Each of us tries to understand our own and other people’s personalities. I believe we're better at "reading" someone’s personality if we understand what personality is. But what is it?

In a recent Psychology Today post, I described personality as a person’s global psychological system: the organization of a person's motives and emotions, thoughts, self-awareness and self-control, and plans for action.

The day after my post appeared, I received an e-mail from a colleague who said he saw the discipline of personality as a branch of psychology, “that examines individual differences in how basic processes function.” Does understanding personality involve examining how one person differs from another?

More than a few textbooks that cover Introductory Psychology and Social Psychology focus on the idea that personality psychologists study individual differences. Personality psychologists themselves, however, are in widespread agreement that they examine a system of mental functions: motives, emotions, self-control and the like.

Thinking about personality as a system is central to understanding the people we encounter in our everyday lives. If we look only at individual differences between people, such as that one person is sociable while another is withdrawn, we will be able to make some important predictions about a person. We might expect that our sociable acquaintance would introduce us to his friend if we asked, because social people like making connections. In this case, we are using an individual differences approach that works...to a point.

I believe that we can better understand how people behave if we can understand how personality itself is organized. For example, our expectation of a good introduction from our sociable acquaintance might change if we took a more global, systems view of his mental life. We might reflect on the fact that our acquaintance, though sociable, is also a disagreeable person who habitually criticizes others. We might well wonder if his disagreeableness would affect any introduction he might make for us--whether he might say unkind things about us to the person we hoped to meet, for example. This understanding may help us to evaluate whether we really want to risk asking for the introduction from this particular person. In other words, our ability to understand motives, traits, and other mental functions together helps us to more accurately forecast another person's behavior. That's one of the advantages of a systems viewpoint.

Historically, the discipline of personality psychology has focused on the way the parts of our mental lives work together. Some of the early practitioners of the field including Sigmund Freud, Carl Jung, Gordon Allport, Henry Murray and other “grand theorists” all viewed personality as a system. In Sigmund Freud’s well-known (but now historical) formulation, we each possess an id, ego, and superego, where the id represented our animal instincts, the ego, our rationality, and the superego, our conscience and ideals. Freud emphasized these universal aspects of being human—ditto for Jung, Allport and Murray. Of course, Freud and the others were also interested in individual differences. But their primary focus on an individual’s overall mental organization is why textbooks in personality psychology almost invariably define personality as the study of a global system of psychological qualities.

The scientific study of individual differences had a distinct and separate beginning. Interest in such differences evolved not within the discipline of personality psychology but in the field originally labeled “Differential Psychology.” John P.  Foley and Anne Anastasi published one of the primary textbooks used in this field. In it, they combined discussions of psychological tests with an examination of how the tests could be used to distinguish differences among individuals and among groups of people: How the genius differed from the intellectually-challenged, the criminal from the law-abiding citizen, men from women, and one national or ethnic group from one another. 

Shortly after the publication of that textbook, Anastasi wrote another one titled "Psychological Testing,” which defined a new subspecialty focused on psychological assessment. This created a new field of testing that split off, at least partially, from the differential psychology movement.

Work in Differential Psychology continues today, carried on, for example, by the International Society for the Study of Individual Differences. The mission of that society, as stated on its website, is:

"…to foster research on individual differences in temperament, intelligence, attitudes, and abilities. The aim of the society is to investigate the major dimensions of individual differences…”

But the Society does not regard itself as allied in any particular way to personality psychology. In the same mission statement the members of the Society say that their study of temperament, intellectual and attitudinal traits shall occur

“…in the context of experimental, physiological, pharmacological, clinical, medical, genetical, statistical and social psychology." (from the website; retrieved December, 13, 2013).

Using this short history as a backdrop, I will complete my argument that personality psychology is the study of the personality system and not of individual differences with a summary of the key points that support this viewpoint:

Reason 1: The mission of personality psychologists, since the inception of the field, has been to understand how the parts of personality function together as a system.

Reason 2: People who work within the field of personality (almost) uniformly define their discipline as the study of the psychological system, both in journal articles and textbooks.

Reason 3: Although it is true that authors of Introductory Psychology and Social Psychology textbooks sometimes define personality psychology as the study of individual differences, people working competently within their own scientific discipline ought to know best what they study and should be allowed to define their field as they see it.

Reason 4: Personality psychologists focus on discovering the key parts of personality, and how the parts work together to affect an individual’s life outcomes. Psychologists discover the elements of personality in part by studying individual differences, but their ultimate goal is a description of overall personality.

For example, personality psychologists might study individual differences in extraversion-introversion, discovering that some people are highly extraverted and others highly introverted. They are interested as well in the consequences of extraversion (e.g., Do introverts perform better in some occupations than extraverts?) When all is said and done, these psychologists’ purpose is to discover how personality and its parts work. Learning about extraversion-introversion is a means to an end of understanding how psychological systems interact—studying an individual difference is an important method to be sure, but one that shouldn’t be mistaken for the end itself.

Reason 5: There exists a field of “Individual Differences” (originally“Differential Psychology”) with a long history independent of personality psychology. The practitioners in this field regard their work as pertaining to experimental psychology, neuropsychology, clinical psychology, social and developmental psychology and, of course, to personality psychology. That said, these are distinct fields.

Reason 6: The study of individual differences is as much a part of social and developmental psychology as it is of personality psychology.

Social psychologists study differences in people’s attitudes. Educational psychologists study the differences in students’ classroom performance, and developmental psychologists study individual differences in temperament, parenting, and other qualities. For that reason, “individual differences” fails as a definition, or even a distinguishing feature, of personality psychology.

Reason 7: A field—personality psychology—that examines the high-level integration of the parts of our psychology is needed. How else could we ever identify the most important aspects of our psychological beings?  This field is necessary so that we can understand how the key aspects of who we are fit together and function. Doing so enables us to understand how we and the people around us act. Personality psychology enables us to see the many qualities we share in common with others, as well as the differences among us that serve to provide us with the distinctive features of our mental lives.


For a list of examples of how personality psychologists define their field as the study of the mental system, and for examples of how psychologists in other fields often focus on the individual differences aspects of personality, see Mayer, J. D. (Spring, 2007). Asserting the definition of personality psychology. P: The Online Newsletter for Personality Science. Issue 1. Online here and  here (the original; scroll down the page to see).

© Copyright 2013 John D. Mayer

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