International auxiliary language
An international auxiliary language (sometimes abbreviated as IAL or auxlang) or interlanguage is a language meant for communication between people from different nations who do not share a common native language. An auxiliary language is primarily a second language.
Languages of dominant societies over the centuries have served as auxiliary languages, sometimes approaching the international level. Arabic, English, French, Mandarin, Russian and Spanish have been used as such in recent times in many parts of the world. However, as these languages are associated with the very dominance—cultural, political, and economic—that made them popular, they are often also met with resistance. For this reason, some have turned to the idea of promoting an artificial or constructed language as a possible solution.
The term "auxiliary" implies that it is intended to be an additional language for the people of the world, rather than to replace their native languages. Often, the phrase is used to refer to planned or constructed languages proposed specifically to ease worldwide international communication, such as Esperanto, Ido and Interlingua. However, it can also refer to the concept of such a language being determined by international consensus, including even a standardized natural language (e.g., International English), and has also been connected to the project of constructing a universal language.
Some of the philosophical languages of the 17th–18th centuries could be regarded as proto-auxlangs, as they were intended by their creators to serve as bridges among people of different languages as well as to disambiguate and clarify thought. However, most or all of these languages were, as far as can be told from the surviving publications about them, too incomplete and unfinished to serve as auxlangs (or for any other practical purpose). The first fully developed constructed languages we know of, as well as the first constructed languages devised primarily as auxlangs, originated in the 19th century; Solresol by François Sudre, a language based on musical notes, was the first to gain widespread attention although not, apparently, fluent speakers. Volapük, first described in an article in 1879 by Johann Martin Schleyer and in book form the following year, was the first to garner a widespread international speaker community. Three major Volapük conventions were held, in 1884, 1887, and 1889; the last of them used Volapük as its working language. André Cherpillod writes of the third Volapük convention,
- In August 1889 the third convention was held in Paris. About two hundred people from many countries attended. And, unlike in the first two conventions, people spoke only Volapük. For the first time in the history of mankind, sixteen years before the Boulogne convention, an international convention spoke an international language.
However, not long after this the Volapük speaker community broke up due to various factors, including controversies between Schleyer and other prominent Volapük speakers, and the appearance of newer, easier-to-learn planned languages, primarily Esperanto. This language was developed from about 1878–1887, and published in that year, by L. L. Zamenhof. Within a few years it had thousands of fluent speakers, primarily in eastern Europe. In 1905 its first world convention was held in Boulogne-sur-Mer. A wide variety of other auxlangs were devised and proposed in the 1880s–1900s, but none except Esperanto gathered a speaker community until Ido.
The "Délégation pour l'adoption d'une langue auxiliaire internationale" was founded in 1900 by Louis Couturat and others; it tried to get the International Association of Academies to take up the question of an international auxiliary language, study the existing ones and pick one or design a new one. However, the meta-academy declining to do so, the Delegation decided to do the job itself. Among Esperanto speakers there was a general impression that the Delegation would of course choose Esperanto, as it was the only auxlang with a sizable speaker community at the time; it was felt as a betrayal by many Esperanto speakers when in 1907 the Delegation came up with its own reformed version of Esperanto, Ido. Ido drew a significant number of speakers away from Esperanto in the short term, but in the longer term most of these either returned to Esperanto or moved on to other new auxlangs. Still, Ido remains today one of the three most widely spoken auxlangs.
Edgar von Wahl's Occidental (also called "Interlingue"; 1922) was in reaction against the perceived artificiality of some earlier auxlangs, particularly Esperanto; von Wahl created a language whose words, including compound words, would have a high degree of recognizability for those who already know a Romance language. However, this design criterion was in conflict with ease of coining new compound or derived words on the fly while speaking. Occidental gained a small speaker community in the 1920s and 1930s, and supported several publications, but had almost entirely died out by the 1980s. More recently Occidental has been revived on the Internet.
The International Auxiliary Language Association was founded in 1924 by Alice Vanderbilt Morris; like the earlier Delegation, it at first worked on studying language problems and the existing auxlangs and proposals for auxlangs, and attempted to negotiate some consensus between the supporters of various auxlangs. However, like the Delegation, it finally decided to create its own auxlang; Interlingua, published in 1951, was primarily the work of Alexander Gode, though he built on preliminary work by earlier IALA linguists including André Martinet. Interlingua, like Occidental, was designed to have words recognizable at sight by those who already know a Romance language or a language like English with much vocabulary borrowed from Romance languages; to attain this end Gode accepted a degree of grammatical and orthographic irregularity and complexity considerably greater than in Volapük, Esperanto or Ido, though still less than in most natural languages. Interlingua gained a significant speaker community, perhaps roughly the same size as that of Ido (considerably less than the size of Esperanto.)
Esperanto suffered a setback after the 1922 proposal by Iran and several other small countries in the League of Nations to have Esperanto taught in member nations' schools failed, and Esperanto speakers were subject to persecution under Hitler and Stalin's regimes, but in spite of these factors more people continued to learn Esperanto, and significant literary work (both poetry and novels) began to appear in Esperanto in the period between the World Wars.
All of the auxlangs with a surviving speaker community seem to have benefited from the advent of the Internet, Esperanto more than most. The CONLANG mailing list was founded in 1991; in its early years discussion focused on international auxiliary languages. As people interested in artistic languages and engineered languages grew to be the majority of the list members, and flame-wars between proponents of particular auxlangs irritated these members, a separate AUXLANG mailing list was created, which has been the primary venue for discussion of auxlangs since then. Besides giving the existing auxlangs with speaker communities a chance to interact rapidly online as well as slowly through postal mail or more rarely in personal meetings, the Internet has also made it easier to publicize new auxlang projects, and a handful of these have gained a small speaker community, including Kotava, Lingua Franca Nova, Mondlango and Toki Pona.
List of languages 
19th century 
|Language name||ISO||Year of first
|Solresol||1827||François Sudre||Based on pitch levels sounded with their solfege syllables (a "musical language")|
|Communicationssprache||1839||Joseph Schipfer||Based on French|
|Universalglot||1868||Jean Pirro||An early a posteriori language, predating even Volapük|
|Volapük||vo, vol||1879–1880||Johann Martin Schleyer||First to generate international interest in IALs|
|Esperanto||eo, epo||1887||L. L. Zamenhof||Easily the most popular auxiliary language ever invented, including tens of thousands of speakers and the only one to date with its own native speakers|
|Spokil||1887 or 1890||Adolph Nicolas||An a priori language by a former Volapük advocate|
|Mundolinco||1888||J. Braakman||The first esperantido|
|Bolak||1899||Léon Bollack||Prospered fairly well in its initial years, now almost forgotten|
20th century 
|Language name||ISO||Year of first
|Idiom Neutral||1902||Waldemar Rosenberger||A naturalistic IAL by a former advocate of Volapük|
|Latino sine Flexione||1903||Giuseppe Peano||"Latin without inflections," it replaced Idiom Neutral in 1908|
|Ro||1904||Rev. Edward Powell Foster||An a priori language using categories of knowledge|
|Ido||io, ido||1907||A group of reformist Esperanto speakers||The most successful offspring of Esperanto|
|Adjuvilo||1910||Claudius Colas||An esperantido some believe was created to cause dissent among Idoists|
|Occidental||ile||1922||Edgar de Wahl||A sophisticated naturalistic IAL, also known as Interlingue|
|Novial||nov||1928||Otto Jespersen||Another sophisticated naturalistic IAL by a famous Danish linguist|
|Basic English||1930||Charles Kay Ogden||A reduced and simplified form of English, proposed as an international auxiliary language|
|Sona||1935||Kenneth Searight||Best known attempt at universality of vocabulary|
|Esperanto II||1937||René de Saussure||Last of linguist Saussure's many esperantidos|
|Mondial||1940s||Dr. Helge Heimer||Naturalistic European language|
|Glosa||igs||1943||Lancelot Hogben, et al.||Originally called Interglossa, has a strong Greco-Latin vocabulary|
|Blissymbols||zbl||1949||Charles Bliss||An ideographic writing system, with its own grammar and syntax.|
|Interlingua||ia, ina||1951||International Auxiliary Language Association||A major effort to develop a common Romance vocabulary|
|Intal||1956||Erich Weferling||An effort to unite the most common systems of constructed languages|
|Lingua sistemfrater||1957||Pham Xuan Thai||Greco-Latin vocabulary with southeast Asian grammar|
|Neo||1961||Arturo Alfandari||A very terse European language|
|Babm||1962||Rikichi Okamoto||Noted for using Latin letters as an abjad|
|Unilingua||1966||Noubar Agapoff||An a priori language with systematic vocabulary, also known as Mirad|
|Arcaicam Esperantom||1969||Manuel Halvelik||'Archaic Esperanto', developed for use in Esperanto literature|
|Afrihili||afh||1970||K. A. Kumi Attobrah||A pan-African language|
|Nuwaubic||1970s?||Malachi Z. York||The language of a black supremacist religious group|
|Kotava||avk||1978||Staren Fetcey||A sophisticated a priori IAL|
|Uropi||1986||Joël Landais||Based on the common Indo-European roots and the common grammatical points of the IE languages|
|Poliespo||1990s?||Nvwtohiyada Idehesdi Sequoyah||Esperanto grammar with significant Cherokee vocabulary|
|Europanto||1996||Diego Marani||A "linguistic jest" by a European diplomat|
|Unish||1996||Language Research Institute, Sejong University||Vocabulary from fifteen representative languages|
|Noxilo||1997||Mizta Sentaro||a language trying to avoid any regional or ethnic bias|
|Lingua Franca Nova||lfn||1998||C. George Boeree and others||Romance vocabulary with creole-like grammar|
|Slovio||1999||Mark Hučko||A constructed language based on the Slavic languages and Esperanto grammar|
21st century 
|Language name||ISO||Year of first
|Mondlango||2002||He Yafu||Simple English-Romance language from Asia|
|Slovianski||2006||Ondrej Rečnik, Gabriel Svoboda, Jan van Steenbergen, Igor Polyakov||A naturalistic language based on the Slavic languages|
|Kah||2006||Anonymous||An analytic a priori language designed to be easy to learn and pronounce|
|Modern Indo-European||2006||Carlos Quiles, María Teresa Batalla||Based on Proto-Indo-European language|
|Sambahsa-Mundialect||2007||Olivier Simon||Mixture of simplified Proto-Indo-European and other languages|
|Angos||2012||Benjamin Wood||Simplified worldlang with a strict grammar|
Scholarly study 
In the early 1900s auxlangs were already becoming a subject of academic study. Louis Couturat et al. described the controversy in the preface to their book International Language and Science:
- The question of a so-called world-language, or better expressed, an international auxiliary language, was during the now past Volapük period, and is still in the present Esperanto movement, so much in the hands of Utopians, fanatics and enthusiasts, that it is difficult to form an unbiased opinion concerning it, although a good idea lies at its basis. (1910, p. v).
For Couturat et al., both Volapukists and Esperantists confounded the linguistic aspect of the question with many side issues, and they considered this a main reason why discussion about the idea of an international auxiliary language has appeared unpractical. Leopold Pfaundler wrote that an IAL was needed for more effective communication among scientists:
- All who are occupied with the reading or writing of scientific literature have assuredly very often felt the want of a common scientific language, and regretted the great loss of time and trouble caused by the multiplicity of languages employed in scientific literature.
The following classification of auxiliary languages was developed by Pierre Janton in 1993:
- A priori languages are characterized by largely artificial morphemes (not borrowed from natural languages), schematic derivation, simple phonology, grammar and morphology. Some a priori languages are called philosophical languages, referring to their basis in philosophical ideas about thought and language. These include some of the earliest efforts at auxiliary language in the 17th century. Some more specific subcategories:
- Oligosynthetic or oligoisolating languages have no more than a few hundred morphemes. Most of their vocabulary is made of compound words or set phrases formed from these morphemes. Sona and Toki Pona are well known examples, although Toki Pona's word stock is mostly based on other languages and therefore not a priori.
- Taxonomic languages form their words using a taxonomic hierarchy, with each phoneme of a word helping specify its position in a semantic hierarchy of some kind; for example, Solresol and Ro.
- Pasigraphies are purely written languages without a spoken form, or with a spoken form left at the discretion of the reader; many of the 17th–18th century philosophical languages and auxlangs were pasigraphies. This set historically tends to overlap with taxonomic languages, though there is no inherent reason a pasigraphy needs to be taxonomic.
- Logical languages, for example, Loglan and Lojban, aim to eliminate ambiguity. Both these examples, it should be noted, derive their morphemes from a broad range of natural languages using statistical methods.
- A posteriori languages are based on existing natural languages. Nearly all the auxiliary languages with fluent speakers are in this category. Most of the a posteriori auxiliary languages borrow their vocabulary primarily or solely from European languages, and base their grammar more or less on European models. (Sometimes these European-based languages are referred to as "euroclones", although this term has negative connotations and is not used in the academic literature.) Interlingua was drawn originally from international scientific vocabulary, in turn based primarily on Greek and Latin roots. Glosa did likewise, with a stronger dependence of Greek roots. Although a posteriori languages have been based on most of the families of European languages, the most successful of these (notably Esperanto, Ido and Interlingua) have been based largely on Romance elements.
- Schematic (or "mixed") languages have some a priori qualities. Some have ethnic morphemes but alter them significantly to fit a simplified phonotactic pattern (e.g., Volapük, Toki Pona) or both artificial and natural morphemes (e.g., Perio). Partly schematic languages have partly schematic and partly naturalistic derivation (e.g. Esperanto and Ido). Natural morphemes of languages in this group are rarely altered greatly from their source-language form, but compound and derived words are generally not recognizable at sight by people familiar with the source languages.
- Naturalistic languages resemble existing natural languages. For example, Occidental, Interlingua, and Lingua Franca Nova were developed so that not only the root words but their compounds and derivations will often be recognizable immediately by large numbers of people. Some naturalistic languages do have a limited number of artificial morphemes or invented grammatical devices (e.g. Novial). (Note that the term "naturalistic" as used in auxiliary language scholarship[which?] does not mean the same thing as the homophonous term used in describing artistic languages.[better source needed])
- Simplified natural languages reduce the full extent of vocabulary and partially regularize the grammar of a natural language (e.g. Basic English, Special English and Globish).
Comparison of sample texts 
Some examples of the best known international auxiliary languages are shown below for comparative purposes. As a reference for comparison, you can find the English and Latin versions of the Lord's Prayer (a text which is regularly used for linguistic comparisons) here:
|The Lord's Prayer in English (traditional)||The Lord's Prayer in Latin|
Our Father, who art in heaven,
Pater noster, qui es in cælis,
Schematic languages 
|Volapük version||Esperanto version||Ido version||Idiom Neutral version|
O Fat obas, kel binol in süls,
Patro Nia, kiu estas en la ĉielo,
Patro nia, qua esas en la cielo,
Nostr patr kel es in sieli!
Naturalistic languages 
|Latino sine flexione version||Occidental version||Novial version||Interlingua version|
Patre nostro, qui es in celos,
Patre nor, qui es in li cieles,
Nusen Patre, kel es in siele,
Patre nostre, qui es in le celos,
Methods of propagation 
As has been pointed out, the issue of an international language is not so much which, but how. Several approaches exist toward the eventual full expansion and consolidation of an international auxiliary language.
- Laissez-faire. This approach is taken in the belief that one language will eventually and inevitably "win out" as a world auxiliary language (e.g. International English) without any need for specific action.
- Institutional sponsorship and grass-roots promotion of language programs. This approach has taken various forms, depending on the language and language type, ranging from government promotion of a particular language to one-on-one encouragement to learn the language to instructional or marketing programs.
- National legislation. This approach seeks to have individual countries (or even localities) progressively endorse a given language as an official language (or to promote the concept of international legislation).
- International legislation. This approach involves promotion of the future holding of a binding international convention (perhaps to be under the auspices of such international organizations as the United Nations or Inter-Parliamentary Union) to formally agree upon an official international auxiliary language which would then be taught in all schools around the world, beginning at the primary level. This approach seeks to put international opinion and law behind the language and thus to expand or consolidate it as a full official world language. This approach could either give more credibility to a natural language already serving this purpose to a certain degree (e.g. if English were chosen) or to give a greatly enhanced chance for a constructed language to take root. For constructed languages particularly, this approach has been seen by various individuals in the IAL movement as holding the most promise of ensuring that promotion of studies in the language would not be met with skepticism at its practicality by its would-be learners.
Pictorial languages 
There have been a number of proposals for using pictures, ideograms, diagrams, and other pictorial representations for international communications. Examples range from the original Characteristica Universalis proposed by the philosopher Leibniz, to suggestions for the adoption of Chinese writing, to recent inventions such as Blissymbol.
Within the scientific community, there is already considerable agreement in the form of the schematics used to represent electronic circuits, chemical symbols, mathematical symbols,and the Energy Systems Language of systems ecology. We can also see the international efforts at regularizing symbols used to regulate traffic, to indicate resources for tourists, and in maps. Some symbols have become nearly universal through their consistent use in computers and on the internet.
Sign languages 
An international auxiliary sign language has been developed by deaf people who meet regularly at international forums such as sporting events or in political organisations. Previously referred to as Gestuno but now more commonly known simply as 'international sign', the language has continued to develop since the first signs were standardised in 1973, and it is now in widespread use. International sign is distinct in many ways from spoken IALs; many signs are iconic and signers tend to insert these signs into the grammar of their own sign language, with an emphasis on visually intuitive gestures and mime. A simple sign language called Plains Indian Sign Language was used by indigenous peoples of the Americas.
Gestuno is not to be confused with the separate and unrelated sign language Signuno, which is essentially a Signed Exact Esperanto. Signuno is not in any significant use, and is based on the Esperanto community rather than based on the international Deaf community.
There has been considerable criticism of international auxiliary languages, both in terms of individual proposals, types of proposals, and in more general terms.
Criticisms directed against Esperanto and other early auxlangs in the late 19th century included the idea that different races have sufficiently different speech organs that an international language might work locally in Europe, but hardly worldwide, and the prediction that if adopted, such an auxlang would rapidly break up into local dialects. Advances in linguistics have done away with the first of these, and the limited but significant[dubious ] use of Esperanto, Ido and Interlingua on an international scale, without breakup into unintelligible dialects, has shown that either a rapid break-up into dialects shall not happen too soon in the future, or that there is enough constant 'standardisation' to reduce the diversity of the language. Subsequently, much criticism has been focused either on the artificiality of these auxlangs, or on the argumentativeness of auxlang proponents and their failure to agree on one auxlang, or even on objective criteria by which to judge auxlangs. However, probably the most common criticism is that a constructed auxlang is unnecessary because natural languages such as English are already in wide use as auxlangs and work well enough for that purpose.
One criticism already prevalent in the late 19th century, and still sometimes heard today, is that an international language might hasten the extinction of minority languages. One response has been that, even if this happens, the benefits would outweigh the costs; another, that proponents of auxlangs, particularly in the Esperanto movement, are generally also proponents of measures to conserve and promote minority languages[why?] and cultures.
Although referred to as international languages, most of these languages have historically been constructed on the basis of Western European languages. In the late 19th and early 20th centuries it was common for Volapük and Esperanto, and to some extent Ido, to be criticized for not being Western European enough; Occidental and Interlingua were (among other things) responses to this kind of criticism. More recently all these major auxlangs have been criticized for being too European and not global enough. One response to this criticism has been that doing otherwise in no way makes the language easier for anyone, while drawing away from the sources of much international vocabulary, technical and popular. Another response, primarily from Esperanto speakers, is that the internationality of a language has more to do with the culture of its speakers than with its linguistic properties. The term "Euroclone" was coined to refer to these languages in contrast to "worldlangs" with global vocabulary sources; the term is sometimes applied only to self-proclaimed "naturalistic" auxlangs such as Occidental and Interlingua, sometimes to all auxlangs with primarily European vocabulary sources, regardless of their grammar, including Esperanto and Lingua Franca Nova.
The response to this argument was made by Alexander Gode and reiterated by Mario Pei: A vocabulary selected from a broad variety of languages does not make the language any easier for speakers of any one language. Gode's example compares a paragraph in Interlingua with a paragraph with words from Chinese, Japanese, Malay, and other non-European languages. The first is readily understood by anyone familiar with the Romance languages, and not difficult for most English speakers:
- La sol dice: "io me appella sol. Io es multo brillante. Io me leva al est, e cuando io me leva, il es die. Io reguarda per tu fenestra con mi oculo brillante como le auro, e io te dice quando il es tempore a levar te. E io te dice: 'Pigro, leva te. Io non brilla a fin que tu resta al lecto a dormir, sed que tu lege e que tu te promena.'"
The second is not only difficult for Europeans, but the Malay speaker will not understand the Chinese words, the Chinese speaker will not understand the Japanese words, and the Japanese speaker will not understand the Malay words:
- Mata-hari yu: "Wo-ti nama mata-hari. Wo taihen brillante. Wo leva wo a est, dan toki wo leva wo, ada hari. Wo miru per ni-ti fenestra sama wo-ti mata brillante como kin, dan wo yu ni toki ada tempo a levar ni. Dan wo yu ni: 'Sust, leva ni. Wo non brilla sam-rap ni tomaru a toko a nemuru, sed wo brilla sam-rap ni leva ni, dan que ni suru kam, ni yomu, dan ni aruku.'"
Gode argues, additionally, that the western languages are the unofficial languages of international science, medicine, and technology, and therefore an IAL based on them provides the best access to that literature. Nevertheless, it must be said that a more neutral vocabulary, perhaps even an a priori one, would be less offensive to some non-Europeans.
In the 1990s and early 2000s, many proposals for auxlangs based on global sources of vocabulary and grammar have been made, but most (like the majority of the European-based auxlangs of earlier decades) remain sketches too incomplete to be speakable, and of the more complete ones, few have gained any speakers. More recently there has been a trend, on the AUXLANG mailing list and on the more recently founded worldlang mailing list, to greater collaboration between various proponents of a more globally based auxlang.
See also 
See List of constructed languages#Auxiliary languages for a list of designed international auxiliary languages.
- International Language Review
- Language education
- Language planning
- Lingua franca
- Bahá'í Faith and auxiliary language
- Zonal constructed languages
- Bodmer, Frederick. The loom of language and Pei, Mario. One language for the world.
- Foreword to Konciza Gramatiko de Volapuko, André Cherpillod. Courgenard, 1995.
- Otto Jesperson, An International Language. "The Delegation. Ido." 1928.
- Harlow, Don. The Esperanto Book, chapter 3: "How to Build a Language".
- Le Defi des Langues by Claude Piron, L'Harmattan 1994.
- The Esperanto Book, Chapter 7: History in Fine by Don Harlow. 1995.
- Lins, Ulrich. La Danĝera Lingvo. Gerlingen, Germany: Bleicher Eldonejo, 1988.
- The Esperanto Book, Chapter 9: "The Literary Scene" by Don Harlow. 1995.
- Although Toki Pona was not intended by its creator as an auxlang, it has been used for communication between people of different native languages far more often than most of the thousands of auxlang proposals throughout history.
- L. Couturat, O. Jespersen, R. Lorenz, W.Ostwalkd and L.Pfaundler. International Language and Science: Considerations on the Introduction of an International Language into Science. 1910.
- Pierre Janton, Esperanto: Language, Literature, and Community. Translated by Humphrey Tonkin et al. State University of New York Press, 1993. ISBN 0-7914-1254-7.
- "Essay (hopefully long)", by Don Harlow. AUXLANG mailing list post, 7 January 2006.
- "Re: "Naturalistic" for auxlangers vs artlangers?" AUXLANG mailing list post by Jörg Rhiemeier, 30 August 2009
- Mario Pei, One language for the world (1958)
- Charles Keisel Bliss, Semantography (Blissymbolics)
- Rubino, F., Hayhurst, A., and Guejlman, J., Gestuno: International sign language of the deaf.
- "Esenco kaj Estonteco de la Ideo de Lingvo Internacia", L. L. Zamenhof, 1900. Reprinted in Fundamenta Krestomatio, 1992 .
- "Farewell to auxiliary languages", by Richard K. Harrison. 1997.
- "Ĉu Zamenhof Pravis?", Vinko Ošlak, Fonto, februaro 2005.
- "Types of neutrality, and central concerns for an IAL". AUXLANG mailing list post by Risto Kupsala, 2 December 2005.
- Alexander Gode, quoted by Mario Pei in One language for the world (1958).
- Gode, Alexander, et al. Interlingua-English: a dictionary of the international language. Storm Publishers, New York, 1951.
- Pei, Mario. One Language for the World. N.Y.: Devin-Adair, 1958:
- Bliss, Charles Keisel. Semantography (Blissymbolics). Semantography Press: Sydney, 1965.
- Bodmer, Frederick, and Lancelot Hogben. The Loom of Language. N.Y.: Norton, 1944.
- Couturat, L., Jespersen, O., Lorenz, R., Ostwalkd, W., and Pfaundler, L. International Language and Science: Considerations on the Introduction of an International Language into Science. Constable and Company Limited, London, 1910.
- De Wahl, Edgar. Radicarium directiv del lingue international (Occidental) in 8 lingues. A.-S. "Ühisell" Trükk. Pikk Uul. 42, Tallinn, 1925.
- Drezen, Ernst: Historio de la Mondlingvo ("History of the World Language"). Oosaka: Pirato, 1969 (3d ed.).
- Eco, Umberto, [tra. James Fentress], The Search for the Perfect Language. Oxford: Blackwell, 1995.
- Gär, Joseph. Deutsch-Occidental Wörterbuch nach dem Kürschners "Sechs-Sprachen-Lexicon", mit kurzer Occidental-Grammatik. Kosmoglott, Reval, Estland, 1925/1928.
- Gode, Alexander, et al. Interlingua-English: a dictionary of the international language. Storm Publishers, New York, 1951.
- Jesperson, Otto. An International Language. (1928)
- Mainzer, Ludwig, Karlsruhe. Linguo international di la Delegitaro (Sistemo Ido), Vollständiges Lehrbuch der Internationalen Sprache (Reform-Esperanto). Otto Nemmich Verlag, Leipzig (Germany), 1909.
- Meyjes, Gregory P. P. 2006. "Language and world order in Bahá'í perspective: a new paradigm revealed." In T. Omoniyi & J. A. Fishman (Eds.) Explorations in the Sociology of Language and Religion, 26 – 41, Amsterdam: John Benjamins.
- Nerrière, Jean-Paul, and Hon, David Globish The World Over. Paris, IGI, 2009
- Pei, Mario. One Language for the World. N.Y.: Devin-Adair, 1958.
- Pham Xuan Thai. Frater (Lingua sistemfrater). The simplest International Language Ever Constructed. TU-HAI Publishing-House, Saigon (Republic of Vietnam), 1957.
- Pigal, E. and the Hauptstelle der Occidental-Union in Mauern bei Wien. Occidental, Die Weltsprache, Einführung samt Lehrkursus, Lesestücken, Häufigkeitswörterverzeichnis u. a., Franckh. Verlagshandlung, Stuttgart, 1930.
- Pirro, Jean. Versuch einer Universalischen Sprache. Guerin und Cie., Bar-Le-Duc (France), 1868.
- Rubino, F., Hayhurst, A., and Guejlman, J. Gestuno: International sign language of the deaf. Carlisle: British Deaf Association, 1975.
- Sudre, François. Langue musicale universelle inventée par François Sudre également inventeur de la téléphonie. G. Flaxland, Editeur, 4, place de la Madeleine, Paris (France), 1866.
- Proposed Guidelines for the Design of an Optimal International Auxiliary Language — An article written by Richard K. Harrison.
- The Function of an International Auxiliary Language — An article written by linguist Edward Sapir discussing the need for prospects of an international language.
- Farewell to auxiliary languages, a criticism of the auxiliary language movement by Richard K. Harrison.
- Thoughts on IAL Success, an essay by Paul O. Bartlett
- OneTongue.com — A project for promoting a world auxiliary language.
- Language International