Even for the purposes of constructing a narrative about theories of the self, the main issue in the seventeenth century was not the self but the emergence of a new approach to science, ushered in by a new theory of the physical world. This approach regarded natural objects as machines and on that basis sought to figure out how they work. The theory was corpuscularism (or, corpuscular mechanism). The transition from old to new took an entire century. However, once the goal of mechanizing nature had taken hold, there would be no turning back. Hence-forth, the entire natural world, eventually including humans, would be portrayed in a new way.
There were two notions at the heart of Aristotelian physics: substantial forms, which combine with prime matter to make each thing the sort of thing it is; and teleology, specifically the issue of what things of various sorts are trying to become, their so-called entelechies. From the perspective of a physics that rests on these two notions, the universe as a whole, as well as many of its parts, can seem like a conscious mind trying to attain some goal.
In the world according to corpuscularism, there is no place either for substantial forms or teleology. Instead, the universe and its parts are conceptualized as if they were clocks, pushed along by springs and pulleys, which—as efficient causes—have no prevision of the ends they might achieve. Corpuscularism removed talk of ends from the science of nature and consigned it to theology and to theories of human consciousness.
But what is the relation of human consciousness to the rest of nature? This question arose in a new light. How it was answered had profound implications not just for what today we would call science but for metaphysics, epistemology, and religion. Prior to the introduction of corpuscularism, metaphysics, epistemology, and religion tended to be viewed as different aspects of one scientific mode of inquiry. Afterward, they were viewed as separate from science.
Objectivity and Subjectivity in a Scientific Mold
From ordinary experience we know that grass is green; water, wet; and snow, cold. From modern science we know that the greenness of grass, the wetness of water, and the coldness of snow are not the familiar greenness, wetness, and coldness of our experience but something entirely different. A blind person can understand the physics of color. Only a sighted person can understand what it’s like to experience the greenness of grass.
According to common sense, when an observer seems to himself to be directly observing the greenness of grass, he is directly observing it. According to modern science, when an observer seems to himself to be directly observing the greenness of grass, what’s happening is that light is reflected off the grass, hits the retinas of his eyes, and then triggers electrochemical signals that travel up his optic nerves to his brain. It is in the observer’s brain, if anywhere in physical space, that the experience of greenness takes place.
How and when did we, as a culture, make the transition from the commonsense view of what happens in ordinary experience to the view suggested by modern science? The change happened toward the beginning of the seventeenth century, as we began to attend to what eventually became known as the distinction between primary and secondary qualities. Although there had been intimations of this distinction in earlier thinkers, it was Galileo Galilei (1564–1642) who first drew attention to it clearly. He explained that primary qualities (weight, texture, and so on) are inherent in bodies, while secondary qualities (taste, perceived color, and so on) are not in the external world but in the minds of observers. In other words, Galileo claimed that primary qualities are objective and secondary ones subjective.
Galileo motivated his version of the distinction between objective and subjective by means of two thought experiments. In the first, he pointed out that while we can conceive of a material object that is devoid of any secondary quality—one, say, that is without taste or color—we cannot conceive of a material object that lacks primary qualities—one, say, without shape or texture. In the second, he asked the reader to imagine the difference between tickling a marble statue and a human being. So far as the motion of one’s fingers is concerned, he claimed, the two ticklings might be identical. What distinguishes them takes place on the side of what gets “tickled.” On that side, there is a subjective sensation. There is no such sensation in the statue. As a consequence, the secondary qualities of things should be understood as the effects of the primary qualities of those things on the sensory mechanisms of sentient beings. In the absence of such effects, secondary qualities would not even exist. In Galileo’s view, natural philosophy—what today we call physical science—could make progress only by attending to primary qualities and ignoring secondary ones.
In Aristotelian science, in which mathematics had little role, the focus was on a world populated by macroscopic objects composed of matter and form. The main goal was to systematically classify different kinds of objects, in the process identifying their so-called substantial forms, which were expressed not mathematically but in a natural language such as Greek or Latin.
Modern science, as Galileo envisaged it, would be different. It would rest metaphysically not on macroscopic objects but on the tiny impenetrable atoms out of which macroscopic objects are composed. And its results would be expressed mathematically. We cannot read the Book of Nature, Galileo wrote, unless we understand the language in which it is written. The symbols of this language are “triangles, circles, and other geometrical figures.” Without these, he said, “it is impossible to comprehend a word,” and “one wanders in vain through a dark labyrinth.”1
For the purpose of advancing scientific inquiry into the external physical world, Galileo was wise to sweep troublesome secondary qualities under the rug of the mind. But for philosophers who soon would seek a more comprehensive view of reality that encompassed not only the external physical world but everything, this strategy created as many problems as it solved.
As we have seen, subjectivity had already come to the fore in the sixteenth century, through Montaigne. Its reemergence in the seventeenth, through Galileo, was not a case of two thinkers independently hitting upon the same idea. The kinds of subjectivity with which each was concerned, and their reasons for being concerned with it, differed. Montaigne’s preoccupation with subjectivity was born of skepticism and a negative assessment of the European culture in which he was enmeshed. Galileo’s was born of optimism and reflection not on culture but on the implications of the new science. Montaigne’s investigations were fueled by the quest for qualitative knowledge of self; Galileo’s, for quantified knowledge of nature. Montaigne, who eschewed any reliance on generalizations and laws of nature, entered the realm of the subjective by immersing himself in what is individual and particular. Galileo segregated subjectivity by abstracting away from the individual and particular in order to discern the regularity of lawful connections. Montaigne’s approach was intensely first-personal. Galileo’s was rigorously third-personal. The obstacles that worried Montaigne in his quest for self-knowledge were passion and spiritual pride. Galileo worried about neither of these. His interest in subjectivity was not to know himself but to clear the debris of the subjective from the path of natural philosophy.
Close on Galileo’s heels, René Descartes (1596–1650) was about to enter the fray. Unlike Galileo, who was unbothered by Montaigne’s existential crisis and seems even to have sought to marginalize inquiry into skeptical epistemology and human psychology, Descartes had one foot firmly planted in the tradition out of which Montaigne’s pessimism had sprung and the other in the new initiatives that spawned Galileo’s optimism. To deal with the differences in these two approaches, he refocused Montaigne’s dilemmas through the lens of Galileo’s conception of subjectivity, but with this difference: unlike Galileo, Descartes had no intention of marginalizing subjectivity, and, unlike Montaigne, he had no intention of dealing with it nonscientifically. Instead, Descartes proposed the certain knowledge of one’s own existence as the basis for all knowledge, thereby relocating subjectivity at the epistemological foundations of modern physical science.
The Soul in a Mechanized World
Descartes freed the Platonic view of the soul from its Aristotelian accretions. In doing so, he inadvertently exposed its scientific irrelevance, a consequence that would not become apparent to most philosophers until the end of the eighteenth century. Even so, the main question for Descartes, insofar as the soul is concerned, was also the main question that worried his critics: How could the soul fit into an otherwise wholly material world governed by mechanistic laws?
The metaphysical view at which Descartes ultimately arrived marked the end of Renaissance science and the beginning of a new era in which the main project was the complete and total mechanization of nature.2 There were two major shifts in perspective: first, the physical world lost its spirituality and became a machine—that is, it became a world in which everything was moved along not by purposes but by the motion of inanimate objects that mindlessly passed on momentum; second, the subjective world lost its physicality—it seemed unlikely, on the new paradigm, that the world as it appears in our immediate experience closely resembles external physical objects.3
Descartes was the first major thinker to start using the word mind (Latin, mens) as an alternative to the word soul (anima). He declared that the “I” is the mind, which is unextended, and that the essence of mind is thinking. In other words, all thinking is done by mental (unextended) substances, and mental substances are always thinking. His main argument that there are such mental substances is epistemological. He reasoned that each of us can be certain that he or she exists as a thinking thing but not (as immediately) certain that there are material objects. From this, he seemed to infer, erroneously, that we cannot be material objects, an inference that, as we have seen, may well have been inspired by Augustine or Avicenna or both.4
Nevertheless, in Descartes’s view, everything in the physical world, including the bodies of humans, is composed of matter in various configurations. How this matter moves is governed by laws of motion that have remained unchanged since the origin of the universe. So far as living things are concerned, nonhuman animals are simply complex automata, lacking consciousness. According to this view, in contrast to Aristotle and even Plato, neither plants nor nonhuman animals have a soul, and soul is not required for life. Instead, life is merely an apparent property of complex mechanisms. Humans differ from other living things only in having nonmaterial, immortal souls, which are conscious. Except for the concession that humans have an immaterial soul, Descartes viewed the entire human body and brain as a machine.
Descartes assumed that independently of the activity of the nonmaterial soul, the neural organization of the brain accounts for sensation, perception, and imagination, and that in animals this entirely mechanical system is all that there is. He assumed that during the experience of sensation, “animal spirits” in the sense organs of nonhuman animals are stimulated mechanically by the sizes, shapes, and motions of the matter impinging on their organs. He claimed that this matter carries decodable information about objects external to the organism. This information, he said, is then transmitted physiologically to the brain and eventually to the pineal gland in the brain, where it results in a redirected signal to some other region of the brain or body. In the case of humans, the process works much the same, with some important exceptions. Chief among these is that thoughts are mental acts of the rational soul that remain in the soul and are not coded in the brain at all. Nevertheless, through the pineal gland they do sometimes causally affect the motion of the animal spirits and hence the behavior of the organism. In addition, agreeing with Augustine’s claims, Descartes said that what humans sense and imagine, in addition to having bodily concomitants, is directly experienced by the immaterial soul.
Even so, Descartes’s mature view of the relationship between humans and other animals is somewhat unsettled. He distinguished sharply, though not always consistently, between those psychological processes that involve the thought of the nonmaterial soul and those other processes involved in sensation, perception, imagination, emotion, learning, and so on that he assumed could be brought about mechanically by the body and brain outside of the realm of consciousness. He is notorious for having suggested that animals are no different than clocks and hence have no qualitative experiences at all. However, in some letters written toward the end of his life, he suggested that animals have sensations and might even have something like thoughts, although they lack anything like human rational thought.5 On the whole, though, what he seems to have wanted to say is, first, that only beings with nonmaterial souls have consciousness in the full sense, which involves self-awareness, and, second, that lower organisms might have something like consciousness, but of a lower order that lacks self-awareness.
Descartes made an additional proposal that was enormously influential and relevant to many of the main problems that plagued his metaphysical views. This was that all thought is necessarily reflexive. What this means is that if a person is aware, then necessarily he is also aware that he is aware. This view surfaced, among other places, in the seventh set of objections to the Meditations (1642; the first edition of the Meditations was published in 1641 with six objections and replies), in which the Jesuit Bourdin complained that by holding that it is “not sufficient for [mental substance] to think” and that it “is further required that it should think that it is thinking by means of a reflexive act,” Descartes was multiplying entities beyond necessity. Descartes replied that “the initial thought by means of which we become aware of something does not differ from the second thought by means of which we become aware that we are aware of it, anymore than this second thought differs from a third thought by which we become aware that we are aware that we are aware.” Thus, in his view, each thought not only encapsulates perhaps infinitely many reflexive mental acts but necessarily incorporates a self-reference. Subsequently, this view may have inhibited the emergence of a developmental psychology of the acquisition of self-concepts. For if a person cannot think at all without also thinking that he or she thinks, then it is impossible to trace in the pattern of the ways people learn to think the gradual development of their ability to think of themselves.6
However, just as importantly, Descartes’s view that all thinking is necessarily self-referential suggested to some later thinkers, who were more materialist than Descartes, a way of explaining what it is about consciousness that makes it special. What makes it special, they suggested, is not its immateriality but its being self-reflective. John Locke, who was officially a dualist but often sounds as if he were a closet materialist, was among the first to pick up on Descartes’s suggestion that what is called consciousness might be understood simply as a capacity for self-reflection.
Substance
Descartes defined substance as something that is capable of existing by itself, without dependence on any other thing. In his view, it follows that, strictly speaking, there is only one substance: God. However, he allowed that, in a looser sense of the word substance, mind and body are also substances and that, in a still looser sense, individual humans, which are a combination of mind and body, are substances. God, who is unique, is a mental substance. Angels, of which presumably there are many, are mental substances. Individual human minds, of which there is one per human, are also mental substances. Human bodies, animal bodies, plants, and inanimate objects are material substances.
Descartes never addressed the question of what individuates mental substances, that is, what makes one mental substance, one angel for instance, different from another. As we have seen, this was a problem in the High Middle Ages that Aquinas solved in part by making every angel the only member of its own species. Descartes’s way with this issue was simply to ignore it.
In the case of body—material substance—Descartes’s view was that since God is the only substance and God is nonmaterial, strictly speaking there are no material substances. However, in the same looser sense of substance in which individual minds are mental substances, individual material substances also exist. But curiously, whereas for Descartes there are many mental substances, there may be only one material substance. This would be the case if for there to be two material substances, they have to be separated by empty space. For empty space, if it were to exist, would be extended, in which case it would not be empty, for whatever has extension is material. So, either there is a way to distinguish among material substances other than by their being separated by empty space or else the entire material world is just one thing. There is no record that Descartes ever spoke to the question of which of these alternatives he favored.
Descartes’s view of how bodies are individuated caused a split among corpuscular mechanists between those, such as himself, who denied the existence of the void (empty space) and those, such as Pierre Gassendi, Robert Boyle, Isaac Newton, and John Locke, who insisted on it. A closely related issue is whether material substances even have essential properties in any but a pragmatic sense. Descartes claimed that they do but that, unlike Aristotelian forms, material substances have only one essential property: extension. Others, such as Boyle, denied that things have genuine essences, while allowing that for some theoretical purposes, we can talk as if they do.
As we have seen, in addition to thinking that God, angels, and human souls are mental substances and that bodies are material substances, Descartes held that each human soul, or mind, is so intimately connected to its own body as to form with it a separate substance of a third sort. What impressed Descartes about the union of mind and body was that each can bring about changes in the other. But how could two things that have almost nothing in common interact? Descartes answered that mind and body influence each other through the pineal gland, a small organ located in the brain at the meeting point of the symmetries between the left and right hemispheres. He may have selected this organ as the point of interaction because it is the only organ in the brain of which he had knowledge that is not bilaterally duplicated. However, even were he right about the pineal gland, that would not have solved the big mystery about his view, which is not about where but how, a point that was not lost on his contemporary critics.7 How two things that have almost nothing in common could interact thus became a question that plagued thinkers at the time, and into modern times, who were otherwise drawn toward substance dualism.
Personal Unity
Descartes rejected the idea, which was congenial to Plato, that the soul’s relation to the body is merely instrumental—like that of a pilot to his ship. According to Descartes, Nature teaches each of us by “sensations of pain, hunger, thirst and so on, that I am not merely present in my body as a sailor is present in a ship but that I am very closely joined and, as it were, intermingled with it, so that I and the body form a unit.” Otherwise, he reasoned, “I, who am nothing but a thinking thing, would not feel pain when the body was hurt, but would perceive the damage purely by the intellect, just as a sailor perceives by sight if anything in his ship is broken.” By the same token, he continued, if I were not one with my body, then “when the body needed food or drink, I should have an explicit understanding of the fact, instead of having confused sensations of hunger and thirst,” which are “nothing but confused modes of thinking which arise from the union and, as it were, intermingling of the mind with the body.”8
The idea for which Descartes seems to be groping in such remarks is that self-concern for our bodies is expressed phenomenologically by a kind of identification we make with the content of our sensations. As a consequence of this identification, when we are aware that our bodies are being stimulated, we feel that something has happened to us, rather than merely think that it has happened to our bodies. Nevertheless, in his view, that mind and body form a substance is not an illusion but a real insight, even though mind and body together are not as deeply real a substance as are mind and body individually.
It seemed to some of Descartes’s critics that in his view, the mind should be related to the body as a pilot to his ship. His response to these critics is unclear and problematic. What he sometimes seems to have been trying to say is that individual nonmaterial minds and their associated bodies form one substance in virtue of their unity as a causal mechanism. In other words, they systematically affect each other, but not other things, in ways that make the two of them together function as if they were one.
As we shall see, Locke would elevate the theme of a human’s identification with the content of his or her sensations to a central position in his own theory of personal identity. Perhaps influenced by the Stoics, his word for the form of identification that interested him was appropriation, a notion he employed to put together the first phenomenological account of self-constitution both at-a-time and over-time. This aspect of his view was mostly ignored by subsequent eighteenth- century philosophers. However, Bishop Butler, one of his keenest critics, picked up on this aspect of his account. In claiming that if Locke’s account of self- constitution were correct, then the self would be fictional, Butler reasserted the pre-Cartesian, Platonic view that a self’s relation to its body is like those of a pilot to his ship.
In sum, in a narrow sense, Descartes’s main contributions to theorizing about the self and personal identity were, first, to lend the tremendous weight of his authority to a Platonic view of the self, which would eventually be recognized as scientifically useless, and, second, to introduce the idea of the reflexive nature of consciousness, which seems to have inhibited the emergence of developmental accounts of the acquisition of self-concepts. In a larger sense, however, he championed the new mechanistic view of nature that in the hands of others would eventually undo even his own theories of the self. He also provided a naturalistic framework for the development of what by the end of the eighteenth century would become an empirical science of psychology.
Alternatives to Descartes’s Dualistic Interactionism
The new science provided philosophers with a powerful motive to be materialists. Christianity provided them with a powerful motive to resist materialism. Among those who responded sympathetically, though not always consistently, to the lure of materialism were the French Catholic Pierre Gassendi (1592–1655) and the English Protestant Thomas Hobbes (1588–1679), both contemporaries of Descartes.
When Gassendi was in a materialistic frame of mind, he basically followed Epicurean atomism, arguing that the soul, or mind, is corporeal on the grounds that it produces corporeal effects, like sensation, reproduction, and digestion. To do this, he reasoned, the soul itself has to be corporeal. However, in his less materialistic moments, which may have been inspired by the Lateran Council’s instruction to Christian philosophers to prove the existence of the immaterial soul, he maintained that one could know that dualism is true—that, in addition to a corporeal soul, humans must have an incorporeal soul. Otherwise, he said, humans would not be able to be self-conscious. Imagination, for instance, which is corporeal, cannot itself perceive its own imaginings or be conscious that it imagines. To self-reflect, one must have an incorporeal soul. In addition, humans know universals, and corporeal souls could not know universals. Humans must then have two souls, one corporeal and one noncorporeal.
In Gassendi’s view, the human incorporeal soul is an unextended substance, somehow joined to the body, but without density or figure, and whole and complete in all parts of the body. With no organic function, its only activity is to think, including to reflect upon itself. In contrast to the corporeal soul, which is produced biologically, each human’s incorporeal soul is created directly by God. Since it is simple and unextended, it cannot be decomposed or divided and is, thus, immortal.
Hobbes made no such concessions. His view was that human bodies, like all bodies, are pushed from behind by forces that have no prevision of their ends. He claimed that these forces wholly account for human mentality. He even went so far as to claim that the very idea of an immaterial substance is a contradiction. Thus, in his view, human souls, angels, and even God, all of which he thought existed, are material.
The potential threat to Christianity posed by Hobbes’s materialism was blunted by the crudity of his physiological explanations of mental phenomena. Few were willing to follow his lead, especially since Descartes had recently shown philosophers how they could accommodate the new scientific developments while remaining dualists. But there were obvious problems with Descartes’s views too, especially in connection with his account of substance and the influence of mind and body on each other.
As these problems were discussed by dualists, materialism waited in the background. But at the time few were able to embrace materialism wholeheartedly. An interesting case in point is Thomas Willis (1621–1675), who, as an English follower of Gassendi, focused his attention on the “animal soul,” which he held to be material, though capable of thought. This is the only soul that nonhuman animals have. Humans have an additional immaterial soul, which controls their animal souls but is not itself open to empirical investigation.
Willis wrote a book on the animal soul in which he described his anatomical studies of animal and human brains, as well as psychophysiological speculations. Nevertheless, he insisted on the special nature of the human rational soul, which fell outside of these speculations. His major contribution to neuroscience was to argue that various brain regions have different functions. For instance, he concluded, based on comparative studies in brain size among different species and on clinical studies of humans, that the cerebral cortex is involved in higher intellectual functions like memory while the cerebellum is involved in more primitive reflexive motor activities. He denied any importance to the ventricles, which from the time of the early church fathers had been taken to be centers of mental function. Willis was one of Locke’s teachers at Oxford and, along with Boyle, a major source for Locke’s later views on thinking matter.
One of the most imaginative and enduring attempts to resolve the problems in Descartes’s approach was that of the Jewish thinker Benedictus (Baruch) de Spinoza (1632–1677). In Spinoza’s masterpiece, Ethics (1677), which was published in the year of his death, he agreed with Descartes that mental properties and physical properties are qualitatively distinct. However, Spinoza rejected the Cartesian view that each is an attribute of a different sort of finite substance. Instead, he claimed that, in spite of appearances, each mental event is identical to a physical event and vice versa; he also claimed that each is an attribute of the one and only substance, which is infinite and the essence of everything that exists. Conceived under the attribute of thought, this one substance is God; conceived under the attribute of extension, it is Nature.
In his own time, Spinoza was mistakenly denounced as a materialist. He was, rather, what is today called a neutral monist. In his view, unlike in the view of Descartes, a human being is not a substance, let alone a mysterious union of two different substances, but an organized collection of attributes of God, who manifests infinitely many different kinds of attributes. Humans, because of the way they are constituted, can be aware only of God’s mental and material attributes. But these are two only from a human perspective—that is, they are not different sorts of attributes but only different ways in which humans perceive the same attributes.
Spinoza, unlike Descartes, thus did away with causal relations between minds and bodies. He thereby avoided the embarrassment of not being able to explain how a mental event could cause a bodily event and vice versa. But he did not stop there. In his view, all causal relations are disguised logical relations. This aspect of his view won few followers, but it was symptomatic of a growing unease with the idea of causal relationships in general, which Spinoza, like many who would come after him, found too mysterious to accept at face value, quite apart from the special problems that causality posed for dualism.
Nevertheless, according to Spinoza, everything behaves in accordance with strictly deterministic laws. Hence, he thought, all human choices and actions are determined (in the end, logically) by prior events over which, ultimately, the people whose choices and actions they are have no control. So, in his view, people have no more free will than do trees or stones, which is to say, they have no free will at all. In his view, the closest one can get to freedom—and getting there is the goal of human life—is to accept one’s place in the infinite deterministic system. This does not free one from the web of causality, but from anxiety and ignorance. Philosophical understanding brings equanimity in its wake, which is itself the supreme form of human freedom.
Another notable attempt to resolve the problems in Descartes’s dualism was that of the Catholic priest Nicolas Malebranche (1638–1715), who subscribed to a view called occasionalism. In The Search After Truth (1674), Malebranche argued that God is the one and only true cause. When it seems that something other than God has been a cause, there has been in reality only the appearance of causation, due to God’s having arranged a co-occurrence of mental and physical events. Thus, for example, if in normal circumstances a person were to will to move his finger, that would serve as the occasion for God to move the person’s finger; and were an object in normal circumstances suddenly to appear in someone’s field of view, that would serve as the occasion for God to produce a visual perception of the object in the person’s mind.
Still another alternative to Cartesian interactionism is the view called psychophysical parallelism, whose most famous proponent was Gottfried Wilhelm Leibniz (1646–1716). In his view, at the level of perception it seems that mind differs from body and that natural causal relations are real. But ultimately, he claimed, everything is mind, and there are no genuine causal relationships in nature. In comparing the series of mental and physical events to two clocks that agree perfectly, Leibniz argued that the agreement can be explained in only one of three ways: through mutual influence (dualistic interactionism); through the continual intervention of a skilled craftsman who keeps the clocks in agreement (occasionalism); or due to the clocks having been constructed originally so that their future agreement is assured (parallelism). He rejected dualistic interactionism on the grounds that it is impossible to conceive of how it could work. He rejected occasionalism as invoking constant miracles interrupting the regular course of nature. There remains just psychophysical parallelism—mind and body exist in a harmony that was preestablished by God at the moment of creation. Thus Leibniz, like Spinoza, held that dualism of mind and body is an illusion and that both are really the same thing. However, whereas Spinoza held that this thing is neither mind nor body, Leibniz held that it is mind.
Why did Leibniz suppose that ultimately everything is mind? Refusing, as Descartes had done, to take extension as primitive and unanalyzable, he analyzed extended objects into infinite series of points, which are like mathematical points except that they are real. These “points” cannot be physical, he thought, because they lack extension, which he accepted from Descartes as the essence of matter. So, they must be mental, that is, souls (what else is there left for them to be?). He called them monads. Today, when people use the word soul, they tend to mean something that is conscious. So did Leibniz, in speaking of monads. He held that each of the infinitesimal monads of which each material thing is composed is conscious. However, the consciousness of most of these monads is quite inferior to human consciousness, consisting only in their “mirroring” the rest of the universe, that is, in their being related to other things in whatever ways they are related.
Personal Identity and Immortality
As we suggested at the outset, in the seventeenth century the main event intellectually, even so far as self and personal-identity theory was concerned, was not self and personal identity theory per se, but science. Nevertheless, each of the philosophers we considered expressed a view about the nature of personal identity and its implications for survival of bodily death. In the case of Descartes, although it was an announced goal of his Meditations to prove the immortality of the soul, it was as if he forgot to do it, which puzzled some of his critics. In response to them, he claimed that by proving that the mind is an immaterial substance distinct from the body he had, in effect, done the main work. Apparently, his target had been contemporary Aristotelians. Some, following Averroës, claimed that nothing that belongs specifically to the individual survives bodily death. Others, in the tradition of Pomponazzi and Zabarella, took the more extreme view that soul, wherever it occurs, is simply the form of the body and hence souls decompose, and so end, at bodily death.
In the Meditations, Descartes imagined that he held a lump of wax in his hand and then brought it close to a lighted candle, which rapidly caused all of the sensible properties of the wax to change. “Does the same wax remain?” he asked, answering that “no one thinks otherwise.” But then, he continued, “What was it in the wax that I understood with such distinctness? Evidently none of the features which I arrived at by means of the senses; for whatever came under taste, smell, sight, touch, or hearing has now altered—yet the wax remains.”9 He answered that in spite of these changes, he nevertheless knew that it is the same lump of wax at the end as it was at the beginning. He used this example to make the point that we learn of the identity of external things over time not through the senses but through understanding, that is, through rational intuition. Later he suggested that we know our own identities in the same way.10
In spite of Descartes’s far greater influence, it was Hobbes, the materialist, not Descartes, the dualist, who laid the foundations for modern theories of personal identity. In Leviathan (1651), Hobbes distinguished between man (human) and person. In De corpore (1665), he then raised the problem of identity over time, to which he considered three possible solutions: that the answer lies in “the unity of matter”; that it lies “in the unity of form”; and that it lies “in the unity of the aggregate of all the accidents together.”11
After discussing the pros and cons of these three answers, Hobbes concluded that “when we inquire concerning the identity” of something, “we must consider by what name” it is called. “For it is one thing to ask concerning Socrates, whether he be the same man [human], and another to ask whether he be the same body; for his body, when he is old, cannot be the same it was when he was an infant, by reason of the difference in magnitude; yet nevertheless he may be the same man.”12 Men (humans), as opposed to their bodies, can change the parts out of which they are composed and still remain the same men:
Also, if the name be given for such form as is the beginning of motion, then as long as that motion remains, it will be the same individual thing; as that man will always be the same, whose actions and thoughts all proceed from the same beginning of motion, namely that which was in his generation; and that will be the same river which flows from one and the same fountain, whether the same water, or other water, or something else than water, flow from thence; and that the same city, whose acts proceed continually from the same institution, whether the men be the same or no.13
Hobbes, thus, had what is called a relational, rather than a substance, view of personal identity.
In Hobbes’s time, European philosophy was not yet ready either for his materialism or for a relational view of personal identity, even though neither were new ideas. As we have seen, toward the end of the second century, Irenaeus, Minucius Felix, and Tertullian had all been materialists and had each proposed a relational view of personal identity. But, after Origen, as dualists within the church gained ascendancy, subsequent Christian thinkers held to a substance view of the identity of the soul and proposed a relational theory only of the identity of the body. After Hobbes, but still in the seventeenth century, Spinoza, Boyle, and Locke also proposed relational views of the identity of the body, and Spinoza and Locke relational views of personal identity. To thinkers in earlier centuries, a relational theory of personal identity had not suggested that the self might be a fiction. To eighteenth century thinkers, it did.
Hobbes was also ahead of his time in his distinguishing between the identity conditions of humans and human bodies. While he was mistaken in thinking of the identity conditions of human bodies as if they were the same as those of inanimate objects, such as a pile of sand, his idea that different sorts of things may have different identity conditions is one that would be endorsed by Locke and most subsequent philosophers. Locke, for instance, ensconced his account of personal identity in a more general account of the identity conditions for all objects that change over time. In this more general account, Locke distinguished among the identity conditions for inanimate objects, plants and animals (including human animals), and people.
After Hobbes but before Locke, it may seem as if Spinoza had left no room in his account for the possibility of personal survival of bodily death. His view that mind and body are just two perspectives on the same thing precluded the mind’s outliving the body. Yet, he claimed, inconsistently it would seem, that “the human mind cannot be absolutely destroyed with the body” and that “something of it remains which is eternal,” something that “we feel and know [to be so] by experience.”14 However, he added, presumably because memory is dependent on the body, that this immortal remnant cannot remember anything of its prior existence.15
Spinoza claimed that not everyone enjoys the same postmortem fate. The ignorant man, who is driven by his appetites and is constantly distracted, ceases to be “as soon as he ceases to be acted on,” whereas the wise man “is hardly troubled in spirit, but being, by a certain eternal necessity, conscious of himself, and of God, and of things, he never ceases to be.”16 By means of the superior sort of knowledge the wise man acquires, he experiences the intellectual love of God and hence knows this love intuitively. This intuitive knowledge, which is indestructible, makes him immortal. So, in the case of the wise man, what remains after the death of his body is simply the divine idea of him and the personality it expresses, which is perhaps best conceived as a thought or memory of God, or Nature. So long as a human is alive, whether he is wise or foolish, he exists as a body and also as an idea in the mind of God. At bodily death, for reasons that in Spinoza’s more general philosophy are unclear, God, or Nature, continues to think the idea of the wise man but not that of the ignorant man. In this sense, the wise man persists as an individual.
Such aberrations in Spinoza’s thoughts about the self are remarkably similar to, and probably dependent on, medieval Jewish philosophical speculations. His more consistent view was that what we call individual human beings are not substances, let alone combinations of two different sorts of substances, but rather modes of God. A consequence of this view, but one which he never paused to develop, is that personal identity has to be understood not as the persistence of a substance, since individual people are not substances, but as a relation among qualitative states. In any case, in Spinoza’s view, “a free man thinks of nothing less than of death.”17
In sum, so far as theories of identity in general and personal identity in particular are concerned, Hobbes and Spinoza, while less influential overall than Descartes, were more progressive. Both Hobbes and Spinoza, by embracing relational views of personal identity, set the stage for Locke’s relational view. Of the two, Hobbes was more influential, primarily for introducing the idea that the organizational structure of something over time, rather than the stuff of which that thing is composed, can be used as a criterion of the thing’s identity. In Locke’s hands, this idea would be used to construct a powerful rival to the Platonic conception of the person.
Prior to his late reading of and response to Locke, Leibniz’s unpublished reflections on personal identity were on two separate, but closely related issues: what accounts for personal identity and what matters in survival. So far as the first issue is concerned, while wavering somewhat, particularly with respect to the question of whether the self is ever separated from body, Leibniz basically took the view that the self is an immaterial substance whose persistence is assured by its being unextended. However, his early work is progressive in connection with two other issues. One of these is his anticipations of what today we would call the question of what matters in survival, the other in his anticipations of what today we would call a four-dimensional view of persons.
So far as the question of what matters in survival is concerned, Leibniz remarked, “But the intelligent soul, knowing what it is—having the ability to utter the word ‘I,’ a word so full of meaning—does not merely remain and subsist metaphysically, which it does to a greater degree than the others, but also remains the same morally, and constitutes the same person. For it is memory or the knowledge of this self that renders it capable of punishment or reward.”18 Leibniz then distinguished between what is required for the soul to persist metaphysically and what it would take for it to matter to the individual whose soul it is whether it persists: “Thus the immortality required in morality and religion does not consist merely in this perpetual subsistence common to all substances, for without the memory of what one has been, there would be nothing desirable about it.” As we shall see, his thought here is similar to Locke’s later thought that “forensic” concerns involving this life, as well as any future life, do not depend on mere substance but on memory.
However, Leibniz continued the remarks just quoted with thoughts that are more reminiscent of Lucretius (who may have been his source): “Suppose that some person all of a sudden becomes the king of China, but only on the condition that he forgets what he has been, as if he were born anew; practically, or as far as the effects could be perceived, wouldn’t that be the same as if he were annihilated and a king of China created at the same instant in his place? That is something this individual would have no reason to desire.”19 Leibniz supposed that without memory, even a reconstituted “self” would not really be oneself, at least with respect to self-concern, and that this would be so even if the reconstituted self were a continuation (or reconstitution) of one’s substance.
Leibniz’s anticipations of what today we would call a four-dimensional view of persons appears in his early unpublished writing and correspondence. The topic comes up against the backdrop of Leibniz’s distinction between the a priori and a posteriori ground of the identity over time of any object, including persons. Here Leibniz has two noteworthy ideas. One is that one cannot tell from experience what individuates one person from another: “It is not enough that I sense myself to be a substance that thinks; I must distinctly conceive what distinguishes me from all other minds, and I have only a confused experience of this.”20 The other is that while a posteriori we attempt to arrive at a true view about the identity of things and persons by comparing their characteristics at different times, it is a separate question, to be answered a priori, what identity over time consists in.
Leibniz’s answer to the question of what identity over time consists in, together with his main reason for that answer, is that “since from the very time that I began to exist it could be said of me truly that this or that would happen to me, we must grant that these predicates were principles involved in the subject or in my complete concept, which constitutes the so-called me, and which is the basis of the interconnection of all my different states,” which predicates “God has known perfectly from all eternity.”21 A subject’s complete concept will include his or her states not just at a given time but throughout his or her entire existence. The view that Leibniz seems to be anticipating here is that the stage (that is, time slice) of a thing or person that exists at any moment or short interval of time is not the whole person but only part of the person and that the whole person consists of an aggregate of such stages that begin whenever the person begins, presumably at bodily birth, and ends whenever the person ends—which in the view of a naturalist would be at bodily death. In Leibniz’s view, people are immortal; hence, they never end.
In the New Essays, which were written later in response to Locke’s Essay Concerning Human Understanding and published posthumously, Leibniz discussed a different example that also anticipates developments in philosophy in our own time:
It may be that in another place in the universe or at another time a globe may be found which does not differ sensibly from this earthly globe, in which we live, and that each of the men who inhabit it does not differ sensibly from each of us who corresponds to him. Thus, there are at once more than a hundred million pairs of similar persons, i.e. of two persons with the same appearances and consciousnesses; and God might transfer spirits alone or with their bodies from one globe to the other without their perceiving it; but be they transferred or let alone, what will you say of their person or self according to your authors? Are they two persons or the same since the consciousness and the internal and external appearance of the men of these globes cannot make the distinction?
Leibniz answered that God and certain spirits could distinguish them. But then asked:
But according to your hypotheses consciousness alone discerning the persons without being obliged to trouble itself with the real identity or diversity of the substance, or even of that which would appear to others, how is it prevented from saying that these two persons who are at the same time in these two similar globes, but separated from each other by an inexpressible distance, are only one and the same person; which is however, a manifest absurdity?22
This “twin-earth” example never found a home in the eighteenth or nineteenth century debates over personal identity, but it found a different one, in our own times, in formal semantics.23 In any case, none of Leibniz’s later reflections, which were not published until 1765, well after Leibniz’s death, had any effect on theory in the seventeenth or early eighteenth centuries.
Summary
The seventeenth century began with the revolutionary theoretical innovations of Kepler and Galileo. It ended with the dazzling theories of Newton, who showed once and for all that there could be a natural philosophy of the external world. Yet to most European thinkers of the seventeenth century, the self remained an anomaly. On the eve of the eighteenth century, with the appearance of Locke’s Essay, the focus was put back on the self. Subsequently, progressive eighteenth-century thinkers were intent on showing that whereas Newton had shown that there could be a natural philosophy of the external world, their job was to show that there could be a natural philosophy of the internal world. By the end of the eighteenth century, leading theorists tended either to marginalize or reject theories that depended for their understanding of the self, or person, on the persistence of an immaterial substance. In place of these, they substituted the view that our minds are dynamic natural systems subject to general laws of growth and development. There would be no transition in the history of Western discussions of the self and personal identity more consequential than this one.