Nomothetic and Idiographic: Two Approaches to Personality
The Nomothetic and Idiographic approaches tackle Personality Psychology from opposing angles. Personality psychologists study something that is supposedly unique to each of us, yet also something we all have. So is Personality Psychology the psychological equivalent of studying fingerprints?
Psychologists tend to fall into one of two camps when approaching personality: idiographic and nomothetic.
Idiographic Personality Psychology
The idiographic approach to personality suggests that we each possess a unique psychological structure. Certain traits, or combinations of traits, might be held by just one person, and therefore it is impossible to compare people like for like. This approach nestles within the study of individual differences and therefore relies on Case Study research. However, solely identifying and describing a personality characteristic is not the same as explaining it, which can be a challenge for idiosyncratic researchers due to the small sample sizes (of one 'participant').
Nomothetic Personality Psychology
The nomothetic approach looks for similarities between individuals. What is it that makes us (as a species) human. Nomothetic researchers study traits, which are assumed to have the same psychological effects for everyone; individual differences are accounted for as variations along a commonly shared scale for each measurable trait or quality. Nomothetic researchers all share an assumption that individuals share a series of traits in common, and therefore they aim to discover the basis of these common traits, for example considering biological and environmental determinants and contributory factors affecting personality.
Trait theorists think of personality as the expression of personality types and traits. Some of the assumptions of trait theory have trickled into the common understanding of personality, so much of the research may seem familiar.
Freud's Theory of Psychosexual Development is also a nomothetic theory, as Freud sought to discover a common process shared by all humans. In general, any psychological theory which proposes stages of 'normal' or typical development is nomothetic in nature, and seeks to draw comparisons between individuals.
Note to students: You will find idiosyncratic and nomethetic theories in many different psychological research areas; these terms are not specific to personality. They are general terms to distinguish between wide brush/narrow brush research focuses. The distinction is similar to that of broadcasting (nomothetic) and talking to one person at a time (idiographic). Do you want to 'tarnish all with the same brush' (nomothetic) or leave 'each to their own' (idiographic)?