d’alembert’s philosophy: finding descartes & locke in the preliminary discourse


“Men abuse the best things.” –Jean le Rond d’Alembert / Preliminary Discourse[1]

Abstract: Jean d’Alembert’s introduction to the Encyclopédie, the Preliminary Discourse (hereafter PD) of 1749, stands as a wonderful expression of French Enlightenment philosophy. In the PD the two philosophical branches of rationalism and empiricism are followed by d’Alembert with varying degrees of commitment. This issue will be examined by first sketching out the historical circumstances of the PD, along with what the philosophical problem looks like. Then I’ll offer a brief synopsis on the intellectual background of the Enlightenment, which served as the cultural and intellectual milieu for such geniuses as d’Alembert and Diderot to emerge. Next, I’ll illustrate the positions of Descartes and Locke with regard to their influence on d’Alembert and the wider Enlightenment. After this I will return to the problem, aiming to provide an analysis of how the rationalism of Descartes and the empiricism of Locke are combined, and how they differ, for d’Alembert in the PD. D’Alembert’s PD owes its influence to many thinkers—of predominance are Descartes and Locke. The PD is the reference from where to draw on d’Alembert’s ideas concerning the philosophical underpinnings of the Encyclopédie. This is where his ideas on Descartes and Locke, rationality and empiricism are used as evidence of his (and Diderot’s) brand of French Enlightenment philosophy. Despite d’Alembert’s theoretical inconsistencies, his project should not be left to conclude a negative thesis. His energetic ideas, and his work with the Encyclopédie, stand at the epicenter of anti-authoritarian Enlightenment thinking.

§1. Circumstances and Problems of the PD: D’Alembert was a precocious mathematician who took a vibrant part in the proliferation of scientific interests of the time. When he was in his mid-twenties, he quickly earned himself a place in the cutting edge scientific community of his day. He gained widespread acclaim with his early publication on Newtonian mechanics, the Treatise on Dynamics (Traité de dynamique) from 1743.[2] Sometime in 1746, because he was becoming widely recognized as a rising star, he was invited in regular attendance to the fashionable, high-society salons of the day. It is likely that he met Diderot around this time.[3]

D’Alembert and Diderot were invited by the eccentric editor abbé Gua de Malves, to help with an English to French translation of Ephraim Chambers’ Cyclopedia, otherwise known as the Universal Dictionary of the Arts and Sciences.[4] It is not altogether clear who was invited to participate first.[5] It was the abbé Gua de Malves who had big plans for the project, but he dropped out early on. D’Alembert was brought on to edit and author the mathematical and scientific entries, and Diderot would take care of the rest. This co-editorship went beyond these original positions, with d’Alembert taking charge of much more than the mathematical and scientific entries, including his introduction to the Encyclopédie, otherwise known as the PD. The PD was first published in 1751. This was not the work of an established philosopher, instead it was one man’s expression of the age, brought forth by this mathematician/scientist. D’Alembert’s efforts serve as a classic example of Enlightenment cross-disciplinary élan.

That d’Alembert ran with the best of the French intellectual luminaries of his day earned him the position as a French philosophe. To be a philosophe like d’Alembert and Diderot meant to be counted among such legends as Voltaire and Rousseau. The philosophe’s were not necessarily philosophers, they were more like public intellectuals who took it upon themselves to critique the status quo. Primarily, they were critics of religious dogma and the unquestioned authority of aristocratic ideals. The PD set d’Alembert’s fame, with laudatory comments on his work coming from none other than the political philosopher Montesquieu and the Prussian king Frederick the Great.

D’Alembert introduces us to his brand of empiricism in the opening of the PD: “in short, we must go back to the origin and generation of our ideas.”[6] This fundamental thought aligns d’Alembert to his mentor the philosophe abbé de Condilliac who was an avid Lockean, hence a declaration of d’Alembert’s empiricism.[7] D’Alembert makes use of rational and empiricist principles. There are passages in the PD where his implicit allegiance to innate ideas, undercuts his alleged empiricist project. One example of this is in connection to d’Alembert’s method of judgment as to the validity and certainty of ideas. He wants to be certain of ideas in order to determine what subjects to include in the Encyclopédie, and of course, he wants to know what things we as thinking beings can be certain of. For example, on the tenuous ground of moral evidence, i.e. when we are able to judge, and to be certain of, the rights and wrongs of an ethical situation, d’Alembert writes in the PD that: “Feeling is of two sorts. The one concerned with moral truths is called conscience. It is the result of natural law and our conception of good and evil. One could call it evidence of the heart…”[8] It can be argued that the so-called evidence of the heart is actually evidence of innate ideas. That is to say, if we are to assume that d’Alembert, as he states, is operating from a strictly empirical framework, such a moral idea is not grounded in an experiential account. Instead, his evidence of the heart must be coming from a feeling or conviction based in something other than experience.

This is in contrast to another claim d’Alembert makes in the opening pages of the PD where he asks: “Why suppose that we have purely intellectual notions [innate ideas] at the onset if all we need do in order to form them is to reflect on our sensations?”[9] Throughout the PD it is not entirely obvious that d’Alembert sufficiently mends the thorny issue between his denial of Descartes’ innate ideas, contrasted with his allegiance to Locke’s empirical sense certainty. We will return with a closer examination of this problem in §6 (“Philosophy and d’Alembert,” p.8). Before that, let’s look at the wider framework of the Enlightenment, so as to situate the intellectual and cultural milieu under which the Encyclopédie took center stage. This will be followed by summaries of Descartes and Locke’s positions in relation to the PD and the Enlightenment.

§2. The Enlightenment: Frankel sums up the spirit of the Enlightenment as: “Two great traditions, humanism and science, came together in the eighteenth century. The first had acquired a weapon, the second a conscience: together they constituted a revolutionary program.”[10] The efforts of the philosophes during The Age of Enlightenment were to awaken humanity to its own potential. We needed to reposition ourselves as rational thinkers who rely on the surety of scientific observation. Superstition and religious dogma were undermined in favor of our own human capacities for positive inquiry. Science became a weapon for humanity to wrestle out of the obscurity and unfounded authority of the middle ages and scholasticism. We take it upon ourselves to know about the world starting from our desire to eradicate conjecture. The power of scientific authority is, during the Enlightenment, made to shift from speculation to the power of the individual. To precisely investigate the world by way of simple observation, experimentation, and hypothesis was a new challenge to harness. This impetus meant that the Enlightenment fostered intellectual growth with an emphasis on how the intellect can help the human condition transcend its own limitations. The Enlightenment was an intellectual revolution in favor of the progress of humanity, and the philosophical and scientific ways we come to know the wider universe.[11] The progress of intellectual freedom meant that humankind needed to master the natural world in order to take a firm hold of our destiny away from previous divine dictates.

The Enlightenment was born from the crucible of scientific and philosophical inquiry. In France, with the philosophes, empirical inspiration was imported from England. This rose with such figures as Locke, Bacon, and Newton (among others) who were, more or less responsible for the ever-rising popularity of empirical science and the application of empirical knowledge. These important English thinkers would also serve as the intellectual framework of d’Alembert’s PD. Also, the apparent contradictions between rationalism and empiricism were not unique to d’Alembert alone. This conflict was a problem for many of the French Enlightenment philosophes.[12]

Descartes gained widespread acceptance during the Enlightenment, and with the philosophes, his reception was slightly more ambiguous. This was due to his problematic metaphysics stemming from his mind/body dualism—this had to do with his radical claim for the separation of the human mind from the natural world.[13] His innatism would also be a point of contention. Nevertheless, his significance cannot be overstated. For example, his method of Cartesian doubting, in the name of getting to the necessity of mathematics, physics, and other scientific certainties, endeared Descartes’ rationalism to the energetic inquiry of the French philosophes.

These two thinkers, Locke and Descartes, would inadvertently bring about a central philosophical problem of the Enlightenment: should we as thinking persons adhere to a rationalist outlook, complete with its overreaching metaphysics, or should we ascribe to nothing but empirical evidence, with its reliance on sensory data? The issue of fusing rationalism and empiricism would not be unique to d’Alembert’s PD. Kant would famously tackle this complicated epistemological issue with brilliant results, thirty years later (1780s) in Germany (then Prussia), with his first critique, the Critique of Pure Reason.[14]

§3. Descartes: The wealthy chevalier Destouches, d’Alembert’s father, took care that the young man received a good private education at the Jansenist Collège de Quatre Nations in Paris, and it is likely that the Jansenists were the ones who introduced him to the philosophy of Descartes.[15] The progression of philosophy, as d’Alembert puts it in the PD, is that to the ancient philosophers and scholastics an empirical idea was an “axiom.” From here historically, the empirical axiom allegedly takes a turn during the philosophy of the Renaissance toward innate ideas, as d’Alembert has it anyway. As we will see soon, d’Alembert like Descartes, wants to see a metaphysics of knowledge, as reliant on innate ideas. Locke would aggressively challenge this notion in his Essay Concerning Human Understanding, published in 1690.

In the 1630s, sometime before Locke, Descartes’ ideas had a great influence in the birth of early Modern philosophy because of his philosophical method of bringing rational thinking and questioning to the ground zero of the cogito. Descartes helped to get scientific certainty going, and as mentioned, Locke would later take issue with the grounding of Cartesian certainty with innate ideas. Descartes starts with a fundamental doubting of previous modes of securing a method of scientific and philosophical inquiry. As a rationalist, Descartes wanted to figure out a way to justify scientific knowledge by identifying human rationality as innate and God-given. His epistemic method was to begin by doubting all the ways in which we come to know things. For Descartes, this doubt starts with the premise that sense perception is not reliable, where we, by way of this reductive doubt, eventually arrives at the certainty of our own thinking. When most ways of knowing are in doubt, the first thing a person can be sure of is that they are thinking. Hence, Descartes arrives at the famous cogito: “I am thinking, therefore I exist.”[16]

The cogito cannot be doubted, and it is made known to us by what Descartes terms a “natural light.” This natural light is akin to reason. Therefore, anything that cannot be doubted must be certain, and anything that is certain includes such things as universality, mathematical necessity, logic, physics, and metaphysical relations. These things are known prior to experience, and because they are known prior to experience, they must be innate. In the Meditations Descartes writes: “Among my ideas, some appear to be innate, some to be adventitious [not innate], and others to have been invented by me.”[17] Incidentally, for Descartes, God provides us with this innate rational capacity.

§5. Locke: Both Descartes and Locke’s philosophy were on minds of the French thinkers including the abbé de Condillac. He was an abbé (or abbot), but he was not a religious man. In fact, he was decidedly empiricist—after the teachings of Locke. The abbé de Condillac was not only Lockean, his ideas also made use of rationalist components of Descartes.[18] In fact, the PD can be said to be mostly an empirical project. Locke’s empiricism placed a premium on our sensual experience of the world. Essentially, his idea is that our thinking comes about by experience only. In the opening lines of Book I of Locke’s Essay Concerning Human Understanding, is a refutation of Descartes’ innate ideas. “It is an established opinion amongst some men, that there are in the understanding certain innate principles…”[19] Locke’s brand of empiricism is typically identified by the so-called tabula rasa theory.[20] The idea is fairly straightforward: we are born not knowing anything, our minds are blank of knowledge, and as we directly experience the world with our senses, knowledge is learned and reflected upon. Our ability to reflect, for Locke, means that we put together the things we have learned by our senses. D’Alembert would also go on to utilize Locke’s theory of direct and reflective knowledge.

§6. Philosophy and d’Alembert: Let us not forget that the Encyclopédie had the immodest goal to survey all human knowledge up to the time of it publication in the 1750s. According to d’Alembert, the Encyclopédie had two aims: one was to set down the order and the connections of the various disciplines of human knowledge. The other was to lay down the principles of mechanical sciences, and the liberal arts.[21] It was d’Alembert’s idea that the manufacturing trades, science, the arts, and philosophy were mutually interconnected as emblematic of the unity of human knowledge. Moreover, if any one of these disciplines would provide a structure to the vast comprehensiveness of knowledge, it would have to be the discipline of philosophy. Because philosophy is concerned with the origins of knowledge, the ordering of human understanding would have recourse to essential philosophical issues, such as epistemological questions having to do with where our thoughts of the world originate.

D’Alembert’s conceptual structure of the PD divides human knowledge into three main branches of thought: memory, reason and imagination.[22] Memory has to do with recalling and bringing to mind sensations and ideas. Reason has to do with the logic, comparison, sequentiality, and assessments of cognition. Imagination combines the faculties of memory and reason to create new ideas and new possibilities.[23] These branches of thought are brought in as an organizational device from which to classify the various subjects of the Encyclopédie. For instance, under the category of memory we find the disciplines of history. With reason we find the disciplines of philosophy and the sciences, and with the imagination we find the disciplines of the fine arts. However, before this Baconian division of human interests and disciplines, d’Alembert will have to go further into positing and verifying where our ideas come from—and for d’Alembert empiricism fits the bill.

Before the division of knowledge mentioned above, knowledge as it is experienced, is initially subdivided into what d’Alembert calls “direct” and “reflective” knowledge. The direct base of knowledge is attributable to Locke, where d’Alembert writes: “all our direct knowledge can be reduced to what we receive through our senses; whence it follows that we owe all our ideas to sensations.”[24] The reflective area of knowledge is also linked to Locke’s reflection, otherwise known as introspection. Introspection itself is reliant on the base of our sense experience. Employing this model, d’Alembert has the dilemma of showing how direct and reflective knowledge transitions into necessary and universal truths.[25] Because d’Alembert stridently rejects innate ideas, he has to find a way that reflection is based on nothing more than a series of sensations.

During his discussion of Lockean reflective knowledge in the PD, d’Alembert takes on the immensely difficult task of justifying our thoughts, and the objects that bring about these thoughts, as somehow one in the same. In other words, he wants to know how “…all of these things produce an irresistible impulse in us to affirm that the objects we relate to these sensations, and which appear to be their cause, actually exist.”[26] His next move is decidedly unsatisfying with his justification that the way we affirm the connection between thoughts and the objects of those thoughts, is with a supra-reasonable instinct: “only a kind of instinct, surer than reason itself, can compel us to leap so great a gap.”[27] There is no way to justify this claim other than to suggest that this instinct must originate in our mind as an innate idea, especially with the claim that the instinct is “surer than reason.” To be sure, part of d’Alembert’s problem rests with Locke, since Locke’s reflective knowledge also cannot justify our ability to go beyond sense data without recourse to some kind of metaphysical connectivity that still sounds a lot like innatism.[28] Such issues like determining the apodictic certainty of mathematics becomes extremely difficult to conclude on the grounds of direct sense perception and reflection alone. Sense certainty cannot account for necessity without recourse to some form of rational connectivity that precedes it, and is intermeshed, with empirical experience.

Surprisingly, Lockean empiricism becomes the unsolved problem for d’Alembert’s philosophical commitments. For Descartes, the issue is one of overreaching. Rationalism overextends its conclusions into areas it cannot verify, i.e. God’s placement of innate ideas into our minds, and does not sufficiently explain where ideas our come from without a structuring principle that accounts for truth. For Locke, our issue is one of limitation. Empiricism limits all thinking as originative and deriving from sensory data. While it fails to provide an adequate explanation as to how sensorial ideas are brought together in the mind, or how we verify truth.[29] Empiricism struggles to adequately provide justification for scientific universals and rigors of mathematical necessity without organizational principles in place prior to experience.

With all this said we must still try acknowledging Descartes’ innovation, for d’Alembert and for the Enlightenment, which surely was his specific method of Cartesian doubting to arrive at the certainty of the cogito. If we are certain that we think, knowledge easily extends from this certainty if we are able to understand the importance of our methods of verification, scientific or otherwise. As for Locke, it is debatable whether or not he did away with innate ideas, yet his contribution to the Enlightenment was enormous. Most of his innovation stands with his attempt to ground human knowledge in an empirical understanding that sought to contain the far-reaching excesses of rational metaphysics.

§7. Conclusions: In 1749, when the Encyclopédie was getting underway, Diderot was thrown into the prison at Vincennes for his publication Lettre sur les aveugles (Letter on the blind).[30] It was around this time that a number of important works were published by Montesquieu, Voltaire, Rousseau, and of course, the PD with the Encyclopédie sees its first publication in 1751.[31] Diderot and d’Alembert would eventually split on philosophical grounds, with d’Alembert leaving the Encyclopédie project altogether by 1758.[32] The atheistic and anti-authoritarianism of the Encyclopédie had the vast publication swirling in controversy since its inception. The constant pressure likely wore d’Alembert down. However, publication of the Encyclopédie didn’t stop in spite of d’Alembert’s absence and the seemingly endless attacks from religious conservatives. Its run would last for twenty one years: 1751-1772.

Sorting through d’Alembert’s philosophical problems directs attention to the mistakes we easily make in our own empirical understanding of nature, science, and religion. Knowledge of the Enlightenment is greatly enhanced with our familiarity of the combined emphasis on philosophy and scientific investigation in the PD. Both fields are better understood in the context of the French Enlightenment due to the fantastic inquisitive energy of intellectuals like d’Alembert and Diderot. Opposed to embellishing traditional values, the Encyclopédie was highly innovative in its day, with its multiple articles on manufacturing and the trades. The Encyclopédie also had the audacious goal to bring all of human knowledge into a single system. Apart from the knotted problems with d’Alembert’s philosophical commitments, what can be found in his work that demonstrates the intellectual value of his philosophy? The PD and the Encyclopédie demonstrate the value of independent free thinking and vigorous curiosity. The Age of the Enlightenment is defined by its breathtaking enthusiasm for new scientific ideas, intellectual autonomy and philosophical discovery. D’Alembert and Diderot helped fuse these notions into the project of knowledge brought together as a vast one-of-a-kind monument, in the Encyclopédie, and its introduction, the PD. They wanted to know the world and they wanted to help people understand themselves in their own vital connection with the world. It is only when we are certain of the knowledge we’ve gained that we are able to think of the possibility of something else—something radical.

Aurelio Madrid

[1] Jean le Rond d’Alembert, Preliminary Discourse to the Encyclopedia of Diderot, translated by Richard N. Schwab (Chicago, IL: University of Chicago Press, 1995), 96.

[2] Richard Schwab, introduction to D’Alembert’s The Preliminary Discourse to the Encyclopedia of Diderot, translated by Richard N. Schwab (Chicago, IL: University of Chicago Press, 1995), xvi.

[3] On the other hand, Robert Grimsley notes that Marquis de Condorcet (1743-1794) suggested that d’Alembert and Diderot were childhood friends.

[4] Robert Grimsley, Jean d’Alembert, 9-10.

[5] Robert Grimsley writes that it wasn’t till 1939 that the accounting books for the Encyclopédie show that, contrary to popular belief, d’Alembert was brought into the project as “early as December 1745, while Diderot was not put on the pay-roll until February of the following year.” Robert Grimsley, Jean d’Alembert, 3.

[6] Jean le Rond d’Alembert, Preliminary Discourse to the Encyclopedia of Diderot, 4.

[7] Richard Schwab notes that d’Alembert’s thought corresponds to these lines of Étienne Bonnot de Condillac: “Our first object, which we should never lose from sight, is the study of the human mind—not to discover its nature, but to learn to know its operations, to observe how they are combined and how we ought to use them to acquire all the intelligence of which we are capable. It is necessary to go back to the origin of our ideas, to work out their generation, to follow them to the limits which nature has prescribed for them, and by these means to establish the extent and limits of our knowledge and renew all of human understanding.” Schwab quoting Condillac in Jean Le Rond d’Alembert’s, Preliminary Discourse to the Encyclopedia of Diderot, n. 8, 5.

[8] D’Alembert, The Preliminary Discourse to the Encyclopedia of Diderot, translated by Richard N. Schwab (Chicago, IL: University of Chicago Press, 1995), 44-45.

[9] D’Alembert, The Preliminary Discourse to the Encyclopedia of Diderot, 7.

[10] Charles Frankel, The Faith of Reason, 7.

[11] Charles Frankel quotes d’Alembert: “Happy are men of letters if they recognize at last that the surest way of making themselves respectable is to live united and almost shut up among themselves; that by this union they will come, without any trouble, to give the law to the rest of the nation in all affairs of taste and philosophy…As if the art of instructing and enlightening men were not, after the too rare art of good government, the noblest portion and gift in human reach.” Charles Frankel, The Faith of Reason, 10.

[12] Charles Frankel writes: The philosophes stressed the fact that they had broken with Cartesianism as a system: Descartes, as Voltaire and others wrote, had discovered the mistakes of antiquity, but he had substituted his own in their place, In following Locke, who had ‘reduced metaphysics to what it ought to be in fact, the experimental physics of the soul,’ the philosophes had ceremoniously rejected Descartes’ ‘metaphysical romance.’” Charles Frankel, The Faith of Reason, 14.

[13] Charles Farnkel writes: “At the same time that the great works in social criticism written during the first decade of the century were attacks upon the superstitions of the ancient régime, they were also, for the most part, revolts against the Cartesian reinforcement of supernaturalism—the separation of the mind from physical nature.” Charles Frankel, The Faith of Reason, 13.

[14] Kant writes on the battle between rationalism and empiricism in the preface to the first edition (1781) of the Critique of Pure Reason: “The perplexity into which it [reason] thus falls is not due to any fault of its own. It begins with principles which it has no option save to employ in the course of experience, and which this experience at the same time abundantly justifies it in using. Rising with their aid (since it is determined to this also by its own nature) to even higher, even more remote, conditions, it soon becomes aware that in this way—the questions never ceasing—its work must always remain incomplete, and it therefore finds itself compelled to resort to principles which overstep all possible empirical employment, and which yet seem so unobjectionable that even ordinary consciousness readily accepts them. But by this procedure human reason precipitates itself into darkness and contradictions; and while it may indeed conjecture that these must be in some way due to concealed errors, and it is not in a position to be able to detect them. For since the principles of which it is making use transcend the limits of experience, they are no longer subject to any empirical test. The battle-field of these endless controversies is called metaphysics.” Immanuel Kant, Immanuel Kant’s Critique of Pure Reason, translated by Norman Kemp Smith (New York, NY: St. Martin’s Press, 1965), 7.

[15] Robert Grimsley, Jean d’Alembert: (1717-83), (London, GB: Oxford University Press, 1963), 3.

[16] Descartes writes, “Lastly, considering that the very thoughts we have while awake may also occur while we sleep without any of them being at that time true, I resolved to pretend that all things that had ever entered my mind were no more true than the illusions of my dreams. But immediately I noticed that while I was endeavoring in this way to think that everything is false, it was necessary that I, who was thinking this, was something. And observing that this truth ‘I am thinking, therefore I exist’ was so firm and sure that all the most extravagant suppositions of the skeptics were incapable shaking it, I decided that I could accept it without scruple as the first principle of the philosophy I was seeking.” René Descartes “Discourse on the Method,” in Selected Philosophical Writings, translated by John Cottingham, Robert Stoothoff, and Dugald Murdoch (New York, NY: Cambridge University Press, 1988), 36.

Another version of the cogito can be found in the Meditations, “Sense-perception? This surely does not occur without a body, and besides, when asleep I have appeared to perceive through the sense many things which I afterwards realized I did not perceive through the senses at all. Thinking? At last I have discovered it—thought; this alone is inseparable from me. I am, I exist—that is certain.” Descartes, “Meditations on First Philosophy” in Selected Philosophical Writings, 82.

[17] Descartes, “Meditations on First Philosophy,” 89.

[18] Richard Schwab writes on the abbé de Condillac, “the great French student of Locke, the abbé de Condillac, presented to his compatriots a combination of certain features of Cartesian rationalism with the empiricism of Locke and Newton that was accepted as doctrine among the philosophes, and much of his thought was incorporated into the Preliminary Discourse.” In Schwab’s introduction to The Preliminary Discourse, xxxiii.

[19] In a footnote to the opening lines of Locke’s Essay, an editor’s note reads, “ Locke does not name the ‘men’ of ‘innate principles’ whose ‘opinion’ he proceeds to criticize; nor doe he quote their words in evidence of what they intended by the opinion. […] From the first, Descartes, with whose writings he [Locke] was early familiar, was probably in his view.” Alexander C. Fraser editor, John Locke, An Essay Concerning Human Understanding, Vol., 1, (New York, NY: Dover Publications, Inc., 1959), n. 1, 37.

[20] It is commonly known that Locke did not use the actual term tabula rasa, instead we find this in Book II of the Essay, “Let us then suppose the mind to be, as we say, white paper, void of all characteristics, without any ideas […],” John Locke, An Essay Concerning Human Understanding, 121.

[21] D’Alembert writes in the PR: “The work whose first volume we are presenting today has two aims. As in the Encyclopédie, it is to set forth as well as possible the order and connection of the parts of human knowledge. As a Reasoned Dictionary of the Sciences, Arts, and Trades, it is to contain the general principles that form the basis of each science and art, liberal and mechanical, and the most essential facts that make up the body and substance of each.” Jean Le Rond d’Alembert, Preliminary Discourse to the Encyclopedia of Diderot, translated by Richard N. Schwab (Chicago, IL: University of Chicago Press, 1995), 4.

[22] Charles Frankel tells us that this is known as “the encyclopedic tree” and that the idea was borrowed from Sir Francis Bacon: “This encyclopedic tree presents something of a problem because, after telling us that we find the unity of science by the empiricist analysis of the origin of ideas, d’Alembert tells us that the order of the encyclopedic tree, the order and connection of the various branches of knowledge, is not identical with the true order of discovery.” Charles Frankel, The Faith of Reason: The Idea of Progress in the French Enlightenment (New York, NY: Octagon Books, 1969), 114.

[23] Richard Schwab, Introduction to The Preliminary Discourse, xxxvi.

[24] Jean Le Rond d’Alembert, Preliminary Discourse to the Encyclopedia of Diderot, 6.

[25] Ronald Grimsley writes: “D’Alembert was obviously too engrossed with his original assumption that we never perceive anything but particulars to face squarely the problem of universals.” Grimsley, Jean d’Alembert, 233.

[26]D’Alembert’s full sentence reads: “The multiplicity of these sensations, the consistency that we note in their evidence, the degrees of difference we observe in them, and the involuntary reactions that they cause us to experience—as compared with that voluntary determination we never have over our reflective ideas, which is operative only upon our sensations themselves—all of these things produce an irresistible impulse in us to affirm that the objects we relate to these sensations, and which appear to be their cause, actually exist.” Jean Le Rond d’Alembert, Preliminary Discourse to the Encyclopedia of Diderot, 8.

[27] Jean Le Rond d’Alembert, Preliminary Discourse to the Encyclopedia of Diderot, 9.

[28] John Locke writes on reflection: “Secondly, the other fountain [reflection] from which experience furnisheth the understanding with ideas is,- the perception of the operations of our own mind within us, as it is employed about the ideas it has got;- which operations, when the soul comes to reflect on and consider, do furnish the understanding with another set of ideas, which could not be had from things without. And such are perception, thinking, doubting, believing, reasoning, knowing, willing, and all the different actings of our own minds;- which we being conscious of, and observing in ourselves, do from these receive into our understandings as distinct ideas as we do from bodies affecting our senses.” John Locke, An Essay Concerning Human Understanding, 26.

[29] Peter Schouls writes on Lockean reflection: “This doctrine of representational realism presents a problem for those holding it, namely how do they know that the idea is a true and adequate representation of the object?” Peter Schouls, Reasoned Freedom: John Locke and the Enlightenment (Ithaca, NY: Cornell University Press, 1992), 80.

[30] Thomas Hankins, Jean d’Alembert: Science and the Enlightenment (London, GB: Oxford University Press, 1970), 67-68.

[31] Thomas Hankins lists these publications: “The year 1749 saw the publication of Diderot’s Lettres sur les aveugles, Buffon’s ‘Premier dicours’ to his Histoire naturelle and Condillac’s Traité des systems. Montesquieu’s Esprit de lois appeared in 1748, but it was not read by d’Alembert until 1749. By the time d’Alembert’s Discours préliminaire [PD] appeared in 28 June 1751, Turgot’s Discours (1750) at the Sorbonne on the progress of the human mind, and Rousseau’s Discours sur les sciences et les arts (1750) had also been published. Voltaire’s Siècle de Louis XIV appeared soon after the first volume of the Encyclopédie and praised it lavishly. The concentration of so many ‘philosophical’ works at a time when the Encyclopédie was also beginning to appear caught up d’Alembert in a burst of enthusiasm for philosophy.” Thomas Hankins, Jean d’Alembert, 68.

[32] Thomas Hankins writes of the schism: “After 1753 d’Alembert and Dierot moved farther apart as Diderot turned more defiantly towards materialism and towards a belief in the universal sensibility and activity of matter. D’Alembert was not a deist. His religious position was one of extreme skepticism […]”


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Frankel, Charles. The Faith of Reason: The Idea of Progress in the French Enlightenment. New York, NY: Octagon Books, 1969.

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Schouls, Peter A. Descartes and the Enlightenment. Montreal, CA: McGill-Queen’s University Press, 1989.

——. Reasoned Freedom: John Locke and the Enlightenment. Ithaca, NY: Cornell University Press, 1992.

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