Definition
Personality refers to the enduring patterns of thinking, feeling, and behaving that characterize an individual across situations and over time. It is the relatively stable part of a person — the disposition that persists when momentary mood and context change. Psychology has produced multiple competing models for describing personality, each emphasizing different units of analysis: traits, types, motives, defenses, narratives, and learned behavior patterns.
The dominant contemporary framework is the Big Five (or Five Factor Model), which holds that most variation in personality across individuals can be captured by five broad dimensions: openness to experience, conscientiousness, extraversion, agreeableness, and neuroticism. Earlier frameworks include Eysenck's three-factor model, Cattell's sixteen factors, and the Myers-Briggs Type Indicator (popular but psychometrically weak).
Why it matters
How it works
The Big Five emerged from decades of factor-analytic research on the language people use to describe one another. The lexical hypothesis holds that any trait important enough to matter in social life will be encoded in everyday language, so analyzing the structure of personality-descriptive words yields the structure of personality itself. Across multiple languages and cultures, the same five broad factors repeatedly emerge from this analysis. Each factor is itself a hierarchy: extraversion, for example, decomposes into more specific facets like sociability, assertiveness, and positive emotionality.
Personality is shaped by both genetic and environmental factors, with twin studies suggesting that roughly 40-50% of the variance in trait scores is heritable. The remainder reflects life experience, but not in the way intuition suggests: most of the environmental variance is non-shared — the parts of experience that siblings raised together do not have in common. This finding shifted developmental psychology away from broad family-environment explanations toward individual experiences, peer groups, and the unique ways each person constructs meaning from their circumstances.