Otto Jespersen was born in Randers in Jutland, to Jens Bloch Jespersen (1813–70) and Sophie Caroline Bentzien (1833–74).^[2] He was one of nine children.^[3] As a boy, he was inspired by works of the Danish philologist Rasmus Rask and Niels Matthias Petersen [da; de; fr; sv] biography of Rask,^[4] and with the help of Rask's grammars taught himself some Icelandic, Italian, and Spanish.^[5]

Jespersen entered the University of Copenhagen in 1877 when he was 17, initially studying law but not forgetting his language studies.^[6] in his first year at university, he attended a lecture course by Sophus Heegaard [da; sv] on the history of Evolutionism since the Greeks; this introduced him to the ideas of Herbert Spencer, and later in life he looked back on the course warmly.^[7] Jespersen taught languages in a lower secondary school,^[8] and from 1880 to 1887 was a stenographer for the Rigsdag (Danish parliament). The income from these allowed him in 1881 to shift his focus completely to languages.^[2] Following the introduction of a new degree, Skoleembedseksamen, Jespersen switched to this, choosing French as the major subject and English as the second minor subject, the first compulsorily being Latin. He was one of a large number of students who appealed for Latin to be made voluntary, but the appeal was unsuccessful.^[9] Jespersen studied under Karl Verner, Hermann Möller and particularly Vilhelm Thomsen among linguists; and more broadly, under Harald Høffding: it was thanks to Høffding that Jespersen was further exposed to the writings and ideas of Darwin, Mill and Spencer, and to introspective psychology.^[10]

In 1887 he passed Skoleembedseksamen. For French, he chose to be examined on Diderot, reflecting a lasting enthusiasm for the ideals of the French Revolution and the Age of Enlightenment. Throughout his life Jespersen remained faithful to the ideals and methods of his early teachers. Positivist and evolutionary attitudes, physiological and psychological methods in their classical form, and finally, liberal humanism were essential to his character.^[10]

Jespersen's views on language owed less to theoretical considerations than to a practical and thus largely functional conception of language; as a language theorist, Jespersen could remain tethered to reality thanks to the common sense fundamental to his character. Even when making such bold proposals as that of the "progress" of a language, he could avoid extremes.^[11]

In 1887–1888, he traveled to England, Germany and France, meeting linguists like Henry Sweet and Paul Passy and attending lectures at institutions such as Oxford University.^{[citation needed]} Following a tip from his mentor Vilhelm Thomsen that not many years would pass before there would be a vacancy for a specialist in English, he returned to Copenhagen in August 1888 and began work on his doctoral dissertation on the English case system, which he defended in 1891. His doctorate entitled Jespersen to teach in the university without pay as a Privatdocent; he took this opportunity to teach classes on Chaucer and Old English, thereby adding to his qualifications for the post; he also wrote a book on Chaucer.^[12]

On the resignation of George Stephens as Docent, his newly vacant post was upgraded to that of Professorship of English language and literature. Jespersen was one of four applicants; the others were Adolf Hansen [da] and Jón Stefánsson (both rather lacklustre), and William Craigie (then very young). Up to date in English philology, familiar with English literature, and "[speaking] English perfectly", Jespersen was chosen.^[13]

Jespersen was a professor of English at the University of Copenhagen from 1893 to his retirement in 1925. This was not such a comfortable position: in 1911 he published an article in the newspaper Politiken^[a] describing poor conditions for academic work (serious underfunding, and the lack of a compulsory retirement age for professors), and also how he had got his wife to promise to shoot him if he failed to retire at 65.^[14] He remained something of a radical, in a magazine article published in 1914^[b] he made further recommendations: that Denmark should have more than one university (its second would only arrive in 1928), that a Faculty of Divinity did not belong in a modern university, that there should be financial incentives for students to proceed to postgraduate work, and more. However, although Jespersen succeeded in having Latin removed as a compulsory minor, it can be inferred^[c] that he backed the compulsory inclusion of Chaucer, Spenser and Milton in the English course.^[16]

Jespersen was Dean of the Faculty of Arts from November 1904 to November 1906; and Rector (vice-chancellor, or president) of the university from November 1920 to November 1921. Among his engagements while Rector was an address at the inauguration in March 1921 of the Institute of Theoretical Physics (later renamed Niels Bohr Institute). Another was a speech^[d] welcoming new students in September 1921 "he exhorts [them] to absorb the scholarly and scientific tradition (to the extent of being critical of their professors!), the only genuine hallmark of academics".^[17]

Jespersen's early work focused primarily on language teaching reform and on phonetics, but he is better known for his later work on syntax and on language development.

At the end of the 19th century the teaching in Denmark of contemporaneous foreign languages was ossified, and very similar to that of long-dead classical languages. This was despite the belief of N. M. Petersen [da; de; fr; sv], expressed decades earlier, that pupils should be encouraged to acquire a second language as they had acquired their first, and indeed despite the writings of Jan Amos Comenius in the 17th century.^[18]

In 1886, Jespersen, August Western [no] and Johan August Lundell cofounded a Scandinavian group for a revitalization of language teaching, naming the group "Quousque Tandem" after Wilhelm Viëtor's pseudonym as author of the 1882 pamphlet Der Sprachunterricht muss umkehren! ("Language teaching must start afresh!"). The group opposed the use of theoretical grammar and translation exercises, advocating in its place the teaching of a language in its spoken and living form by the "direct" method, informed by phonetics. As a campaigner, he was an extremist: Hjelmslev writes that this was an area where Jespersen's normal moderation and common sense were counterbalanced by a revolutionary fervour, and that he was a "Jacobin" among linguists.^[19]

Jespersen's first book (1884) was a Danish translation, Praktisk tilegnelse af fremmede sprog ("Practical acquisition of foreign languages"), of Die praktische Spracherlernung,^[20] by Felix Franke. Both Franke (also born in 1860) and Jespersen first assumed that the other was much older than himself, but from its start in 1884 their correspondence quickly became a lively discussion (about two hundred letters and postcards survive) of such matters as second language education and phonetic scripts; it was cut short in 1886 when Franke succumbed to tuberculosis.^[21][e]

In an article published in 1886^[f] (and elaborated in his 1901 book Sprogundervisning, translated as How to teach a foreign language, 1904), Jespersen argued for the following principles in language teaching:

1. Teaching should be based on spoken rather than written language. To this end, at early stages of language teaching, only a phonetic script should be used, and this script should be clear and precise.
2. Material for reading should not consist of unrelated sentences. It should instead constitute coherent texts, preferably designed so that the meanings of unfamiliar words can be inferred from their contexts.
3. At early stages the teaching of grammar should be minimized, and the pupils encouraged to infer grammatical patterns for themselves. Grammar may be examined and practised later, but time should not be spent on grammatical curios, and form and function should not be separated.
4. Exercises in translating the second language into the first should not be emphasized; exercises in translating the first into the second are of very little utility.^[22]

Jespersen followed his 1884 translation of Franke with Kortfattet Engelsk grammatik for tale- og skriftsproget (1885), Fransk læsebog efter lydskriftsmetoden (1889), and (with Christian Sarauw [da; sv]) Engelsk begynderbog (1895): books which, together with those written by others that similarly used the "direct method", soon took over from the "grammar–translation" material against which Jespersen and Quousque Tandem had rebelled.^[23]

Jespersen's interest in phonetics was prompted by Henry Sweet's Handbook of Phonetics (1877), and the lectures of Vilhelm Thomsen.^[24] In the 1880s, inspired by Melville Bell and other British phoneticians, he developed what he first called an "analphabetic" system^[g] – which, "to avoid ridicule", he later termed an "antalphabetic" system – that used a series of three variables for any phone: lowercase Roman for the passive articulator, lowercase Greek for the active articulator, and numerals and more for "the degree and shape of the aperture at a place of constriction". Jørgen Rischel points out that a given "anatomical feature" can be labelled according to its use: thus rather than simply "uvular", the role of the uvula can be described as "a passive articulator in uvular consonants but an active articulator in nasalized sounds".^[25]

In June 1886, he became a member of the International Phonetic Association (IPA), then called the Phonetic Teachers' Association. The idea of creating a phonetic alphabet that could be used by every language was first put forward by Jespersen in a letter he sent to Paul Passy.^[26] Jespersen's transcription system for English, used in John Brynildsen [no]'s Engelsk–Dansk–Norsk Ordbog = A Dictionary of the English and Dano-Norwegian Languages (1902–1907), is very close to that of Daniel Jones, which it preceded by some years.^[27] Language-specific systems were not unusual at the time (Johan Storm devised Norvegia for Norwegian in 1884);^[28] and Jespersen devised a system, named Dania, for the phonetic transcription of Danish (1890), which has remained in use for philological, dialectological and lexicographic work in Danish.^[29] Jespersen was sceptical of a single phonetic transcription system for universal application, and did not use the IPA's International Phonetic Alphabet.^[30]

With continued encouragement by Thomsen and a new friendship with Paul Passy, whom he met in Paris, Jespersen was well informed on phonetics. His own major work on this was Fonetik, published in 1897–1899. In it, Jespersen bases his descriptions on his observations of his own production of sounds in a variety of languages, where this production satisfies native speakers. Jespersen was keen to supplant metaphorical and impressionistic terms with those that described the vocal tract, and had considerable success. Jørgen Rischel calls Fonetik "a landmark in Danish phonetics because of its terminology", much of which has lasted.^[31] Stripped of content specific to Danish, but updated, it was published in German translation in 1904.

The Danish-specific material within Fonetik was republished in 1906 within the booklet Modersmålets fonetik ("Phonetics of the mother tongue"). This treated not only the sounds of Danish but also its prosody, an area in which Jespersen was a pioneer. Repeatedly reprinted, the booklet was long used as a standard textbook.^[32]

Two books, Phonetische Grundfragen ("Phonetics essentials") and Lehrbuch der Phonetik ("Textbook of phonetics"), presented portions of Fonetik to readers of German in 1904. Jespersen hoped for an English translation, and plans were made for a translation by Hans Jørgen Uldall, and later for a revision by Uldall, no English translation ever appeared.^[33]

Rischel writes that: "It is Jespersen's amazing breadth in [his studies of phonetics], paired with his never failing linguistic intuition as a safeguard against errors or downright nonsense, which impresses the reader today."^[33] In Eli Fischer-Jørgensen's estimate (1979), Jespersen was not a great innovator, but was unusually adept at the pronunciation and description of articulatory phonetics, and also aware of the importance of contrast.^[34]

Early dialectological and other fieldwork on East Slesvig and North Jutland dialects, Faroese, and West Greenlandic work was indebted to Jespersen's methodology (although for the last, William Thalbitzer, the researcher, "did not live up to Jespersen's standards at all").^[35]

Although not a phonologist himself, Jespersen was the first to propose a conceptual distinction between phonetics and phonology that is commonly observed today.^[h]

Stød, "a particular kind of laryngealisation (creaky voice) characterizing some Danish syllables" had been studied since Jens Høysgaard in the mid-18th century, but Jespersen's synchronic study of stød and of its morphology and also his study of the relationship between the Danish stød and "the Norwegian and Swedish tonal ('musical') accents" were major advances from the work done by Rasmus Rask, Karl Verner, and Henry Sweet.^[38]

Hans Basbøll evaluates Jespersen as "a true pioneer in his analysis of stress" saying that:

he developed a whole system of types of stress and described it in detail: both syntactic principles of stress reduction (unitary stress, or unit accentuation), of compound stress, of value stress (different types of emphatic stress), and so on.^[39]

Basbøll has coined the term "New Jespersen School" (Ny-Jespersenianerne) for "the main editors of [Den Store Danske Udtaleordbog (a major pronunciation dictionary for Danish)^[i]], namely, Lars Brink [da], Jørn Lund and Steffen Heger, and their collaborators and pupils"; their major achievement aside from SDU has been Brink and Lund's two-volume historical phonetics work Dansk Rigsmål (1975).^[40][j][41]

While still regarding himself as less of a scholar of English than a scholar of French, Jespersen published Kortfattet engelsk grammatik for tale- og skriftsproget ("A concise English grammar for the spoken and written language") in 1885. Most unusually for a grammar book, this employed phonetic script. Inge Kabell comments: "All other grammars of English published in Denmark were for many, many years to come modelled on it and all middle-aged Danes have been taught English according to the principles found in it."^[42]

Jespersen continued to study in Paris (especially under Gaston Paris), England, Berlin (under Julius Zupitza), and Leipzig. Particularly important were his friendships with Paul Passy and Henry Sweet. Sweet's views on phonetics, grammar, and historical linguistics, and his concentration on English, had a great influence on Jespersen. Jespersen's choice of the case system of English as the subject of his doctoral dissertation was probably also prompted by advice from Vilhelm Thomsen to prepare for a chair in English at the University of Copenhagen that would soon be vacant upon the retirement of George Stephens. He successfully defended his dissertation in 1891. Once installed as chair, Jespersen devoted most of his energy to the study and teaching of English, but he retained his broader interests. His prolific output was of great importance for the linguistic study of all aspects of English, for linguistics in general, and to a lesser degree for Nordic philology. Jespersen was the first great linguist to hold the chair of English at the Copenhagen, while his friend Kristoffer Nyrop [ca; de; fr; it; ro; ru; sv] had much the same role for the university's chair of French.^[43]

Jespersen continued as chair of English until he retired in 1925, following his resolve not to continue after reaching 65, in order to help make way for younger scholars.^[44]

Jespersen advanced the concepts of rank in two papers: Sprogets logik (1913) and De to hovedarter af grammatiske forbindelser (1921); and in the latter, nexus as well.^[30] In this theory of ranks Jespersen removes the parts of speech from the syntax, and differentiates between primaries, secondaries, and tertiaries; e.g. in well honed phrase, the primary is phrase, this being defined by a secondary, honed, which itself is defined by a tertiary, well. The term nexus is applied to sentences, structures similar to sentences and sentences in formation, in which two concepts are expressed in one unit; e.g., it rained, he ran indoors. This term is qualified by a further concept called a junction which represents one idea, expressed by means of two or more elements, whereas a nexus combines two ideas. Junction and nexus have had a mixed evaluation: Hjelmslev finds the distinction between them confused, and Jespersen's theory of them in need of revision, in contrast to his refinement in "Tid og tempus" (1914)^[k] of Sweet's distinction between tense (Danish tempus) and time (Danish tid).^[45]

Jespersen's work helped point the way towards our current understanding of a grammatical head.^[46]

In Hjelmslev's opinion, Negation in English and Other Languages (1917) offers a great number of observations and considerable food for thought, but fails to constitute a general examination of negation, for which purpose it would have to be based on more solid materials, from a greater variety of languages^[47] (the overwhelming majority of the examples examined are from the Indo-European languages of west Europe). Jespersen coined the terms paratactic negation^[48] and resumptive negation (negation with an element added to the end of the sentence to strengthen the already negative meaning of the sentence);^[49] he also advanced understanding of negative concord.^[50]

In The Philosophy of Grammar (1924) Jespersen challenges the accepted views of common concepts in grammar and proposes corrections to the basic definitions of case, pronoun, object, voice etc., and further develops his notions of Rank and Nexus. In the 21st century this book is still used as one of the basic texts in modern structural linguistics.^{[citation needed]}

With The Philosophy of Grammar particularly in mind, Noam Chomsky said in 1975: "I think it is fair to say that the work of recent years tends generally to support the basic ideas that Jespersen outlined 50 years ago, and extends and advances the program that he outlined."^[51]

Jespersen advanced the study of the Great Vowel Shift, and was the first to present it in diagram form; he also coined its name.^[l][52]

From his doctoral dissertation of 1891 onwards, Jespersen maintained that over time language did not merely change but progressed. Inspired by Spencer's ideas on the progress of language, this was also a reaction against August Schleicher's theory that, after increasing in complexity, languages become senescent and decay. In his books Language: Its nature, development and origin (1922) and Efficiency in linguistic change (1941) and elsewhere, Jespersen attempted to show that linguistics was a biological science, and that an evolutionary perspective, in which the fittest expression (that whose efficiency is maximized with minimum effort) survived, explained language change over time.^[53]

Hjelmslev criticizes the ambiguity of "efficiency" and "effort"; and adds that even if these are understood only loosely, there have been counter-examples.^[m] He concludes that, as propounded by Jespersen, the thesis is far from convincing, but is put forward vividly and has aroused considerable interest.^[53]

Richard C. Smith considers Language: Its nature, development and origin to be Jespersen's "masterpiece".^[6]

As Jespersen believed that linguistics was a biological science and that in evolution ontogeny recapitulates phylogeny, his interest in historical linguistics led him both to examine child language and to propound interlinguistics, the encouragement of linguistic progress.^[53]

Jespersen's writings on child language appear in Nutidssprog hos børn og voxne (1916), Børnesprog (1923), Sproget: barnet, kvinden, slægten (1941); they are summarized within Language: Its nature, development, and origin (1922).^[53]

Jespersen applied both his theories on grammar and his ideas of efficiency of expression into the quest for an international auxiliary language. He was an early supporter of the Esperanto offshoot Ido, collaborating with Louis Couturat and others on International Language and Science (1910), a book advocating its adoption.^[n][53]

Jespersen later broke with Ido and created an alternative, Novial. His significant publications here include An International language (1928), Novial Lexike (1930), and "A new science: Interlinguistics" (1931).^[o][53]

He also worked with the International Auxiliary Language Association.^[54]

The seven-volume, descriptive reference work A Modern English Grammar on Historical Principles (1909–1949) is likely Jespersen's most influential work and concentrates on syntax,

Jespersen's specialism for the longest period was the English language. Within this, the foremost work was A Modern English Grammar on Historical Principles, published in six volumes during his lifetime, from 1909 to 1942, and a seventh, posthumous volume in 1949. The first volume is devoted to historical phonetics, the sixth to morphology (both derivational and inflectional) Five of the seven volumes are devoted to syntax, which Jespersen particularly enjoyed.^[p]

A Modern English grammar had a high repute at the time: writing in Jespersen's obituary, Helmslev calls it a "monumental work", one that "will maintain its immense value for an incalculable future thanks to the rich documentation of facts it provides".^[q][55]

In his own work The Syntactic Phenomena of English (1988), James D. McCawley attributes various of his analyses, or the insights pointing towards them, to Jespersen: raising;^[56] "worthwhile criticism of traditional systems of parts of speech"^[57] and classification of what are traditionally termed "subordinating conjunctions" (as in "You must look at this before you leave") as prepositions with sentential objects;^[58] and more specifically, classification of that in relative clauses (as in "The necktie that he bought was polyester") not as a relative pronoun but as a complementizer.^[59] Asked how the 20th-century Dutch grammarians of English Hendrik Poutsma, Etsko Kruisinga and R. W. Zandvoort compared with Jespersen, McCawley replied: "Of course, Jespersen is in a class by himself. He was a fantastically original, broad, and deep thinker."^[60]

Growth and Structure of the English Language (1905, and reprinted at numerous times thereafter) is a broad history of the English language. It won Jespersen the Prix Volney.^[61]

Essentials of English Grammar (1933), primarily intended for university teaching, is for the most part synchronic.^[62]

Terms related to English that were introduced by Jespersen and are still widely used today include cleft sentence,^[63][64] content clause,^[65] light verb,^[66] mass noun,^[67] and yes-or-no question.^[68] Jespersen's writings have also influenced today's conceptions of existential sentence.^[69]

Robert I. Binnick calls Jespersen "one of the greatest students of the English language . . . , at once the last of the traditional grammarians and the first modern linguist–grammarian".^[70]

Mankind, Nation and Individual: From a linguistic point of view (1925) is one of the pioneering works on sociolinguistics.

Late in his life Jespersen published Analytic Syntax (1937), in which he presents his views on syntactic structure using an idiosyncratic shorthand notation.

During the decades of his activity, Jespersen followed what other, younger linguists were doing but refrained from unreservedly welcoming any advance, let alone from aligning himself with any new approach. He remained individualistic, but "there was a conservative streak in his radicalism"^[r] as he seemed to take seriously only the standpoints that had influenced him in his youth and to interpret newer work as mere repetition of this or that older theory.^[61]

Jespersen's main interest was not that of seeking patterns and explanations of the langue behind parole, but rather its opposite, the major concern of the phonetics and semantics of his youth: "the psychophysiological fact of parole".^[s][61]

Jespersen visited the United States twice: he lectured at the Congress of Arts and Sciences in St. Louis in 1904, and in 1909–1910 he visited both the University of California and Columbia University.^[71] While in the U.S., he studied its education system. His autobiography (En sprogmands levned) was first published in English translation (A linguist's life) as recently as 1995.

After his retirement in 1925, Jespersen remained active in the international linguistic community. As well as continuing to write, he convened and chaired the first International Meeting on Linguistic Research in Geneva in 1930, and presided over the Fourth International Congress of Linguists in Copenhagen in 1936.^[71]

Jespersen received honorary degrees from Columbia University in New York (1910), the University of St Andrews in Scotland (1925), and the Sorbonne in Paris (1927).^[5] He was one of the first six international scholars to be elected as honorary members of the Linguistic Society of America.^[71] He was elected a foreign member of the Royal Netherlands Academy of Arts and Sciences in 1931.^[72]

• Praktisk tilegnelse af fremmede sprog ("Practical acquisition of foreign languages"). [A translation of Felix Franke, Die praktische Spracherlernung auf Grund der Psychologie und Physiologie der Sprache dargestellt von Felix Franke.] Copenhagen: Carl Larsen, 1884. OCLC 466303017.
• Kortfattet engelsk grammatik for tale- og skriftsproget ("A concise English grammar for the spoken and written language"). Copenhagen: Carl Larsen, 1885. OCLC 477786006. (Also later editions.)
• Fransk læsebog efter lydskriftsmethode ("A French reader using the phonetic method"). Copenhagen, 1889.
• The articulations of speech sounds represented by means of analphabetic symbols. Marburg: N.G. Elwert, 1889. OCLC 903926262. At the Internet Archive; Again at the Internet Archive.
• Studier over Engelske kasus. Med en indledning om fremskridt i sproget ("Studies on case in English: With an introduction on progress in language"). [Jespersen's doctoral dissertation.] Copenhagen: Kleins Vorlag, 1891. OCLC 457568603.
  • Progress in language: With special reference to English. London: Swan Sonnenschein & Co., 1894. OCLC 607098829. At the Internet Archive. New York: Macmillan & Co. Amsterdam and Philadelphia: John Benjamins, 1993; with an introduction by James D. McCawley. ISBN 9789027219923, ISBN 9781556193149. Abingdon, Oxfordshire: Routledge, 2006. ISBN 978-0-415-40258-3. Abingdon, Oxfordshire: Routledge, 2013. ISBN 978-0-415-86027-7. [Jespersen's adaptation of his doctoral dissertation.]
  • Chapters on English. London: George Allen & Unwin, 1918. OCLC 8977427. Selected writings. 1960. Pp. 153–346. Selected writings. 2010. Pp. 81–165. [Excerpted from Progress in language.]
• Chaucers liv og digtning ("Chaucer's life and poetry"). Studier fra sprog- og oldtidsforskning. Copenhagen: Klein, 1893. OCLC 246601722.
• With Chr[istian] Sarauw [da; sv]. Engelsk begynderbog ("English primer"). 1895. OCLC 476427495. (Often later reprinted.)^[73]
• Fonetik: En systematisk fremstilling af læren om sproglyd ("Phonetics: A systematic presentation of the study of the sounds of language"). Copenhagen: Schubotheske Forlag, 1899. OCLC 185591363.
  • Phonetische Grundfragen ("Phonetics essentials"). Leipzig: B.G. Teubner, 1904. OCLC 1020799. [German translation by N. Andersen and Hermann Davidsen of portions of Fonetik; with additions written by Jespersen.]
  • Lehrbuch der Phonetik ("Textbook of phonetics"). Leipzig: B.G. Teubner, 1904. OCLC 1159076996. (Also later editions.) [German translation by Hermann Davidsen of portions of Fonetik.]
• Sprogundervisning ("Language teaching"). Copenhagen: Det Schubotheske forlag, 1901. OCLC 16159085. 2nd ed. ("revised, less polemical"^[74]). Copenhagen: Gyldendalske Boghandel, 1935. OCLC 29990346.
  • How to teach a foreign language. Translation by Sophia Yhlen-Olsen Bertelsen of Sprogundervisning. London: George Allen & Unwin, 1904. OCLC 1017209528. London: S. Sonnenschein & Co., 1904. 1904 printing and 1928 printing at the Internet Archive. Abingdon, Oxfordshire: Routledge, 2007. ISBN 978-0-415-40245-3. Abingdon, Oxfordshire: Routledge, 2010. ISBN 978-0-415-61130-5.
• The England and America Reader. Copenhagen, 1904.
  • A British Reader. 1931. OCLC 467735339.
• Growth and structure of the English language. Leipzig: B.G. Teubner; New York: G.E. Stechert, 1905. OCLC 4287175. Chicago: University of Chicago Press; Oxford: Basil Blackwell, 1982; with a foreword by Randolph Quirk. ISBN 9780226398778, ISBN 9780631129868, ISBN 9780631129875.
• Modersmålets fonetik ("Phonetics of the mother tongue"). Copenhagen: Schubotheske, 1906. OCLC 29995287. (Revised and augmented in later editions.^[75])
• John Hart's pronunciation of English (1569 and 1570). Heidelberg: Carl Winter, 1907. Anglistische Forschungen, Heft 22. OCLC 1907819. At the Internet Archive. [About the content of John Hart's An orthographie (1569) and A methode or comfortable beginning for all vnlearned, whereby they may bee taught to read English (1570).]
• A Modern English grammar on historical principles. Seven volumes, 1909–1949. Earliest volumes first published by Carl Winter, Heidelberg, later vols. by Ejnar Munksgaard, Copenhagen and George Allen & Unwin, London. Vols. 5–7, issued without series title, have imprint: Copenhagen, E. Munksgaard, 1940–49; Imprint varies: Pt.5–6: London: George Allen & Unwin; pt.7: Copenhagen: Munksgaard, London: George Allen & Unwin. [The title should be understood as "A grammar of Modern English".]
• Sprogets logik ("The logic of language"). Copenhagen: J. H. Schultz, 1913. OCLC 952935015.
• Nutidssprog hos børn og voxne ("Modern language in children and adults"). Copenhagen: Nordisk forlag, 1916. OCLC 8661242.
• Negation in English and other languages. Det Kongelige Danske Videnskabernes Selskab: Historisk-filologiske Meddelelser I, 5. Copenhagen: Andr. Fred. Høst og søn, 1917. OCLC 457568567. At the Internet Archive; at the Royal Danish Academy of Sciences and Letters. Selected writings. 1960. Pp. 1–152. Selected writings. 2010. Pp. 2–80.
• Rasmus Rask i hundredåret efter hans hovedværk ("Rasmus Rask a hundred years after his major work"). Copenhagen: Gyldendal, 1918. OCLC 561462317. At Danskernes Historie Online.
• De to hovedarter av grammattiske forbindelser ("The two main types of grammatical relations"). Det Kongelige Danske Videnskabernes Selskab: Historisk-filologiske Meddelelser IV, 3. Copenhagen: Andr. Fred. Høst og søn, 1921. OCLC 16310596. At the Royal Danish Academy of Sciences and Letters.
• Language: Its nature, development, and origin. London: George Allen & Unwin, 1922. London: George Allen & Unwin, 1968. ISBN 0-04-400007-3. Abingdon, Oxfordshire: Routledge, 2007. ISBN 978-0-415-40247-7. Abingdon, Oxfordshire: Routledge, 2013. ISBN 978-0-415-84556-4.
• Sprogets udvikling og opstaaen ("The development and origin of language"). Copenhagen: V. Pio, 1926. OCLC 466067329.
• Børnesprog: En bog for foraldre ("Children's language: A book for parents"). Copenhagen: Gyldendal, 1923. OCLC 492461187.
• The philosophy of grammar. London: George Allen & Unwin, 1924. OCLC 308037. At the Internet Archive. New York: Henry Holt, 1924. OCLC 19939152. New York: W. W. Norton, 1965. OCLC 1120578615. Chicago: University of Chicago Press, 1992; with an introduction by James D. McCawley. ISBN 0-226-39881-1. Abingdon, Oxfordshire: Routledge, 2006. ISBN 978-0-415-40257-6. Abingdon, Oxfordshire: Routledge, 2010. ISBN 978-0-415-86027-7.
• Mankind, nation and individual: From a linguistic point of view. Oslo: H. Aschehoug, 1925. OCLC 1445547. At the Internet Archive. Abingdon, Oxfordshire: Routledge, 2006. ISBN 978-0-415-40248-4. Abingdon, Oxfordshire: Routledge, 2013. ISBN 978-0-415-86461-9.
• Et verdenssprog: Et forsøg på spørsmålets løsning ("A world language: An attempt to solve the question"). Copenhagen: V. Pios, 1928. OCLC 925814712.
• An international language. London: George Allen & Unwin, 1928. OCLC 251023739. Abingdon, Oxfordshire: Routledge, 2006. ISBN 978-0-415-40246-0. Abingdon, Oxfordshire: Routledge, 2013. ISBN 978-0-415-84526-7. S.l.: Feedbooks, n.d. Archived by the Wayback Machine on 21 August 2018. [The introduction of the Novial language.]
• Novial lexike: International dictionary = Dictionnaire international = Internationales Wörterbuch. Heidelberg: C. Winter, 1930. OCLC 39992226. Abingdon, Oxfordshire: Routledge, 2006. ISBN 978-0-415-40256-9. Abingdon, Oxfordshire: Routledge, 2013. ISBN 978-0-415-86464-0. Text file edition, blahedo.org (Don Blaheta). [Novial to English, French and German dictionary.]
• Tanker og Studier ("Thoughts and studies"). Copenhagen: Gyldendalske Boghandel, 1932. OCLC 1508095448. [Collection of papers in Danish.]
• Linguistica: Selected papers in English, French and German. London: George Allen & Unwin; Copenhagen: Levin & Munksgaard, 1933. OCLC 459619574. At Internet Archive. College Park, Maryland: McGrath, 1970. OCLC 1000569708. Abingdon, Oxfordshire: Routledge, 2015. ISBN 9781317439363, ISBN 9781315694368, ISBN 9781317439349, ISBN 9781317439356, ISBN 9781138908284, ISBN 9781138908529.
• Essentials of English grammar. London: George Allen & Unwin, 1933. (And later impressions.) OCLC 1593202. Tokyo: Kaitakusha (開拓社), 1943. 2nd ed. 1944. NCID BA12049306. University of Alabama Press, 1965. OCLC 561462021. Abingdon, Oxfordshire: Routledge, 2006. ISBN 978-0-415-40244-6. Abingdon, Oxfordshire: Routledge, 2013. ISBN 978-0-415-84746-9. [Greatly condensed derivative of A Modern English grammar.]
• Analytic syntax: A system of expressing grammatical formulae by symbols. London: George Allen & Unwin, [1937]. OCLC 5154890. Copenhagen: Levin & Munksgaard, 1937. OCLC 1469370. New York: Rinehart & Winston, 1969. OCLC 463148117. Tokyo: Senjo, 1971. OCLC 21741533. Chicago: University of Chicago Press, 1984; with an introduction by James D. McCawley. ISBN 0-226-39880-3.
• En sprogmands levned ("A linguist's life"). Copenhagen, 1938. OCLC 7136679. [Jespersen's autobiography.]
  • A linguist's life. (English translation, by David Stoner, of En sprogmands levned.) Edited by Arne Juul, Hans Frede Nielsen and Jørgen Erik Nielsen, foreword by Paul Christophersen. Odense: Odense University Press, 1995. (ISBN 87-7838-132-0)
• Sproget: Barnet, kvinden, slægten ("Language: Child, woman, family"). Copenhagen: Gyldendal, 1941. OCLC 247794469.
• Efficiency in linguistic change. Det Kongelige Danske Videnskabernes Selskab. Historisk-filosofiske meddelelser 27, 4, 1941. 2nd ed. Copenhagen: Ejnar Munksgaard, 1949. 3rd ed. Copenhagen: Ejnar Munksgaard, 1969. At the Royal Danish Academy of Sciences and Letters. Selected writings. 1960. Pp. 381–466. Selected writings. 2010. Pp. 190–231.
• Selected writings. London: George Allen & Unwin; Tokyo: Senjo, 1960. OCLC 213821474. At the Internet Archive. London: Routledge, 2010. ISBN 978-0-415-57137-1, ISBN 978-0-203-85719-9.

As a student, Jespersen enjoyed chess and reading French and English literature.^[76]

Jespersen married Ane Marie Djørup on 13 April 1897; the couple, later together with their son, lived in Frederiksberg (distinct from Copenhagen but geographically part of it), until their move in 1901 to Ermelundsly, a large house in Jægersborg, near Gentofte. In 1934 they again moved to a large house, Lundehave, in the outskirts of Helsingør, provided by the Royal Danish Academy of Sciences and Letters for a distinguished academician.^[77]

Ane Marie died on 30 March 1937. Jespersen became ill in December 1942; he died on 30 April 1943, and his urn was interred in a cemetery at Helsingør.^[78]

• Interlinguistics
• Jespersen's Cycle
• Prosiopesis

• Andersen, Alsing; Vilhelm Andersen; Carl Adolf Bodelsen [da; sv]; Harald Bohr; Niels Bohr; Viggo Brøndal; Torsten Dahl; Niels Haislund; Chr. Nielsen; Valdemar Poulsen; Valdemar Østerberg, eds. Hilsen til Otto Jespersen på firs-aarsdagen 16. juli 1940 ("Greetings to Otto Jespersen on his eightieth birthday, 16 July 1940"). Copenhagen: Munksgaard, 1940. OCLC 13021793
• Bøgholm, Niels; Aage Brusendorff; and Carl Adolf Bodelsen [da; sv], eds. A grammatical miscellany offered to Otto Jespersen on his seventieth birthday. Copenhagen: Levin & Munksgaard; London: George Allen & Unwin, 1930. OCLC 2335192.
• Cerbasi, Donato. Introduzione ad Otto Jespersen. Rome: Nuova Cultura, 2011. ISBN 9788861347649.
• 石橋幸太郎、他 (Ishibashi, Kōtarō; et al). O.イエスペルセン (O. Jespersen). 不死鳥英文法ライブラリ. Tokyo: Nan'undō, 1964. NCID BN07459377.
• Juul, Arne; and Hans F. Nielsen, eds. Otto Jespersen: Facets of his life and work. Amsterdam Studies in the Theory and History of Linguistic Science, vol. 52. Amsterdam: Benjamins, 1989. ISBN 9789027278357. At the Internet Archive.
• 宮畑一郎 (Miyahata, Ichirō). イェスペルセン研究 (Jespersen kenkyū). Tokyo: Kobian Shobō, 1985. ISBN 4875580207, NCID BN00673040.
• Nielsen, Jørgen Erik; and Arne Zettersten, eds. A literary miscellany: Proceedings of the Otto Jespersen Symposium April 29–30, 1993. Copenhagen: Department of English, University of Copenhagen, 1994. ISBN 8788648605.

•   Media related to Otto Jespersen at Wikimedia Commons
•   Works related to Otto Jespersen at Wikisource
• Works by Otto Jespersen at Project Gutenberg
• Works by or about Otto Jespersen at the Internet Archive
• "Otto Jespersen Online Bibliography", International Auxiliary Languages.
• "Otto Jespersen", Encyclopædia Britannica