|Pronunciation||//; IA: [inteɾˈliŋɡwa]|
|Created by||International Auxiliary Language Association|
|Setting and usage||Scientific registration of international vocabulary; international auxiliary language|
|Users||A few hundred (date missing)|
|Writing system||Latin script|
|Sources||Source languages: French, Italian, Portuguese, Spanish, German, English, Russian and Latin|
|Regulated by||No regulating body|
Interlingua (pron.: //; ISO 639 language codes ia, ina) is an international auxiliary language (IAL), developed between 1937 and 1951 by the International Auxiliary Language Association (IALA). It ranks among the top three most widely used IALs (after Esperanto and perhaps Ido), and is the most widely used naturalistic IAL: in other words, its vocabulary, grammar and other characteristics are largely derived from natural languages. Interlingua was developed to combine a simple, mostly regular grammar with a vocabulary common to the widest possible range of languages, making it unusually easy to learn, at least for those whose native languages were sources of Interlingua's vocabulary and grammar. Conversely, it is used as a rapid introduction to many natural languages. Interlingua literature maintains that (written) Interlingua is comprehensible to the hundreds of millions of people who speak a Romance language, though it is actively spoken by only a few hundred.
The name Interlingua comes from the Latin words inter, meaning between, and lingua, meaning tongue or language. These morphemes are identical in Interlingua. Thus, Interlingua would be "between language", or intermediary language.
The expansive movements of science, technology, trade, diplomacy, and the arts, combined with the historical dominance of the Greek and Latin languages have resulted in a large common vocabulary among European languages. With Interlingua an objective procedure is used to extract and standardize the most widespread word or words for a concept found in a set of control languages: English, French, Italian, Spanish and Portuguese, with German and Russian as secondary references. Words from any language are eligible for inclusion, so long as their internationality is shown by their presence in these control languages. Hence, Interlingua includes such diverse word forms as Japanese geisha and samurai, Arabic califa, Aboriginal kanguru, and Finnish sauna.
Interlingua combines this pre-existing vocabulary with a minimal grammar based on the control languages. People with a good knowledge of a Romance language, or a smattering of a Romance language plus a good knowledge of the international scientific vocabulary can frequently understand it immediately on reading or hearing it. Educated speakers of English also enjoy this easy comprehension. The immediate comprehension of Interlingua, in turn, makes it unusually easy to learn. Speakers of other languages can also learn to speak and write Interlingua in a short time, thanks to its simple grammar and regular word formation using a small number of roots and affixes.
Once learned, Interlingua can be used to learn other related languages quickly and easily, and in some studies, even to understand them immediately. Research with Swedish students has shown that, after learning Interlingua, they can translate elementary texts from Italian, Portuguese, and Spanish. In one 1974 study, an Interlingua class translated a Spanish text that students who had taken 150 hours of Spanish found too difficult to understand. Gopsill has suggested that Interlingua's freedom from irregularities allowed the students to grasp the mechanisms of language quickly.
Words in Interlingua retain their original form from the source language; they are altered as little as possible to fit Interlingua's phonotactics. Each word retains its original spelling, pronunciation, and meanings. For this reason, Interlingua is frequently termed a naturalistic IAL.
The American heiress Alice Vanderbilt Morris (1874–1950) became interested in linguistics and the international auxiliary language movement in the early 1920s, and in 1924, Morris and her husband, Dave Hennen Morris, established the non-profit International Auxiliary Language Association (IALA) in New York City. Their aim was to place the study of IALs on a scientific basis. Morris developed the research program of IALA in consultation with Edward Sapir, William Edward Collinson, and Otto Jespersen.
International Auxiliary Language Association 
The IALA became a major supporter of mainstream American linguistics, funding, for example, numerous studies by Sapir, Collinson, and Morris Swadesh in the 1930s and 1940s. Alice Morris edited several of these studies and provided much of IALA's financial support. IALA also received support from such prestigious groups as the Carnegie Corporation, the Ford Foundation, the Research Corporation, and the Rockefeller Foundation.
In its early years, IALA concerned itself with three tasks: finding other organizations around the world with similar goals; building a library of books about languages and interlinguistics; and comparing extant IALs, including Esperanto, Esperanto II, Ido, Peano’s Interlingua (Latino sine flexione), Novial, and Interlingue (Occidental). In pursuit of the last goal, it conducted parallel studies of these languages, with comparative studies of national languages, under the direction of scholars at American and European universities. It also arranged conferences with proponents of these IALs, who debated features and goals of their respective languages. With a "concession rule" that required participants to make a certain number of concessions, early debates at IALA sometimes grew from heated to explosive.
At the Second International Interlanguage Congress, held in Geneva in 1931, IALA began to break new ground; 27 recognized linguists signed a testimonial of support for IALA's research program. An additional eight added their signatures at the third congress, convened in Rome in 1933. That same year, Professor Herbert N. Shenton and Dr. Edward L. Thorndike became influential in IALA's work by authoring key studies in the interlinguistic field.
The first steps towards the finalization of Interlingua were taken in 1937, when a committee of 24 eminent linguists from 19 universities published Some Criteria for an International Language and Commentary. However, the outbreak of World War II in 1939 cut short the intended biannual meetings of the committee.
Development of a new language 
Originally, the association had not set out to create its own language. Its goal was to identify which auxiliary language already available was best suited for international communication, and how to promote it most effectively. However, after ten years of research, more and more members of IALA concluded that none of the existing interlanguages were up to the task. By 1937, the members had made the decision to create a new language, to the surprise of the world's interlanguage community.
To that point, much of the debate had been equivocal on the decision to use naturalistic (e.g., Peano’s Interlingua, Novial and Occidental) or systematic (e.g., Esperanto and Ido) words. During the war years, proponents of a naturalistic interlanguage won out. The first support was Dr. Thorndike's paper; the second was a concession by proponents of the systematic languages that thousands of words were already present in many – or even a majority – of the European languages. Their argument was that systematic derivation of words was a Procrustian bed, forcing the learner to unlearn and re-memorize a new derivation scheme when a usable vocabulary was already available. This finally convinced supporters of the systematic languages, and IALA from that point assumed the position that a naturalistic language would be best.
At the outbreak of World War II, IALA's research activities were moved from Liverpool to New York, where E. Clark Stillman established a new research staff. Stillman, with the assistance of Dr. Alexander Gode, developed a prototyping technique – an objective methodology for selecting and standardizing vocabulary based on a comparison of control languages.
In 1943 Stillman left for war work and Gode became Acting Director of Research. IALA began to develop models of the proposed language, the first of which were presented in Morris's General Report in 1945.
From 1946 to 1948, renowned French linguist André Martinet was Director of Research. During this period IALA continued to develop models and conducted polling to determine the optimal form of the final language. In 1946, IALA sent an extensive survey to more than 3,000 language teachers and related professionals on three continents.
Four models were canvassed:
|Model P||highly naturalistic, with word forms unchanged from the prototypes|
|Model M||moderately naturalistic, similar to Occidental|
|Model C||slightly schematic, along the lines of Novial|
|Model K||moderately schematic, similar to Ido (less schematic than Esperanto)|
The results of the survey were striking. The two more schematic models were rejected – K overwhelmingly. Of the two naturalistic models, M received somewhat more support than P. IALA decided on a compromise between P and M, with certain elements of C.
Martinet took up a position at Columbia University in 1948, and Gode took on the last phase of Interlingua's development. The vocabulary and grammar of Interlingua were first presented in 1951, when IALA published the finalized Interlingua Grammar and the 27,000-word Interlingua–English Dictionary (IED). In 1954, IALA published an introductory manual entitled Interlingua a Prime Vista ("Interlingua at First Sight").
Interestingly, the Interlingua presented by the IALA is very close to Peano’s Interlingua (Latino sine flexione), both in its grammar and especially in its vocabulary. Accordingly, the very name "Interlingua" was kept, yet a distinct abbreviation was adopted: IA instead of IL.
Success, decline, and resurgence 
An early practical application of Interlingua was the scientific newsletter Spectroscopia Molecular, published from 1952 to 1980. In 1954, Interlingua was used at the Second World Cardiological Congress in Washington, D.C. for both written summaries and oral interpretation. Within a few years, it found similar use at nine further medical congresses. Between the mid-1950s and the late 1970s, some thirty scientific and especially medical journals provided article summaries in Interlingua. Science Service, the publisher of Science Newsletter at the time, published a monthly column in Interlingua from the early 1950s until Gode's death in 1970. In 1967, the powerful International Organization for Standardization, which normalizes terminology, voted almost unanimously to adopt Interlingua as the basis for its dictionaries.
The IALA closed its doors in 1953 but was not formally dissolved until 1956 or later. Its role in promoting Interlingua was largely taken on by Science Service, which hired Gode as head of its newly formed Interlingua Division. Hugh E. Blair, Gode's close friend and colleague, became his assistant. A successor organization, the Interlingua Institute, was founded in 1970 to promote Interlingua in the US and Canada. The new institute supported the work of other linguistic organizations, made considerable scholarly contributions and produced Interlingua summaries for scholarly and medical publications. One of its largest achievements was two immense volumes on phytopathology produced by the American Phytopathological Society in 1976 and 1977.
Interlingua had attracted many former adherents of other international-language projects, notably Occidental and Ido. The former Occidentalist Ric Berger founded The Union Mundial pro Interlingua (UMI) in 1955, and by the late 1950s, interest in Interlingua in Europe had already begun to overtake that in North America.
Beginning in the 1980s UMI has held international conferences every two years (typical attendance at the earlier meetings was 50 to 100) and launched a publishing programme that eventually produced over 100 volumes. Other Interlingua-language works were published by university presses in Sweden and Italy, and in the 1990s, Brazil and Switzerland. Several Scandinavian schools undertook projects that used Interlingua as a means of teaching the international scientific and intellectual vocabulary.
In 2000, the Interlingua Institute was dissolved amid funding disputes with the UMI; the American Interlingua Society, established the following year, succeeded the institute and responded to new interest emerging in Mexico.
In the Socialist bloc 
Interlingua was spoken and promoted in the Socialist countries, despite attempts to suppress the language. In East Germany, government officials confiscated the letters and magazines that the UMI sent to Walter Raédler, the Interlingua representative there.
In Czechoslovakia, Július Tomin published his first article on Interlingua in the Slovak magazine Príroda a spoločnosť (Nature and Society) in 1971, after which he received several anonymous threatening letters. He went on to become the Czech Interlingua representative, teach Interlingua in the school system, and publish a series of articles and books.
Interlingua today 
- See also: Community, below
Today, interest in Interlingua has expanded from the scientific community to the general public. Individuals, governments, and private companies use Interlingua for learning and instruction, travel, online publishing, and communication across language barriers. Interlingua is promoted internationally by the Union Mundial pro Interlingua. Periodicals and books are produced by many national organizations, such as the Societate American pro Interlingua, the Svenska Sällskapet för Interlingua, and the Union Brazilian pro Interlingua.
From an essay by Alexander Gode:
- Interlingua se ha distachate ab le movimento pro le disveloppamento e le introduction de un lingua universal pro tote le humanitate. Si o non on crede que un lingua pro tote le humanitate es possibile, si o non on crede que interlingua va devenir un tal lingua es totalmente indifferente ab le puncto de vista de interlingua mesme. Le sol facto que importa (ab le puncto de vista de interlingua mesme) es que interlingua, gratias a su ambition de reflecter le homogeneitate cultural e ergo linguistic del occidente, es capace de render servicios tangibile a iste precise momento del historia del mundo. Il es per su contributiones actual e non per le promissas de su adherentes que interlingua vole esser judicate.
- Interlingua has detached itself from the movement for the development and introduction of a universal language for all humanity. Whether or not one believes that a language for all humanity is possible, whether or not one believes that Interlingua will become such a language is totally irrelevant from the point of view of Interlingua itself. The only fact that matters (from the point of view of Interlingua itself) is that Interlingua, thanks to its ambition of reflecting the cultural and thus linguistic homogeneity of the West, is capable of rendering tangible services at this precise moment in the history of the world. It is by its present contributions and not by the promises of its adherents that Interlingua wishes to be judged.
|The Lord's Prayer in Interlingua||Latino sine flexione version||Latin version||English version (traditional)|
Patre nostre, qui es in le celos,
Patre nostro, qui es in celos,
Pater noster, qui es in cælis,
Our Father, who art in heaven,
Interlingua's greatest advantage is that it is the most widely understood international auxiliary language by virtue of its naturalistic (as opposed to schematic) grammar and vocabulary, allowing those familiar with a Romance language, and educated speakers of English, to read and understand it without prior study.
Interlingua has active speakers on all continents, especially in South America and in Eastern and Northern Europe, most notably Scandinavia; also in Russia and Ukraine. In Africa, Interlingua has official representation in the Republic of the Congo. There are copious Interlingua web pages, including editions of Wikipedia and Wiktionary, and a number of periodicals, including Panorama in Interlingua from the Union Mundial pro Interlingua (UMI) and magazines of the national societies allied with it. There are several active mailing lists, and Interlingua is also in use in certain Usenet newsgroups, particularly in the europa.* hierarchy. Interlingua is presented on CDs, radio, and television. In recent years, samples of Interlingua have also been seen in music and anime.
Interlingua is taught in many high schools and universities, sometimes as a means of teaching other languages quickly, presenting interlinguistics, or introducing the international vocabulary. The University of Granada in Spain, for example, offers an Interlingua course in collaboration with the Centro de Formación Continua.
Every two years, the UMI organizes an international conference in a different country. In the year between, the Scandinavian Interlingua societies co-organize a conference in Sweden. National organizations such as the Union Brazilian pro Interlingua also organize regular conferences.
Phonology and orthography 
Interlingua is primarily a written language, and the pronunciation is not entirely settled. The sounds in parentheses are not used by all speakers.
|Affricates||(ts ~ tʃ)|
Interlingua alphabet 
|Letters (upper case)||A||B||C||D||E||F||G||H||I||J||K||L||M||N||O||P||Q||R||S||T||U||V||W||X||Y||Z|
|Letters (lower case)||a||b||c||d||e||f||g||h||i||j||k||l||m||n||o||p||q||r||s||t||u||v||w||x||y||z|
|IPA||[a]||[b]||[k], [t͡s] 1||[d]||[e]||[f]||[ɡ]||[h], [∅] 2||[i]||[ʒ]||[k]||[l]||[m]||[n]||[o]||[p]||[k] 3||r||[s], [z]||[t], [t͡s] 4||[u]||[v]||[w], [v]||[ks]||[i]||[z]|
- c is pronounced [t͡s] (or optionally [s]) before "e, i, y"
- h is normally silent
- q only appears in the digraph qu, which is pronounced [kw] (but [k] in the conjunction and pronoun que and pronoun "qui")
- t is generally [t], but ti followed by a vowel, unless stressed or preceded by "s", is pronounced [t͡sj] (or optionally [sj])
Orthography and pronunciation 
Interlingua has a largely phonemic orthography. For the most part, consonants are pronounced as in English, while the vowels are like Spanish. Double consonants are pronounced as single. Interlingua has five falling diphthongs, /ai/, /au/, /ei/, /eu/, and /oi/, although /ei/ and /oi/ are rare.
The general rule is that stress falls on the vowel before the last consonant (e.g., lingua, 'language', esser, 'to be', requirimento, 'requirement'), and where that isn't possible, on the first vowel (via, 'way', io crea, 'I create'). There are a few exceptions, and the following rules account for most of them:
- Adjectives and nouns ending in a vowel followed by -le, -ne, or -re are stressed on the third-last syllable (fragile, margine, altere 'other', but illa impone 'she imposes').
- Words ending in -ica/-ico, -ide/-ido and -ula/-ulo, are stressed on the third-last syllable (politica, scientifico, rapide, stupido, capitula, seculo 'century').
- Words ending in -ic are stressed on the second-last syllable (cubic).
Speakers may pronounce all words according to the general rule mentioned above. For example, kilometro is acceptable, although kilometro is more common.
Unassimilated foreign loanwords, or borrowed words, are pronounced and spelled as in their language of origin. Their spelling may contain diacritics, or accent marks. If the diacritics do not affect pronunciation, they are removed.
Interlingua has no explicitly defined phonotactics. However, the prototyping procedure for determining Interlingua words, which strives for internationality, should in general lead naturally to words that are easy for most learners to pronounce. In the process of forming new words, an ending cannot always be added without a modification of some kind in between. A good example is the plural -s, which is always preceded by a vowel to prevent the occurrence of a hard-to-pronounce consonant cluster at the end. If the singular does not end in a vowel, the final -s becomes -es.
Words in Interlingua may be taken from any language, as long as their internationality is verified by their presence in seven control languages: Spanish, Portuguese, Italian, French, and English, with German and Russian acting as secondary controls. These are the most widely spoken Romance, Germanic, and Slavic languages, respectively. Because of their close relationship, Spanish and Portuguese are treated as one unit. The largest number of Interlingua words are of Latin origin, with the Greek and Germanic languages providing the second and third largest number. The remainder of the vocabulary originates in Slavic and non-Indo-European languages.
A word, that is a form with meaning, is eligible for the Interlingua vocabulary if it is verified by at least three of the four primary control languages. Either secondary control language can substitute for a primary language. Any word of Indo-European origin found in a control language can contribute to the eligibility of an international word. In some cases, the archaic or potential presence of a word can contribute to its eligibility.
A word can be potentially present in a language when a derivative is present, but the word itself is not. English proximity, for example, gives support to Interlingua proxime, meaning 'near, close'. This counts as long as one or more control languages actually have this basic root word, which the Romance languages all do. Potentiality also occurs when a concept is represented as a compound or derivative in a control language, the morphemes that make it up are themselves international, and the combination adequately conveys the meaning of the larger word. An example is Italian fiammifero (lit. flamebearer), meaning "match, lucifer", which leads to Interlingua flammifero, or "match". This word is thus said to be potentially present in the other languages although they may represent the meaning with a single morpheme.
Words do not enter the Interlingua vocabulary solely because cognates exist in a sufficient number of languages. If their meanings have become different over time, they are considered different words for the purpose of Interlingua eligibility. If they still have one or more meanings in common, however, the word can enter Interlingua with this smaller set of meanings.
If this procedure did not produce an international word, the word for a concept was originally taken from Latin (see below). This only occurred with a few grammatical particles.
The form of an Interlingua word is considered an international prototype with respect to the other words. On the one hand, it should be neutral, free from characteristics peculiar to one language. On the other hand, it should maximally capture the characteristics common to all contributing languages. As a result, it can be transformed into any of the contributing variants using only these language-specific characteristics. If the word has any derivatives that occur in the source languages with appropriate parallel meanings, then their morphological connection must remain intact; for example, the Interlingua word for 'time' is spelled tempore and not *tempus or *tempo in order to match it with its derived adjectives, such as temporal.
The language-specific characteristics are closely related to the sound laws of the individual languages; the resulting words are often close or even identical to the most recent form common to the contributing words. This sometimes corresponds with that of Vulgar Latin. At other times, it is much more recent or even contemporary. It is never older than the classical period.
An illustration 
The French œil, Italian occhio, Spanish ojo, and Portuguese olho appear quite different, but they descend from a historical form oculus. German Auge, Dutch oog and English eye (cf. Czech and Polish oko, Ukrainian око (óko)) are related to this form in that all three descend from Proto-Indo-European *okʷ. In addition, international derivatives like ocular and oculista occur in all of Interlingua's control languages. Each of these forms contributes to the eligibility of the Interlingua word. The German and English base words do not influence the form of the Interlingua word, because their Indo-European connection is considered too remote. Instead, the remaining base words and especially the derivatives determine the form oculo found in Interlingua.
Notes on Interlingua vocabulary 
New words can be derived internally – that is, from existing Interlingua words – or extracted from the control languages in the manner of the original vocabulary. Internal word-building, though freer than in the control languages, is more limited than in schematic languages.
Originally, a word was taken from Latin if the usual procedure did not produce a sufficiently international word. More recently, modern alternatives have become generally accepted. For example, the southern Romance comprar, meaning 'to buy', has replaced emer, because the latter occurs only in derivatives in the control languages. Similarly, the modern form troppo, 'too' or 'too much', has replaced nimis, and ma 'but' has largely replaced sed.
Interlingua has been developed to omit any grammatical feature that is absent from even one control language. Thus, Interlingua has no noun-adjective agreement by gender, case, or number (cf. Spanish and Portuguese gatas negras or Italian "gatte nere", 'black female cats'), since this is absent from English, and it has no progressive verb tenses (English I am reading), since they are absent from French. Conversely, Interlingua distinguishes singular nouns from plural nouns since all the control languages do.
The definite article le is invariable, as in English. Nouns have no grammatical gender. Plurals are formed by adding -s, or -es after a final consonant. Personal pronouns take one form for the subject and one for the direct object and reflexive. In the third person, the reflexive is always se. Most adverbs are derived regularly from adjectives by adding -mente, or -amente after a -c. An adverb can be formed from any adjective in this way.
Verbs take the same form for all persons (io, tu, illa vive, 'I live', 'you live', 'she lives'). The indicative (pare, 'appear', 'appears') is the same as the imperative (pare! 'appear!'), and there is no subjunctive. Three common verbs usually take short forms in the present tense: es for 'is', 'am', 'are;' ha for 'has', 'have;' and va for 'go', 'goes'. A few irregular verb forms are available, but rarely used.
There are four simple tenses (present, past, future, and conditional), three compound tenses (past, future, and conditional), and the passive voice. The compound structures employ an auxiliary plus the infinitive or the past participle (e.g., Ille ha arrivate, 'He has arrived'). Simple and compound tenses can be combined in various ways to express more complex tenses (e.g., Nos haberea morite, 'We would have died').
Word order is subject–verb–object, except that a direct object pronoun or reflexive pronoun comes before the verb (Io les vide, 'I see them'). Adjectives may precede or follow the nouns they modify, but they most often follow it. The position of adverbs is flexible, though constrained by common sense.
The grammar of Interlingua has been described as similar to that of the Romance languages, but greatly simplified, primarily under the influence of English. More recently, Interlingua's grammar has been likened to the simple grammars of Japanese and particularly Chinese.
Criticisms and controversies 
||This article's Criticism or Controversy section may compromise the article's neutral point of view of the subject. (December 2012)|
||This section needs additional citations for verification. (July 2012)|
Some opponents[who?] argue that, being based on a few European languages, Interlingua is best suited for speakers of European languages. Others contend that Interlingua has spelling irregularities that, while internationally recognizable in written form, increase the time needed to fully learn the language, especially for those unfamiliar with Indo-European languages. A related point of criticism is that Interlingua's credential as being Standard Average European is too weak outside the Romance languages. Some opponents see the Germanic, Slavic, and Celtic languages, in particular, as having little influence.
Proponents[who?] argue that Interlingua's source languages include not only Romance languages but English, German, and Russian as well. Moreover, the source languages are widely spoken internationally, and large numbers of their words also appear in other languages – still more when derivative forms and loan translations are included. Tests had shown that if a larger number of source languages were used, the results would be about the same. So, IALA selected a much simpler extraction procedure for Interlingua with little adverse effect on its internationality.
See also 
- Esperanto and Interlingua compared
- Grammatica de Interlingua
- Ido and Interlingua compared
- Interlingua and eligibility of international words
- Interlingua dictionaries
- Interlingua, Instrumento Moderne de Communication International (course manual)
- Internationalism (linguistics)
- Irregularities and exceptions in Interlingua
- Sabine Fiedler, 1999, "Phraseology in planned languages", Language Problems and Language Planning, vol. 23 no. 2
- Gopsill, F. P. (1990). International languages: a matter for Interlingua. Sheffield, England: British Interlingua Society. ISBN 0-9511695-6-4. OCLC 27813762.
- See Gopsill, F. P. Interlingua: A course for beginners. Part 1. Sheffield, England: British Interlingua Society, 1987. Gopsill, here and elsewhere, characterizes Interlingua as having a simple grammar and no irregularities.
- The Interlingua Grammar suggests that Interlingua has a small number of irregularities. See Gode (1955).
- Gode, Alexander, "Introduction", Interlingua-English: A dictionary of the international language, Revised Edition, New York: Continuum International Publishing Group, 1971.
- Breinstrup, Thomas, Preface, Interlingua course for beginners, Bilthoven, Netherlands: Union Mundial pro Interlingua, 2006.
- Yeager, Leland B., "Le linguistica como reclamo pro Interlingua" (Linguistics as an advertisement for Interlingua), Interlinguistica e Interlingua: Discursos public, Beekbergen, Netherlands: Servicio de Libros UMI, 1991.
- See for example Sexton, Brian C., "Interlingua at first hearing," Lingua e Vita, 1995, Issue 83.
- Morris, Alice Vanderbilt, General Report, New York: International Auxiliary Language Association, 1945.
- Falk, Julia S. "Words without grammar: Linguists and the international language movement in the United States, Language and Communication, 15(3): pp. 241–259. Pergamon, 1995.
- Bray, Mary Connell  (1971), "Foreword", Interlingua-English: A dictionary of the international Language, Second Edition, New York: Frederick Ungar Publishing Company. ISBN 0-8044-0188-8. OCLC 162319. Retrieved on 2010-04-18.
- Gopsill, F. P., and Sexton, Brian, "Le historia antenatal de interlingua" , Historia de interlingua, 2001, revised 2006.
- Gopsill, F. P., and Sexton, Brian, "Profunde recerca duce a un lingua", Historia de interlingua, 2001, revised 2006.
- Gopsill, F. P., and Sexton, Brian, "Le natura, si – un schema, no", Historia de interlingua, 2001, revised 2006.
- Breinstrup, Thomas, "Un revolution in le mundo scientific" (A revolution in the scientific world). Accessed January 16, 2007.
- Esterhill, Frank, Interlingua Institute: A History. New York: Interlingua Institute, 2000.
- Biographias: Alexander Gottfried Friedrich Gode-von Aesch. Accessed January 16, 2007
- Biographias: Hugh Edward Blair. Accessed January 16, 2007
- Portrait del organisationes de interlingua. Access January 16, 2007.
- Bibliographia de Interlingua. Accessed January 16, 2007.
- Biographias: Ingvar Stenström. Accessed January 16, 2007
- Breinstrup, Thomas, "Interlingua: Forte, Fructuose, Futur", Historia de Interlingua, 2001, Revised 2006.
- "Interlingua usate in le posta". Historia de Interlingua, 2001, revised 2006.
- Breinstrup, Thomas. "Persecutate pro parlar Interlingua." Panorama in Interlingua, 1995, Issue 5.
- Biographias: Július Tomin. Historia de Interlingua, 2001. Revised 2006.
- Breinstrup, Thomas, "Contactos directe con touristas e le gente local", Historia de Interlingua, 2001, Revised 2006.
- Stenström, Ingvar, "Experientias del inseniamento del vocabulario international in le nove gymnasio svedese" (Experiences with the teaching of the international vocabulary in the new Swedish gymnasium), Interlinguistica e Interlingua: Discursos public per Ingvar Stenström e Leland B. Yeager, Beekbergen, Netherlands: Servicio de Libros UMI, 1991. (High school in Europe is often called the gymnasium.)
- Novas de Interlingua, May/June 1958.
- Blandino, Giovanni, "Le problema del linguas international auxiliari", Philosophia del Cognoscentia e del Scientia, Rome, Italy: Pontificia Universitas Lateranensis, Pontificia Universitas Urbaniana, 1989.
- "Radioemissiones in e re Interlingua," Panorama in Interlingua, Issue 3, 2006.
- Stenström, Ingvar, “The Interlingua of IALA: From ‘the linguists’ project’ of 1951 to the working ‘tool of international scientific communication’ of 1981”, Interlinguistica e Interlingua: Discursos public per Ingvar Stenström e Leland B. Yeager, Beekbergen, Netherlands: Servicio de Libros UMI, 1991.
- Stenström, Ingvar, “Utilisation de Interlingua in le inseniamento de linguas” (Utilization of Interlingua in the teaching of languages), Interlinguistica e Interlingua: Discursos public per Ingvar Stenström e Leland B. Yeager, Beekbergen, Netherlands: Servicio de Libros UMI, 1991.
- "A notar," Panorama in Interlingua, Issue 4, 2006.
- Interlingua Alphabet on Omniglot
- Gopsill, F. P., Interlingua today: A course for beginners, Sheffield, UK: British Interlingua Society, 1994.
- Gode, Alexander; Hugh E. Blair (1955) . Interlingua; a grammar of the international language (Second Edition ed.). New York: Frederick Ungar Publishing. ISBN 0-8044-0186-1. OCLC 147452. Retrieved 2007-03-05..
- Morris, Alice Vanderbilt, "IALA's system: Underlying facts and reasoning", General report, New York: International Auxiliary Language Association, 1945.
- Stillman, E. Clark, and Gode, Alexander, Interlinguistic standardization, New York: International Auxiliary Language Association, 1943. Articles 82-100 translated by Stanley Mulaik. Revised 2006.
- Gode, Alexander, "Introduction", Interlingua-English: A dictionary of the international language, Revised Edition, New York: Continuum International Publishing Group, 1971. See "Forms of international words in derivational series".
- Gode, Alexander, "Introduction", Interlingua-English: A dictionary of the international language, Revised Edition, New York: Continuum International Publishing Group, 1971. See "Methods and techniques: Non-Latin examples".
- Wilgenhof, Karel. Grammatica de Interlingua. Union Mundial pro Interlingua, Beekbergen, Netherlands, 1995.
- Brauers, Karl. Grammatica synoptic de Interlingua. Morges, Switzerland: Editiones Interlingua, 1975.
- These are optional short forms for esser, 'to be'. They are found in Wilgenhof, who stops short of calling them irregular verb forms. Two such forms appear in Gode and Blair, and one is labeled irregular; none are in Brauers.
- See for example Gode (1955), §115, "Table of Conjugation", pp. 38–40.
- Yeager, Leland B., "Artificialitate, ethnocentrismo, e le linguas oriental: Le caso de Interlingua", Interlinguistica e Interlingua: Discursos public per Ingvar Stenstrom e Leland B. Yeager, Beekbergen, Netherlands: Servicio de Libros UMI, 1991.
- Falk, Julia S. Women, Language and Linguistics: Three American stories from the first half of the twentieth century. Routledge, London & New York: 1999.
- Gode, Alexander; Hugh E. Blair (1955) . Interlingua; a grammar of the international language (Second Edition ed.). New York: Frederick Ungar Publishing. ISBN 0-8044-0186-1. OCLC 147452. Retrieved 2007-03-05.
- Gopsill, F.P. Le historia antenatal de Interlingua.. (In Interlingua.) Accessed 28 May 2005.
- International Auxiliary Language Association (IALA). General Report. IALA, New York: 1945.
- International Auxiliary Language Association (1971) . Alexander Gode (ed.), ed. Interlingua-English; a dictionary of the international language. "Foreword" and "Acknowledgements" by Mary Connell Bray (Second Edition ed.). New York: Frederick Ungar Publishing. ISBN 0-8044-0188-8. OCLC 162319. Retrieved 2010-04-18.
- Pei, Mario. One Language for the World and How To Achieve It. Devin-Adair, New York; 1958.
- Union Mundial pro Interlingua (UMI). Interlingua 2001: communication sin frontieras durante 50 annos (in Interlingua). Accessed 17 August 2006.
Interlingua organizations 
Interlingua dictionaries