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|Types of conlangs|
A posteriori language
An auxiliary language or auxlang (often expanded to international auxiliary language or IAL) is a conlang which is designed primarily to function as a lingua-franca or means of communication between different people(s) who speak otherwise incompatible languages. However, unlike most natural linguas-franca and as the name implies, auxlangs are usually not intentionally created to assert its own dominance nor that of a language family over native languages, but rather to provide a secondary "neutral" language to find common ground over.
While there technically are no formal limits on the creativity of an auxlang, most creators choose to make them naturalistic and further, a posteriori, often choosing to base them off of a select few languages or language families to aid in the learning of the conlang by speakers of such. Two extreme examples of this phenomenon are the subcategories of universal and zonal languages, the first of which is usually either syncretized from a wide variety of sources or a priori with many a posteriori modifications and are designed to be a common language of all people, whereas the second is syncretized almost solely from a definite group of languages (often some combination of geographically and/or familially related) and tailored so that the people who speak such languages find relative ease in learning it.
A zonal language (similarly expanded to zonal auxiliary language) is a form of auxlang designed specifically for the languages/dialects and people living within a certain region, as touched briefly on previously. While most often these conlangs are designed as an artificial standard for a group of related dialects, it's not a total prerequisite just as in all other auxlangs. In the former cases, this subcategory can be considered the conlang equivalent of a naturally-formed koiné language, a standardized and independent dialect of a language formed from averaging and emphasizing the shared components of multiple divergent dialects with varying levels of mutual intelligibility, versus the latter sharing potentially certain aspects with pidgins and creoles.
Auxlangs in general can be considered one of the oldest types of conlangs, being an idea naturally born out of the drive for mutual understanding. Examples of auxiliary languages can be found in some of the most famous constructed languages, namely languages such as Esperanto, Volapük, Ido, Interlingua, Interlingue/Occidental, and Novial.