Nomothetic means of or pertaining to the study or discovery of general laws.
Personality Traits: Idiographic vs. Nomothetic
The Idiographic view emphasizes that each person has a unique psychological structure and that some traits are possessed by only one person; and that there are times when it is impossible to compare one person with others. This viewpoint also emphasizes that traits may differ in importance from person to person (cardinal, central and secondary traits). It tends to use case studies, bibliographical information, diaries etc for information gathering.
The Nomothetic view, on the other hand, emphasizes
comparability among individuals but sees people as unique in their combination of traits.
This viewpoint sees traits as having the same psychological meaning in everyone. The
belief is that people differ only in the amount of each trait. It is this which
constitutes their uniqueness. This approach tends to use self-report personality
questions, factor analysis etc. People differ in their positions along a continuum in the
same set of traits.
Ideographic explanations are explanations of specific events, phenomenon or behaviours which are sought in the careful examination of specific preceding events.
For example, why did Mary murder the butler? Or, What caused World War I? For the most part clinical psychologists and historians are interested in ideographic explanations.
Other disciplines, like sociology, are interested in explanations of classes of events or behaviours and seek these in a careful examination of a few general categories or classes of preceding events.
For example, why do men murder their partners? Or, What are the causes of international violence? These explanations are known as nomothetic explanations.