Roget and his Thesaurus

JMS Pearce
East Yorks, UK


Peter Mark Roget
Fig 1. Peter Mark Roget (1779-1869). William. Drummond, after Eden Upton Eddis. c.1830s. Credit National Portrait Gallery 

There was much more to Peter Mark Roget (1779–1869)(Fig 1) than his indispensable Thesaurus of English Words and Phrases (Fig 2).1 But little is remembered of his illustrious career in medicine and scientific discovery, which is surprising since in these endeavors he was highly regarded in his time.2 This may stem from the fact that the Thesaurus, written in the last few years of his life, eclipsed his other works, which have thereby faded into obscurity.

Roget was an eminent nineteenth-century physician, physiologist, mathematician, writer, and inventor. Born in London, his father was the Rev. John Roget, a Swiss cleric; his mother was a sister of the law reformer Sir Samuel Romilly. When his father died the family moved to Edinburgh, where he enrolled in the medical school and graduated MD at the age of only nineteen in 1798. Roget then attended lectures at London medical schools and embarked on a voyage of research to satisfy his ardent curiosity.


Medicine and science

After graduation, he assisted in Humphry Davy’s discovery of the anesthetic action of laughing gas, nitrous oxide, helped to establish medical schools, invented a slide-rule, and discovered new optical phenomena.

At the conclusion of the Peace of Amiens in 1802, Roget visited Paris and Geneva for two years. He was imprisoned for two months when hostilities resumed between France and England because the fickle Napoleon Bonaparte suddenly confined all Englishmen living in the French territory. When released he became private physician to William Petty, the Marquis of Lansdowne, after whose death in 1805 he was appointed physician to the Manchester Infirmary, where for three years he practiced medicine and lectured on comparative anatomy and physiology, topics then little studied.

His next move in 1808 was to London, where he became physician to the Northern Dispensary. He lived with his mother and sister at 30 Bernard Street. He lectured at the Royal Institution, where he was later appointed the first Fullerian Professor of Physiology (1833)—a hallmark of his academic standing.3 At William Hunter’s anatomical theatre and museum in Great Windmill Street, Soho, he lectured on the theory and practice of medicine; his colleagues there included Sir Charles Bell and Sir Benjamin Brodie.2 Continually seeking new areas to explore, Roget devised a new “log-log” slide rule based on the idea that the multiplication of two numbers can be achieved by adding their logarithms. He extended the idea so that powers and roots of numbers could be found. For example, the cube of a number is found by multiplying its logarithm by three, and the cube root by dividing the logarithm by three. This was perhaps his most important invention. He published this device in Philosophical Transactions,4 which resulted in his election as a Fellow of the Royal Society on 16 March 1815.

In 1820 he worked with Michael Faraday and Joseph Plateau on vision, resulting in Roget’s paper to the Royal Society on the illusion of visual after-images. (Will Hays, a father of Hollywood, linked this discovery to the invention of motion pictures.) In 1821 he became a Fellow of the Royal College of Physicians and was later a censor. He advised on outbreaks of dysentery and scurvy in London prisons and assisted Jeremy Bentham’s investigation of sewage and water pollution. He helped in the founding of the University of London. In 1820 he was appointed physician to the Spanish embassy.

In 1833, he wrote his much praised Bridgewater Treatise on Animal and Vegetable Physiology considered with reference to Natural Theology.5 This “applied the facts of the structure and actions of animals and plants to demonstrate the power, the wisdom, and the benevolence of the Supreme Being . . .”

Not only an inventor and investigator, he was also a prolific writer on many subjects: medicine, the kaleidoscope, physiology and phrenology, galvanism, electro-magnetism, and even chess.


Title Page of Peter Mark Roget’s Thesaurus of English Words and Phrases
Fig 2. Title Page of Roget’s Thesaurus of English Words and Phrases, 1852. Source

Roget’s Thesaurus

Shortly after his sixtieth birthday, he retired from medical practice and spent the rest of his life on the project that made his name.6 Two types of dictionary were already established: synonym dictionaries and conventional topical dictionaries such as Samuel Johnson’s (1755). Roget’s Thesaurus combined them effectively into a topical dictionary of synonyms.7

His original ordonnance of words had started at the age of twenty-six when he compiled a small catalog of words, indexed by their meanings, to help his writing. However, it was not until his retirement that Roget began to complete his magnum opus, published in 1852, priced fourteen shillings [70 pence]. He chose for its title the Greek word “thesaurus” (θησαυρός), meaning a treasury or storehouse.

Whereas a conventional dictionary starts with words and discloses their meanings, pronunciations, and etymology, Roget’s Thesaurus was the converse, namely, an idea being given to find the word or words by which that idea may most fitly and aptly be expressed. Although philosophically orientated, the result was a compendium of thematically arranged concepts, a classification of words by their meaning.

Devoted to Linnaeus’s classification of living organisms, Roget arranged all ideas, meanings, and concepts into six classes: Abstract Relations, Space, Matter, Intellect, Volition, and Affections. The contents were not arranged alphabetically but as an ordonnance where a given idea fitted into his classification. But shortly before publication, he inserted an alphabetical index as an appendix, thus enabling its easier use. He worked diligently for four years in its preparation.

Roget continued to make changes until his death at the age of ninety, by which time there had been twenty-eight editions.8 His son, John Lewis Roget (1828-1908), continued its revision. Roget’s Thesaurus has never been out of print and by its 150th anniversary in 2002 had sold thirty-two million copies. From his original six classes, by the time of the eighth edition in 2019 it included 1,075 word categories. However, much larger is the 2009 Historical Thesaurus of the Oxford English Dictionary, a two-volume collection of 800,000 words divided into more than 200,000 categories.

Nonetheless, his life of brilliant originality and ceaseless energy was marred by several unhappy incidents: his father and his wife died young; his uncle and mentor Sir Samuel Romilly died in his arms, having cut his throat shortly after his wife’s death. Roget, like his mother and sister, struggled with depression for much of his life; some biographers9 with uncertain evidence have conjectured that his obsession with list-making and classification may have served to mollify his miseries.

In 1824 he married Mary Taylor (1795–1833). They had a son John and a daughter Kate. In old age he became deaf but his tall, dignified, slender, and still handsome figure was a familiar sight walking around Bloomsbury. He was cared for by his daughter Kate. At the age of ninety he joined her on their annual holiday in West Malvern, Worcestershire, but during a heatwave he became ill and died on 12 September 1869. Roget died on September 10th at West Malvern and was buried at St. James’s Church.



  1. Roget’s Thesaurus of English Words and Phrases 1852. Project Gutenberg 2004.
  2. Munk W. Peter Mark Roget MD Edin (1798) FRS (1814) LRCP (1820) FRCP (1821). Munk’s Roll 1779-1869 Vol III, Pg 71
  3. Snell WE. Peter Mark Roget, FRCP. (1779-1869), J. Roy. Coll. Physicians Lond 1974;8(3):276-282.
  4. Roget Peter Mark. Description Of A New Instrument For Performing Mechanically The Involution And Evolution Of Numbers. Philosophical Transactions Of The Royal Society Of London, 1815;105:9-28.
  5. Roget PM. Animal and Vegetable Physiology, Considered with Reference to Natural Theology. Edinb Med Surg J 1835; 43(123): 365–409.
  6. Peter Mark Roget. Obituary British Medical Journal Sept. 25, 1869
  7. Kendall J. The Man Who Made Lists: Love, Death, Madness, and the Creation of Roget’s Thesaurus. Putnam Adult. 2008.
  8. Emblem DL. Peter Mark Roget The Word and the Man. London: Longman, 1970
  9. Kendall J. The Man Who Made Lists. New York. Putnam, 2008.



JMS PEARCE, MD, FRCP, is a retired neurologist and author with a particular interest in the history of science and medicine.


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