Personality Psychology.

OpeningWhat personality is.

A working definition: stable patterns of thought, feeling, and behaviour that distinguish individuals and persist across time and situations.

The discipline has, over the past century, organised itself around five competing approaches: the trait approach (the one that won most empirical battles); the psychodynamic tradition (Freud, Jung, Adler — historically influential, currently marginal in academic personality science); the humanistic approach (Rogers, Maslow); the social-cognitive approach (Bandura, Mischel); and the biological approach (twin studies, genome-wide association). Most contemporary research synthesises across these, with traits as the empirical workhorse.

This deck covers each, with particular emphasis on what has held up under scrutiny and what has not.

Chapter IAllport and the lexical hypothesis.

Gordon Allport (1937) argued that the most important individual differences will, over time, become encoded in language as common adjectives — kind, brave, lazy, anxious. If you systematically extract every adjective in a dictionary that could describe a person, factor-analyse them into clusters, you should reveal the underlying structure of personality.

Allport and Henry Odbert (1936) extracted 17,953 trait terms from Webster's Dictionary. Subsequent reductions — Cattell narrowed to 4,500, then to 16 dimensions; Tupes & Christal in 1961 found five robust factors; Norman, Goldberg, McCrae, and Costa converged on the same five through the 1960s–80s.

By the 1990s, the Five-Factor Model (FFM, OCEAN) was the empirical consensus. The lexical hypothesis was largely vindicated.

Chapter IIThe pre-Big-Five.

Raymond Cattell (1905–1998). Used factor analysis on Allport's terms to identify 16 personality factors — the basis of the 16PF questionnaire (1949), still in use. The factor structure has not held up perfectly; subsequent factor analyses on Cattell's own data find five higher-order factors.

Hans Eysenck (1916–1997). German-born British. Three-factor PEN model: Psychoticism (impulsivity, aggression), Extraversion, Neuroticism. Eysenck argued the factors had biological substrates — extraversion linked to cortical arousal, neuroticism to autonomic reactivity. The neurobiological claims have had mixed empirical support.

By the late 1980s, the field had converged on five factors, integrating Cattell's lexical work, Eysenck's biological framing, and the work of Costa, McCrae, Norman, and Goldberg. The competing structures were resolved by the consilience.

Chapter IIIOCEAN.

The empirical consensus model since the late 1980s. Each trait is a continuous dimension; everyone falls somewhere on each.

Chapter IVHEXACO.

Kibeom Lee and Michael Ashton's HEXACO model (2004) extends the Big Five with a sixth factor: Honesty-Humility. The model emerged from cross-language lexical studies in Korean, German, French, Italian, Hungarian, and others — the sixth factor recurred robustly.

Honesty-Humility captures sincerity, fairness, greed-avoidance, and modesty. Low scorers are willing to manipulate, exploit, and break rules for personal gain; high scorers are scrupulously honest and dislike privilege. The trait correlates strongly (negative) with the dark triad.

HEXACO also relabels Big Five Agreeableness as a slightly different construct (less about trust, more about temperance) and Emotionality replaces Neuroticism with a slightly different valence (more about anxiety/sentimentality, less about hostility).

HEXACO has not displaced the Big Five in the academic literature, but is increasingly used in research where dishonest behaviour is the outcome of interest (workplace cheating, white-collar crime).

Chapter VHow stable is personality?

Two questions, two answers.

Rank-order stability

How much does a person's relative position on a trait remain consistent? Quite stable. Test-retest correlations over a decade are around r = 0.6–0.7 for Big Five traits in adulthood; over 30 years, r ≈ 0.4–0.5. Higher than many critics expected, lower than absolute stability.

Mean-level change

How does the average person change as they age? Maturity principle: people on average become more agreeable, more conscientious, and less neurotic across adulthood. Roberts, Walton, and Viechtbauer's 2006 meta-analysis documented the pattern. The effect is most pronounced in young adulthood (20s and 30s).

Personality change is real but slow. Major life events (marriage, parenthood, divorce, job loss, illness) produce only modest changes on Big Five dimensions. Targeted interventions (therapy, coaching) can produce somewhat larger shifts in specific domains, especially in neuroticism (Roberts et al. 2017).

Chapter VIGenes and personality.

Behaviour-genetic studies (Bouchard's Minnesota Study of Twins Reared Apart, 1979–2000; Plomin's longitudinal work; Polderman et al.'s 2015 meta-meta-analysis of 50 years of twin studies) converge on an estimate that Big Five traits are roughly 40–55% heritable.

What "heritable" means: in the studied population, that proportion of variance can be attributed to genetic differences. It does not mean: 40% of an individual's personality is genetic. Heritability estimates rise across the lifespan as environments become more chosen and behavioural feedback loops compound (a person high in extraversion seeks out social environments that reinforce extraversion).

The genome-wide picture

Genome-wide association studies (GWAS) have identified hundreds of common variants associated with personality traits, each contributing a tiny effect. The polygenic scores derived from these now predict a few percent of variance in target outcomes — useful for research, not yet for prediction at the individual level. The missing heritability problem (the gap between twin-study heritability estimates and what GWAS can locate) remains partly unresolved.

Chapter VIIFreud and the structural model.

Sigmund Freud's structural model of personality (introduced in The Ego and the Id, 1923): id (unconscious, drive-based, pleasure-seeking), ego (executive, reality-oriented), superego (internalised moral standards). Conflicts among these systems produce anxiety, which the ego manages through defence mechanisms: repression, denial, projection, displacement, sublimation, rationalisation, reaction formation, regression, intellectualisation.

The defence-mechanism literature has had a longer afterlife than the rest of Freudian theory. George Vaillant's longitudinal Grant Study showed that mature defences (sublimation, humour, altruism) predict better outcomes across decades than primitive ones (denial, projection).

Most of Freud's specific developmental claims (psychosexual stages, the Oedipus complex as universal, repressed memory as the mechanism of neurosis) have not been empirically supported. The broader insight — much of mental life is unconscious; people defend against psychological pain — has been supported and extended by cognitive psychology and neuroscience under different terminology.

Chapter VIIIJung.

Carl Jung (1875–1961). Initially Freud's heir-apparent; broke with him in 1913 over the role of sexuality. Jung's contributions to personality:

Extraversion vs. introversion. Jung introduced the dichotomy in Psychological Types (1921). The contemporary Big Five Extraversion factor has clear lineage (though academic personality psychology treats it as a continuous dimension, not a categorical one).

Functions. Thinking, Feeling, Sensation, Intuition. Each can be directed inward or outward. The framework was elaborated into the four-letter typology used by the MBTI.

Archetypes and the collective unconscious. The shadow, the anima/animus, the wise old man, the great mother. Jung argued these were universal patterns, encoded in inherited psychic structure. Empirically untestable; not part of contemporary academic psychology; influential in literature, mythology, and Jordan-Peterson-style popular psychology.

Jung himself disliked the rigidity that subsequent typology systems imposed on his ideas. He emphasised that types were tendencies, not categories.

Chapter IXAdler & Horney.

Alfred Adler (1870–1937). Founder of Individual Psychology. Argued that personality is shaped not by sexual drive but by the striving for superiority — a compensation for childhood feelings of inferiority. The well-known concept of the inferiority complex is Adler's.

Adler emphasised social interest — the capacity to feel connected to and contribute to the wider human community — as the central marker of mental health. Birth-order theory (firstborns vs middle children vs youngest) is Adler's; the empirical evidence for birth-order effects on personality is weak (Damian & Roberts 2015; large-sample studies find effects close to zero).

Karen Horney (1885–1952). German-American. Critiqued Freud's account of female psychology, particularly penis envy. Argued that what Freud called penis envy was better understood as women's reasonable response to male social privilege. Her three styles of relating (moving toward, against, away from people) anticipate later attachment-style frameworks.

Chapter XRogers and Maslow.

Carl Rogers (1902–1987). The founder of person-centred (client-centred) therapy. Personality, in Rogers's account, is organised around the self-concept. Psychological distress arises from incongruence between one's self-concept and one's actual experience. The therapist's role is to provide unconditional positive regard, congruence (genuineness), and empathic understanding — three "core conditions" that, Rogers argued, were sufficient for therapeutic change.

Rogers's emphasis on the therapeutic relationship has been substantially supported by empirical research on therapeutic alliance (Bordin 1979 onward). The "necessary and sufficient" claim for the three core conditions has been weakened — most contemporary therapy traditions consider them necessary but not sufficient.

Abraham Maslow (1908–1970). Hierarchy of needs (1943). Self-actualisation as the apex. The list of self-actualised characteristics — reality-perception, problem-centeredness, spontaneity, peak experiences, autonomy, ethical-mindedness — was derived from biographical study of figures Maslow admired (Eleanor Roosevelt, Lincoln, Einstein), not from controlled research.

Chapter XISocial-cognitive personality.

Bandura's reciprocal determinism: personality, environment, and behaviour mutually influence each other in a continuous loop. The framework rejected both pure trait determinism and pure environmental determinism.

Self-efficacy

Bandura's most-influential concept: a person's belief in their capacity to execute behaviours necessary to produce specific outcomes. Self-efficacy beliefs predict effort, persistence, and choice of activity better than objective skill in many domains. Self-efficacy is not a generic trait — it is task-specific and built through four sources: mastery experience, vicarious experience, social persuasion, physiological/emotional states.

Beyond Bandura

Walter Mischel's Personality and Assessment (1968) — the famous attack on trait psychology, arguing that situations were better predictors of behaviour than traits. Mischel's Cognitive-Affective Personality System (CAPS) proposed that personality consisted of stable patterns of if-situation, then-behaviour contingencies.

The contemporary integration: traits and situations both matter. Stable patterns of behaviour-across-situations are real (the trait view), and the situations that elicit them are real (the social-cognitive view).

Chapter XIIThe person-situation debate.

Walter Mischel's Personality and Assessment (1968) argued that the cross-situational consistency of behaviour was much lower than personality theorists assumed — typical correlations of behaviour across situations hovered around r = 0.2–0.3 (the "personality coefficient"). The implication: trait constructs were of limited predictive value.

The resolution

Three things stabilised the debate. First, aggregation: traits predict aggregated behaviour across many situations far better than they predict any single act (Epstein 1979). Second, relevance: traits predict best in trait-relevant situations. Third, consensus: traits predict aggregated perceptions by knowledgeable others very well.

The contemporary view: behaviour at a single moment is largely situational; behaviour aggregated over many moments is largely traited. Both views are correct at their respective levels of analysis. Mischel himself (in CAPS, 1995) integrated his earlier critique into a synthesis that preserved trait-like consistency through stable if-then patterns.

Chapter XIIISelf-determination theory.

Edward Deci and Richard Ryan's Self-Determination Theory (SDT) proposes three innate psychological needs whose satisfaction predicts well-being and growth across cultures.

Autonomy. The experience of choosing one's actions, of acting in alignment with one's values. Threatened by surveillance, deadlines, contingent rewards.

Competence. The experience of being effective in one's environment. Threatened by overly easy or overly difficult tasks, by negative feedback divorced from improvement information.

Relatedness. The experience of being connected to others and feeling cared for. Threatened by social rejection, isolation, and conditional regard.

The intrinsic-extrinsic distinction

SDT's most-tested empirical claim: extrinsic rewards can undermine intrinsic motivation when applied to activities that were already intrinsically rewarding. The Deci-Ryan-Koestner 1999 meta-analysis (128 studies) supported this. Caveat: rewards can also be experienced as informational rather than controlling, and in those cases do not undermine intrinsic motivation.

SDT now structures research in education, sport, work motivation, and health behaviour.

Chapter XIVThe dark triad.

Three socially aversive personality traits that share a common core (low Honesty-Humility, low Agreeableness, callous self-interest):

Narcissism. Grandiosity, entitlement, need for admiration. Distinguishable into grandiose narcissism (overt, self-aggrandising) and vulnerable narcissism (covert, self-doubting, hypersensitive to criticism). The clinical diagnosis (Narcissistic Personality Disorder) is rare; subclinical narcissism is common.

Machiavellianism. Strategic manipulation, cynical view of human nature, willingness to deceive for personal gain. Operationalised through Christie & Geis's Mach IV scale (1970).

Psychopathy. Callous-unemotional traits, impulsive antisocial behaviour, lack of remorse. Measured by the Hare Psychopathy Checklist-Revised (PCL-R) in clinical/forensic settings; the Self-Report Psychopathy Scale (SRP) in general samples.

The dark tetrad

Adds sadism — taking pleasure in others' suffering. The tetrad better predicts online trolling, internet aggression, and certain forms of workplace exploitation than the triad alone.

Chapter XVPersonality disorders, dimensionally.

The DSM-5 retained the categorical 10-disorder model (paranoid, schizoid, schizotypal, antisocial, borderline, histrionic, narcissistic, avoidant, dependent, obsessive-compulsive) but added a dimensional Alternative Model for Personality Disorders (AMPD) in Section III. The ICD-11 has fully shifted to a dimensional model with five trait domains.

The dimensional model treats personality pathology as the extreme end of normal personality dimensions plus impairment in self- and interpersonal functioning. The five trait domains in ICD-11: Negative Affectivity, Detachment, Dissociality, Disinhibition, Anankastia. These map approximately onto Big Five traits.

The dimensional model has stronger empirical support than the categorical model, but the categorical labels have entrenched clinical and legal use. The shift is happening slowly.

Chapter XVIWhy personality scientists don't use the MBTI.

The Myers-Briggs Type Indicator (MBTI) was developed by Isabel Myers and Katharine Briggs in the 1940s, based on a popularised reading of Jung. It produces a four-letter type from binary preferences: Introversion/Extraversion, Sensing/Intuition, Thinking/Feeling, Judging/Perceiving. Sixteen types result.

The technical problems

1. Bimodality. The MBTI assumes traits are categorical (you're an I or an E). The empirical distributions are normal, not bimodal — most people score near the middle on each dimension and are classified arbitrarily.

2. Test-retest reliability. Around 50% of test-takers receive a different type on retest within five weeks. For a categorical measure, that is essentially random.

3. Predictive validity. MBTI types do not predict important outcomes (job performance, leadership, relationship satisfaction) better than chance, while Big Five traits do.

4. Construct validity. The four MBTI dimensions don't independently capture variance the Big Five does not — Extraversion is roughly equivalent; the others map weakly to Openness and Agreeableness.

The MBTI persists because it is fun and feels meaningful. The empirical case against it is overwhelming. If you want a scientifically grounded version of similar self-knowledge, take a Big Five test — the IPIP-NEO is free online.

Chapter XVIIHow personality is measured.

Three primary approaches:

Self-report inventories

The dominant method. Subjects rate themselves on series of statements ("I see myself as someone who is talkative" — strongly disagree to strongly agree). The major Big Five inventories: NEO-PI-R, BFI-2, IPIP-NEO, HEXACO-PI-R. The MMPI (Minnesota Multiphasic Personality Inventory) is the most-used clinical inventory.

Informant report

Knowledgeable others (spouses, close friends, parents) rate the target. Informant reports correlate ~0.5 with self-reports. Combining self- and informant- reports yields more accurate measurement than either alone.

Behavioural and life-data

Direct observation of behaviour; analysis of life-history data (academic records, criminal records, residential moves, financial decisions). Increasingly: digital footprints — Facebook likes, Twitter language, smartphone-sensor data — predict Big Five traits at correlations that approach informant accuracy.

Chapter XVIIIWhat has held up.

Findings strongly supported by replication: the five-factor structure of personality across languages and cultures; the heritability of Big Five traits at roughly 40–55%; the maturity principle (people on average become more agreeable, conscientious, and emotionally stable across adulthood); the predictive validity of Conscientiousness for life outcomes; the relationship between personality and psychopathology; the dark triad's structural validity.

Findings substantially weakened: the strong claim of major personality change from any specific intervention (effect sizes are smaller than coaching-industry claims); birth-order effects on personality (essentially null in well-powered studies); the strong-form claim that personality is essentially fixed by age 30 (Costa & McCrae walked this back themselves); some specific MBTI-style category claims; the predictive validity of certain handwriting-, astrology-, and Enneagram-based assessments.

Open questions: the precise mechanisms by which genes shape traits; the developmental timeline of trait emergence; cross-cultural variability in trait structure; the role of culture-specific traits not captured by the Big Five.