1. Introduction

Every era has its challenges. The invention of the printing press posed the challenge of an overflow of information in the form of printed books to the 17th century. This revolution impacted the lives of scholars, who had to find ways to cope with scientific reports, literature, and news. It also had a social dimension in that it motivated the scholarly community to establish official practices for dealing with products of knowledge, making ideas accessible without time-consuming reading practices. Reviews and excerpts became the main means of doing so.

G. W. Leibniz participated in the rethinking of cultural and scientific exchanges as a producer, consumer, and administrator. He served as librarian and as an influence on journals such as Monatlicher Auszug, as recently documented by Beiderbeck and Gantet (2021, 3–6). In his letters and writings, Leibniz expresses concern about the growing volume of published materials and the insufficient time allotted for reviewing them. This challenge motivates him to reflect on the role of the savant in society. The writing Mémoire pour des personnes éclairées et de bonne intention (1692, A IV 4 617) paradigmatically testifies of Leibniz’s commitment to rethinking the role of savants, portraying them as learned individuals who must give back to society by investing their valuable time in community-benefiting activities. Among the charitable activities that advance the public good, Leibniz lists those that promote science, such as meditations, observations, experiments, and instructions. Savants should pursue authentic scientific improvements rather than honor and public approval.1

In addition to the services that scholars can offer the public, there are also products that organize knowledge, such as encyclopedias, book catalogs, and book excerpts (excerpta). The latter seem to have a mere subsidiary function; they are useful for finding passages quickly and for providing an initial overview of the subject matter and the author’s approach.

As testified by the Academy Edition, excerpta was a practice used by Leibniz not just as a private way of studying a book, but also for sharing contents with other thinkers of the time. Few pages could easily be sent by mail and shared with other scholars, or published in journals. As Gantet (2021a, 263) has showed, the distinction between excerpta and reviews was not so sharp at the time. Both excerpta and reviews are published anonymously and must avoid controversies, even when they express merits and demerits of the book.

In another study, Gantet (2021b) reconstructs Leibniz’s publication and review activity in scientific journals and shows that Leibniz extensively exercised the practice of excerpta as book reviews. Moreover, his review and publication activity appears to be guided by a dissemination strategy that prioritizes high-impact journals over other media.

This strategy can be seen as reflecting what Leibniz wrote in Memoires pour des personnes ecclaires: high-impact journals guarantee a larger audience for ideas that contribute to scientific advancement. However, it can also be seen as a strategy to control and manipulate the dissemination of these ideas by influencing their readership. In this paper, I address the question of whether there is more to Leibniz’s review activity than disinterested scientific improvement or if he envisions the potential of reviews to influence reception and debate about the reviewed work.

The question of Leibniz’s ambivalent review activity stems from the role of reviews during his time. As Gantet (2021a, 263) points out, reviews were not intended to criticize an author’s work. Rather, they were a means of sharing information about a book’s content without engaging in critical debate with the author. Jean Gallois, the editor of the Journal des sçavans from 1666 to 1674, provides the following guidelines for writing a good review:

It is good that he makes the excerpt long enough so that I may have more knowledge of the book. It is necessary to note what is good or bad in the book, what purpose the book may serve, and what is the advantage of reading it, whether anything has already been written on the same subject matter, and compare the author of this book to those who have written on it before. [II est bon qu’il fasse l’extrait un peu ample afin que je puisse avoir plus de connaissance du livre. Il fault remarquer ce qu’il y a dans le livre de bon ou de mauvais, a quoy le livre peut servir et quel profit on en peut tirer, si on a desja escrit sur cette matière, et faire comparaison de ceux qui en ont escrit avant l’auteur de ce livre, quoted from Gantet (2021, 263 n. 27), my translation.]

Although Leibniz apparently follows these instructions, he uses them as camouflage to deliver more than a report on the contents of the book. His reviews serve as a scientific tool to instill prejudices in scientific users. By “prejudices” I do not mean false judgments about a book, but rather some precognition in the form of knowledge one must have to critically assess the content of the book, which may eventually incline readers to reject the author’s arguments. To support my thesis, I analyze Leibniz’s review of John Locke’s An Essay Concerning Human Understanding, published in 1700. Before I begin the analysis, I would like to address a methodological concern.

Leibniz’s review activity spanned his entire scientific life. During this time, he produced a remarkable number of reviews of books on philosophy, mathematics, physics, and more (see Gantet 2021b).2 Therefore, limiting the analysis to one review is methodologically unsound. A rigorous approach should survey all of this material and address other variables, such as the periodization of reviews (are there differences between early reviews, when Leibniz was young, and later reviews, when he was a well-known, acclaimed scholar?), the variety of disciplines (is there continuity between reviews of philosophical works and reviews of works in other disciplines?), and, finally, similarities that could be used to argue for a strategic use of reviews, as I suggest. Another way to support my thesis would be to examine Leibniz’s reviews of his own work (see Giampietri 2012) for clues as to whether he employed this strategy also to his own work. This paper is just the beginning of such research. As one must start somewhere, I will focus on what I consider a paradigmatic case: Leibniz’s review of Locke. Therefore, the support for my thesis would be modest. All I argue is that Leibniz used the strategy of deploying book reviews to influence readers at least once. This naturally raises the question of whether he did so systematically.

In par. 1, I explain why Leibniz’s review of Locke is paradigmatic in supporting my thesis. In par. 2, I analyze the review and demonstrate that, beneath the surface of what appears to be a fair and objective report, Leibniz offers a critical evaluation of John Locke’s work. This evaluation is designed so that readers familiar with Leibniz’s philosophy, including his intended audience, can immediately grasp the issues and contradictions of Locke’s empiricism. In par. 3, I conclude by examining the differences between the first review, published in 1700, and the addendum, published in 1701, in the same journal.

2. Leibniz and Locke

Among the most influential and important controversies between early modern intellectuals, the debate between Leibniz and Locke regarding the existence of innate ideas and their role in knowledge acquisition, as well as the question of whether the mind can develop its abilities only through the material provided by the senses, occupies a unique place, at least in terms of its influence on topics that are still debated today.3 If this is not reason enough why Leibniz’s review of Locke is a paradigmatic case, three aspects of the controversy support this view: First, the long-standing confrontation that led Leibniz to write a book-length rejection of Locke’s theses. Second, the abundance of public and private sources that shed light on Leibniz’s attitude toward Locke’s work. Third, the issue of diverging languages and the use of translations that shaped the reception of Locke’s work.

Regarding the first issue, Leibniz engaged with the work of Locke over a period of nearly ten years (1695–1704), which culminated in the writing of Nouveaux essais sur l’entendement humain. During this period, Leibniz hoped to engage Locke in direct dialogue, but Locke refused. In addition to his many indirect exchanges with Locke through Thomas Burnett (see Robinet and Schepers in the Introduction A VI 6, XVII–XXIII), Leibniz began corresponding with Lady Masham, Locke’s close friend and the daughter of Cudworth (see Meier-Oeser in the Introduction to A II 4 LXXXI–LXXXVIII). Locke spent the last years of his life at her house until his death in 1704. Leibniz abandoned the idea of publishing the New Essays because the reason for their completion—a live confrontation with Locke—disappeared with his death (Leibniz to Lady Masham, July 10, 1705, A II 4 325). The book was published more than fifty years later, in 1765, by Raspe, after Leibniz’s death.

From its structure to its content, the book New Essays on Human Understanding documents that the reason for engaging in a lively correspondence with Locke is not solely due to a difference in philosophical views. Leibniz is concerned that Locke’s writing style and his use of English, his native language, give him an advantage. Locke is able to express himself in a more accessible and appealing way, making his ideas easier to comprehend and share. This concern is explicit in a passage drawn from the Preface to the New Essays:

Indeed, although the author of the Essay says hundreds of fine things which I applaud, our systems are very different. His is closer to Aristotle and mine to Plato, although each of us parts company at many points from the teachings of both of these ancient writers. He is more popular whereas I am sometimes forced to be a little more esoteric and abstract—which is no advantage for me, particularly when writing in a living language. However, I think that by using two speakers, one of whom presents opinions drawn from that author’s Essay and the other adds my comments, the confrontation will be more to the reader’s taste than a dry commentary from which he would have to be continually turning back to the author’s book in order to understand mine. [En effet, quoique l’Auteur de l’Essay, dise mille belles choses où j’applaudis, nos systemes different beaucoup. Le sien a plus de rapport à Aristote et le mien à Platon, quoique nous nous eloignions en bien des choses l’un et l’autre de la doctrine de ces deux anciens. Il est plus populaire, et moi je suis forcé quelque fois d’etre un peu plus acroamatique et plus abstrait, ce qui n’est pas un avantage pour moi, sur tout écrivant dans une langue vivante. Je crois cependant qu’en faisant parler deux personnes, dont l’une expose les sentimens, tirés de l’essay de cet auteur, et l’autre y joint mes observations; le parallele sera plus au gré du lecteur, que des remarques toutes seches, dont la lecture auroit été interrompuë à tout moment par la necessité de recourir à son livre pour entendre le mien.] (NE 47–48/A VI 6 47–48).

These lines from the Preface condense the three points I made to support the relevance of the review as a paradigmatic case. First, Leibniz’s strategy of turning the book into a dialogue is meant to make his position more appealing and less abstract than it would have been in a treatise. It further compensates for Locke’s linguistic advantage. Furthermore, a dialogue allows for a more focused debate, as both participants’ positions are presented to the readers. Symbolically, it represents Leibniz’s partnership with Plato. What he writes in the Preface testifies that he was afraid of the apparent soundness of Locke’s argumentation and the popular and simple way of exposition of his thought. Locke’s philosophy was not simply attractive, but capable to generate assent. These two features of Locke’s expository capacities increased the risk factor of wide dissemination of dangerous philosophical contents, like Locke’s criticism of innate ideas.

Leibniz likely had these concerns even before writing those lines in the Preface. When the dissemination of Locke’s philosophy increases through the translation of his Essay first into French by Pierre Coste in 1700 and then into Latin in 1701, he likely was searching for ways to contrast Locke’s philosophy. The translations gave him the opportunity to address Locke’s philosophy publicly, although anonymously. The first long review appeared in September 1700 and the shorter Zusatz in January 1701. Both reviews were written in German, a language Locke did not read. They were never sent to Locke, even though they were published before his death in 1704, when Leibniz was still trying to convince Locke to engage in a public debate.

For these reasons, I hypothesize that the purpose of this review is not the kind of public utility that Leibniz mentions in the quoted text of Mémoire pour des personnes éclairées et de bonne intention (1692). However, this is not because Leibniz is searching for public approval. An analysis of the review’s contents led me to conclude that Leibniz intended to influence the German reception of Locke’s work.

3. Leibniz’s First Review of John Locke

The Review and the Zusatz appear in Monatlicher Auszug aus allerhand neu herausgegeben, nütlzlichen und artigen Büchern, the former in the issue of September 1700, as a review of the French edition of the book; the latter in January 1701, occasioned by the publication of the Latin translation of Locke’s book. They are anonymous but attributed to Leibniz already early, as testified by their inclusion into Leibnitz’s Deutschen Schriften by Guhrauer in 1838.4 As the title of the Journal suggests, and as the first line of the review openly claim, it is written in the form of excerpta (Auszüge).

Since summarizing the entire Essay was impossible and unnecessary—Locke had already written an excerpt that was published in Le Clerc’s journal before his Essay was published (Locke 1688, 49–142)—, Leibniz decides to focus on two chapters added to the fourth edition of Locke’s book (1700):5 Book II, Chap. 33 On the association of ideas and Book IV, Chap. 19 On Enthusiasm.

The first set of remarks I would like to offer concerns the choice made by Leibniz of presenting these two chapters. The main reason he adduces is that they are added in the fourth edition of Locke’s work, but, as he also mentions, these are not the only changes Locke has made in the course of the four editions. In the second edition, Chap. 21, Book II, On Power was largely revised, and another, Chap. 27, Book II, On identity and Diversity, newly added. The reason to focus on Associations of ideas and Enthusiasm is not simply their recent addition in the fourth edition. I first focus on why Leibniz does not offer an overview of the other two chapters mentioned, Chap. 21 and 27 of Book II, although he does not refrain from saying something about Chap. 21.

Both chapters are philosophically significant, and what Leibniz writes about them in New Essays can be used to indicate his philosophical attitude toward the theses Locke defends there. Leibniz devotes a significant amount of discussion to opposing Locke’s notions of power and personal identity in New Essays. Conversely, Leibniz’s discussion of the two chapters of the Review in the New Essays manifests agreement with Locke’s ideas. According to the guidelines of the time, this conciliatory attitude is better suited to a review. However, if Locke and Leibniz agree on the theses of the chapters discussed in the review, then the review is not critical and my thesis is false. What is relevant to ground my thesis is the underlying disagreement beneath the apparent agreement. First, I focus on Leibniz’s criticism of Chapter 21 in New Essays and demonstrate how it builds on what Leibniz only mentions in the review.

Leibniz finds Locke’s analysis of the beginning of an action and free will (Essay II 21), as well as his analysis of personal identity (Essay II 27) highly problematic. In Leibniz’s view, Locke follows Descartes in his conception of thinking substance, insofar as the mind’s thoughts are always conscious.6 This thesis holds that to have a thought the mind has a perception both of the content of the act (the idea), and the kind of act the mind is using to consider its idea (either desiring, or imagining, or dreaming). This perception of the content and of the act amounts for Leibniz to an act of reflection. Locke uses this notion of mind (or of Cartesian thinking substance) as ground for his arguments that there are no innate ideas and truths;7 for his distinction between voluntary actions and free actions; for his conception of personal identity as the continuity between conscious acts of thought. I shortly highlight these three Lockean theses and Leibniz’s rejection (for an extensive treatment, see Oliveri 2016, 27–33).

Locke’s rejection of innate ideas and truths hinges on the notion that a mind is conscious of both the content and the type of state it has. According to Locke, a mind has an idea only if it knows it has that idea. This is similar to saying that the mind remembers encountering the same content in perception or reflection. For Locke, perception through the senses and reflection are the only “windows” through which the mind can acquire ideas. If one denies that having an idea means remembering that the mind has encountered the idea’s content, then any idea, including those of the senses, such as colors, turns out to be innate, which is absurd. (Essay I 4, par. 20 in Locke 1975, 96–9). Leibniz rejects this thesis, arguing that Locke’s criterion for determining whether an idea is innate or acquired is flawed because innate ideas can and must be learned. As Leibniz states: “I cannot accept the proposition that whatever is learned is not innate” (NE 85/A VI 6 85). In other words, remembering that one has previously considered the content does not mean that the content cannot be innate just because it is acquired.

Leibniz references Plato’s Meno, according to which geometric truths must be learned yet are innate (NE 77/A VI 6 77). Indeed, innate means that the source of the idea must be the mind’s abilities and dispositions, without which perceptions could not be processed to yield truths. To support this view, Leibniz rejects the idea that the mind is always conscious of its thoughts. He argues that conscious thoughts are merely the tip of the iceberg of a mind’s states, as they arise from minute perceptions and endeavors. These perceptions and endeavors represent the mind’s permanent and constant activity, whose task is to harmoniously express the entire world and other substances throughout its changes.8

Therefore, the mind is always perceiving and active, though not because it is conscious of its perceptions. Perception is the activity of the substance and is more fundamental than thinking. Thinking is constituted by perceptual states that are processed to represent perception in clear and distinct ways, i.e., through general notions, necessary truths, and innate ideas. The mind can eventually become conscious of its processing, and conscious thoughts serve very specific purposes, such as providing reasons and causes for actions and knowledge. In other words, minds represent motives and causes; however, the determination to act in a certain way or continue a series of thought is not solely determined by what is consciously represented. Minute perceptions and endeavors determine the mind’s internal states, which it then rationalizes by finding causes and motives (see Priarolo 2016, 745–64). For an example, consider that I believe that I chose to study philosophy because of the value I find in the discipline (rational cause), but the pleasure I feel in philosophizing (minute perceptual activity) played a decisive role in my decision. Therefore, my determination to study philosophy does not solely follow from rationalization; pleasure is a confused expression of metaphysical reasons that inclined me to study philosophy. In short, the unsaid beneath the said is Leibniz’s theory of substance, which Locke could never accept.9

This divergent view is only suggested in Leibniz’s review when he briefly mentions what Locke changed in Essay II 21. In the second edition, the conscious perception of motives for performing an action is considered insufficient to determine the action. Thus, voluntary determination through conscious motives cannot be the reason an action is considered free. For Locke, free action is simply the metaphysical possibility of the opposite action (see Essay II 21, par. 28 in Locke 1975, 247–48), while the determination of an action depends on what Locke defines as uneasiness of the mind (Essay II 21, par. 30 in Locke 1975, 249). Leibniz translates uneasiness as Unruhigkeit, a term that expresses the idea that the mind cannot be absolutely at rest (Ruhe) and is therefore always active.

Leibniz understood Locke’s definition of free action to be consistent with his own position, and therefore inconsistent with Locke’s initial premise that the mind is always aware of its actions. The agreement consists in the fact that actions are not the result of the apperception (Gewahrnehmung) of a greater good.10 Rather, action is the consequence of the activity of a substance of which conscious thought is merely a part. This substance is rooted in perceptions that are minute and nonconscious. In short, Leibniz points to an agreement between Locke’s concept of uneasiness and his own notion of minute perceptions. However, this agreement would have meant for Locke a rejection of the main thesis on which hinges his criticism of innate ideas and his denial of knowledge of metaphysical notions, like substance, identity, modes, and so on.

In the review, Leibniz presents the modifications to Essay II 21 as corrections to some of Locke’s false judgments in the previous edition. However, this report is inaccurate because Locke never presents the chapter as a correction of mistakes. The chapter is an expansion on the topic of voluntary action requiring the perception of volitions. However, volitions and self-determination are not sufficient to label an action as free. Interestingly, the choice of terminology in presenting Locke’s alleged change of mind incorporates Leibnizian ideas, particularly regarding his theory of minute perceptions.

The thesis that thoughts are conscious acts is used by Locke to argue that the mind not always think which is tantamount to saying that it is not always active, like in sleep (Essay II 1, par. 19 in Locke 1975, 114–15). This thesis grounds Locke’s distinction in Essay II 27 between man—the physical individual—; person—the collection of the conscious states of a mind—; and substance—as what we illegitimately infer as the metaphysical ground of the man and the person, since we cannot know what the substance is.

In New Essays, Leibniz finds this definition of personal identity too narrow as it implies the denial of a substance that perdures over time and metaphysically grounds all acts of the mind without the mind being conscious of them. Locke’s thesis of personal identity hinges on the thesis that thoughts is always conscious because the mind can be sure to be active only when it perceives and is conscious of its activity.11 Since the mind is not always conscious of its activity, it is intermittently active and the person consists only of those states the mind can acknowledge as its own. It follows that one cannot infer with certainty that the mind/person is always active even if unconsciously (this is possible, but not probable (Essay II 1, par. 19 in Locke 1975, 114–15). This idea undermines Leibniz’s conception of substance as always active. As the activity of the substance is a metaphysical necessary truth to argue that substances change, but perdure over the changes, Leibniz has to reject the thesis that personal identity is tantamount to conscious thoughts in order to affirm his notion of substance, as he does in NE II 27 (see Oliveri 2016 for an extensive comment).

To conclude this first set of considerations, we can say that, when considering what Leibniz writes against the theses expressed in Essay II 21 and II 27, it is apparent that he could not base his review on a discussion of these two chapters, as he would have resulted too critical towards Locke position, breaking the rules of good reviews. So, he is critical, but in a subtler way, and he does so by focusing on Essay II 33 On the association of ideas, and Essay IV 19, On enthusiasm.

These two chapters express theses that partially find Leibniz’s approval, though Leibniz’s reasons to approve those theses differ from Locke’s. Locke’s main thesis in Essay II 33 is that associations of ideas result from habits and exposure to frequent occurrences of those ideas in temporal and spatial proximity, often motivated by society and education. Therefore, associations of ideas have an empirical source and are not motivated by reason because there are no logical, necessary relations on which to base connections; only experience exists. Any association entails a degree of madness that cannot be avoided by any reasoning.

Leibniz also argues for a type of empirical knowledge (see Oliveri 2021). Unlike Locke, however, Leibniz believes that rational knowledge is possible if one accepts the existence of innate ideas and necessary truths. His approach to acknowledging empirical knowledge begins with an objection to Descartes’s thesis that thought is always conscious, which led Descartes to deny that animals have sensible souls or perceptions.12 To reject Descartes’s denial of animal souls, Leibniz contrasts Descartes’s dualism of substances with his theory of substances as active entelechies, whose basic activities are perceptions and appetites. The basic activities of substances do not require consciousness. (see Oliveri 2024). This metaphysical basis enables Leibniz to argue that there are other souls with perceptions that, unlike minds, cannot be conscious of those perceptions. However, these souls have empirical knowledge because it is based on associations of ideas through experience. Although it is true that minds also have and use empirical knowledge, they are also capable of knowledge based on reason, which rests on the human capacity to conceive and understand necessary truths. Once again, Leibniz thinks that Locke is right in pointing to the limit of human knowledge through the acknowledgment that most of human associations of ideas have their sources in their experience and education, and basically are nothing but some prejudices that almost mechanically influence human responses to input provided by nature and society (when I see the night, I look for the moon; when someone waves at me, I wave back, Guhrauer 1838, 315); he is wrong in thinking that any association can be exclusively of this kind.

To summarize, Locke’s associations of ideas claim that most of human knowledge is not based on reason. Locke proves this by accepting Descartes’s thesis of thoughts as conscious acts of the mind in order to deny that innate ideas are possible. Leibniz denies Descartes’s thesis that thought is always conscious because this implies the denial of animal cognition. He argues for a kind of basic activity of substances that does not require consciousness and can account for associations of ideas that are empirical, like those advanced by Locke Essay II 33. However, Leibniz’s reason to accept associations of ideas that are empirical rests on the denial of the thesis that thoughts are conscious acts on which Locke bases his criticism of innate ideas, necessary to argue for experience as the only source of association. Therefore, Leibniz’s agreement with Locke, as expressed in the review, is supported by an underlying criticism that allows Leibniz to accept what Locke denies: rational knowledge based on an internal, natural light. The topic of reason as an internal (divine) light is the second link to the chapter On Enthusiasm.

Leibniz thinks that Locke’s denial of innate ideas is directly related to Essay IV 19, On Enthusiasm, also added in the fourth edition.13 Those who base their knowledge on God’s revelation of truths through an internal light are enthusiastic. As Leibniz writes in New Essays, Locke is right to criticize those who appeal to God to justify what they perceive as good and true. However, Leibniz notes that enthusiasm has become a negative concept.

“Enthusiasm” was at first a favourable name. Just as “sophism” indicates literally an exercise of wisdom, so “enthusiasm” signifies that there is a divinity inside us. “There is a God within us” [Ovid]. And Socrates claimed that a God or Daemon gave him inner warnings, so that “enthusiasm” [in his case] would be a divine instinct. But men sanctified their passions, and took their fancies and dreams and even their ravings to be something divine, and as a result “enthusiasm” began to signify a disorder of the mind ascribed to the action of some divinity…[.] More recently the term has been applied to people who believe groundlessly that their impulses come from God. [L’Enthousiasme estoit au commencement un bon nom. Et comme le sophisme marque proprement un exercice de la sagesse, l’Enthousiasme signifie qu’il y a une divinité en nous. Est Deus in nobis. Et Socrate pretendoit qu’un Dieu ou Demon luy donnoit des avertissemens interieurs, de sorte qu’Enthousiasme seroit un instinct divin. Mais les hommes ayant consacré leurs passions, [et fait passer] leurs fantaisies, et leurs songes et jusqu’à leur fureur pour quelque chose de divin; l’Enthousiasme commença à signifier un dereglement d’esprit attribué à la force de quelque divinité, qu’on supposoit dans ceux qui en estoient frappés] (NE 504–5 / A VI 6 504–5).

Although Leibniz shares Locke’s criticism of those who groundlessly appeal to God to justify what they believe to be true, he rejects the denial of a natural light as the source of acknowledge of eternal truths because of the abuse some philosophical sects made of the internal light as a source of knowledge. The lack of distinction between abuse of something good and what is good about what is abused is the reason why Locke fails to consider that a natural internal light can be the source of ideas and necessary truths required for associations of ideas based on reason.

Even if Leibniz’s criticism of Locke is not the focus of the review, the two chapters object of the review are directly related to his stronger criticism through the position of two distinct issues. If Locke is right in arguing that associations of ideas is mostly empirical; he is wrong in arguing that all associations are empirical. If he is right in arguing against the abuse of an internal light, he exaggerates his criticism to the denial of innate ideas, for which reason as the internal light is required. These two issues derive from an overall lack of discernment about Cartesian positions that Locke criticizes but at the same time uses, like the Cartesian criterion of truth, evidence.

Leibniz’s criticism of Locke concerns the use he does of his criticism against evidence. Leibniz thinks that Locke considers Descartes’s use of evidence as a criterion sufficient to gain knowledge about the innateness of ideas and truths (since the idea is evident, it does not need experience, therefore is innate). Locke criticizes the possibility to know about the innateness of an idea from evidence, but he uses the criterion of evidence himself, which makes him accept the distinction between matter and mind. Leibniz rebuts that the denial of evidence as the criterion for an idea’s innate status still is no argument against the possibility of innate ideas. An alternative to Descartes’s evidence could be the dependency argument which states that empirical knowledge depends on innate truths, such as identity and contradiction. These truths are therefore presupposed (a priori) to experience (see Oliveri 2021, Chap. 9, for a reconstruction of Leibniz’s argument). As discussed in the next paragraph, this epistemological flaw costs Locke the assumption of unsound metaphysical thesis, like Descartes distinction between res cogitans and res extensa.

The soundness of Locke’s criticism of philosophical ideas stemming from Cartesian theses increases the risk that Locke’s philosophy finds approval among those unsatisfied with Descartes’s philosophy. Once his criticism is accepted, his philosophy seems to be the only natural alternative. Leibniz aims to prevent this outcome and demonstrate that one can agree with Locke’s criticism for different reasons. Thus, Locke’s solution is not the only natural alternative for those dissatisfied with Cartesian philosophy.

As a proof of this worry, let me just mention the success of Locke’s chapter on Enthusiasm in Germany. As Konstantin Pollok (2004, XI n. 16) notices, the Lockean chapter played a decisive role in the development of the German Aufklärung: on one hand, it is used by Christian Thomasius to reject his previous pietist position and it is published separately in 1720 by Georg Michael Preu with the title Geist der wahren oder falsch befundenen Inspirationen […angefügt] Joh. Locks Gedanken von der Enthusiasterey. As Leibniz himself mentions in New Essays, Locke’s critique of enthusiasts will find resonance with those who in Germany find new prophets a philosophical fraud.14 So, even if Leibniz could not foresee the success of this chapter after his death, he could understand the potential it has to attract a German audience, like Christian Thomasius who, along with his father, Jocob, he knew personally. The acclamation of Locke’s rationale philosophy could so motivate the approval of his theses and the dissemination of his dangerous philosophy. An accurate objection to Locke’s theses and the dangerous implications they entail, like a lack of sufficient distinction between the abuser of a natural light and the “right” way to understand “the natural light” as reason, urged. Through his review, Leibniz aimed to provide the German readership with the tools necessary to recognize the merits of Locke’s criticism and the demerits of his philosophical solutions. Though camouflaged, this was Leibniz’s intention, which becomes clearer through a comparison of the long review of 1700 with the Zusatz of 1701.

4. The Zusatz to the Review: an Overt Criticism

In summary, we can say that Leibniz felt the need to publicly draw important philosophical distinctions that were overlooked by Locke’s philosophy. His own philosophy, similar to Locke’s in many respects, diverges from it by claiming the necessity of theses that Locke considered unsound, such as innate ideas and the notion of substance.

Table 1 – Comparison Between the Two Reviews.

1700

1701

Number of pages

16

2

Form

It looks like an objective report

It presents a more critical position

spirit

conciliatory

critical

General observations

The form and the spirit of the review hide Leibniz’s criticism that in this phase is still supported by the hope of convincing Locke (and the public) that Locke’s philosophy and the epistemic problems he raises can be overcome by Leibniz’s metaphysics and doctrine of preestablished harmony.

The spirit and form let transpire Leibniz’s problem with Locke’s philosophy whose shortcomings are now stressed over Locke’s philosophical merits.

Method

By and large, it is a fair report of Locke’s chapters.

Direct reference to the unsolved issues of Locke’s philosophy or reference to alleged mistakes Locke has acknowledged as such:

1- The reason for association of ideas is not just education: persuasion to have the proof for the connection;

2- The nature of the body is not extension (reference to the controversy with Stillingfleet on the nature of substance);

3- Incapacity to explain eternal and necessary truth;

4- Locke is closer to Aristotle than to Plato;

5- Necessity but insufficiency of factual knowledge for knowledge of necessary truth (letter to What is beyond senses and matter sent to John Toland via Sophie Charlotte 1702).

This urge was also dictated by the growing reception of Locke’s philosophy on the Continent. The Latin translation of Locke’s Essay appears one year after the French translation in 1701. In January of that year, Leibniz published the Zusatz in the section VIII. Einige Ausbesserungen und Zugaben des ersten Jahres der Monatl. Auszüge of Monatlicher Auszug as an improvement to the original review published in the September 1700 issue (see also Guhrauer 1838, 328–29). Besides the difference in length between the two reviews (sixteen pages vs. two), the Zusatz takes an overtly critical stance against Locke’s philosophy by directly expressing its problems. Table 1 offers a synoptic comparison of the two reviews. In the following, I will focus on the problems reported by Leibniz in the Zusatz.

First, Leibniz rejects the idea that the association of ideas is solely the result of education and experience. A stronger reason to associate ideas is the conviction that one has a proof of the association of ideas without testing whether there is actually a proof of the idea’s possibility. This criticism echoes the one Leibniz leveled against Descartes in his Meditations on Knowledge, Truth, and Ideas, his epistemology paper published in 1684 in the Acta Eruditorum. In it, he criticizes Descartes’s criterion of truth, which states that anything perceived as clear and distinct is true (see A VI 4 591). This criterion is used to disseminate a philosopher’s beliefs as infallible truths. The association of ideas based on evidence simply presupposes the capacity to offer proof without undertaking it, and therefore without knowledge of the possibility of having sound proof. Leibniz analyzes the ontological proof of the existence of God as an example of this error based on evidence. The ontological proof is not a proof because it links God’s perfection to God’s existence, presupposing the idea that a perfect being is possible. In other words, one assumes the possibility of the perfect being, whose existence cannot be denied, without proving whether such a perfect being is possible. (see A VI 589–90, for a discussion, Oliveri 2021).

This reference resonates with his criticism of Locke’s notions of body and matter. Locke’s mistake was accepting the Cartesian notion of the body as res extensa. Leibniz believes that the argument for Descartes’s substance dualism hinges on evidence as a criterion for truth. Therefore, he finds it puzzling that Locke accepts the result of Descartes’s reasoning, which is based on a criterion—evidence—that Locke also criticizes (Essay I 2, par. 19–21 in Locke 1975, 58–60, and Essay II 29 Of Clear and Obscure, Distinct and Confused ideas in Locke 1975, 363–72, and Essay IV 7, par. 1–3 in Locke 1975, 591–94). If Locke’s criticism of evidence aligns with Leibniz’s criticism in Meditations on Knowledge, Truth, and Ideas, then Locke is inconsistent in his criticism because he accepts certain doctrines without further inquiring into their metaphysical soundness, as his claim that God could make matter think without imparting a soul to matter. This thesis of Locke was criticized by Edward Stillingfleet and the controversy between the two plays a pivotal role in Leibniz’s criticism in the Zusatz.

As Leibniz reports in the Zusatz, Locke himself allegedly recognized his lack of metaphysical understanding of the implications of his notions of matter and substance in his controversy with the Bishop of Worcester, Edward Stillingfleet. Stillingfleet claimed that Locke’s philosophy was openly materialist and opposed the immortality of the soul and the doctrine of the Trinity (see Stewart 2015). Leibniz followed the controversy with great interest and concern, as evidenced by the materials collected in vol. VI 6 of the Academy Edition.15 Between 1697 and 1700, he read and marked a copy of Stillingfleet’s A Vindication of the Doctrine of the Trinity (1697), which features three criticisms of An Essay Concerning Human Understanding. At the end of 1698, he wrote a Compte rendu de la Vindication de Stillingfleet et de la lettre de Locke. Exactly around the year of the review, in 1700, Leibniz wrote Réflexions sur la seconde réplique de Locke. As Schepers and Robinet remark, Locke was aware of Leibniz’s interest in the controversy and informed him through Thomas Burnett that he was interested in hearing Leibniz’s position. In 1699, Leibniz sent Locke a long letter via Burnett that explicitly stated his position (Leibniz to Thomas Burnett of Kemney, Hanover, January 20–30, 1699, A I 16, 506–18). Later, in another letter to Burnett dated February 2–12, 1700, Leibniz attached his Réflexions sur la seconde réplique de Locke. Although Burnett sent both documents to Locke, and, although Locke read and commented on them, he never replied (A VI 6 XXI).

Leibniz’s reflections on Locke’s second reply to Stillingfleet square with the criticism levelled in the Zusatz. His Reflections turn around epistemological questions concerning certainty about the agreement or disagreement of ideas. Leibniz agrees with Stillingfleet, who criticizes the new way of ideas and refers to his paper in the Acta eruditorum from 1684. The mistake of Descartes, and of Locke, is to accept what they conceive as an agreement among ideas without providing arguments that oblige others to see the same agreement:

So, Mr Stillingfleet seems to have blamed the abuse of those who, in philosophy and especially in matters concerning ideas, appeal to their own interior testimony and ground their judgments in the agreement or disgreement of those ideas that they claim to experience in the interiority of their minds. However, they are unwilling to provide a more distinct explanation of that agreement. In other words, they are unwilling to go through the way of reasoning, through which they could oblige others to enter into their own conceptions. [Ainsi M. Stillingfleet paroist avoir voulu blamer l’abus de ceux qui se contentent ainsi de recourir simplement encor en philosophie et particulierement en matiere d’idées, à leur propre temoignage intérieur et appuyent leur jugemens sur ce qu’ils disent experimenter en eux de l’agrément ou desagrément de ces idées, sans vouloir venir à une explication plus distincte de cet agrément, c’est à dire sans vouloir venir à la voye de raisonnement, par laquelle ils pourroient obliger d’autres d’entrer dans les memes conceptions.] (A VI 6 30, my translation).

In a letter dated January 1700, the same year of Leibniz’s first review, Leibniz wrote to Burnett that he believed it was possible to reconcile Stillingfleet and Locke’s views on knowledge of clear and distinct ideas. This was because Stillingfleet’s idea that truths depend on eternal truths was compatible with Locke’s new theory of ideas, provided Locke acknowledged that clear and distinct ideas require proof of their possibility. (Leibniz to Thomas Burnett of Kemney, Hanover, 2./[12.] February 1700, A I 18 371–73). Without knowledge of the possibility of ideas, ideas are, in Locke’s sense, chimerical, and there is no criterion for truth (see also A. VI 6 31 and the letter of Leibniz to Burnet, January 20–30, 1699, A I 16 508). However, acknowledging the dependence of ideas on the truths of reason would have meant acknowledging the existence of an internal light—a divine part that does not perish with the body since it is not subject to material changes. In other words, it would have meant denying the theory of matter that Locke defends in his Essay, as well as Locke’s claim that God could produce a change in matter that yields a thought as a result. Stillingfleet and others considered this claim to be the source of Locke’s materialism and denial of the soul’s immortality because it amounts to the idea that the body can think without a soul (see Bolton 2015). In summary, Leibniz believes that Locke’s notion of substance is problematic, but this issue stems from Locke’s epistemology of ideas. Although Locke criticizes Descartes’ criterion of clear and distinct perception as evidence of the agreement of ideas, he still uses it in his philosophical arguments.

Against this backdrop, the following lines of the Zusatz about the controversy between Locke and Stillingfleet acquire a new meaning:

Moreover, one must remark on this book by Mr. Locke that, in his later writings against Bishop Stillingfleet, he altered most of his views on the nature of the body (Leib) discussed in the Tentamine, or Attempt Concerning Human Understanding. While he was closer to the new philosophers, especially the Cartesians and Gassendists[.] In the Tentamine, he maintained that a body consists of nothing more than size, solidity, impenetrability, and movement or change of place. In his later writings, however, he begins to consider that there is something more to a body that cannot be explained by these qualities. [Sonst ist bei diesem Buche des Herrn Locks anzumerken, daß er in seinen letzten Schriften gegen den Herrn Bischof Stillingfleet ein großes Theil seiner in diesem Tentamine oder Versuch von menschlichen Verstande enthaltenen Meinung, die Natur eines Leibes betreffend, geändert: indem er in dem Tentamine mit den neuen Philosophis insgemein, sonderlich den Cartesianis und Gassendistis, dafür gehalten, daß bei dem Leibe nichts, als Größe, Solidität oder Undurchdringlichkeit, und Bewegung oder Veränderung der Stelle anzutreffen; anjezo beginnt er dafür zu halten, daß sich noch ein Mehrers darin befinde, so durch diese nicht zu erklären] (Guhrauer 1838, 329–30, my translation).

Had Locke admitted that something more than the body is required to explain thought, he would have had to concede the existence of an internal natural light as a principle of change originating not from the body but from the active part of substances—the form or entelechy, whose nature is to be active, and whose activity is perception and appetite. He would also have agreed to the necessity of positing soul-like substances in animals that differ from minds because only the latter are capable of reflection and consciousness. Thus, he would have distanced himself from the Cartesians. He would have acknowledged the possibility of associations based on reason because he would have found a way to explain necessary truths. Indeed, the Reflections sent to Burnett also close with an exposition of Leibniz’s own philosophy based on the notion of substance. This notion and his principle of pre-established harmony are also the object of his correspondence with Lady Masham, where he refers her and Locke to his comments to the entry Rorarius in Bayle’s Dictionaire (Leibniz to Lady Masham, Hanover, 14. January 1704 in A II 4 187). In short, if Locke had truly begun to believe that the body is more than just extension, he would have agreed with Leibniz’s philosophy.

As the final part of the review notes, the Locke of An Essay is misguided by these errors that led him to believe that ideas are derived from experience and that nothing in the intellect exists that was not previously perceived by the senses. Since substance cannot be perceived through the senses, it cannot be known, and our notion of substance is merely that of a substratum that we suppose as perduring through the changes of bodies, but that we cannot know. In the famous letter What It Is Beyond Senses and Matter, which is a reply to John Toland, a supporter of Locke who argues for empiricism, Leibniz also hints at the distinction between truths of facts and experience (Leibniz to Sophie Charlotte, Hanover, June 1702 A I 21 N. 224 328–46). This distinction is necessary to provide the subject with occasions to conceive and learn necessary truths and to recognize experience as the only source of knowledge. As he argued in his unpublished essay against Locke, the learnability of notions does not prove their dependence on experience for acquisition (see Oliveri 2021, Chap. 9). Therefore, we cannot infer that experience is the only reason we possess those ideas and necessary truths. Without an internal light, the mind would not be able to learn truths that surpass experience because experience requires them to be possible in the first place. Thus, Leibniz hopes that Locke would agree with him.

Perhaps our gifted author will not entirely disagree with my view. For after devoting the whole of his first book to rejecting innate illumination understood in a certain sense, he nevertheless admits at the start of his second book, and from there on, that ideas which do not originate in sensation come from reflection. But reflection is nothing but attention to what is within us, and the senses do not give us what we carry with us already. In view of this, can it be denied that there is a great deal that is innate in our minds, since we are innate to ourselves, so to speak, and since we include Being, Unity, Substance, Duration, Change, Action, Perception, Pleasure, and hosts of other objects of our intellectual ideas? And since these objects are immediately related to our understanding and always present to it (although our distractions and needs prevent our being always aware of them), is it any wonder that we say that these ideas, along with what depends on them, are innate in us? [Peut-étre que nôtre habile auteur ne s’éloignera pas entiérement de mon sentiment. Car aprés avoir employé tout son premier livre à rejetter les lumiéres innées, prises dans un certain sens, il avouë pourtant au commencement du second et dans la suite, que les idées, qui n’ont point leur origine dans la sensation, viennent de la reflexion. Or la reflexion n’est autre chose qu’une attention à ce qui est en nous, et les sens ne nous donnent point ce que nous portons dejà avec nous. Cela êtant, peut-on nier, qu’il y ait beaucoup d’inné en nostre esprit, puisque nous sommes innés à nous mêmes pour ainsi dire, et qu’il y a en nous: Estre, Unité, Substance, Durée, Changement, Action, Perception, Plaisir, et mille autres objects de nos idées intellectuelles? Et ces objects étant immediats et toujours presents à nostre entendement (quoyqu’ils ne sauroient estre toujours apperçûs à cause de nos distractions et de nos besoins), pourquoy s’étonner que nous disions, que ces idées nous sont innées avec tout ce qui en depend?] (NE 51–2/A VI 6 51–2).

In other words, Leibniz thinks that his notion of substance, which has some affinity with Aristotle entelechy, is only possible when supported by Platonic psychology and epistemology. According to this philosophy, the mind learns truths through the exercise of its own rational nature occasioned by experience. If we can know the essence of substance, it is because we are substance, and doing philosophy is merely learning to know ourselves. If this is not possible—if we cannot learn to know ourselves—we cease to be human and never exercise the most natural part of our nature: the understanding.

5. Conclusion

Leibniz’s review of John Locke’s An Essay Concerning Human Understanding demonstrates that he used reviews to reveal its shortcomings to a German audience. This strategy becomes apparent when comparing the first review, published in 1700, with the 1701 Zusatz. While the first review seems to be an objective summary of the chapters added to the fourth edition of Locke’s Essay, the second review is overtly critical and lists Locke’s errors. However, a closer look at the first review shows that, beneath his approval of Locke’s thesis of the associations of ideas and criticism of enthusiasm, Leibniz expresses doubt about whether one should also accept Locke’s reasoning behind his thesis and criticism. The second review confirms Leibniz’s critical stance. Locke’s criticism addresses some epistemological questions correctly, but it also leads him to reject important metaphysical truths. By referencing the controversy with Stillingfleet, Leibniz suggests that Locke changed his mind about the notions of body and substance presented in An Essay Concerning Human Understanding. A review of Leibniz’s correspondence with Burnett reveals that Locke’s flawed metaphysical beliefs stem from an incorrect epistemology that accepts what Locke himself criticized—that truth is based on the agreement or disagreement of ideas based on evidence, which makes a proof of agreement unnecessary. Leibniz’s criticism of Locke is based on questions about knowledge and how to acquire it. This makes the controversy with Locke prominently epistemological and therefore metaphysical.

Does this analysis sufficiently support my thesis that Leibniz used reviews as tools to instill prejudices and influence their readership? Even if I cannot argue for the general thesis, I have provided evidence that Leibniz used reviews as philosophical tools to influence the German community of scholars at least once and in an important case. If he did so once, perhaps he did so more than once, or even systematically.

References

A = Leibniz, G. W. 1923–2021. Sämtliche Schriften und Briefe. Berlin: Akademie Verlag/DeGruyter.

AT = Descartes, René. 1964–1978. Oeuvres de Descartes, édité par C. Adam, et P. Tannery. Paris: Vrin.

Barth, Christian. 2011. “Apperception in the New Essays Concerning Human Understanding. A Critique of the Reflective Account.” In Natur und Subjekt. ix. Internationaler Leibniz-Kongress, hrsg. von Herbert Breger et al., 37–43. Berlin: Akademie Verlag.

Beiderbeck, Friedrich, and Claire Gantet, edited by. 2021. Wissenskulturen in der Leibniz-Zeit: Konzepte – Praktiken – Vermittlung. Berlin-Boston: De Gruyter. https://doi.org/10.1515/9783110730593

Boeker, Ruth. 2021. Locke on Persons and Personal Identity. Oxford: Oxford University Press. https://doi.org/10.1093/oso/9780198846758.003.0001

Bolton, Martha B. 2015. “Locke on Thinking Matter.” In A Companion to Locke, edited by Mattew Stuart, 334–53. Chichester (UK): Wiley-Blackwell. https://doi.org/10.1002/9781118328705.ch17

CSM = Descartes, René. 1984–1991. The Philosophical Writings of Descartes, transleted by J. Cottingham, R. Stoothoff, D. Murdoch, and A. Kenny, 3 vols. Cambridge: Cambridge University Press.

Dascal, Marcelo. 2006. Gottfried Wilhelm Leibniz. The Art of Controversies. Berlin-Amsterdam: Springer Nature. https://doi.org/10.1007/1-4020-5228-6

De Rosa, Raffaella. 2002. Innate Ideas and Intentionality Descartes Vs Locke. Dissertation. New Brunswick: Rutgers University.

De Rosa, Raffaella. 2015. “Locke’s Critique of Innatism.” In A Companion to Locke, edited by Matthew Stuart, 157–74. Chichester (UK): Wiley-Blackwell. https://doi.org/10.1002/9781118328705.ch8

Essay = Locke, John. 17004. An Essay Corning Human Understanding. London: s.n.

Gantet, Claire. 2021a. “Leibniz und die gelehrten Journale.” In Wissenskulturen in der Leibniz-Zeit: Konzepte – Praktiken – Vermittlung, hrsg. von Friedrich Beiderbeck, und Claire Gantet, 253–88. Berlin-Boston: De Gruyter. https://doi.org/10.1515/9783110730593

Gantet, Claire. 2021b. “Leibniz’ Journalartikel – eine Übersicht.” In Wissenskulturen in der Leibniz-Zeit: Konzepte – Praktiken – Vermittlung, hrsg. von Friedrich Beiderbeck, und Claire Gantet, 289–322. Berlin-Boston: De Gruyter. https://doi.org/10.1515/9783110730593

Giampietri, Francesco, a cura di. 2012. Leibniz allo specchio. Dissimulazioni erudite. Milano: Mimesis.

Jorgensen, Larry M. 2009. “The principle of continuity and Leibniz’s theory of consciousness.” Journal of the History of Philosophy 47, 2: 223–48. https://doi.org/10.1353/hph.0.0112

Locke, John. 1688. “Extrait d’un livre anglais qui n’est pas encore publié, intitulé : Essay philosophique concernant l’entendement humain.” Bibliothèque universelle et historique 8: 49–142.

Locke, John. 1975. An Essay Concerning Human Understanding, edited by Peter H. Nidditch, London: Clerendon.

Lodge, Paul, and Tom Stoneham, edited by. 2015. Locke and Leibniz on Substance. New York: Routledge. https://doi.org/10.4324/9781315762418

McRae, Robert. 1976. Leibniz: Perception, Apperception, and Thought. Toronto: University of Toronto Press. https://doi.org/10.3138/9781487579777

Oliveri, Lucia. 2016. “Imagination and Harmony in Leibniz’s Philosophy of Language.” Diss. University of Münster. <https://nbn-resolving.de/urn:nbn:de:hbz:6-05169689910>.

Oliveri, Lucia. 2019. “The Leibniz-Treuer Correspondence. With text and English translation of excerpts from Treuer’s De mente sensu non errante and Correspondence with Leibniz.” The Leibniz Review 29: 83–104. https://doi.org/10.5840/leibniz2019298

Oliveri, Lucia. 2021. Imaginative Animals. Leibniz’s Logic of Imagination. Stuttgart: Steiner Verlag. http://doi.org/10.25162/9783515130516

Oliveri, Lucia. 2021a. “Conceivability Errors and the Role of Imagination in Symbolization.” Jolma the Journal for the Philosophy of Language, Mind and the Arts 2, 2: 293–310. https://doi.org/10.30687/Jolma/2723-9640/2021/02/002

Oliveri, Lucia. 2024. “Perception and Thought. Leibniz’s Criticism of Descartes’s Denial of Perception to Animals.” Giornale di Metafisica 2: 536–50.

Pelletier, Arnaud. 2017. “Attention et aperception selon Leibniz : aspects cognitifs et éthiques.” Les Études philosophiques 120, 1: 103–18. https://doi.org/10.3917/leph.171.0103

Pollok, Konstantin. 2004. Locke In Germany: Early German Translations of John Locke, 1709–61. Bristol: Thoemmes Continuum.

Priarolo, Mariangela. 2016. “The Consequences of Error. Leibniz and Toleration.” Rivista di storia della filosofia 71, 4: 745–64. https://doi.org/10.3280/SF2016-004012

Tabb, Kathryn. 2019. “Locke on Enthusiasm and the Association of Ideas.” In Oxford Studies in Early Modern Philosophy, vol. IX, edited by Ronald Rutherford, 75–104. Oxford: Oxford University Press. https://doi.org/10.1093/oso/9780198852452.003.0003

Thiel, Udo. 2011. The early Modern Subject. Self Conscsiousness and personal identity from Descartes to Hume. Oxford-New York: Oxford University Press.

1 Mémoire pour des personnes éclairées et de bonne intention (1692, A IV 4 618): “Et pour ce qui est des sçavans, capables de contribuer à l’accroissement de nos connoissances; ils doivent songer à des travaux qui ne servent pas seulement à les faire connoistre et applaudir; mais encor à produire quelques nouvelles lumieres; Ces travaux peuvent consister dans des recherches pour nous, et dans des enseignemens pour les autres. Les recherches peuvent consister en meditations et en experiences ou observations[.] Et les enseignemens peuvent estre de vive voix ou par ecrit, communiqué s’en particulier, ou donnés au public. En tout cela il faut regarder au fruit reel, qui s’en peut retirer. Car écrire pour écrire n’est qu’une mauvaise coutume; et écrire seulement pour faire parler de nous, est une vanité, qui fait même du tort aux autres, en les faisant perdre leur temps par une lecture inutile[.]”.

2 Another important tool to accomplish this analysis will be the volume collecting Leibniz’s reviews in scientific journals edited by Antonio Lamarra and Roberto Palaia (forthcoming).

3 Following Dascal (2006), one could also argue that controversies are essential to understanding Leibniz’s philosophy. The controversy between Locke and Leibniz is particularly important, making the review a very important document.

4 In their introduction to the Academy Edition of the New Essays, Robinet and Schepers reject Leibniz’s authorship of the review and claim that Guhrauer’s supposition is wrong (A VI 6 XXII). However, they do not provide reasons for why this is so. More recent studies, such as Gantet (2021), recognize Leibniz as the author of the review.

5 Leibniz writes that the fourth edition appears in 1699, but it appears in 1700. For a closer reconstruction of the four editions and the changes Locke made, see Locke 1975, XII–XXXI.

6 This thesis results from Descartes’s definitions of an idea as “the form of any given thought, immediate perception of which makes me aware of the thought. Hence, whenever I express something in words and understand what I am saying, this very fact makes it certain that there is within me an idea of what is signified by the words in question […]” (AT VII, 160/CSM II, 113), and of thought “I use this term to include everything that is within us in such a way that we are immediately aware [conscii] of it. Thus all the operations of the will, the intellect, the imagination and the senses are thoughts” (AT vii 160/CSM ii 113).

7 See De Rosa (2002 and 2015) for a confrontation between Locke and Descartes on innate ideas.

8 Leibniz’s notion of consciousness is not easy to explain. In the last fifty years, the literature on the topic clustered around the question of whether reflection is necessary for consciousness and of whether consciousness is a higher order act that violates the principle of continuity (see Jorgensen 2009). Oliveri (2024) argues against this view for it rests on a Cartesian understanding of Leibniz’s notion of coscientia.

9 For a survey of the differences between Locke and Leibniz on the notion of substance, see the essays in Lodge and Stoneham (2015).

10 The use of Gewahrnehmung (apperception) in this context squares with the controversy on consciousness. Scholarly debate on Leibniz’s theory of consciousness focuses on his use of “apperception”, a newly coined term to express an act of awareness that does not entail reflection, since also animals are capable of apperception. However, Leibniz’s use of the term appears to be inconsistent as he sometimes equates apperception with consciousness and reflection (see McRae 1976 for the puzzle, and Barth 2011 for a discussion). Recently, Pellettier (2017) has insisted on the technical use of Leibniz’s “apperception” as consciousness. In my view, apperception directed to mind’s content that triggers the use of general ideas and necessary truths are thoughts that might become object of an act of self-consciousness (Oliveri 2024).

11 Locke’s thesis of personal identity and Leibniz’s criticism have sparkled scholarly attention, see for instance the work of Thiel 2011, and Boeker 2021.

12 As also Guhrauer remembers, it is important to read what Leibniz writes in the review with his remarque in New Essays to chapt. 33, where he explicitly relates the topic of association of ideas to animal associations by imagination. See Guhrauer 1838, 329–30. The connection between Descartes’s notion of thought and his denial of animal souls with Locke’s empiricism is explicitly addressed in a short correspondence between Leibniz and Samuel Treuer see Oliveri 2019.

13 For a discussion of the relation between Essay II 33 and Essay IV 19, see Tabb 2019.

14 Leibniz also contests the use of enthusiasts of the metaphor of light: “Mais pourquoy appeller lumiere ce qui ne fait rien voir?” A VI 6 505.

15 In a letter to Thomas Burnett from February 1700, Leibniz writes: “J’ay maintenant toutes les pieces du proces entre M. de Worcester et M. Lock excepté la seconde lettre de celuyci qui me manque encor.” (A I 18 371).

Lucia Oliveri, oliveri.lucia@gmail.com, University of Münster, Germany, 0000-0001-8022-4538

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Lucia Oliveri, Leibniz and the Function of Book Reviews, © Author(s), CC BY 4.0, DOI 10.36253/979-12-215-0999-1.03, in Pasquale Terracciano, Francesco Valerio Tommasi (edited by), Philosophical Reviews in German Territories (1668-1799). Volume 2, pp. -33, 2026, published by Firenze University Press, ISBN 979-12-215-0999-1, DOI 10.36253/979-12-215-0999-1