Trait theory is a popular approach for studying personality; it is closely tied to the everyday concept of personality that many people hold because traits are commonly employed in everyday language and are widely understood. We will begin by defining the concept of traits and identify some of the earliest contributors to the trait approach to personality, including Hippocrates, Galen, Carl Jung, Gordon Allport, Raymond Cattell, and Hans Eysenck.
Traits as Building Blocks of Personality At its most fundamental level, a trait is a unit of analysis to describe, predict, and explain human thought, affect, and behavior. From a distance, it appears as though there are a great many terms (traits) that are used to characterize human activity, but extensive research suggests that these traits can be organized into coherent and meaningful patterns and even enveloped by a smaller number of broad trait categories, thereby simplifying the trait approach.
Hippocrates and Galen: The Ancient Greeks and Humoral Theory The earliest documented work on humoral theory dates back to ancient Greece—and the belief that the body was compromised of four basic fluids and the balance of these fluids could deter- mine behavioral and emotional tendencies (and disease susceptibility). Based originally on early writings in medicine by Hippocrates and later expanded by Galen (On the Temperaments), humoral theory focuses on blood, phlegm, black bile, and yellow bile; these are the four basic fluids (humors) that were thought to be within the human body.
According to the theory, the four humors have to be in balance to achieve and maintain health, and this likewise pre- dicted imbalances in emotion and behavior. An ideal temperament was associated with a balance of the four humors. Excessive blood (sanguine) was associated with a cheerful disposition, excessive black bile (melancholic) was associated with a sad disposition, exces- sive yellow bile (choleric) was character- ized as irritable, and too much phlegm (phlegmatic) meant an unemotional temperament.
Although contemporary personality researchers do not relate the humors to character, the descriptive terms are still employed. For example, an irritable infant is still referred to as choleric, and
the term melancholy still applies to sadness. Moreover, as we shall see when reviewing the work of Eysenck, the basic terminology for characterizing all human behavior has been somewhat con- sistent for more than 2,000 years, suggesting that there may be a core set of personality traits.
expressed by humans that have been stable throughout much of modern history. Moreover, humoral theory also established the framework for connecting traits to biological functioning, and this tradition also continues today (see especially Eysenck’s work on extraversion and research on heritability coefficients for personality).
Carl Jung’s Introduction of Introversion and Extraversion Carl Jung was first and foremost a central contributor to psychodynamic theory. However, he was also one of the first to popularize the terms introversion and extraversion, and these remain two of the most popular and widely recognized trait terms. Jung described the outward manifestation of behavior in very similar ways to modern-day psychologists. For example, extraversion meant someone who is interested in other people and things and is focused on them, whereas introver- sion meant being withdrawn and focusing on the subjective experience of the world. Although Jung did not develop a formal measure of introversion-extraversion, researchers subsequently developed a measure that was based on Jung’s typology, called the Myers Briggs Type Indicator® (MBTI®) (see Chapter 1).
Gordon Allport and the Analysis of Language One of the more enduring early contributions in trait psychology was the method of studying language as the very basis of traits. Gordon W. Allport is often considered the first trait psycholo- gist, and he was interested in classification. Allport adopted traits as his basic unit of analysis. He believed that traits are closely tied to the nervous system, and that they account for behavioral consistency across time and situations (Allport & Allport, 1921). Allport believed that a trait would predict which behavior would manifest with high frequency, with intensity, and over a wide range of situations (see also Allport, 1937).
Beginning an important tradition, Allport used Webster’s New International Dictionary and culled almost 18,000 words, each of which described some aspect of human behavior (Allport & Odbert, 1936). In adopting this methodology, Allport made the assumption that any descriptive character- istics that are important will become part of our language and that language will evolve such that single words will emerge to capture those important constructs. Thus, Allport’s theory is based on the associated meanings of words, as he thought these meanings transcend the word itself and instead speak to human nature. This approach of studying language to understand person- ality was referred to a lexical analysis, and the underlying theory was referred to as the lexical hypothesis (see also John, Angleitner, & Ostendorf, 1988). The general thesis of this work is that by understanding how different adjectives that are used to describe human behavior are related to each other, one can then understand at least two basic questions: What is the minimum num- ber of different personality traits or factors needed to capture all of the adjectives, and what are the best labels for these traits or factors? A third question that often arises focuses on how the different traits/factors relate to each other (i.e., are they independent or correlated?).