Early Modern Philosophy: Spinoza and Leibniz

Waldseemüller map (Martin Waldseemüller) from 1507 is the first map to include the name “America” and the first to depict the Americas as separate from Asia. There is only one surviving copy of the map, which was purchased by the Library of Congress in 2001

By Dr. Garth Kemerling / 11.12.2011
Professor of Philosophy
Capella University

Philosophy Pages

Baruch Spinoza: Life and Works

Portrait of Barch de Spinoza, c.1665 / Gemäldesammlung der Herzog August Bibliothek, Wolfenbüttel, Germany

Baruch Spinoza was born to Portuguese Jews living in exile in Holland, but his life among the Marranos there was often unsettled. Despite an early rabbinical education, he was expelled from the synagogue at Amsterdam for defending heretical opinions in 1656. While engaging privately in serious study of medieval Jewish thought, Cartesian philosophy, and the new science at Rijnburg and the Hague, Spinoza supported himself by grinding optical lenses, an occupation that probably contributed to the consumption that killed him. Private circulation of his philosophical treatises soon earned him a significant reputation throughout Europe, but Spinoza so treasured his intellectual independence that in 1673 he declined the opportunity to teach at Heidelberg, preferring to continue his endeavors alone.

Spinoza’s first published work was a systematic presentation of the philosophy of Descartes, to which he added his own suggestions for its improvement. The Principles of Descartes’s Philosophy (1663) contain many of the characteristic elements of his later work, but Spinoza seems to have realized that a full exposition of his own philosophical views would require many years of devoted reflection. In the meantime, he turned his attention briefly to other issues of personal and social importance. The Tractatus Theologico-Politicus (A Theologico-Political Treatise) (1670) is an examination of superficial popular religion and a vigorous critique of the miltant Protestantism practiced by Holland’s ruling House of Orange. Spinoza disavowed anthropomorphic conceptions of god as both logically and theologically unsound, proposed modern historical-critical methods for biblical interpretation, and defended political toleration of alternative religious practices. Christians and Jews, he argued, could live peaceably together provided that they rose above the petty theological and cultural controversies that divided them.

Although he published nothing else during his lifetime, metaphysicalspeculations continued to dominate Spinoza’s philosophical reflections, and he struggled to find an appropriate way to present his rationalisticconviction that the universe is a unitary whole.  Respect for deductive reasoning and for the precision of the Latin language led Spinoza to express his philosophy in a geometrical form patterned on that empolyed in Euclid’sElements. Thus, each of the five books of Spinoza’s Ethica Ordine Geometrico Demonstrata (Ethics) (1677) comprises a sequence of significant propositions, each of which is deduced from those that have come before, leading back to a small set of self-evident definitions and axioms.

In Book I Spinoza claimed to demonstrate both the necessary existence and the unitary nature of the unique, single substance that comprises all of reality. Spinoza preferred the designation “Deus sive Natura” (“god or nature”) as the most fitting name for this being, and he argued that the its infinite attributes account for every feature of the universe. Book II describes the absolute necessity with which the two attributes best known to us, thought and extension, unfold in the parallel structure that we, with ourdual natures, comprehend as the ideas and things with which we are acquainted in ordinary life. This account also provides for the possibility of genuine human knowledge, which must be based ultimately on the coordination of these diverse realms. Spinoza’s Tractatus de Intellectus Emendatione (On the Improvement of the Understanding) (1677) provides additional guidance on the epistemological consequences of his metaphysical convictions. Here Spinoza proposed a “practical” method for achieving the best knowledge of which human thinkers are capable.

Spinoza applied similar principles to human desires and agency in Books III-V of the Ethics, recommending a way of life that acknowledges and appropriates the fundamental consequences of our position in the world as mere modes of the one true being. It would be moral bondage if we were motivated only by causes of which we remain unaware, Spinoza held, so genuine freedom comes only with knowledge of what it is that necessitates our actions. Recognizing the invariable influence of desire over our passionate natures, we then strive for the peace of mind that comes through an impartial attachment to reason. Although such an attitude is not easy to maintain, Spinoza concluded that “All noble things are as difficult as they are rare.”

Spinoza: God, Nature, and Freedom

Philosophy “ad more geometrico”

Descartes regarded mathematical reasoning as the paradigm for progress in human knowledge, but Baruch Spinoza took this rationalistic appreciation even further, developing and expressing his mature philosophical views “in the geometrical manner.” Thus, in the posthumously-published Ethica Ordine Geometrico Demonstrata (Ethics) (1677), Spinoza claimed to deduce the entire system of thought from a restricted set of definitions and self-evident axioms.

Drawing specific doctrines from Cartesian thought,medieval scholasticism, and the Jewish tradition, Spinoza blended everything together into a comprehensive vision of the universe as a coherent whole governed solely by the immutable laws of logical necessity. Rigorous thought reveals that there can be only a single substance, of which we (and everything else) are merely insignificant parts. Although we may find it difficult to take any comfort in Spinoza’s account of our place in the world, we are bound to admire the logical consistency with which he works out all the details.

The Unity of Substance

The definitions and axioms with which Book I of the Ethics begins are critical to Spinoza’s enterprise, since they are intended to carry his central doctrines as deductive consequences. Although they generally follow the usages of the scholastic tradition, many of them also include special features of great significance to the thought of Spinoza.

Substance, for example, he defined not only as existing in itself but also as “conceived through itself.” (I Def. iii) This places a severe limit on the possibility of interaction between things, since Spinoza delared that causation is a relation of logical necessity, such that knowledge of the effect requires knowledge of its cause. (I Ax. iii-iv) Few will disagree that god is a substance with infinite attributes, but this definition carries some surprising implications in Spinoza’s view of the world; notice also that freedom, according to Spinoza, just means that a thing exists and acts by its own nature rather than by external compulsion. (I Def. vi-vii)

The numbered propositions that follow make it clear what Spinoza is getting at. Since causal interaction is impossible between two substances that differ essentially, and no two substances can share a common attribute or essence, it follows that no substance can produce genuine change in any another substance. Each must be the cause of its own existence and, since it cannot be subject to limitations imposed from outside itself, must also be absolutely infinite. Things that appear to be finite individuals interacting with each other, then, cannot themselves be substances; in reality, they can be nothing more than the modifications of a self-caused, infinite substance. (I Prop. v-viii) And that, of course, is god.

“Deus sive Natura”

Spinoza supposed it easy to demonstrate that such a being does really exist. As the ontological argument makes clear, god’s very essence includes existence. Moreover, nothing else could possibly prevent the existence of that substance which has infinite attributes in itself. Finally, although it depends on a posteriori grounds to which Spinoza would rather not appeal, the cosmological argument helps us to understand that since we ourselves exist, so must an infinite cause of the universe. Thus, god exists. (I Prop. xi)

What is more, god is a being with infinitely many attributes, each of which is itself infinite, upon which no limits of any kind can be imposed. So Spinoza argued that infinite substance must be indivisible, eternal, and unitary. There can be only one such substance, “god or nature,” in which everything else is wholly contained. Thus, Spinoza is an extreme monist, for whom “Whatever is, is in god.” Every mind and every body, every thought and every movement, all are nothing more than aspects of the one true being. Thus, god is an extended as well as a thinking substance.

Finally, god is perfectly free on Spinoza’s definition. Of course it would be incorrect to suppose that god has any choices about what to do. Everything that happens is not only causally determined but actually flows by logical necessity from immutable laws. But since everything is merely a part of god, those laws themselves, and cause and effect alike, are simply aspects of the divine essence, which is wholly self-contained and therefore free. (I Prop. xvii) Because there is no other substance, god’s actions can never be influenced by anything else.

The Natural Order

God is the only genuine cause. From the essence of god, Spinoza held, infinitely many things flow in infinitely many different ways. The entire universe emanates inexorably from the immutable core of infinite substance. Though we often find it natural to think of the world from the outside looking in, as natura naturata (nature natured), its internal structure can be more accurately conceived from the inside looking out, as natura naturans (nature naturing). (I Prop. xxix) Since all that happens radiates from the common core, everything hangs together as part of the coherent whole which just is god or nature in itself.

The infinite substance and each of its infinitely many distinct attributes (among which only thought and extension are familiar to us) are eternal expressions of the immutable essence of god. From each attribute flow the infinite immediate modes (infinite intellect and motion or rest), and out of these in turn come the infinite mediate modes (truth and the face of the universe). Thus, every mode of substance (each individual mind or body) is determined to be as it is because of the divine essence. Even the finite modes (particular thoughts and actions) are inevitably and wholly determined by the nature of god. Hence, everything in the world is as it must be; nothing could be other than it is. (I Prop. xxxiii)

Thought and Extension

In the same deductive geometrical form, Book II of the Ethics offers an extensive account of human beings: our existence, our nature, and our activities. Remember that we are aware of only two of the infinitely many attributes of god, extension and thought, and that each of them independently expresses the entire essence of the one infinite substance.

That is, in the natural world (god’s body), the attribute of extension, modified by varying degrees of motion and rest, produces the face of the universe, which includes all of the particular physical events which are the modes of extension. (This is almost exactly like Descartes’s account of the material world.) Similarly, in the mental realm (god’s idea), the attribute of thought—modified by infinite intellect—produces the truth, which includes all of the particular mental events which are the modes of thought. Since they arise from distinct attributes, each of these realms is causally independent of the other and wholly self-contained: the natural world and the mental realm are separate closed systems.

Despite the impossibility of any causal interaction between the two, Spinozasupposed that the inevitable unfolding of each these two independent attributes must proceed in perfect parallel with that of the other. “The order and connection of ideas is the same as the order and connection of things.” (II Prop. vii) (And so, of course, must be the order and connection of each of the infinitely many other attributes of god.) Since the development of each aspect of the divine nature follows with logical necessity from its own fundamental attribute, and since all of the attributes, in turn, derive from the central essential being of one and the same infinite substance, each exhibits the same characteristic pattern of organization even though they have no influence on each other.

Thus, for every object of the natural world that exists as a mode of the attribute of extension, there is a corresponding idea in the mind of god that exists as a mode of the attribute of thought. For every physical event that takes place in the material realm as the result of exclusively physical causes, a corresponding mental event must occur in the infinite intellect as a result of purely mental causes. Since everything flows from the same infinite being, we may suppose that the structure of thought in infinite intellect comprises an accurate representation of the structure of every other attribute.

Mind and Body

Consider what all of this implies for each of us as a living human being. We are not substances, according to Spinoza, for only god or Nature is truly substantial; we can exist only as modes, depending for our existence upon the reality of the one real being. Since the one infinite substance is the cause of everything, each of us can only be regarded as a tiny cross-section of the whole.

Of course, that cross-section does include elements from each of the infinitely many attributes of that substance. In particular, we know that in each case it involves both a human body, the movements of whose organic parts are all physical events that flow from god via the attribute of extension, and a human mind, the formation of whose ideas are all mental events that flow from god via the attribute of thought. Although there can be no causal interaction between the mind and the body, the order and connection of their internal elements are perfectly correlated.

Thus, in principle, the human mind contains ideas that perfectly represent the parts of the human body. But since many of these ideas are inadequate in the sense that they do not carry with them internal signs of their accuracy, we do not necessarily know our own bodies. (II Prop. xxviii) If, for example, there must be in my mind an idea that corresponds to each particular organic state of my spleen; but since I am unaware of its bodily correlate, it provides me with no clear awareness of that representational object.

Human Knowledge

Spinoza maintained that human beings do have particular faculties whose functions are to provide some degree of knowledge. I typically assume, for example, that there may be some correlation between thought and extension with regard to sensations produced by the action of other bodies upon my eyes, ears, and fingertips. Even my memory may occasionally harbor some evidence of the order and connection common to things and ideas. And in self-conscious awareness, I seem to achieve genuine knowledge of myself by representing my mind to itself, using ideas to signify other ideas.

Near the end of Book II, then, Spinoza distinguished three kinds of knowledge of which we may be capable: First, opinion, derived either from vague sensory experience or from the signification of words in the memory or imagination, provides only inadequate ideas and cannot be relied upon as a source of truth. Second, reason, which begins with simple adequate ideas and by analyzing causal or logical necessity proceeds toward awareness of their more general causes, does provide us with truth. But intuition, in which the mind deduces the structure of reality from the very essence or idea of god, is the great source of adequate ideas, the highest form of knowledge, and the ultimate guarantor of truth. (II Prop. xl)

Spinoza therefore recommends a three-step process for the achievement of human knowledge: First, disregard the misleading testimony of the senses and conventional learning. Second, starting from the adequate idea of any one existing thing, reason back to the eternal attribute of god from which it derives. Finally, use this knowledge of the divine essence to intuit everything else that ever was, is, and will be. Indeed, he supposed that the Ethics itself is an exercise in this ultimate pursuit of indubitable knowledge.

Action, Goodness, and Freedom

The last three Books of the Ethics collectively describe how to live consistently on Spinozistic principles. All human behavior results from desire or the perception of pain, so (like events of any sort) it flows necessarily from the eternal attributes of thought and extension. But Spinoza pointed out a crucial distinction between two kinds of cases: Sometimes I am wholly unaware of the causes that underlie what I do and am simply overwhelmed by the strength of my momentary passions. But at other times I have adequate knowledge of the motives for what I do and can engage in deliberate action because I recognize my place within the grander scheme of reality as a whole.

It is in this fashion that moral value enters Spinoza’s system. Good (or evil) just is what serves (or hinders) the long-term interests of life. Since my actions invariably follow from emotion or desire, I always do what I believe to be the good, which will truly be so if I have adequate ideas of everything involved. The greatest good of human life, then, is to understand one’s place in the structure of the universe as a natural expression of the essence of god.

But how can we speak of moral responsibility when every human action is determined with rigid necessity? Remember that, for Spinoza, freedom is self-determination, so when I acquire adequate knowledge of the emotions and desires that are the internal causes of all my actions, when I understand why I do what I do, then I am truly free. Although I can neither change the way things are nor hope that I will be rewarded, I must continue to live and act with the calm confidence that I am a necessary component of an infinitely greater and more important whole. This way of life may not be easy, Spinoza declared, “But all noble things are as difficult as they are rare.”

Gottfried Wilhelm Leibniz: Life and Works

Engraving of Gottfried Wilhelm Leibniz, by Pierre Savart / Peace Palace Library

After completing his philosophical and legal education at Leipzig and Altdorf, Gottfried Leibniz spent several years as a diplomat in France, England, and Holland, where he became acquainted with the leading intellectuals of the age. He then settled in Hanover, where he devoted most of his adult life to the development of a comprehensive scheme for human knowledge, comprising logic, mathematics, philosophy, theology, history, and jurisprudence. Although his own rationalism was founded uponan advanced understanding of logic, which Leibniz largely kept to himself, he did publish many less technical expositions of his results for the general public. These include a survey of the entire scheme in The New System of Nature (1695), a critical examination of Locke’s philosophy in Nouveaux Essaies sur l’entendement humain (New Essays on Human Understanding) (1704), and an attempt to resolve several theological issues in the Théodicée (Theodicy) (1710).

La Monadologie (Monadology) (1714) is a highly condensed outline of Leibniz’s metaphsics. Complete individual substances, or monads, are dimensionless points which contain all of their properties—past, present, and future—and, indeed, the entire world. The true propositions that express their natures follow inexorably from the principles of contradiction and sufficient reason.

The same themes are presented more popularly in the Discours de Metaphysique (Discourse on Metaphysics) (1686). There Leibniz emphasized the role of a benevolent deity in creating this, the best of all possible worlds, where everything exists in a perfect, pre-established harmony with everything else. Since space and time are merely relations, all of science is a study of phenomenal objects. According to Leibniz, human knowledge involves the discovery within our own minds of all that is a part of our world, and although we cannot make it otherwise, we ought to be grateful for our own inclusion in it.

Leibniz: Logic and Harmony

The Uses of Logic

The last of the great Continental Rationalists was Gottfried Wilhelm Leibniz. Known in his own time as a legal advisor to the Court of Hanover and as a practicing mathematician who co-invented the calculus, Leibniz applied the rigorous standards offormal reasoning in an effort to comprehend everything. A suitably sophisticated logical scheme, he believed, can serve as a reliable guide to the ultimate structure of reality.

But Leibniz published little of his philosophical work during his own lifetime. For an understanding of the technical logical foundations of his system, we must rely upon letters and notebooks which became available only centuries later and upon the aphoristic summary of its results in La Monadologie (Monadology) (1714). His Discours de Metaphysique (Discourse on Metaphysics) (1686) and Théodicée(Theodicy) (1710) present to the general public more popular expositions of Leibniz’s central themes. Our strategy will be to begin with the logical theories and work outward to the more accessible doctrines.

True Propositions

The basis for Leibniz’s philosophy is pure logical analysis. Every proposition, he believed, can be expressed in subject-predicate form. What is more, every true proposition is a statement of identity whose predicate is wholly contained in its subject, like “2 + 3 = 5.” In this sense, all propositions are analytic for Leibniz. But since the required analysis may be difficult, he distinguished two kinds of true propositions: (Monadology 33)

Truths of Reason are explicit statements of identity, or reducible to explicit identities by a substitution of the definitions of their terms. Since a finite analysis always reveals the identity-structure of such truths, they cannot be denied without contradiction and are perfectly necessary.

Truths of Fact, on the other hand, are implicit statements of identity, the grounds for whose truth may not be evident to us. These truths are merely contingent and may be subject to dispute, since only an infinite analysis could show them to be identities.

Anything that human beings can believe or know, Leibniz held, must be expressed in one or the other of these two basic forms. The central insight of Leibniz’s system is that all existential propositions are truths of fact, not truths of reason. This simple doctrine has many significant consequences.

Complete Individual Substances

Consider next how this logic of propositions applies to the structure of reality itself for Leibniz. The subject of any proposition signifies a complete individual substance, a simple, indivisible, dimensionless being or monad, while the predicate signifies some quality, property, or power. Thus, each true proposition represents the fact that some feature is actually contained in this substance.

Each monad is a complete individual substance in the sense that it contains all of its features—past, present, and future. Because statements of identity are timeless, the facts they express perpetually obtain. (Thus, for example, I am the person whose daughter was born in 1982 and the person who now develops this web site and the person who will vacation in Manitoba next summer; since each of these predicates can be truly affirmed of me, each of these features is contained in me.) Everything that was, is, or will ever be true of any substance is already contained in it. (Monadology 22)

Moreover, each monad is a complete individual substance in the sense that its being is utterly independent of everything else. Because statements of identity are self-contained, any apparent relation between substances must actually be a matching pair of features that each possesses alone. (Thus, for example, I happen to have the property of being Aaron’s father, and Aaron happens to have the property of being my son, but these are two facts, not one.) Hence, on Leibniz’s view, there can be no interaction between substances, each of which is purely active. Monads are “windowless.” (Monadology 7)

Where Spinoza saw the world as a single comprehensive substance like Descartes’s extended matter, then, Leibniz supposed that the world is composed of many discrete particles, each of which is simple, active, and independent of every other, like Descartes’s minds or souls. The rationalists’ common reliance upon mathematical models of reasoning led to startlingly different conceptions of the universe. Yet the rationality, consistency, and necessity within each system is clear.

Logical Principles

Another way of summing up the structure of the universe on Leibniz’s view is by reviewing the great logical principles from which all truths are said to flow:

The Principle of Contradiction generates the truths of reason, each of which states the connection between an individual substance and one of its finite number of essential features. (Monadology 31) It would be a contradiction to deny any of these propositions, since the substance would not be what it is unless it had all of these features. Truths of reason, then, are not influenced by any contingent fact about the world; they are true “in all possible worlds.” Thus, for example, “Garth Kemerling is a human being” would be necessarily true even if my parents had been childless.

The Principle of Sufficient Reason generates the truths of fact, each of which states the connection between an existing individual substance and one of its infinitely many accidental features or relations. (Monadology 32) The sufficient reason for the truth of each of these propositions is that this substance does exist as a member of the consistent set of monads which constitutes the actual world. Truths of fact, then, depend upon the reciprocal mirroring of each existing substance by every other. Thus, for example, “Garth Kemerling is an oldest child” is contingently true only because my parents had no children before I was born.

The Principle of the Identity of Indiscernibles establishes the fact that, within the set of monads that constitutes any possible world, no two can be exactly alike. (Monadology 9) If, on the contrary, there were two distinct but perfectly identical substances, Leibniz argued, then there could be no sufficient reason for each to occupy its own location rather than that of the other. More positively, since each monad mirrors the entire structure of the world, each must reflect a unique set of relations to every other.

Finally, the Principle of the Plenum (or principle of plenitude) affirms that the actual world, considered as a set of monads, is as full as it can possibly be. Since there is no genuine interaction among distinct substances, there would be no sufficient reason for the non-existence of any monad that would be consistent with the others within a possible world. Hence, anything that can happen will; every possibility within this world must be actualized. The world in which we live, then, is but one among the infinitely many possible worlds that might have existed. What makes this one special?

Space and Time

Since we experience the actual world as full of physical objects, Leibnizprovided a detailed account of the nature of bodies. As Descartes had correctly noted, the essence of matter is that it is spatially extended. But since every extended thing, no matter how small, is in principle divisible into even smaller parts, it is apparent that all material objects are compound beings made up of simple elements. But from this Leibniz concluded that the ultimate constitutents of the world must be simple, indivisible, and therefore unextended, particles—dimensionless mathematical points. So the entire world of extended matter is in reality constructed from simple immaterial substances, monads, or entelechies.

In fact, Leibniz held that neither space nor time is a fundamental feature of reality. Of course individual substances stand in spatial relation to each other, but relations of this sort are reducible in logic to the non-relational features of windowless monads. In exactly the same way, temporal relations can be logically analyzed as the timeless properties of individual monads. Space and time are unreal, but references to spatial location and temporal duration provide a convenient short-hand for keeping track of the relations among the consistent set of monads which is the actual world.

What is at work here again is Leibniz’s notion of complete individual substances, each of which mirrors every other. A monad not only contains all of its own past, present, and future features but also, by virtue of a complex web of spatio-temporal references, some representation of every other monad, each of which in turn contains . . . . In a universe of windowless mirrors, each reflects any other, along with its reflections of every other, and so on ad infinitum. It is for this reason that an infinite analysis would be required to reveal the otherwise implicit identity at the heart of every truth of fact. In order fully to understand the simple fact that my eyes are brown, one would have to consider the eye-color of all of my ancestors, the anatomical structure of the iris, my personal opthalmological history, the culturally-defined concept of color, the poetical associations of dark eyes, etc., etc., etc.; the slightest difference in any one of these things would undermine the truth of this matter of fact. Existential assertions presuppose the reality of just this one among all possible worlds as the actual world.

The Best of All Possible Worlds

Both in the Monadology and at the more popular level of presentation that characterizes the Discourse on Metaphysics, Leibniz (like Descartes) resolved some of the most thorny philosophical problems by reference to god. God (alone) exists necessarily, and everything else flows from the divine nature. Limited only by contradiction, god first conceives of every possible world—the world with just one monad; the worlds with exactly two monads; those with three, with seventeen, with five billion, etc. Then god simply chooses which of them to create.

Of course even god must have a sufficient reason for actualizing this world rather than any other. The most direct advantage of this world is that (as the plenum principle requires) it is the fullest. That is, more things exist and/or more events actually take place in this world than in any other consistent set of interrelated monads. In a more lofty tone, Leibniz declared that a benevolent god would choose to create whatever possible world contained the smallest amount of evil; hence (in a phrase that would later be mocked by Voltaire) this is “the best of all possible worlds,” according to Leibniz. Nothing about it could be changed without making things worse rather than better on the whole.

Similarly, the existence of a benevolent god can be used to account for the smooth operation of a universe that consists of indefinitely many distinct individual substances, none of which have any causal influence over any other. (Monadology 51) A crucial element of god’s creative activity, Leibniz held, is the establishment of a “pre-established harmony” among all existing things. Like well-made clocks that have been synchronized, wound, and set in motion together, the monads that make up our world are independent, self-contained, purely active beings whose features coincide without any genuine interaction among them.

One special case of this pre-established harmony, of course, accounts for the apparent interaction of mind and body in a human being as nothing more than the perfect parallelism of thier functions. In fact, the human mind is just the dominant member of a local cluster of monads which collectively constitute the associated human body. (Monadology 63) Neither has any real effect on the other, but these monads are most clearly reflected in each others’ foreground. Thus, in both sensation and volition, the divinely-ordained coincidence of bodily movements and mental thoughts creates an illusion of genuine causal influence.

Knowledge and Freedom

The possibility human knowledge emerges more clearly from a slightly more technical account of Leibniz’s position. All monads have the capacity for perception of the external world in the sense that, as complete individual substances, each of them contains as properties unconscious images of its spatio-temporal relations to everything else. (Monadology 19) These innate ideas constitute the unique point of view from which any monad may be said to represent the world as a whole.

But Leibniz held that some monads—namely, the souls of animals and human beings—also have conscious apperception in the sense that they are capable of employing sensory ideas as representations of physical things outside themselves. And a very few monads—namely, spirits such as ourselves and god—possess the even greater capacity of self-consciousness, of which genuine knowledge is the finest example. Although Leibniz himself did not draw the inference directly, notice that if a cluster of dimensionless monads can make up an extended body, it might be equally possible for a cluster of unconscious monads to constitute a thinking thing.

What Leibniz did claim is that we have the free will required for moral responsibility even though all of our future actions are already contained in us (along with the future of the entire actual world). Any awareness of those contingent future actions would follow from the principle of sufficient reason only upon an infinite analysis of my nature. Hence, since I lack knowledge of what I will do tomorrow, it will seem to me as if I act freely when I do it. Like space and time, freedom is a benevolent illusion that adequately provides for life in an uncertain world.

Concluding note on the Rationalists

Descartes, Spinoza, and Leibniz illustrate well the range of diverse outcomes that may result from an effort to understand the world through a prioriknowledge. If their systems of thought seem implausibly remote from the world of ordinary experience, it may help to remember that modern science leads to a similar result. Once we grant that the reality of things may be quite different from the way they appear to us, only the internal coherence of the scheme of thought makes much difference. Next we’ll look at modern philosophers who were more determined to make sense out of the materials provided in everyday life.