substance and that do not require any miracles. E.g. shape to material substance.
2. thus, for instance, matter does not have the natural property of attracting matter or moving in a curved path, since that cannot be explained mechanically (432a-b)
3. if we were to reject the distinction between what is natural and what is miraculous, that would put an end to all philosophy (that is, science) (432b)
I. to get back to whether matter can think:
1. thinking is not an intelligible modification of matter, a mechanical thing like the motion of a watch or windmill, of which we can conceive their workings
2. hence it is not natural for matter to think
3. there are only two ways God could give it this power:
a. add to it a substance that can think
b. endow it with thought through a miracle
4. here Leibniz agreed with the Cartesians
a. that is, that thought requires a separate substance
b. except that Leibniz was willing to extend this power to animals
c. Leibniz added that the immortality of the soul then follows naturally if it’s a separate substance, and that this is better than having immortality depend on a miracle, if the soul were material (433a-b)
d. but again, immaterial substances are always joined to matter (433b)