The Science of Human Nature

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The Science of Human Nature


The revival of science during the European Renaissance included a renewed interest in the workings of the human mind. In the eighteenth century, there were two main schools of thought in the field that became known as "psychology": associationism, or empiricism, and the doctrine of mental faculties. Associationism was championed by such scientists as George Berkeley, David Hume, and David Hartley. This theory held that an individual developed mentally as simple sensations and ideas were associated by the mind into more complex concepts. The opposing theory was the doctrine of mental faculties. Immanuel Kant was among its chief advocates. The doctrine of mental faculties compartmentalized the mind into intellect, emotions, will and other attributes, each of which functioned more or less independently. Both concepts have contributed to our understanding of human nature.


Psychology as an experimental science did not arise until the late nineteenth century. However, since earliest times humans have been speculating about the relationship between themselves and their environment.

Since so many things happened that they could not understand, prescientific humans ascribed them to hidden causes such as deities or spirits. These deities and spirits were thought to control the weather, the behavior of animals, and other natural forces. They could also be invoked to explain the puzzling actions of other people. This belief system is called animism.

Animism contributed to the idea that the ideas and sensations we perceive inside ourselves, which we think of as our consciousness, are also the product of a "spirit," called the mind or the soul. After many thousands of years, we have yet to completely understand the nature of consciousness.

The ancient Greek philosophers were interested in the relationship between the mind and the body. Plato (427-347 b.c.) recognized two types of ideas, those that were products of perception through the senses, and those that were innate and arose in the soul. Plato, by emphasizing rational deduction, encouraged the development of philosophy. Aristotle (384-322 b.c.), by contrast, stressed direct observation leading to the association of ideas formed by previous perception. His methods and observations of the natural world contributed to the development of empirical science.

During the Middle Ages, the promotion and enforcement of religious doctrine was deemed more important than scientific advancement, and little progress beyond Aristotle was made in most areas of science for about 1,800 years after his death. The intellectual boundaries were stretched during the Renaissance, and a great flowering of the arts, geographical exploration, and science began. This was the age of scientists such as Nicolas Copernicus (1473-1543) and Galileo Galilei (1564-1642) in astronomy, and William Harvey (1578-1657) in physiology. As these scientists relied on observation and experiment to prove their theories, philosophers of the mind began examining their own ideas as well.

René Descartes (1596-1650) dealt with the mind-body problem by compartmentalizing it. The body, he reasoned, works in a mechanistic fashion. The mind, on the other hand, consisting of everything that is not physical and mechanistic, he regarded as beyond scientific inquiry. Descartes envisioned the mind and body interacting at a single point. This dualistic or Cartesian concept of the mind-body relationship continues to influence our ideas today.

There were several other theories discussed by seventeenth century philosophers. One was occasionalism, in which God intervenes between mind and body as circumstances require. Double aspect, a theory of Baruch Spinoza (1632-1677) viewed mind and body as two attributes of the same substance. In psychophysical parallelism, the mind and body do not interact, but coordinate in their actions because they are influenced by the same external phenomena.


Among those who adopted the theory of psychophysical parallelism were a group of British philosophers known as associationists, or empiricists. The founders of this school of thought were Thomas Hobbes (1588-1679) and John Locke (1632-1704). They believed that the mind developed through experience, as simple ideas and simple sensations were synthesized into larger concepts. During the eighteenth century, Hobbes and Locke were followed by a number of philosopher-psychologists who advanced some form of associationism, without necessarily agreeing on the source of the ideas that the mind associated.

George Berkeley (1685-1753) was an Anglican bishop who tried to reconcile science and Christianity. He was a philosophical idealist, believing that physical things existed only as ideas or sensations in the mind. Considering how lukewarm water could feel cold to someone stepping out of a warm bath, and hot to someone coming in from the cold, Berkeley concluded that the water had no independent existence at all. If physical things existed only when being observed, and yet we believe them to continue to exist even when we are not observing them ourselves, some universally present mind, that is, God, must be observing them all the time.

Berkeley stressed the use of logical deduction in perception. For example, since the retina is two-dimensional, he reasoned that the human sense of sight could not visualize three-dimensional objects directly. He proposed that, rather than being present at birth, the ability to perceive depth was based on the association of certain visual images with the sense of touch. Modern psychologists agree that the ability to interpret some spatial cues does seem to be learned. However, other related abilities, such as detecting size differences, appear to be innate.

David Hartley (1705-1757) was the first to correlate physiological activity with associationism. Isaac Newton (1642-1727) had written that the vibration of light might cause analogous vibrations in the eye and brain, thereby producing the sensations of vision. Hartley advanced the theory that all human senses were caused by tiny vibrations in the nerves. He proposed further that learning was the result of the association of repetitive juxtapositions of these sensory vibrations with ideas formed in the mind. He believed that the mind was immortal, encoded with accumulated habits and patterns of thinking that persisted after death and, if malevolent, continued to torment the deceased.

Hartley, who was fairly orthodox in his religious views, resisted the idea that his theory had mechanistic implications for the development of the human mind. However, by proposing a specific physical mechanism for learning and adaptation, he provided a secular framework around which to discuss and understand human behavior.

David Hume (1711-1776) distinguished between impressions, which were felt, and ideas, which were thought. Ideas were simply "faint images," except when sleep, fever or insanity made ideas spring into the mind with such violence that they approached the force of impressions. Simple impressions, such as the color red, evoked correspondingly simple ideas. However, complex impressions and complex ideas did not necessarily correspond.

Impressions, Hume went on to propose, were of two kinds, sensation and reflection. He relegated further discussion of sensation to scientists, but was interested in reflection, which followed the formation of ideas about the sensations previously experienced, coupled with ideas about the pleasure or pain they may have caused. Impressions of "desire and aversion, hope and fear" were the result.

Hume's view of the way the mind processed ideas and impressions involved three principles: resemblance, proximity in space and time, and, most importantly, cause-and-effect. The mind tends to interpret an event that preceded another as its cause, and forms habits of expectation accordingly. However, Hume believed that it was impossible to actually prove causality. In fact Hume distrusted philosophical proofs in general, believing that knowledge was based strictly on the experience of the individual's consciousness. Thus, he argued, it was impossible to prove causality, the existence or nonexistence of God, or the existence of the physical world outside the self.

The school of thought opposed to associationism was the doctrine of mental faculties. This theory classified the mind into several properties, such as reasoning, memory, emotions and will, each of which operated independently. Among its proponents was the German philosopher Immanuel Kant (1724-1804).

Kant viewed the idealism of Berkeley as coarse and simplistic, and developed what he called transcendental idealism. He rejected the concept of the mind and physical objects as separate things. Instead, he proposed that the mind is involved in experiencing physical objects by organizing its experiences into patterns. Since everything may be arranged into the mind's patterns, we can have knowledge of that which we have not actually experienced.

The psychology of mental faculties led to the pseudo-science of phrenology, in which areas on the surface of the skull were identified with particular faculties. Bumps or hollows on the skull were interpreted as indicating the level of development of the associated faculties. A more useful effect of the doctrine of mental faculties was to spark the re-examination of textbooks and teaching methods used in schools. New materials were developed with the goal of "exercising the faculties."


Further Reading

Allen, Richard C. David Hartley on Human Nature. Ithaca: State University of New York, 1999.

Buckingham, Hugh W. and Stanley Finger. "David Hartley's Psychobiological Associationism and the Legacy of Aristotle." Journal of the History of the Neurosciences vol. 6 no. 1 (1997): 21-37.

Stack, George J. Berkeley's Analysis of Perception. New York: Peter Lang Publishing, 1991.