Published online by Cambridge University Press: 27 May 2026
Critical for any explanation or theory are well-formulated concepts with clear and unambiguous meaning. Definitions can ensure unambiguous meaning, and the kind of definition most useful for theories are nominal definitions. Nominal definitions have two parts: a definiendum, the term being defined, and definiens, other words that tell what it means. To be useful in explanations a concept should be abstract, clearly defined, and embedded in principles that describe its behavior. Such concepts are the result of thought rather than simply of observations. Their meanings are not tied to any particular time or place. Their definitions include all and only the important elements of whatever phenomena they refer to.
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