This article explains and demonstrates the theory of lexical decomposition originated by Anna Wierzbicka (1972, 1980, 1992, 1996, among other works); cf Goddard and Wierzbicka (1994, In press), Goddard (1998). Wierzbicka and colleagues refer to their approach as the "natural semantic metalanguage" (NSM) theory. It is sometimes referred to as a version of "conceptual axiology". An earlier designation is the "semantic primitives" approach. The foundational assumption of the NSM theory is that the meanings expressible in any language can be adequately described by means of language-internal reductive paraphrase. That is, the theory assumes, first, that any natural language is adequate as its own semantic metalanguage, and, second, that any semantically complex expression can be explicated by means of an exact paraphrase composed on simpler, more intelligible terms. By relying on reductive paraphrase the NSM approach is safeguarded against the twin pitfalls of circularity and obscurity which dog other "definitional" approaches to semantic analysis. No technical terms, neologisms, logical symbols, or abbreviations are allowed in NSW explications - only plain words from ordinary natural language.