Understanding the place of mind and body in nature gave rise to several schools of thought.
Several intertwined questions arose from the new scientific, Cartesian, view of mind and its place in nature. Some are philosophical. If I am locked up in the subjective world of consciousness, how can I know anything about the world with any confidence? Asking this question created a degree of paranoia in subsequent philosophy. Descartes began his quest for a foundation upon which to erect science by suspecting the truth of every belief he had. Eventually he came upon the apparently unassailable assertion that “I think, therefore I am.” But Descartes’s method placed everything else in doubt, including the existence of God and the world. Related to the philosophical questions are psychological ones. How and why does consciousness work as it does? Why do we experience the world as we do, rather than some other way? Because the answers to the philosophical questions depend on the answers to the psychological ones, examining the mind—doing psychology—became the central preoccupation of philosophy. Several philosophical-psychological traditions ensued, the empiricist, realist, idealist, and historical-cultural traditions.
The Empiricist Tradition
The empiricist tradition is the most important for the history of psychology in Britain and America. Notwithstanding the subjectivity of consciousness, empiricism began with John Locke (1632-1794) by accepting consciousness at face value, trusting it as a good, if imperfect, reflection of the world. In many respects, Locke was similar to Descartes. He trained in medicine, worked in science (he was a friend of Newton’s), and aimed for a new philosophy consistent with the new science. However, Locke was less entangled in metaphysical issues than Descartes, and his thought had a more practical, commonsense cast, perhaps because he was an educator and politician, writing for the general public, not philosophers.
Locke concisely summarized the central thrust of empiricism, “We should not judge of things by men’s opinions, but of opinions by things,” striving to know “the things themselves.” Locke’s picture of cognition is essentially that of Descartes. We are acquainted not with objects, but with ideas that represent them. Locke differed from Descartes in denying that any of the mind’s ideas are innate. Descartes had said that some ideas (such as the idea of God) cannot be found in experience, but are inborn, awaiting activation by appropriate experiences. Locke said that the mind was empty of ideas at birth, being a tabula rasa (blank slate) upon which experience writes. However, Locke’s view is not too different from Descartes’s view because he held that the mind is furnished with numerous mental abilities, or faculties, which tend automatically to produce certain ideas (such as the idea of God) from the raw material of experience. Locke distinguished two sources of experience, sensation and reflection: sensation reveals the outside world, whereas reflection reveals the operations of our minds.
Later empiricists took the “way of ideas” further, creating deep and unresolved questions about human knowledge. The Irish Anglican bishop and philosopher George Berkeley (1685-1753) began to reveal startling implications of the way of ideas. Berkeley’s work is an outstanding example of how the new Cartesian conception of consciousness invited psychological investigation of beliefs heretofore taken for granted. The way of ideas assumes with common sense that there is a world outside consciousness. However, through a penetrating analysis of visual perception, Berkeley challenged that assumption. The world of consciousness is three-dimensional, possessing height, width, and depth. However, Berkeley pointed out, visual perception begins with a flat, two-dimensional image on the retina, having only height and width. Thus, as someone leaves us, we experience him or her as getting farther away, while on the retina (the screen of the Cartesian theater) there is only an image getting smaller and smaller.
Berkeley argued that the third dimension of depth was a secondary sense property. We infer the distance of objects from information on the visual screen (such as linear perspective) and from bodily feedback about the operations of our eyes. Painters use the first kind of cues on canvases to create illusions of depth. So far, Berkeley acted as a psychologist proposing a theory about visual perception. However, he went on to develop a striking philosophical position termed immaterialism. Depth is not only an illusion when it’s on canvas, it’s an illusion on the retina, too. Visual experience is, in fact, two-dimensional, and the third dimension is a psychological construction out of bits and pieces of experience assembled by us into the familiar three-dimensional world of consciousness. Belief in an external world depends upon belief in three-dimensional space, and Berkeley reached the breathtaking conclusion that there is no world of physical objects at all, only the world of ideas. Breathtaking as Berkeley’s conclusion may be, but it rested on hardheaded reasoning. Our belief that objects exist independently of our experience of them—that my car continues to exist when I’m indoors—is an act of faith. This act of faith is regularly confirmed, but, Berkeley said, we have no knockdown proof that the world exists outside the Cartesian theater. We see here the paranoid tendency of modern thought: the tendency to be skeptical about every belief. no matter how innocent (true) it may seem, and in Berkeley we see how this tendency depends upon psychological notions about the mind.
Skepticism was developed further by David Hume (1711-1776), one of the most important modern thinkers, and his skeptical philosophy began with psychology: “All the sciences have a relation … to human nature,” and the only foundation “upon which they can stand” is the “science of human nature.” Hume drew out the skeptical implications of the way of ideas by relentlessly applying empiricism to every common sense belief. The world with which we are acquainted is the world of ideas, and ideas are held together by the mental force of association. In the world of ideas we may conceive of things that do not actually exist, but are combinations of simpler ideas that the mind combines on its own. Thus, the chimerical unicorn is only an idea, being a combination of two other ideas that do correspond to objects: the idea of a horse and the idea of a horn. Likewise, God is a chimerical idea, composed from ideas about omniscience, omnipotence, and paternal love. The self, too, dissolves in Hume’s inquiry. He went looking for the self and could find in consciousness nothing that was not a sensation of the world or the body. A good empiricist, Hume thus concluded that because it cannot be observed, the self is a sort of psychological chimera, though he remained uncertain how it was constructed. Hume expunged the soul in the Cartesian theater, leaving its screen as the only psychological reality.
Humean psychology seemed to make scientific knowledge unjustifiable. Our idea of causality—a basic tenet of science—is chimerical. We do not see causes themselves, only regular sequences of events, to which we add a subjective feeling, the feeling of a necessary connection between an effect and its cause. More generally, any universal assertion, such as “All swans are white,” cannot be proved, because they have only been confirmed by experience so far. We might one day find that some swans are black (they live in New Zealand). Hume appeared to reach the alarming conclusion that we can know nothing for certain beyond the immediate content of our conscious sensations. Science, religion, and morality were all thrown in doubt, because all assert theses or depend on assumptions going beyond experience, which may, therefore, some day prove erroneous. Hume was untroubled by this conclusion, anticipating the later post-evolutionary pragmatism of C. S. Peirce and William James. Beliefs formed by the human mind are not provable by rational argument, Hume said, but they are reasonable and useful, aiding us mightily in everyday life. Other thinkers, however, were convinced that philosophy had taken a wrong turn.
The Realist Tradition
Hume’s fellow Scottish philosophers, led by Thomas Reid (1710-1796), offered one diagnosis and remedy. Berkeley and Hume challenged common sense, suggesting that external objects do not exist, or, if they do, we cannot know them or causal relationships among them with any certainty. Reid defended common sense against philosophy, arguing that the way of ideas had led philosophers into a sort of madness. Reid reasserted and reworked the older realist tradition. We see objects themselves, not inner representations of them. Because we perceive the world directly, we may dismiss Berkeley’s immaterialism and Hume’s skepticism as absurd consequences of a mistaken notion, the way of ideas. Reid also defended a form of negativism. God made us, endowing us with mental powers (faculties) upon which we can rely to deliver accurate information about the outside world and its operations.
Scottish realism contained a hidden challenge to the first scientific psychology. The psychology of consciousness was predicated upon the way of ideas. Natural scientists studied the physical objects of the world machine, and psychologists studied the mental objects of the world of consciousness. However, according to realism, the world of consciousness does not exist, because we perceive objects, not ideas. What appears to be introspection of an inner world of consciousness is, in fact, direct perception of the world itself. In the twentieth century, psychologists such as E. C. Tolman and B. F. Skinner used realist arguments to attack introspective psychology in support of behaviorism. Instead of studying mythical ideas, psychologists should study the relationship between the behavior of organisms and the world in which they act.
The Idealist Tradition
Another diagnosis and remedy was offered in Germany by Immanuel Kant (1724-1804), who, like Reid, found Hume’s ideas intolerable because they made genuine knowledge unreachable. Reid located Hume’s error in the way of ideas, abandoning it for a realist analysis of cognition. Kant, on the other hand, located Hume’s error in empiricism and elaborated a new version of the way of ideas that located truth inside the mind. Empiricists taught that ideas reflect, in Locke’s phrase, “things themselves,” the mind conforming itself to objects that impress (Hume’s term) themselves upon it. But for Kant, skepticism deconstructed empiricism. The assumption that mind reflects reality is but an assumption, and once this assumption is revealed—as Berkeley and Hume did—the ground of true knowledge disappears.
Kant upended the empiricist assumption that the mind conforms itself to objects, declaring that objects conform themselves to the mind, which imposes a universal, logically necessary structure upon experience. Things in themselves (noumena) are unknowable, but things as they appear in consciousness (phenomena) are organized by the mind in such a way that we can make absolutely true statements about them. Take, for example, the problem addressed by Berkeley, the perception of depth. Things in themselves may or may not be arranged in Euclidean three-dimensional space; indeed, modern physics says that space is non-Euclidean. However, the human mind imposes Euclidean three-dimensional space on its experience of the world, so we can say truly that phenomena are necessarily arrayed in three-dimensional space. Similarly, the mind imposes other categories of experience on noumena to construct the phenomenal world of human experience.
A science fiction example may clarify Kant’s point. Imagine the citizens of Oz, the Emerald City, in whose eyes are implanted at birth contact lenses making everything a shade of green. Ozzites will make the natural assumption that things seem green because things are green. However, Ozzites’ phenomena are green because of the contact lenses, not because things in themselves are green. Nevertheless, the Ozzites can assert as an absolute and irrefutable truth that every phenomenon is green. Kant argued that the categories of experience are logically necessary preconditions of any experience whatsoever by all sentient beings. Therefore, because science is about the world of phenomena, we can have genuine, irrefutable, absolute knowledge of that world, and should give up inquires into Locke’s “things themselves.”
Kantian idealism produced a radically expansive view of the self. Instead of concluding with Hume that it is a construction out of bits and pieces of experience, Kant said that it exists prior to experience and imposes order on experience. Kant distinguished between the empirical ego (the fleeting contents of consciousness) and the transcendental ego. The transcendental ego is the same in all minds and imposes the categories of understanding on experience. The self is not a construction from experience, it is the active constructor of experience. In empiricism the self vanished; in idealism it became the only reality.
Idealism influenced early German psychology. Because the transcendental ego creates consciousness, it cannot enter into consciousness. Psychology, idealists held, did not deserve the name of science because the most important part of the mind, the self, could not be observed. As a young man psychology’s founder, Wilhelm Wundt sided with Locke saying that introspection could fathom thought. Later, he sided with Kant, restricting experimental psychology to the study of immediate experience, proposing to study the higher mental processes by other methods. One of psychology’s early disputes—the imageless thought controversy— was created by arguments over the scope of introspection. The dispute helped pave the way for behaviorism by throwing doubt on the value of all introspection. The degree to which people know the causes of their behavior remains controversial.
The Historical-Cultural Tradition
Our final tradition opposed the tendencies of the scientific revolution by denying that the human sciences could or should be natural sciences. This dissenting viewpoint was articulated first in obscurity by the Italian philosopher Giambattista Vico (1668-1744), and more influentially by the German writer Johann Herder (1744-1803), who stated its motto: “We live in a world we ourselves create.” Human beings are not solely natural objects (machines) because we live social lives in human cultures constructed by the process of history. Therefore, there can be no science encompassing all human beings. Humans live in different cultures, have lived in different ones in the past, and will construct new ones in the future. The spatiotemporal universality of natural science (gravity and matter are the same in all times and places) does not hold in the human world. Some of human nature has physical roots, but much, perhaps most, has social roots. Whereas part of psychology can emulate physics (studying the human mind as related to its brain), much should emulate history (studying the human mind as related to its culture). The historical-cultural tradition became important in the nineteenth-century German psychology.
Examining Mind and Body
So far we have discussed issues created by the Cartesian separation of consciousness from the world. Descartes also made problematical the nature of the connection between soul and body. It seems obvious that the soul gets information about the world through the body and controls its actions. Descartes taught that soul and body interact through the pineal gland, the screen of the Cartesian theater. By pushing it around, Descartes thought, the soul could control the operations of the nerves. However, Cartesian interactive dualism quickly came under attack. One of Descartes’s correspondents, Princess Elisabeth of Bohemia (1615-1680), asked the key question: “How can body be pushed by something immaterial?” Descartes could give no good answer.
The problem persisted through the eighteenth century, although most early psychologists adopted a variation on dualism: the thesis of psychophysical parallelism proposed by Gottfried Wilhelm von Leibniz (1646-1716). He said that mind and body are separate, that every mental event has a physical event corresponding to it, but that the latter does not actually cause the former. Although this position was convenient, making psychology separate from physiology, it left its own mysteries such as why mind and body seem to interact, or if they do not, of what use is studying an impotent mind? Leibniz’s parallelism gave rise to the first experimental research in psychology, Gustav Fechner’s psychophysics, which tried to precisely measure the correlation of stimulus and sensation.
Idealism (including immaterialism) is a monist answer to the mind-body problem, claiming that only mind exists, matter being an illusion. Another radical— even socially dangerous—monistic answer to the mind-body problem was materialism: the claim that only matter exists, the mind being the illusion. The banner of materialism was first publicly hoisted in 1748 by a physician. Julien-Offray de la Mettrie (1709-1751) in his book L’Homme machine (The man-machine). La Mettrie took the step Descartes would not, could not, or feared to, take, and proposed that thought was a brain process. Discarding the soul was a bold and dangerous step. It threatened Christian belief in the reality and immortality of the soul; it suggested that if human beings are machines, then there is no free will, and moral responsibility is an illusion. For many people, materialism was and is a profound threat to their conception of themselves, society, and their eternal hopes.
Examining Other Minds
In severing the mind from the world and from the body, Descartes made the existence of other minds problematical. In the Cartesian view, mind is private consciousness. But how do I know if other beings have minds? Descartes answered that I know within myself that I think, and that I express my thoughts in language. Therefore, any creature possessing language also possesses a thinking soul. Since only humans have language, only humans have souls.
The problem of other minds did not become important until after the acceptance of evolution in the nineteenth century. Evolution suggested that contrary to Descartes, animals have minds, albeit simpler ones than ours. Modern controversies over other minds were foreshadowed in L’Homme machine, when La Mettrie tackled the problem of other minds from his materialist perspective. He proposed teaching language to apes, as if they were deaf children. If apes can learn language, Descartes would be refuted and the existence of the soul thrown in doubt. In the twentieth century, when Noam Chomsky revived Descartes’s thesis that language is a species-specific human ability, some psychologists put La Mettrie’s hypothesis to the test. In reaching a Cartesian conclusion, the computer scientist Alan Turing (1912-1954) said we would know computers were intelligent when they used language as well as humans do.