OTTO JESPERSEN WAS one of the first philologists to support actively the work for an international auxiliary language. He rejected Volapük, critically examined Esperanto, and followed with interest the preparatory work of Prof. Léopold Leau and Prof. Louis Couturat which led to the foundation of the Délégation pour l'adoption d'une langue auxiliaire internationale. In May, 1907, Jespersen was elected a member of the committee of the delegation. When the delegation had selected Ido, essentially a reformed Esperanto, he became president of its Academy and took an active part in the linguistic discussion in the journal Progreso, a discussion which led to further improvements in Ido and a considerable development of the vocabulary of the language. He has described the beginning of the work which he carried on in conjunction with others in his History of our language. The system known as Ido owes much to Otto Jespersen, his experiences as a linguist, and the criteria which he applied to all proposals for the formation and development of the international auxiliary language.
Many points had been criticised in Esperanto and the members of the delegation introduced improvements in Ido to meet this criticism. The accented letters were suppressed; the plurals in -aj were replaced by the invariable adjective and -i was used instead of -oj for the plural forms of nouns; the accusative -n was retained only in cases of inversion; the arbitrary table of correlative words was replaced by words taken from the ethnic languages; the consonants w, x, y were reintroduced and the international spelling of many words restored; thousands of new roots were added to the vocabulary; the system of word derivation was completely revised and the new rules were based on Couturat's study Etude sur la dérivation. Jespersen formulated a principle in 1908 which became very popular among interlinguists, and was adhered to, to the extent practicable, and according to the development of interlinguistics at that time. "THAT INTERNATIONAL LANGUAGE IS BEST WHICH IN EVERY POINT OFFERS THE GREATEST FACILITY TO THE GREATEST NUMBER."
The war of 1914-1918 interrupted the propaganda for Ido and, in spite of the initial success, the world which needed a means for international communication remained indifferent. Jespersen explains the reasons for this indifference in his book (An International Language, 1928, Allen and Unwin, pp. 44-45), "In the first place the time was not yet ripe (in 1907) for a final decision; the principles for an interlanguage had not been thrashed out scientifically, and much of the short time at the committee's disposal had to be spent in clearing away much old rubbish, so that a great many details had to be left for further discussion in Progreso .... but in spite of all - in spite also of the amount of energy squandered away in the quarrels of Esperantists and Idists - the Delegation and the Ido Academy have left their indelible mark on the interlanguage movement, and their influence has been chiefly for the good."
In 1928 Jespersen published a system mainly based on Ido and called Novial. In introducing his new system, Otto Jespersen speaks of the unmistakable family likeness of all types of international language, refuting an objection which has often been raised because of the great number of different systems. These languages may differ in detail but they contain many common features and principles. Of all of them Jespersen said that "the less arbitrary and the more rational the forms, the more stable they will be." An examination of a comparative text of the systems of demonstrated usefulness, found at the end of this booklet, will show that to one who knows one of these languages the other systems are easily understood. They may differ, but their differences are not profound. While some tend to strive after greater similarity with the existing national or ethnic tongues at the cost of regularity, others tend to follow a more regulated system of grammar and derivation. All are workable languages which in every case are easier to learn and easier to use than any existing ethnic language, a criterion which we do well to remember.