Nomothetic literally means "proposition of the law" (Greek derivation) and is used in philosophy (see also Nomothetic and idiographic), psychology, and law with differing meanings. In psychology, nomothetic measures are contrasted to ipsative or idiothetic measures, where nomothetic measures are measures that are observed on a relatively large sample and have a more general outlook while the idiographic approach is relating to a more singular case as is done in case studies.
In general humanities usage, "nomothetic" may be used in the sense of "able to lay down the law", "having the capacity to posit lasting sense" (from Ancient Greek: nomothetikos - νομοθετικός, from nomothetēs νομοθέτης "lawgiver", from νόμος "law" and the root θη- "posit, place, lay down"), e.g., 'the nomothetic capability of the early mythmakers' or 'the nomothetic skill of Adam, given the power to name things.'
In psychological theories of personality, the following could be categorized as nomothetic theories: Carl Jung's Psychological Types, Eysenck's three factor model, the Big Five personality traits, and the Myers Briggs Type Indicator. An approach to personality and psychological research in which a person is understood in relation to principle or norms rather than by their own individual uniqueness.
In other fields
In sociology, nomothetic explanation presents a generalized understanding of a given case, and is contrasted with ideographic explanation, which presents a full description of a given case. Nomothetic approaches are most appropriate to the deductive approach to social research in as much as they include the more highly structured research methodologies which can be replicated and controlled, and which focuses on generating quantitative data with a view to explaining causal relationships.
In anthropology, nomothetic refers to the use of generalization rather than specific properties in the context of a group as an entity.
In law, nomothetic propositions are law strictu sensu. That is, a nomo thesis (legal position) is an invariable "fact of life" and is invariable and cannot be other than it is. Legal science is generally not considered nomothetical in late modernity though some scholars in antiquity and in the Middle Ages seemed to believe that law, or at least some laws, were nomothetic (see natural law). The field of "nomothetics" can also refer to the science of the creation of legal systems, as in jurisprudence and the ordered arrangement of law systemization in new and constructed ways.
The Nomothetic Fallacy
One important use of the word "Nomothetic" is in the term "Nomothetic Fallacy," which is the belief that naming a problem effectively solves it. For example, in applied psychology a patient may learn that his or her sad mood is termed "depression" and is considered a mental disorder. Naming the problem can bring such relief (relief of personal responsibility or hope of treatability) that the client feels their depression is cured. This relief may improve the patient's mood temporarily, but it is unlikely to fix the social, situational or internal factors that originally led to the depression. The problem has been named and the client feels that awareness of the problem solves or ought to solve it, but in reality the problem remains unsolved.