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A constructed script is a new writing system specifically created by an individual or group, rather than having evolved as part of a language or culture like a natural script. Some are designed for use with constructed languages, although several of them are used in linguistic experimentation or for other more practical ends in existing languages.
The most prominent of constructed scripts may be Glagolitic, Korean Hangul and the International Phonetic Alphabet. Some, such as the Shavian alphabet, Quikscript, Alphabet 26, and the Deseret alphabet, were devised as English spelling reforms. Others, including Alexander Melville Bell's Visible Speech and John Malone's Unifon were developed for pedagogical use. Blissymbols were developed as a written international auxiliary language. Shorthand systems may be considered constructed scripts.
Constructed scripts and traditional "natural" writing systems
All scripts, including traditional scripts such as the Chinese or the Arabic script, are human creations. However, scripts usually evolve out of other scripts rather than being designed by an individual. In most cases, alphabets are adopted, i.e. a language is written in another language's script at first, and gradually develops peculiarities specific to its new environment over the centuries (such as the letters w and j added to the Latin alphabet over time, not being formally considered full members of the English (as opposed to Latin) alphabet until the mid-1800s). Construction of a script presupposes that the author is aware of at least one writing system already. Otherwise, the invention would not just comprise a script, but the concept of writing itself. Therefore, a constructed script is always informed by at least one older writing system, making it difficult in some cases to decide whether a new script is simply an adoption or a new creation (for example the Cyrillic and the Gothic alphabets, which are nearly identical to the Greek alphabet but were nevertheless designed by individual authors).
In the rare cases where a script evolved not out of a previous script, but out of proto-writing (the only known cases being the Cuneiform script, Egyptian hieroglyphs, the Chinese script and arguably the Mayan script), the process was nevertheless a gradual evolution of a system of symbols, not a creation by design.
Overview of constructed writing systems
For previously unwritten languages
Some, like the Korean Hangul, Cherokee, N'Ko, Fraser, Tangut and Pollard scripts, were invented to allow certain spoken natural languages that did not have adequate writing systems to be written. Armenian, Georgian, and Glagolitic may fit in this category, though their origin is not known.
For fictional languages
The best-known constructed scripts dedicated to fictional languages are J. R. R. Tolkien's elaborate Tengwar and Cirth, but many others exist, such as the Klingon script from Star Trek, Aurebesh from Star Wars, D'ni from the Myst series of video games, and the Orokin language (referred to by members of the community as "Tennobet", a portmanteau of alphabet) from the video game Warframe.
For technical purposes
Several writing systems have been devised for technical purposes by specialists in various fields. One of the most prominent of these is the International Phonetic Alphabet (IPA), used by linguists to describe the sounds of human language in exhaustive detail. While based on the Latin alphabet, IPA also contains invented letters, Greek letters, and numerous diacritics.
The Shavian alphabet has been designed to have an easier writing system for English.
Some neographies have been encoded in Unicode, in particular the Shavian alphabet and the Deseret alphabet. A proposal for Klingon pIqaD was turned down because most users of the Klingon language wrote it using the Latin alphabet, but both Tengwar and Cirth were under consideration in 2010. An unofficial project exists to coordinate the encoding of many constructed scripts in specific places in the Unicode Private Use Areas (U+E000 to U+F8FF and U+000F0000 to U+0010FFFF), known as the ConScript Unicode Registry.