Hans Jürgen Eysenck was born March 4, 1916 in Berlin, Germany. In 1940, he received his Ph.D. in Psychology from the University of London. In addition to 75 books, he has authored more than 700 articles. Despite retiring in 1983, he continued writing until his death on September 4, 1997. The most cited living psychologist before he passed away in 1997, he was also the third most cited psychologist of all time after Freud and Piaget. Eysenck developed a very influential theory of personality traits, which has successfully infiltrated the public mindset when it comes to how we think about personality in the contemporary world.  

Eysenck’s theories are primarily based on physiology and genetics.  Despite being a behaviorist who considers learned habits important, he believes that personality differences are a result of our genetics.  His primary interest is in what is known as temperament. Eysenck is also a research psychologist.  In his analysis, he uses the statistical technique known as factor analysis.  The technique identifies a number of dimensions in large amounts of data.  Suppose, for instance, you give a large number of people a long list of adjectives and ask them to rate themselves on those, you have the raw material for factor analysis.  

According to Eysenck , “Personality is the sum-total of the actual or potential behavior-patterns of the organism, as determined by heredity and environment it originates and develops through the functional interaction of the four main sectors into which these behavior-patterns are organized”. For Eysenck, personality consists of acts and dispositions organized in a hierarchical fashion in terms of their level of generality. The cognitive sector (intelligence), the conative sector (character), the affective sector (temperament), and the somatic sector (constitution).


  • Much of the personality is genetically determined.
  • There’s a biological basis of personality.
  • It’s based on factor analysis (study multiple variables and club common variables intactor- advanced statistical technique).


Specific responses to different stimuli become habitual responses over a time period. These different habits become traits that are difficult to modify. These similar traits clubbed become super factor or type of personality (e.g., introversion). Hans Eysenck based his two-factor theory on these ideas. For this, he analyzed the responses people gave to personality questionnaires. As part of the factorial analysis, Eyesenck used statistical data reduction and agglutination. In this case, he used this technique to reduce behaviors to a series of factors with common attributes: the super factors. Each set of factors is grouped under one dimension.

According to Eysenck, the three independent dimensions of personality are Psychoticism (P), Extraversion (E), and Neuroticism (N), which is why it’s called the PEN model. In his view, these three super factors are adequate descriptors of personality.  

  • Specific response : sp1, sp2, sp3
  • Habitual response : H1, H2, H3 •Traits : T1, T2, T3
  • Super factor/ type of personality

3-Dimensional structure of personality: (PEN Model)

Based on factor analysis, Eysenck (1947, 1966) identified three factors of personality: extroversion, neuroticism, and psychoticism. Eysenck Theory factors have a bipolar dimension, meaning each has a direct opposition:  

Extroversion vs. Introversion: People with higher scores in extraversion have greater traits of sociability, impulsiveness, lack of inhibitions, vitality, optimism, and ingenuity. On the other hand, the more introverted people are generally more tranquil, passive, are less social, and more pessimistic. However, this personality theory considers that the main difference between the two factors is physiological. It’s based on the level of cortical arousal.

Neuroticism vs. Emotional Stability: Eysenck understands neuroticism as the highest degree of emotional instability. Using this dimension, Eyesenck explains why some people are more likely than others to suffer anxiety, hysteria, depression, or obsession. According to him, neurotic people exhibit exaggerated reactions more often and find it difficult to rediscover a normal emotional level. At the other extreme of the dimension, they are emotionally stable, calm, reasonable people who have a high degree of self-control.  

Psychoticism vs. Impulse control: The level of a person’s psychoticism reflects their vulnerability to impulsiveness, aggressiveness, and a lack of empathy. People with these characteristics are often insensitive, antisocial, violent, aggressive, and extravagant. Psychoticism is a trait that suggests a predisposition to issues such as psychosis. Whereas, people who score low are conventional, interpersonal active, and show empathy. There is no inverse or opposite extreme to psychoticism, as there are for the other two dimensions. In fact, psychoticism occurs at many levels in individuals.  


“Biological causes act in such a way as to predispose an individual in certain ways to stimulation; this stimulation may or may not occur, depending on circumstances which are entirely under environmental control”

– Eysenck, 1997

Biological Basis of Personality types results from differences in central nervous system (CNS) functioning. Implications are on :

  • Genetic basis of personality
  • Relatively stable & unchanging
  • The environment interacts with biological predispositions

For introversion/extroversion:

ARAS (Ascending Reticular Activation System): Responsible for arousal level (motivation, attention, active, attentive) nuclei move in down to.

Cortical excitation and inhibition: Introverts have ARAS more active and cortical activity (frontal cortex) shows great activity. Extroverts ARAS is less activated, the frontal lobe has lower activity. Have to seek stimulation from outside because it lacks inside the brain.

For neuroticism :

Hypothalamus and limbic system: Responsible for an emotional reaction. For high neuroticism, the hypothalamus and limbic system are hyperactive.

Autonomous Nervous System: Responsible for the stress reaction. The sympathetic Nervous System gets activated in stress. For high neuroticism, ANS is highly active.


  • Used in psychometric testing.
  • Eysenck’s Personality Questionnaire (EPQ) has 90 items in yes/no, used for 60 yrs and above, which measures 3 dimensions (E-I, N, P).
  • It has a lie scale (score is above 7 then it’s discarded).
  • Recent latest version is EPQ-R.
  • It can be used in non-clinical settings as well.
  • Junior EPQ (7-15 yrs), 81 items, yes/ no responses format, and the lie scale.


  • It has been supported by sufficient empirical evidence.
  • This theory is easy to understand and has a layman appeal.
  • Finds application in psychometric testing.
  • It’s one of the 1st scientific attempt at providing biological basis of personality.
  • It doesn’t cover other important factors like openness to experience etc which is covered by recent theories.
  • This theory overemphasis the role of genetics.

Share with others

Leave a Reply

Your email address will not be published. Required fields are marked *