Later this week is January 18th, which for taxonomists is notable for two things: 1) it’s Thesaurus Day; and 2) it’s the birthday of Peter Mark Roget. This double occurrence is no coincidence. We may consider Doctor Roget to be the inventor of the thesaurus (or at least one of its pioneers), and a person whose birthday is cause for taxonomists’ celebration.


Yes, this is the man who compiled the first “Thesaurus of English Words and Phrases.” He started writing it in 1805 but didn’t have it published until much later, in 1852. The full title of the first edition was Thesaurus of English Words and Phrases, Classified and Arranged so as to Facilitate the Expression of Ideas.



Did you catch the “Classified” part of the title? And the “Arranged”?

Most people think of Roget’s thesaurus as a simple list of words and their synonyms. This is understandable, as some of the more recent synonymies that include “thesaurus” in their titles really are just strictly alphabetical lists of words, annotated with some synonyms. Taxonomists sometimes consider Roget’s synonym resource to be much different than modern taxonomic thesauri. After all, hasn’t it always lacked any sort of classification scheme?

No, no, no.

As much of a habitual list maker as Roget was (since he was eight years old, in fact), he recognized that the full potential of a lengthy vocabulary could not be achieved unless there was some sort of categorization or classification of the list entries. Classification was an intrinsic part of Roget’s compilation of synonyms throughout its long development.

As he explained in the preface to the first edition of the Thesaurus of English Words and Phrases: 

“It is now nearly fifty years since I first projected a system of verbal classification similar to that on which the present work is founded. Conceiving that such a compilation might help to supply my own deficiencies [as a writer], I had, in the year 1805, completed a classed catalogue of words on a small scale, but on the same principle, and nearly in the same form, as the Thesaurus now published. I had often during that long interval found this little collection, scanty and imperfect though it was, of much use to me in literary composition, and often contemplated its extension and improvement; but a sense of the magnitude of the task, amidst a multiple of other avocations, deterred me from the attempt. Since my retirement from the duties of Secretary to the Royal Society, however, finding myself possessed of more leisure, and believing that a repertory of which I had myself experienced the advantage might, when amplified, prove useful to others, I resolved to embark in an undertaking which, for the last three or four years, has given me incessant occupation .” (“Roget’s Thesaurus: The Original Manuscript”)

Part of Roget’s classification efforts involved choosing a single term to represent each concept, rather than repeating each synonym in some other part of the list. This is akin to modern taxonomic thesauri, in which each concept is represented by only one term, and alternative ways of expressing that concept are indicated in the term record as non-preferred terms. Roget’s approach was oriented toward findability of a concept through the choice of words that users were most likely to associate with particular concepts.

Beyond that, though, the overall structure of the thesaurus was hierarchical. The table of contents of Project Gutenberg’s presentation of Roget’s thesaurus shows the organization of the book into six main classes, with numerous subdivisions. Wikipedia provides an “Outline of Roget’s Thesaurus” that shows the hierarchical depth to seven levels; this resource also includes links from many of the categories to relevant Wikipedia articles, as does the related Wiktionary resource “Appendix: Roget’s thesaurus classification”.

Roget crafted the thesaurus categories and subdivisions according to principles set out by some eminent philosophers, as explained in the Wikipedia article on “Roget’s Thesaurus”:

“Each class is composed of multiple divisions and then sections. This may be conceptualized as a tree containing over a thousand branches for individual “meaning clusters” or semantically linked words. These words are not exactly synonyms, but can be viewed as colours or connotations of a meaning or as a spectrum of a concept. One of the most general words is chosen to typify the spectrum as its headword, which labels the whole group.

“Roget’s schema of classes and their subdivisions is based on the philosophical work of Leibniz (see Leibniz—Symbolic thought), itself following a long tradition of epistemological work starting with Aristotle. Some of Aristotle’s Categories are included in Roget’s first class “abstract relations”.”

So was Roget an inventor? An originator? A pioneer? Consider these eclectic accomplishments:

  • He invented the log-log slide rule, which greatly simplified the exponential and root calculations.
  • He designed a pocket chessboard and invented several chess problems.
  • He made insightful observations about the perception of motion, thus contributing to the development of mechanical animation devices and, more importantly, to the early development of cinema.
  • He helped found the wonderfully named Society for the Diffusion of Useful Knowledge.
  • He was a co-founder of the Medical and Chirurgical Society of London, the forerunner of the Royal Society of Medicine.
  • He was the first Fullerian Professor of Physiology at the Royal Institution.
  • He helped establish the University of London.
  • He compiled Roget’s Thesaurus, which writers still use to perfect their prose.
  • He developed a classification approach that set an example for modern taxonomists and thesaurians.

Yes, I think we can conclude that Peter Mark Roget was an inventor, an originator, and a pioneer. And a thesaurian, of course. And yes, a taxonomist.

All good reason to celebrate his birthday on Thesaurus Day!

Barbara Gilles, Taxonomist
Access Innovations, Inc.