Interlingue is a constructed language. It was called Occidental between 1922 and 1947. Edgar de Wahl, one of the first Esperantists, created it. De Wahl was from the city of Tallinn in Estonia, which was in the Russian Empire but later became its own country. He spoke German, Russian, Estonian and French since he was a child and had natural ability in languages. He is often called de Wahl.

Interlingue looks a lot like languages in the Romance language family: French, Spanish, Italian, and so on. De Wahl made a rule called De Wahl's rule that made changing verbs to nouns easier and more regular. For example, the change of d in the word exploder (to explode) to s (making explosion and explosiv) is a regular change when following this rule.

De Wahl was not happy with Esperanto. He decided to create a language called "Occidental". He published it in 1922. In 1949 the users of Occidental voted to change the name to Interlingue.

There were already many types of constructed languages during de Wahl's time. Some of them, like Esperanto and Ido, are called schematic because they follow their own design even if the words look more artificial. Others, like Latino sine flexione and Idiom Neutral, are called naturalistic because they try to look like natural languages. The difficulty was that creators had to choose between being regular or looking natural. Louis Couturat, the creator of Ido, wrote the same thing in 1903, and called it a paradox: "The international words are not regular, and the regular words are not international." The language that de Wahl made had a goal to be a language that was both regular and natural at the same time.

History

How Occidental (Interlingue) started 
De Wahl announced his language in the magazine Kosmoglott in 1922, and this is where the Occidental activities can be seen. However, de Wahl started making the language long before this. Between 1906 and 1921 he started experimenting with his own language, and it changed a lot. At the time he called it Auli, or "auxiliary language" (auxiliary means helpful). The other nickname for Auli is proto-Occidental (which means "old Occidental"). When de Wahl announced his language in 1922, it was almost but not quite done. He actually wanted to wait a bit longer, but there was big news in 1921: the League of Nations was looking at the idea of an international language. De Wahl had also sent a letter and got a positive reply from the League of Nations in September 1921.

People began using Occidental because it was easy to read and understand, even without grammars and dictionaries. 

Kosmoglott changed its name to Cosmoglotta in 1927 and began promoting Occidental over other languages. In January of the same year, they moved Cosmoglotta's office to Vienna in the region of Mauer (now part of Liesing). This helped Occidental have success during this period because the office was now in a central location. Engelbert Pigal, who is also from Austria, helped too with his article Li Ovre de Edgar de Wahl (The Work of Edgar de Wahl) which convinced some users of the Ido language to try Occidental. By early 1930, people were using Occidental in Germany, Austria, Sweden, Czechoslovakia, Switzerland, and most recently in France.

Vienna period and World War II 
When the magazine Cosmoglotta was based in Vienna, the users of the language had enough money for the first time. This was thanks to two people: Hans Hörbiger, also from Vienna, and G.A. Moore, from London. The world economy was not doing well at this time, but with the help of people like Hörbiger and Moore, Cosmoglotta was able to do well and gained readers. But Hörbiger and Moore both died in 1931, so this period did not last long. After this Cosmoglotta had to find money from other places: subscriptions, books, magazines, and so on.

The growing movement began a stronger campaign for the language in the early 1930s in which it promoted Occidental's easy understanding at first sight. They contacted organizations with letters completely in Occidental, and these organizations often understood the letters and sent responses. The Occidentalists also introduced the idea of Occidental being the answer to Europe's "tower of Babel".

The years 1935 to 1939 were even more active. This is when Cosmoglotta started publishing a second edition. The second edition first had the name Cosmoglotta-Informationes, but was soon called Cosmoglotta B. Cosmoglotta B had more discussions that were interesting to the users of Occidental such as the language's development, Occidental in the news, and how much money they had.

Meanwhile, the years before the World War II led to problems for Occidental and other planned languages because they were made illegal in Germany, Austria and Czechoslovakia. Their groups were forced to break up, the Gestapo watched their activities, and their educational materials were destroyed. Germany had the largest number of Occidentalists, so making planned languages illegal in Germany was especially damaging. 

World War Two suddenly started in 1939, and this stopped the publications of both Cosmoglottas until 1940. This was when Cosmoglotta was most active. One Cosmoglotta A or B was published every month between January 1937 and September 1939 when the war started. Then one edition was published every month from September 1941 to June 1951. During the Second World War, only Switzerland and Sweden were neutral countries. Because of this, only the Occidentalists in these countries could carry on their activities.

During the war, telegrams were checked by censors before approving them to send. The Occidentalists noticed that their telegrams were being sent, especially between Switzerland and Sweden. This meant that the censors could probably understand it and maybe thought the language was Spanish or Romansch. With this, the Occidentalists in Switzerland and Sweden could communicate with each other a bit.

The other centres of Occidental activity in Europe did not continue. Contacts began again soon after the war by those who survived. Cosmoglotta had subscribers in 58 cities in Switzerland a few months before the end of World War II in Europe, and Cosmoglotta A started again in 1946.

Setting up the language standard 
One of these activities was language standardization. De Wahl had created Occidental with some unchangeable features, but believed that it could follow a "natural evolution".

Orthography was another area in which several possibilities existed: etymologic orthography (adtractiv, obpression), historic orthography (attractiv, oppression), or simplified orthography (atractiv, opression). Simplified orthography became the standard by 1939. Much of the standardization of the language took place in this way through community preference (e.g. both ac and anc were proposed for the word "also" but the community quickly settled on anc), but not all.

As there was a lack of general material destined for the general public, much time during World War II was spend creating courses and standardizing the language. In August 1943, as the war was still going on, it was decided to create an academy to officialize the process. The Swiss Occidentalist, isolated from the rest of the continent, concentrated on developing educational materials. The standardization efforts were based on actual usage.

IALA, Interlingua, and name change to Interlingue 
The International Auxiliary Language Association (IALA), founded in 1924 to study and decide the best planned language for international communication, was at first viewed with disbelief by the Occidental community. Many of its members, including its co-founder Alice Vanderbilt Morris, were Esperantists. This made many Occidentalists including de Wahl himself believed that it had been set up as a pretext to give the impressoin of a "neutral and professional" committee that would finally choose Esperanto. Relations soon improved, however, as it became clear that the IALA intended to be as impartial as possible by familiarizing itself with all existing planned languages. 

In 1945, the IALA announced that it planned to create its own language. It showed four possible versions under consideration. They were naturalistic as opposed to schematic. Some Occidentalists were happy that the IALA had decided to create a language almost the same as Occidental. They believed that it supported their argument for a naturalistic auxiliary language. 

The two languages had somewhat different spellings (e.g. filosofie in Occidental and philosophia in Interlingua for 'philosophy'), but besides this both languages had 90% the same vocabulary. However, their structure and word creation systems were very different: 
 De Wahl's Rule in Occidental had eliminated Latin double stem verbs (verbs such as act: ager, act- or send: mitter, miss-), while Interlingua simply accepted them as an important part of a naturalistic system.
 Occidental had a bigger Germanic substrate.
 Interlingua also allowed optional irregular verbal conjugations (such as so, son and sia as the first-person singular, third-person plural and subjunctive form of esser, the verb 'to be') that Occidental had never even considered and viewed as incompatible with an easy international auxiliary language.

All of this happened in a time when Occidental, based in Europe, was still recovering from the war. Besides the economic difficulties that the movement was suffering (not like the well-funded IALA, which was based in New York), the beginning of the Cold War created a difficult situation for the Occidental-Union, which had the same name as an anti-Russian political league. In early 1948 the Czechoslovak Occidentalists had begun asking for the approval for a new name that would allow them to continue their linguistic activities without problems. The Union responded that they were free to introduce the language as "Interlingue (Occidental)", or even remove the mention of Occidental if they felt it necessary. Ric Berger began supporting a change of name from Occidental to Interlingue in 1948 which he also hoped would help in uniting it with Interlingua. With a 91% support in a ballot done by the Occidental Union in 1949, Interlingue was made the official name of the language, with Interlingue (Occidental) also permitted, valid as of 1 September 1949.

Interlingue-Occidental suffered when Interlingua was announced in 1951. This was because now it had a competitor in the field of naturalistic planned auxiliary languages. In fact, Ric Berger, one of the most important Occidentalists, stopped supporting Interlingue to support IALA's project. He also tried to convince other Occidentalists to do the same.

Pause and revival 

Interlingue was quite weakened after many users moved to Interlingua, though the drop in activity was gradual and happened over decades.

Cosmoglotta B stopped publishing after 1950, and Cosmoglotta A was published less frequently. Other bulletins in Interlingue continued to appear during this time. Barandovská-Frank believed that the decrease of interest in Occidental-Interlingue happened at the same time as generation that was first drawn to it from other planned languages was getting older (translated from Esperanto):Most of those interested in Interlingue belonged to the generation that became familiar in turn with Volapük, Esperanto and Ido, later on finding the most aesthetic (basically naturalistic) solution in Occidental-Interlingue. After that, many moved to IALA's Interlingua, which however did not prove to be much more successful despite the impression its scientific origin made, and those who remained loyal to Occidental-Interlingue did not succeed in giving their excitement to a new generation.

Activity in Interlingue eventually reached a low during the 1980s and early 1990s, when Cosmoglotta publication stopped for a some years. According to Harlow, "in 1985 Occidental's last periodical, Cosmoglotta, ceased publication, and its editor, Mr. Adrian Pilgrim, is quoted as having described Occidental as a 'dead language.'" A decade later, a documentary film in 1994 by Steve Hawley and Steyger on planned languages introduced Interlingue speaker Donald Gasper as "one of the last remaining speakers of the language Occidental".

The arrival of the internet helped many other planned languages, and the same happened for Interlingue which came back to life. In the year 1999, the first Yahoo! Group in Occidental was founded. That same year, Cosmoglotta began publishing again from time to time. Also in 1999, the language started being discussed in literature on auxiliary languages. One example is The Esperanto Book published in 1995 by Harlow, who wrote that Occidental had an intentional emphasis on European forms and that some of its leading followers had an Eurocentric philosophy, which may have set back its spread. Still, the opposite view was also common in the community and Occidental gained supporters in many nations including Asian nations. An Interlingue Wikipedia was approved in 2004. In recent years official meetings between Interlingue speakers have begun taking place again: a meeting in Ulm on 10 January 2013, another in Munich in 2014 with three participants, and a third in Ulm on 16 August 2015 with five participants.

Grammar

Alphabet and pronunciation 
Interlingue is written with 26 Latin letters: 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. The letters of the alphabet are pronounced as a, be, ce, de, e, ef, ge, ha, i, jot, ka, el, em, en, o, pe, qu, er, es, te, u, ve, duplic ve, ix, ypsilon, and zet. Accents are written on the five vowels to indicate irregular stress, with the acute accent (á é í ó ú) preferred, but others (è, ê, etc.) permitted.

The vowels are usually pronounced as follows:
 a as English father.
 e open or closed, as  English bed and yes.
 i as English machine.
 o open or closed as in English door, hot.
 u as English rule, pull.
 y is a consonant after a vowel or beginning a word before a vowel, otherwise is pronounced as i.

The consonants are pronounced as in English, with the following exceptions:
c when before e and i = [ts]: cive, helice
g when before e and i = English s in pleasure: plage, giraffe; but elsewhere c and g are as in can, go
ss = [s] as in pass
s between vowels = [z]: rose, positiv
z = [dz]
zz = [ts]
ch = [ʃ], English sh: chambre
j = [ʒ], English s in pleasure
t as [t], except when followed by ia, io, iu, or ie and not preceded by an s. Thus the t in nation is pronounced [ts] but in bastion as [t].

Article 
Like English, Interlingue has a definite article and an indefinite article. The definite article (the) is li, and the indefinite (a, an) is un. Plural of a noun is made by adding -s after a vowel, or -es after most consonants. To avoid pronunciation and stress changes, words ending in -c, -g, and -m only add an -s: un libre, du libres, un angul, tri angules, li tric, li trics, li plug, li plugs, li album, pluri albums, li tram, du trams.

Personal pronouns
Interlingue has two forms for the personal pronouns: one for the subject form (nominative), and the other for the object form (accusative or dative).

Grammatical endings are used, but less than in Esperanto and Ido. Esperanto and Ido mark parts of speech with obligatory endings. Only a few parts of speech (such as verb infinitives) in Interlingue have entirely obligatory endings, while many others either have endings the usage of which is optional and sometimes recommended. Some grammatical endings are:

ar, er, ir: verb infinitive. far (to do), posser (be able), scrir (to write)
e: the general noun ending used obligatorily to differentiate nouns from other parts or speech or for reasons of pronunciation. Examples of obligatory -e endings: capitale (capital, noun) vs. capital (capital, adjective), contenete (content) vs, contenet (contained), sud (south, adjective) vs. sude (south as an independent noun, as in the north and the south). Optional -e endings: can or cane (dog), Pentecost or Pentecoste (Pentecost).
i: the general adjectival ending, similar to -e in usage. Examples of obligatory -i endings: pigri (lazy) and acri (sharp) to enable pronunciation, verdi (green, adjective) to distinguish from verde (green, noun). Examples of optional -i endings: etern vs. eterni (eternal), imens vs. imensi (immense).
a: nouns that end in e formed from an -ar verb are often written with the -a ending if one wishes to emphasize the verbal (active) aspect. A me veni un pensa (a thought occurs to me) vs. Penses e paroles (thoughts and words). The a ending also makes nouns feminine: anglese (English person), angleso (Englishman), anglesa (English woman). This does not apply to nouns that on their own indicate the gender (patre, matre).
o: indicates the masculine gender in the same way a indicates the feminine.

Verbs 
Verbs in Interlingue have three endings: -ar, -er, and -ir. Conjugation is performed with a combination of endings and auxiliary verbs. The verb esser (to be) is exceptional in being written es in the present  tense, though the esse form is seen in the imperative.

Adverbs 
Interlingue has primary adverbs and derived adverbs. Primary adverbs are adverbs without special endings: tre (very), sempre (always), etc.

Derived adverbs are adverbs made by putting -men at the end of an adjective (rapid = quick, rapidmen = quickly). The ending may be omitted when the meaning is clear: tu deve far it rapid(men) = you must do it quick(ly).

Literature 
The main literary texts in Occidental appeared in Cosmoglotta. There were also some works, both original and translated, published in Interlingue. Other texts appeared in the magazine Helvetia but these were less common. Micri chrestomathie is an example of a translated work, featuring a compilation of texts by Jaroslav Podobský, H. Pášma and Jan Kajš published in 1933.

Some original texts published as separate books are:
 Krasina, raconta del subterrania del Moravian carst, published in 1938 by Jan Amos Kajš.
 Li astres del Verne, a collection of original poetry by Jaroslav Podobský, published both in 1935 and 1947.
 Li sercha in li castelle Dewahl e altri racontas, written and published by Vicente Costalago in 2021.

Some translations are:
 Antologie hispan, written and published by Vicente Costalago in 2021.
 Fabules, racontas e mites, written and published by Vicente Costalago in 2021.

Writings on the subject 
 Haas, Fritz. 1956. Grammatica de Interlingue in Interlingue. Interlingue-Servicie Winterthur (Svissia).  (in Interlingue)
 Jacob, Henry. 1947 Occidental (1922) by Edgar de Wahl en  A Planned Auxiliary Language Publicate: London, Dobson, London. 1947   (in English)
 Rodriguez, José María. 1999. Breve gramática de Interlingue/Occidental en Gazeto Andaluzia (órgano oficial de la Asociación Andaluza de Esperanto) N° 57 marzo 1999.   (in Esperanto)
 Stenström, Ingvar. 1997. Occidental-Interlingue: Factos e fato de un lingua international. Societate Svedese pro Interlingua. . (in Interlingua)

References

Other websites 

 Official Site of Interlingue-Union 
 Cosmoglotta 

Constructed languages