1. The document discusses the history and development of lexicography and thematic dictionaries from Old English glossaries to Peter Mark Roget's Thesaurus. 2. It provides examples of thematic categories from early glossaries and describes how Roget arranged concepts in his Thesaurus according to six classes based on philosophical principles of classification. 3. Since its first publication in 1852, Roget's Thesaurus has sold over 40 million copies and become one of the most recognizable books in the English language.