is achieved, and in order to function well, a language must be such that it allows respecting these maxims, which languages not always do. Most publications in the field of interlinguistics are, however, not so constructive, but rather descriptive, comparative, historic, sociolinguistic, or concerned with translation by humans or machines. As for Esperanto, which is the most widely used constructed interlanguage, there is a relatively abundant literature about the language itself and its philology (see Esperantology). Only a few of the many constructed languages have been applied practically to any noteworthy extent. The most prosperous were Volapük (1879, Johann Martin Schleyer), Esperanto (1887 Ludwik Lejzer Zamenhof), Latino sine flexione (1903, Giuseppe Peano), Ido (1907, Louis Couturat), Occidental-Interlingue (1922, Edgar de Wahl) and Interlingua (1951, IALA and Alexander Gode), with Esperanto being the one gathering the most significant community of active speakers at present. Here, the Bliss symbols (1949, Charles K. Bliss) deserve also to be mentioned. These were intended for international communication, but have found their field of application elsewhere, namely as an aid for persons who lack an adequate ability of using ordinary language, because of motorical or cognitive handicaps. Kinds of interlanguages The following table lists only one representative for each type explicitly. Among constructed languages, it is usual to distinguish between a priori languages and a posteriori languages. The latter are based on one or, more often, several source languages, while this is not evident for a priori languages, e.g., the philosophical languages of the 17th century, Solresol and the logical languages of the 20th century, such as Loglan and Lojban. Spontaneously arisen Interlanguages are necessarily a posteriori or iconic (using imaging or imitating signs). Bibliography On the initiative of Klaus Schubert, Detlev Blanke's 1985 book "Internationale Plansprachen (Eine Einführung)" ["International Constructed Languages (An Introduction)"], still the standard German work on interlinguistics, is now available online. It can be downloaded, as scanned pages in a PDF file (250 MB in size), from the German National Library. Gobbo, Federico, 2020, Introduction to Interlinguistics. Munich: GRIN Publishing (eo) Vĕra Barandovská-Frank, (2020), Interlingvistiko. Enkonduko en la sciencon pri planlingvoj, 333 pp., Poznań, Univ. Adam Mickiewicz, Gode, Alexander, Interlingua: A Dictionary of the International Language. New York: Storm Publishers, 1951. Interlinguistic Standardization, Historia de Interlingua, 2001, revised 2006. Jespersen, Otto, Interlinguistics, International Communication, 1931. Schubert, Klaus (Ed.): Interlinguistics. Aspects of the Science of Planned Languages. Mouton de Gruyter, Berlin / New