The Scientific Revolution

The story of scientific psychology begins with the Scientific Revolution. The scientific revolution did more than create the idea that psychology might be a science, it gave rise to new conceptions of mind and body fundamental to psychology’s development. The Scientific Revolution created the concept of consciousness, around which the first psychologies were organized, and created the concept that the universe is a machine, suggesting that living bodies were organic machines.

The Transformation of Matter

Ancient people thought of the universe as a living organism or as a book. As a living organism, the universe was an interconnected whole developing in an orderly way. The Stoics especially taught this, and Christians picked up the idea, seeing the universe as God’s handiwork and history as God’s unfolding plan. As a book, the universe was set of symbols to be deciphered. Thus, people tried to interpret the meaning of a comet as a sign of some impending event.

Basic to the Scientific Revolution was the idea that the world was neither a living organism nor a book, but a machine—a giant clockwork—following regular mechanical principles expressible in mathematical laws. The triumphant epitome and capstone of the revolution was the Principia Mathematica (1687) by Isaac Newton (1642-1727). Newton showed that the motions of the stars and planets, and the motions of physical bodies anywhere in the universe could be accounted for by a few laws of motion and gravity. Moreover, the mechanical conception of the universe promised that science would fulfill Bacon’s promise and give humans power over nature. On the other hand, in the Newtonian scheme, Halley’s comet was a dirty snowball in solar orbit, possessing no cosmic meaning at all.

Psychology would be deeply concerned with questions raised by the new mechanical philosophy. If the universe is not a living being, but a machine, are animals—and human beings—machines, too? What place, if any, does the soul have in science and the physical world? If things and events have no meaning, why do they seem to? How much of our perceptual experience belongs to things in themselves, and how much belongs only to us?

The Transformation of Experience

Prior to the scientific revolution, philosophers taught that we perceive the world directly. Objects in the world around us possess features, such as size, shape, and color, which are picked up by our perceptual apparatus. Moreover, ancient and medieval philosophers believed that properties of objects, events, and actions, such as being beautiful or moral, were likewise objective facts about the world that we perceive directly. Thus, for example, people find Michelangelo’s David beautiful because it is, in fact, beautiful, and people find heroism in battle morally worthy because it is, in fact, morally worthy.

However, beginning with Galileo Galilei (1564­1642), scientists distinguished between primary and secondary sense properties (the terms are Locke’s). Primary sense properties are those that actually belong to the physical world machine: they are objective. Secondary properties are those added to experience by our sensory apparatus: they are subjective. Galileo wrote in his book The Assayer:

Whenever I conceive any material or corporeal substance I immediately … think of it as bounded, and as having this or that shape; as being large or small [and] as being in motion or at rest. … From these conditions I cannot separate such a substance by any stretch of my imagination. But that it must be white or red, bitter or sweet, noisy or silent, and of sweet or foul odor, my mind does not feel compelled to bring in as necessary accompaniments…. Hence, I think that tastes, odors, colors, and so on …reside only in the consciousness [so that] if the living creature were removed all these qualities would be wiped away and annihilated. (Cited in Smith, 1990)

The key word is consciousness. For ancient philosophers there was only one world, the real physical world with which we are in direct touch. But the concept of secondary sense properties created a new world, the inner world of consciousness, populated by mental objects (ideas) possessing sensory properties not found in objects themselves. Some of these secondary properties correspond to physical features. For example, color corresponds to different wavelengths of light to which retinal receptors respond. That color is not a primary property, however, is demonstrated by the existence of color-blind individuals, whose color perception is limited or absent. Objects are not colored, only ideas are colored. Other secondary properties, such as being beautiful or good are more troublesome, because they seem to correspond to no physical facts, but reside only in consciousness. Our modern opinion that beauty and goodness are subjective judgments informed by cultural norms is one consequence of the transformation of experience wrought by the scientific revolution.

Creating Psychology: Rene Descartes

The currents set in motion by the Renaissance and the scientific revolution came together in the work of Rene Descartes (1596-1650), who created an influential framework for thinking about mind and body fundamental to the founding of psychology. A devout reforming Catholic and working scientist, Descartes tried to reconcile his religious belief in the existence of a soul with his commitment to a mechanical view of the material universe as a clockwork machine governed by rigid mathematical laws. Although many of Descartes’s specific theses were soon rejected, his framework endured for centuries. Descartes said that humans were souls united to mechanical bodies; animals were soulless machines. The only mental function he assigned to the soul was thinking—Descartes’s famous cogito, ergo sum (“I think, therefore I exist”)—including self-awareness and language.

Descartes inherited a problem that, although rooted in Greek philosophy and medicine, had become more urgent during the scientific revolution. Humans and animals share much that is commonly called mental, for example, animals clearly perceive, learn, and remember, therefore, because animals have no souls, perception, learning, and memory must be functions of the body, not of the soul or mind. This realization led some thinkers to formulate two heresies. One placed the human soul outside the body altogether, seeing it as a divine inner light flowing from God during life and returning to him at death. The other—adopted by Renaissance naturalism—dispensed with the soul altogether, seeing humans as sophisticated animals and mind as a function of the brain.

Because both theories were inconsistent with personal immortality, Descartes was placed in a quandary. As a scientist, he accepted that animals were machines, and that therefore much of mental functioning was really the mechanical functioning of the body. As a Christian, he believed in a human soul that was spirit, not matter. Descartes’s quandary became a crisis in 1633, when the Inquisition condemned Galileo. Descartes suppressed publication of his physical work. The World, and abandoned his book on psychology, L’Homme (Man), In it, Descartes had treated human beings as machines only, investigating how far human behavior could be explained physiologically. In two philosophical works, Discourse on Method, and Meditations on First Philosophy, Descartes tried to create a philosophy that would justify his science and protect him from heresy, drawing the Cartesian picture of consciousness, mind, and brain.

Descartes’s dualism of body and soul reflected the new scientific distinction of physical and mental worlds. Descartes assumed living bodies were complex machines no different from the world machine. Animals were machines only; human beings were machines wherein dwelled the soul, the self. Descartes’s picture has been aptly termed the Cartesian theater: The soul sits inside the body and views the world as on a theater screen, a veil of ideas interposed between knowing self and known world. Within the Cartesian framework, one could adopt two attitudes toward experience. The first attitude was that of natural science. Scientists continued to think of ideas as partial reflections of the physical world. Primary properties corresponded to reality; secondary ones did not.

The notion of consciousness as populated by ideas created the second, distinctively Cartesian attitude to experience that gave rise to psychology. One could examine ideas as such, not as projections from the world outside, but as objects in the subjective world of consciousness. Descartes created the idea of stepping back from experience and reflecting on it. A good route to understanding the Cartesian theater is through modern art, which began in the nineteenth century at the same time as scientific psychology. Prior to the Impressionists, painters had mainly tried to depict persons and places as they really were. Thus, our interest in a portrait of Napoleon is discovering what he looked like. Realistic paintings embody the traditional attitude to experience; our interest lies chiefly in the object painted. not the painting. Beginning with the Impressionists, however, painters adopted a new psychological attitude, asking people to look at the canvas, not through it to the world. They tried to capture subjective experience, how things looked and felt to the painter at one moment in time. The first experimental psychologists did the same, asking observers to describe how things appeared in consciousness rather than as the observers thought them to be in reality.

Psychology was created by introspection, reflecting on the screen of consciousness. The natural scientist inspects the objective natural world of physical objects; the psychologist introspects the subjective mental world of ideas. To psychologists was given the problem of explaining whence secondary properties come. If color does not exist in the world, why and how do we see color? Descartes also made psychology important for philosophy and science. For them to pursue truth, it became vital to sort out what parts of experience were objective and what parts were subjective chimeras of consciousness.

Descartes also participated in another project central to the founding of scientific psychology, linking mind to brain. Prior to Descartes, living bodies had been seen as markedly different from nonliving things either by possession of a life-giving spirit (the Greek psuche) or by possession of special powers denied nonliving matter. Descartes rejected both views, separating the thinking soul radically from the mechanical body. He formulated the important concept of the nervous reflex, creating the image of the bodily machine as a device responding automatically to external stimuli. Conceiving of living bodies as clockwork machines was implicitly accepted by most psychologists throughout the nineteenth and early twentieth centuries, creating conceptual problems that would not begin to dissolve until recently.