Lexical hypothesis

The Lexical Hypothesis (also the Fundamental Lexical Hypothesis, Lexical Approach, or Sedimentation Hypothesis ) is one of the most important and widely-used guiding scientific theories in personality psychology. Despite some variation in its definition and application, the Lexical Hypothesis is generally defined by two postulates. The first states that those personality characteristics that are most important in peoples' lives will eventually become a part of their language. The second follows from the first, stating that more important personality characteristics are more likely to be encoded into language as a single word. With origins in the late-19th century, use of the Lexical Hypothesis began to flourish in English and German psychology in the early 20th century. The Lexical Hypothesis is the foundation for the HEXACO model of personality structure and the 16PF Questionnaire and has been used to study the structure of personality traits in a number of cultural and linguistic settings.

Early estimates
Sir Francis Galton was one of the first scientists to apply the Lexical Hypothesis to the study of personality, stating:

"I tried to gain an idea of the number of the more conspicuous aspects of the character by counting in an appropriate dictionary the words used to express them... I examined many pages of its index here and there as samples of the whole, and estimated that it contained fully one thousand words expressive of character, each of which has a separate shade of meaning, while each shares a large part of its meaning with some of the rest."

- Francis Galton

Despite Galton's early ventures into the lexical study of personality, over two decades passed before English-language scholars continued his work. A 1910 study by G. E. Partridge listed approximately 750 English adjectives used to describe mental states, while a 1926 study of Webster's New International Dictionary by M. L. Perkins provided an estimate of 3,000 such terms. These early explorations and estimates were not limited to the English-speaking world, with philosopher and psychologist Ludwig Klages stating in 1929 that the German language contains approximately 4,000 words to describe inner states.

Allport & Odbert
Nearly half a century after Galton first investigated the Lexical Hypothesis, Franziska Baumgarten published the first psycholexical classification of personality-descriptive terms. Using dictionaries and characterology publications, Baumgarten identified 1,093 separate terms in the German language used in the description of personality and mental states. Although this figure is similar in size to the German and English estimates offered by earlier researchers, Gordon Allport and Henry S. Odbert revealed this to be a severe underestimate in a 1936 study. Similar to the earlier work of M. L. Perkins, they used Webster's New International Dictionary as their source. From this list of approximately 400,000 words, Allport and Odbert identified 17,953 unique terms used to describe personality or behavior.

This is one of the most influential psycholexical studies in the history of trait psychology. Not only was it the longest, most exhaustive list of personality-descriptive words at the time, it was also one of the earliest attempts at classifying English-language terms with the use of psychological principles. Using their list of nearly 18,000 terms, Allport and Odbert separated these into four categories or "columns":


 * Column I: This group contains 4,504 terms that describe or are related to personality traits. Being the most important of the four columns to Allport and Odbert and future psychologists, its terms most closely relate to those used by modern personality psychologists (e.g., aggressive, introverted, sociable). Allport and Odbert suggested that this column represented a minimum rather than final list of trait terms. Because of this, they recommended that other researchers consult the remaining three columns in their studies.


 * Column II: In contrast with the more stable dispositions described by terms in Column I, this group includes terms describing present states, attitudes, emotions, and moods (e.g., rejoicing, frantic). Reflecting this focus on temporary states, present participles represent the majority of the 4,541 terms in Column II.


 * Column III: The largest of the four groups, Column III contains 5,226 words related to social evaluations of an individual's character (e.g., worthy, insignificant). Unlike the previous two columns, this group does not refer to internal psychological attributes of a person. As such, Allport and Odbert acknowledged that Column III did not meet their definition of trait-related terms. Predating the person-situation debate by over 30 years, Allport and Odbert included this group to appease researchers in social psychology, sociology, and ethics.


 * Column IV: The last of Allport and Odbert's four columns contained 3,682 words. Called the "miscellaneous column" by the authors, Column IV contains important personality-descriptive terms that did not fit into the other three columns. Allport and Odbert offered potential subgroups for terms describing behaviors (e.g., pampered, crazed), physical qualities associated with psychological traits (e.g., lean, roly-poly), and talents or abilities (e.g., gifted, prolific). However, they noted that these subdivisions were not necessarily accurate, as: (i) innumerable subgroups were possible, (ii) these subgroups would not incorporate all of the miscellaneous terms, and (iii) further editing might reveal that these terms do fit into the other three columns.

Allport and Odbert did not present these four columns as representing orthogonal concepts. Many of their nearly 18,000 terms could have been differently classified or placed into multiple categories, particularly those in Columns I and II. Although the authors attempted to remedy this with the aid of three outside editors, the average level of agreement between these independent reviewers was approximately 47%. Noting that each outside judge seemed to have a preferred column, the authors decided to present the classifications performed by Odbert. Rather than try to rationalize this decision, Allport and Odbert presented the results of their study as somewhat arbitrary and unfinished.

Warren Norman
Throughout the 1940s, researchers such as Raymond Cattell and Donald Fiske used factor analysis to explore the overarching structure of the trait terms in Allport and Odbert's Column I. Rather than rely on the factors obtained by these researchers, Warren Norman conducted an independent analysis of Allport and Odbert's terms in 1963. Despite finding a five-factor structure similar to Fiske's, Norman decided to return to Allport and Odbert's original list to create a more precise and better-structured taxonomy of terms. Using the 1961 edition of Webster's International Dictionary, Norman added relevant terms and removed those from Allport and Odbert's list that were no longer in use. This resulted in a source list of approximately 40,000 potential trait-descriptive terms. Using this list, Norman then removed terms that were deemed archaic or obsolete, solely evaluative, overly obscure, dialect-specific, loosely related to personality, and purely physical. By doing so, Norman reduced his original list to 2,797 unique trait-descriptive terms. Norman's work would eventually serve as the basis for Dean Peabody and Lewis Goldberg's explorations of the Big Five personality traits.

Philosophy
Concepts similar to the lexical hypothesis are at the root of ordinary language philosophy. Similar to the use of the Lexical Hypothesis to understand personality, ordinary language philosophers propose that philosophical problems can be solved or better understood through an exploration of everyday language. In his essay "A Plea for Excuses," J. L. Austin cited three main justifications for this approach: words are tools, words are not only facts or things, and commonly used words "embod[y] all the distinctions men have found worth drawing...we are using a sharpened awareness of words to sharpen our perception of, though not as the final arbiter of, the phenomena."

Criticism
Despite its widespread use in the study of personality, the Lexical Hypothesis has been challenged for a number of reasons. The following list describes some of the major critiques levelled against the Lexical Hypothesis and personality models founded on psycholexical studies.
 * Many traits of psychological importance are too complex to be encoded into single terms or used in everyday language. In fact, an entire text may be the only way to accurately capture and reflect some important personality characteristics.
 * Laypeople use personality-descriptive terms in an ambiguous manner. Similarly, many of the terms used in psycholexical studies are too ambiguous to be useful in a psychological context.
 * The Lexical Hypothesis relies on terms that were not developed by experts. As such, any models developed with the Lexical Hypothesis reflect lay perceptions rather than expert psychological knowledge.
 * Language accounts for a minority of communication and is inadequate to describe much of human experience.
 * The mechanisms that led to the development of personality lexicons are poorly understood.
 * Personality-descriptive terms change over time and differ in meaning across dialects, languages, and cultures.
 * The methods used to test the Lexical Hypothesis are unscientific.
 * Personality-descriptive language is too broad to be captured with a single word class, yet psycholexical studies of personality largely rely on adjectives.